JP2930340B2 - Coating sensitive material condition monitoring system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This application is a continuation-in-part of US application Ser. is there.

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a system for monitoring a condition of a substance. In particular, the present invention relates to a condition monitoring system responsive to a plurality of material conditions. Further, the invention relates to a condition monitoring system that can be used to monitor substances that can leave a coating on a condition sensitive device. Still further, the present invention relates to a condition monitoring system that provides an output regarding the degree to which the condition sensitive device is coated.

2. Description of the Prior Art Many systems are known that are sensitive to material conditions, such as whether or not there is a material at a monitoring location. Such systems are often used as level controls such as level switches that include high level alarms. One of the well-known monitoring techniques for high level alarms also involves the positioning of a material sensitive sensor including a measurement electrode in the container and monitoring the electrical properties of the electrode relative to a reference voltage, such as a grounded container wall. Such monitoring is usually for the conductive and / or sensitive part of the admittance between the electrodes and can be performed in radio frequency bridge circuits or other admittance sensitive circuits. Such monitoring is based on the principle that, when the substance level increases and covers the measuring electrode, an increase in the admittance between the electrodes with respect to the value of the empty container is detected.

However, such admittance sensitive systems generate high levels of false indications because the admittance that appears on the sensor due to the coating of the substance is substantially the same as the admittance that appears when the sensor is completely covered. It has long been recognized that it is easy. To reduce this effect, systems have been devised that have a capacitance and substantially ignore the coating of the sensor. Such a system is described in U.S. Pat.
No. 06980 discloses a "card" (or "shield") electrode between the measuring and reference electrodes, this guard being driven substantially by the potential of the measuring electrode, reducing the leakage surface current along the sensor. Let it. However, such systems still have false high level indications. That is,
When the coating thickness is increased sufficiently, the guard is not enough to distinguish the condition from a true high level condition. This is an essential attribute of the admittance response system.

Many other systems are two-state systems. That is, these outputs are high or low level, closed / open relay contact, lamp on, off, or the presence or absence of material near the sensor, ie, a similar two-level output corresponding to the high or low material level condition. It is. In practice, coated sensors that fall in the third condition range are designed or appropriately assigned to one of two available output states. Typically, a sufficiently large thickness, conductance or susceptance indicates the same output condition as a full container. Although this system can be designed to ignore some amount of coating,
It always malfunctions under certain coating conditions.

The conventional systems described above can exhibit decisive drawbacks in certain applications, especially if the coating can be deposited, ie, grown over time. However, by chance at an unknown time, the system gives a false high level output when the coating thickness exceeds an acceptable value. This application is the monitoring of aircraft litter holding tanks. In airplanes, the output of the waste monitoring system is used to lock the toilet door so that it is no longer in use. False high alarms unnecessarily cause passenger discomfort on long flights. Other applications are inconvenient, expensive, or risk from false low level signals due to coating.

It is particularly desirable that the condition monitoring system determine the extent of the coating on the internal components of the container, especially on the sensor, in order to clean the coating before interfering with the desired level or measurement in the presence of the coating. However, conventional binary output admittance response systems cannot. This is because the admittance appearing on the sensor is a function of the electrical properties of the material as well as the conditions of the material near the sensor. Since the electrical properties of a material vary very widely and in unknown ways between applications or over time in one application, or at various locations within a container, coated sensors and true high It is in principle impossible to devise an admittance response system that can clearly distinguish between level sensor conditions. The admittance response system used here is one in which the monitored substance responds to the admittance that appears to the sensor electrode.

The state of matter at multiple discrete condition points (eg,
Devices for monitoring substance levels, proximity, etc.) are already known. These devices generally fall into two categories.

Devices of the first category operate by converting something like a measurable variable capacitance or admittance generally related to the material condition to be studied, such as height, into an analog value related to the measured variable. Thereafter, the analog value is compared to several discrete signals,
Alternatively, it is converted into a digital signal that is compared with a plurality of discrete values. In a first category of multipoint monitoring devices known to the inventor, high frequency admittance measurements are converted to analog signals sent to a plurality of current sensing set point relays. A major problem with this device is that each stage of operation on a measured variable, such as amplification, conversion or comparison, has a potential that leads to a false effect. Combined, these effects produce erroneous outputs in the comparison phase. In order to prevent false effects from occurring, it is necessary to use relatively expensive, high quality and very tight tolerance circuit elements.

A second type of device incorporates a bridge. This bridge compares measured and reference variables corresponding to the material conditions to be studied. The output of the bridge is then processed to provide a useful signal. An advantage of this arrangement over the first one is that the introduction of false effects from the processing circuit is limited, which occurs when the critical stage in the bridge comparison occurs before the amplification and subsequent signal processing stages. Because. Known multiple set point monitors, including bridges, generally operate at signal points balanced and otherwise unbalanced. The equilibrium point may or may not be a useful set point.

A problem with all known multiple set point devices of both categories above is that the potential interference signal is present where the substance is measured or where the resulting measured signal is processed. is there. It is necessary to guard the measurement signal from these interfering signals in order to prevent accidental reading of the device. It is significantly more difficult to guard a signal over a wide range of values than to guard a signal at a single value. This particular difference is significant, in that a more expensive and interfering signal present analog monitor is turned off, allowing a relatively low cost single point monitor. Such a signal is generated, for example, in a high frequency admittance type substance level device by residual coating of the substance on the detection element.

A single set point bridge device is suitably balanced near the point to be examined. In a single setpoint guard device, the reference potential of the bridge will typically provide a low impedance source of the same voltage as the sensing element voltage when the bridge is in equilibrium. This allows the guard electrode shielding the sensing element a reference potential to be used effectively to provide a guard voltage. Unfortunately, if the bridge is not balanced, the voltage at the sensing electrode will deviate from the reference potential. This reduces the effect on the guard electrode that is coupled to the reference potential.

Several other single set point material condition monitoring devices are known, which allow for the generation of multiple series of reference signals for calibration. For example, U.S. Pat. No. 4,485,673 to Stern discloses a single set point two-line level measurement device that utilizes a pair of admittance sensitivity sensors each including a capacitive balance bridge. A wide variety of capacities are used in a pair of set point calibration devices. Capacitance is selectively coupled to each of the two bridge networks provided for set point calibration. The device then operates with a fixed reference volume. U.S. Pat. No. 4,555,941 discloses a substance level detection device having an automatic calibration circuit in which the capacitance switches automatically between the LC and the resonance circuit. Both of these devices are not suitable for multiple set point operation in their current form. Each has no means to change the reference set point during the monitoring operation. Also, each does not have a feedback loop that adapts to changes at the reference set point during the monitoring operation.

U.S. Pat. No. 4,063,447 to Mathison discloses a monitoring device having a bridge network in which a reference current source is automatically adjusted to compensate for device drift. This is also not suitable for multiple set point operation in certain configurations.

U.S. Pat. No. 4,383,444 discloses a first category of capacitance level sensing device in which a measured volume is processed and compared to a reference volume. A microprocessor is provided as part of the automatic calibration device. There is no suggestion or teaching as to whether the device is useful or capable of multiple set point operation. The first categorical device accepts erroneous effects during measurement and signal processing.

Finally, adjustable differential set point monitors are known. This device is generally for monitoring pools and the like. The bridge is provided with a material condition responsive sensor that deploys admittance dependent variables and materials. Primary capacity provides a reference admittance. Occurs when the material in the basin falls below a first level when the bridge output switches as a result of lower material associated with admittance from the sensor, and the second capacitance couples to the first capacitance. To increase the reference admittance.
The bridge output does not switch until the material rises above the first to the second level. The single output signal of such a device is indeterminate for a particular set point with respect to either of the two reference capacitances.

[Object and Summary of the Invention]

It is a general object of the present invention to provide a material condition monitoring system that can automatically perform multiple set point operations.

It is a more specific object of the present invention to provide a condition monitoring system that can reliably respond to monitoring conditions even if there is an accumulation of coating on the monitoring device.

It is another object of the present invention to provide such a condition monitoring system that can react substantially independently of the electrical properties of the monitored substance, and in particular, the electrical properties of a wide range of substances. It is in.

It is another object of the present invention to provide a condition monitoring system that provides an output that includes information relating to the thickness of the coating.

Another object of the present invention is to provide a condition monitoring system in which coating thickness information and information relating to other monitoring conditions are output separately or together in one communication channel. It is in.

Another object of the present invention is to provide a condition monitoring system in which the accuracy of each monitoring condition is not affected by all other monitoring conditions.

It is another object of the present invention to provide a condition monitoring system that is automatically tested by automatically creating conditions corresponding to covered sensors.

In response to the aforementioned objectives, the system of the present invention may be a substance response sensor, a bridge means or a bridge-like means for comparing the sensor output with a reference value, changing the state with the sensor and a predetermined bridge condition. Detecting means coupled to a reference that produces a two-level output responsive to the bridging, and automatically and repetitively of the bridging means to change the material conditions when predetermined bridging conditions occur. Means for changing a parameter. The output means coupled to the detector is usually, but not always, required to provide an output signal with the characteristics required or desired to interface the other system with the system of the present invention. Is done.

In a preferred embodiment, the bridge means is a high frequency admittance bridge. In a preferred embodiment of the present invention,
The means for changing the bridge parameters is controlled variable admittance, such that a predetermined continuous admittance is assumed, one admittance corresponding to each one of the interesting set points of the material condition. Is controlled.

It is yet another object of the present invention to provide a condition monitoring system that outputs a composite signal of interest at the same single value regardless of the number of set points being monitored.

It is yet another object of the present invention to provide a multi-point set point system that automatically provides an effective guard voltage level for a substance monitoring sensor.

It is yet another object of the present invention to provide a condition monitoring system that uses a bridge that is in equilibrium at each of a plurality of points during a monitoring operation.

It is yet another object of the present invention to provide a condition monitoring system that does not become unstable to the system at any one or more of the multiple set points.

To achieve the above object, according to one aspect of the present invention, there is provided a substance monitoring system, wherein when a sensor is disposed in a container containing a fluid substance, the sensor according to the level of the substance in the container and the sensor A sensor that generates a sensor signal corresponding to the thickness of the coating of the material above, and changes among a plurality of reference signal values including a reference signal value representing a substance level set point and a reference signal representing a sensor film thickness set point. A reference signal generator that generates a reference signal having a value that is connected to the sensor and the reference signal generator, and an output signal generation circuit that compares the sensor signal with the reference signal to generate a response output signal; The output signal includes a first state representing a high substance level for the substance level set point, a second state representing a low substance level for the substance level set point,
A substance monitoring system is provided having at least three different states, including a third state indicating that the thickness of the coating of the substance on the sensor has exceeded the sensor film thickness set point.

 The sensor includes a substantially planar material sensing surface.

 The sensor is an admittance sensor.

 The output signal generation circuit includes a bridge.

The output signal generation circuit includes a switch that changes a reference signal value when driven.

The reference generator includes a switch that changes a reference signal value when activated.

The switch further includes a switch controller connected to the switch, wherein the switch controller automatically and repeatedly drives the switch.

According to another aspect of the present invention, there is provided a method of monitoring a fluid material in a container, comprising: arranging a sensor in the container, driving the sensor, depending on the level of the fluid material in the container, and on the sensor. Generate a sensor signal according to the thickness of the film of, generate a level reference signal representing the substance level set point and a film thickness reference signal representing the sensor film thickness set point, compare the sensor signal and the reference signal, And generating an output signal comprising at least one selected from at least three different states according to the result of the comparing step, two of the states representing the level of the substance relative to the substance level set point, and one of the states representing the sensor coating. A method is provided for monitoring a fluid substance in a container, the method representing the thickness of the coating of the substance on the sensor relative to the thickness set point.

The step of disposing the sensor includes disposing a sensor having a substantially planar surface in the container, such that the substantially planar surface is substantially the same as the inner surface of the container.

Driving the sensor includes applying a radio frequency signal to the sensor.

Placing the sensor includes placing an admittance sensor in the container.

Generating the reference signal includes driving a switch that selects one of the reference signals for comparison in the comparing step.

Generating the reference signal includes automatically and repeatedly driving the switch.

The comparing step includes providing a bridge that compares the sensor signal with the reference signal.

In accordance with yet another aspect of the present invention, an instrument system includes an instrument system that includes a sensor disposed in the container and an instrument connected to the sensor to provide a level output signal indicative of the level of the substance in the container. In the fluid substance level monitoring process, the sensor is made to be coated with the substance, and the coating of the substance on the sensor affects the ability of the instrument to produce a level output signal that accurately represents the level of the substance, The method of operation of the instrument system is to detect the coating of the substance on the sensor in the instrument and to generate a coating output signal indicating the coating of the substance on the sensor, and the output signal indicating the coating is different from the level output signal. There is provided a method of operating an instrument system that enables it to do so.

The output signal indicative of the coating is indicative of the thickness of the coating on the sensor.

The output signal indicating the coating indicates whether the thickness of the coating on the sensor exceeds the coating thickness set point.

The instrument is in one of at least three predetermined states.
Generating an output signal having one of the predetermined states and generating an output signal representative of the coating includes generating an output signal having one of the predetermined states.

These and other aspects of the invention will be apparent from the accompanying drawings and the following detailed description of the preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic block diagram of the main operating components of the present invention.

FIG. 2 is a schematic depiction of an environment in which the present invention can be used.

FIG. 2a shows a suitable substance response sensor useful in the present invention viewed from the inside of the container containing the substance to be monitored.

FIG. 2b schematically shows a cross section of the sensor of FIG. 2a, including the electrical effects of the coating.

FIG. 3 is a more detailed block diagram for identifying the subsystem of the first embodiment of the present invention.

FIG. 4 is a composite diagram showing the relative positions of FIGS. 4a-4e and is a schematic of the circuit of FIG.

FIG. 4a is a schematic diagram of a bridge network connected to the oscillator of the first embodiment.

FIG. 4b is a schematic of the rest of the bridge circuit, including the reference admittance generator and decoder logic of the first embodiment.

FIG. 4c is a schematic of the error amplifier and demodulator of the first embodiment.

FIG. 4d is a schematic of the output amplifier and power supply of the first embodiment.

FIG. 4e is a schematic diagram of the address generator, feedback and output circuit of the first embodiment.

FIG. 5 is a schematic depiction of an equivalent bridge of the first embodiment.

FIG. 6 schematically depicts the variable gain provided by the error amplifier of the first embodiment.

FIG. 7 schematically depicts various timing and control signals of the first embodiment.

Figures 8a, 8b and 8c schematically depict three bridge circuits useful in the present invention.

FIG. 9 is a more detailed block diagram of the second embodiment of the present invention.

FIG. 10 is a composite diagram showing the relative positions of FIGS. 10a to 10d and is a schematic diagram of the second embodiment.

FIG. 10a is a schematic diagram of a power supply and an oscillator of the second embodiment.

FIG. 10b is a schematic diagram of the bridge of the second embodiment.

FIG. 10c is a schematic diagram of the error amplifier and the demodulator of the second embodiment.

FIG. 10d is a schematic diagram of the output amplifier of the second embodiment.

FIG. 11 is a graph illustrating the system transfer function of the second embodiment.

FIG. 12 is a graph illustrating a sensor output with respect to a substance state according to an embodiment of the present invention.

FIG. 13 is a schematic diagram of an output circuit useful in the first embodiment of the present invention to generate another useful output signal.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 is a block diagram showing basic components of a substance state monitoring system 10 according to the present invention. The system includes a reference signal generating circuit 14 and a bridging means 13 including a substance response sensor 12 that generates a single signal responsive to a plurality of states of the monitored substance. The output of the bridge means 13 is connected to a detection circuit 16 which generates a two-level output 17 which changes state under predetermined bridge conditions. The output circuit 23 is provided for generating an output 25 and, when necessary, interfacing information of the processing circuit output 17 to signal requests of a plurality of devices outside the monitor 10.
The controller 22 is provided for automatically and repeatedly changing one parameter of the bridge means 13. Thus, a plurality of material states corresponding to the above-mentioned predetermined bridging condition, that is, a state in which the system responds to the bridging condition, are automatically and repeatedly changed. In one embodiment of the present invention, a feedback circuit 20 is connected to a controller 22 and an output circuit 23 to apply feedback to the processing circuit 16. The feedback provided varies in response to a number of parameters of the bridge. In particular, when one bridge parameter changes in response to a particular material state, the feedback applied first corresponds to the most recently applied feedback in which the bridge parameter changed to correspond to that material state. Done to be done. In this way, the monitor 10 can respond to each material state of interest regardless of the occurrence of other material states of interest.

Output 25 includes information relating to a plurality of conditions monitored by one sensor 10. In one embodiment of the present invention, one output 25 containing all such information is generated. In other embodiments, output signal 25 may include separate outputs related to the states being monitored, or a combination thereof.

FIG. 2 illustrates one environment in which the present invention may be used. A container or vessel 40, not shown, having an inlet and outlet for the substance, receives the substance. If the fluid substance can coat the surface of the object with which it comes into contact, the multiple substance states to be monitored are whether the container is full, ie,
It can be a high level measurement and whether the coating has grown to such an extent that it may interfere with the high level measurement described above. These material conditions to be monitored are, for example, those in the monitor of the waste storage tank in the toilet of an aircraft. For example, Boeing 74
Large aircraft such as 7 may have 4 tanks for 11 toilets. Monitor system to prevent the toilet from being used when the tank is full
10 is connected by connection means 15 to the remaining part 50 of the monitoring system. The sensor 12 is mounted on the wall of the container 40 so as to be exposed to the substance 42. In this system, the level of substance 42 rises above
It is intended to provide output when covering 12. The output 25 may be used as a means to prevent further use of the toilet, for example, to lock a door. Such a system for one container
A plurality of 10 may be provided.

Conventional systems operate by monitoring the capacitance between one measurement electrode and the vessel wall. The container is typically a high frequency ground, and may be formed by an inner layer of stainless steel mesh and an outer layer of fiberglass. As discussed above, a substantial problem with conventional systems is due to the normal accumulation of deposits (coatings) covering the interior surface of the container 40 containing the sensor 12. This material can be substantially electrically conductive (eg, 4000 micro ohms per centimeter), soaking even very thin coatings (adhesion) into the capacitance measurement environment, resulting in false high level output. twenty five
May occur. An increase in coating thickness or conductivity that can accumulate before erroneous high-level output can occur can result in a "guard" or "shield" between the measurement electrode and the vessel wall. It can be determined by placing an electrode. When driven at substantially the potential of the measurement electrode, such a shield electrode may substantially reduce surface leakage current.
However, even with the use of such guard electrodes, the thickness of the coating of material eventually leads to false high level signals that cannot be distinguished from high level output due to high levels of the material. Reach the thickness until it occurs.
The present invention is intended to solve such problems in the prior art.

FIGS. 2a and 2b show sensors useful in the present invention.
12 is shown. FIG. 2a shows the height of the sensor when viewed from inside the container 40, ie when exposed to the substance. The sensor 12 includes a measurement electrode 32 and a shield electrode 36 inserted between the measurement electrode 32 and the vessel wall 40 in all surface paths therebetween. These electrodes are insulated from each other by electrical insulation means 34 and 38. As shown, in addition to the case where the reference potential from which the measurement is made is given by the wall of the container 40, if the container wall is a non-conductive material or not high-frequency ground, this sensor It will be readily understood that additional electrodes can be provided for the configuration of. Other than the case where the electrodes and insulators have a circular arrangement as shown, other arrangements could be used. Further, while it is desirable for the sensor to be substantially flush with the surface of the container 40, a sensor in which the components are not flat and protrude relative to the container may also be used.

FIG. 2b shows a partial cross section of the sensor electrode configuration of FIG. This figure shows only the electrical features of the sensor and the substance 49 deposited over the sensor, not the mechanical or other structural features of the actual sensor. Absent. The measurement electrode 32, the shield electrode 36, and the ground electrode 40 are connected by a plurality of conductors 45, 46, and 47 to a plurality of terminals 52, 53, and 54 in other portions of the monitor system 10.
Desirably, these conductors are short and minimize impedance, but if substantial separation of system components is required, a coaxial cable may be used as shown. FIG. 2b shows a cross section of this sensor where the substance 42 has a thickness t and adheres 49. If a bridge circuit of the type described in more detail below is used, the above-mentioned coating (adhesion) will result in an effective admittance Y ₁ between the measurement electrode and the shield electrode, and between the shield electrode and the ground electrode. An effective admittance Y ₂ and an effective admittance Y ₃ between the measurement electrode and the ground electrode are given. The effect of measuring these effective admittances will be described in more detail below.

8a, 8b, and 8c show various bridge circuits that can be used in the present invention. These bridge circuits are powered by one or more AC voltage sources. The illustrated bridge circuit is intended to be connected to a three-dimensional sensor of the type shown in FIGS. 2a and 2b, and has a material response differential output V ₀ that is substantially zero in the material state to be detected. Is configured to occur. The monitored substance is, as shown in FIG.
Provide effective admittances Y ₁ , Y ₂ , and Y ₃ to the sensor.

Bridge circuit of Figure 8a, respectively, voltages V ₁ and V ₂
And a pair of voltage sources 502 and 504 forming the first side of the bridge described above. Second of the above bridge
The admittances Y ₁ , Y ₂ , and Y that respond to the substance
It is connected to _3, having admittance components 506 having admittance Y _a. The bridge is an equilibrium under the conditions of _{V 1 Y a = V 2 Y} 3. Admittance Y ₁ does not affect the measurement since it is parallel to the voltage source. When the bridge is in equilibrium, admittance Y ₂ also does not affect the measurement.

Bridge circuit Figure 8b is usually in terms of the effective admittance Y ₁ is a parasitic condition to be ignored is absolutely necessary part in the measurement is different from the circuit of Figure 8a. The bridge is balanced even when the measuring electrode voltage V _P is different from the shield electrode voltage, i.e. the output V ₀ which the processing circuit becomes zero. The first side of the bridge, are equipped with AC source 508 and 510 for generating a voltage V ₁ and V _2. The bridge includes an admittance element 512 and 514 further have an admittance Y _b and Y _c. Before further explaining the operation of the bridge, reference coating admittance model FIG. 2b, and a graph of Figure 12 showing the measuring electrode voltage V _P which is a function of coating thickness t of the model of FIG. 2b.

In the bridge circuit according to FIG. 8b, it is desirable that the source impedance of the monitor circuit combined with the shield and ground electrodes is sufficiently low that this impedance is not substantially affected by the admittance of the substance of interest between these electrodes. This can be performed by taking into account the electrode shape and minimizing the low-impedance power supply impedance and connection impedance. Further, it is desirable that the material admittance given to the measurement electrode when the target substance is under the predetermined condition is sufficiently high and does not depend on the input admittance of the monitor circuit combined with the measurement electrode. Under these conditions, the effect of ground admittance Y ₂ of the shield, measured on the almost negligible. The voltage to the ground of the shield activates the substance and electrically couples it to the substance response sensor 12,
A voltage which is a function of the voltage V _S of the power supply and the admittances Y ₁ and Y ₃ is applied to the measuring electrode 32.

In particular, regarding the shield voltage V _S , the measurement electrode voltages V _P and V _P
= V _S Y ₃ / (Y ₁ + Y ₃ ). Under the above preferred conditions, _VS is constant. Y ₁ and Y ₃ are the first
It changes as shown in FIG. For very thin coatings with respect to the width of the shield electrode, the coating on the shield electrode is driven at substantially V _S, Y ₃ is lower than that of Y _1. That measurement electrode voltage V _P is equal to substantially shield voltage V _S. Coating thickness t sub is I to increase, the outer portion of the coating electrical coupling decreases sharply for the shield electrode, so that Y ₃ is increased. Y ₁ also increases with coating thickness, but at a rate less than Y ₁ . That as the thickness increases, V _P is separated from the V _S. If the thickness t becomes sufficiently thick, no effect any more on the admittance of even coating thickness is increased further electrode, V _P approaches the smaller limit than V _3. These features are shown in FIG.

An important feature of the bridge Figure 8b operating in preferred conditions described above is that although the measuring electrode voltage V _P corresponding to the material thickness t is dependent on the admittance ratio does not depend on the absolute value of the admittance . Since the admittance rate depends on the shape of the sensor and the coating but not on the conductance and susceptance of the substance, the voltage applied to the measuring electrode is substantially independent of the electrical properties of the substance, and for a given sensor shape Changes only with the coating thickness.

Returning to FIG. 8b, under all conditions of being coated or of interest, the substance is charged to one arm of the bridge
It can be seen that the application of a Y _c from V _P. The bridge must be balanced when V ₀ = 0, at which time V ₃ Y _b = V _P Y _c .

The 8c diagram is shown a bridge with similar properties to that shown in Figure 8b, it is operated by a single power source 516 for applying an AC voltage V ₅ between the shield and ground electrodes.
The bridge, the first side of the bridge further comprises a admittance elements 518 and 520 having admittance Y _d and Y _e, admittance to the second side of the bridge
And a admittance elements 522 and 524 having a Y _f and Y _g. Y _f and Y _g divides the V _S, the division voltage is applied to one input of the detection circuit. Y _d and Y _e divide _VP with respect to V _S and apply the divided voltage to the processing circuit. Output V ₀
The latter voltage hits, the function V _P, that is a function of the material thickness.

It can be seen that there can be many variations equivalent to the bridge described above. For example, various voltage sources that are replaced to produce performance equivalent to the illustrated bridge. Further 502
And 506 operating via admittance can be replaced by a Thevenin equivalent current source.

According to the invention, means are provided for automatically and periodically changing the parameters of the bridge. The parameter to be changed is preferably one of the admittances in the bridge, so that in this case it is easy to do. Preferably, the changing admittance is a susceptance, but it is also possible to use its conductance or a combination thereof. However, it is also possible to vary other bridge elements, such as voltage or current sources, with equivalent results. For example, in FIG. 8b, the voltage source 508 comprises a transformer winding having a plurality of taps, and the controller automatically and periodically combines the admittance 512 with the taps based on a predetermined sequence.

Preferably, the means for automatically and periodically changing the bridge parameters use control switch means that are either electrical or electromechanical. When the bridge parameter to be changed is admittance, such switching means binds different admittances or different combinations thereof to the bridge. One or more of such admittances can be adjusted, and the bridge parameters, which are selected automatically and periodically, are adjusted in different applications depending on the conditions of the substance of interest and the sensor characteristics. However, the control means for changing the bridge parameter may further comprise a continuously controllable admittance, such as a diode combined as a voltage variable capacitance.

If a bridge parameter is changed between automatic and repeated a plurality of values, the monitoring system may react to the critical number of measurements electrode voltage V _P. For example with reference to FIG. 12, voltage V _c the system corresponding to the coating thickness t _c
First reaction, the coating thickness t _c is considered sufficient thickness to be required in order to avoid false high signal capable cleaning action. The system may be responsive to a second voltage _Vf corresponding to a thickness that is sufficient for the sensor to be considered coated, for example, for the entire container. Further, multiple voltage levels may be monitored corresponding to different coating thicknesses of interest. For a sufficiently large number of monitored thicknesses, the system can approach a continuous thickness monitoring system, and the continuous system may be configured by continuously changing the bridge parameters.

Referring to FIG. In a first embodiment of the present invention,
The main circuit elements of the circuit 50 coupled to the sensor are represented in a block diagram. Admittance bridge 72 is coupled to oscillator 70. The bridge comprises a proportional side transformer 74 forming the fixed side of the bridge and having a reference potential. The bridge 72 has a reference admittance generator 78,
Coupled to the generator 78, the external connections 52-54 from the sensor 12
And a circuit 76 comprising The output of bridge 72 is passed through variable gain error amplifier 80. The output of the amplifier is passed through a demodulator 82. The demodulator is usually configured to ignore any conductive components of the bridge output and react to sensitive components of the bridge output. This is, in turn, related to the sensitive elements of reference and sensor admittance. Demodulator outputs an analog voltage level signal that is passed through amplifier. The amplifier 84 generates a two-level (binary) signal indicating the direction of the bridge imbalance. Output amplifier 84
Are passed through a feedback circuit 20, which in the preferred embodiment comprises a latch 86 provided as a combination memory means and signal generator and a multiplexer 88 provided as a feedback signal selector. The latch 86
Outputs a separate signal for each admittance value generated by the reference admittance generator. These signals are sent to an equal number of output circuits 90. Each output circuit comprises one of a 60a-60d set of controls, indicators, and output connections, and is further associated with a single admittance setpoint value. Multiplexer 88 is feedback latch 86
, One of several signals output to the demodulator 88 is sequentially selected. Both the reference admittance generator 78 and the feedback circuit 20 are controlled by the control unit 22. The control unit 22 includes a clock 92 that drives a continuous counter 94 that controls both the address generator 96 and the latch 86. Address generator 96 is coupled to decoder circuit 98 associated with bridge 72. Decoder 98 controls the operation of reference admittance generator 78. The address generator 96
Further, the operation of the latch 86 and the multiplexer 88 is controlled. Power supply circuit 58 is 120VAC, 60 cycles, current source 57
Combined with Power supply circuit 58 includes system ground and three different positive supply voltage levels, approximately +12, +8.
And + B are maintained to energize the various circuits.

The system of FIG. 3 operates schematically as follows. Oscillator 70 provides energy to bridge circuit 72, which includes a proportional side transformer 74; this transformer may form part of oscillator 70 as well. The admittance generated by the condition of the substance to be monitored via the sensor 12 is coupled via connections 52 and 54 to one arm on the variable side of the bridge. A reference admittance generator 78 is coupled to the remaining arm on the variable side of the bridge. The proportional side transformer 74 provides the fixed side of the bridge. Generator 78 generates a number of stable admittance values in a predetermined order. This sequence is repeated continuously during the system monitoring operation. Each different reference admittance value corresponds to a material condition set point. As described in detail with respect to the following figures, the generator 78 of the preferred embodiment includes a number of adjustable capacitors. Each capacitor is switched in and out of the variable side of the bridge network under the control of the controller 22 which is accomplished in a predetermined sequence that is repeated. Generally speaking, the bridge will be balanced when the ratio of the sensor admittance to the reference admittance is equal to the ratio of the proportional side transformer. Error amplifier 80 and demodulator 82 respond to the degree, phase, and direction of bridge imbalance. The output of demodulator 82 is an analog voltage level signal indicating the direction, phase and degree of unbalance. The output amplifier is configured to convert the analog signal to a two-level (eg, binary or logic level) signal that indicates the condition of the bridge, particularly the direction of unbalance.

An important point of the first embodiment of the present invention is a mechanism for giving independent positive feedback, that is, hysteresis, to each reference admittance value. Latch 86 provides a separate output for each reference admittance value indicating the imbalance of the bridge for that particular admittance value. The signal for each reference admittance value is selected by the feedback multiplier and sent to the demodulator. This is accomplished by first providing the variable side of the bridge 72 with a new reference admittance value and, after the bridge 72 has had a chance for stability, writing the two-level value of the output amplifier signal to the latch. This two-level value is then used to generate an output signal for a particular reference admittance value, and the demodulator is used until the new two-level value is written to the latch after that particular reference admittance value is again provided to the bridge circuit. Used to control the feedback to If the feedback signal were to be output directly from the demodulator, the demodulator would affect the feedback signal due to a different reference admittance value when the new reference admittance value was coupled to the bridge circuit 72. And this will create interference between the settings. If two or more consecutive setpoints are close in value, this will switch the output signals together rather than individually. Thus, the value of the output signal is latched relative to the respective setting value corresponding to the value of the output signal of the output amplifier written to the latch when the monitored reference admittance value was last transmitted to the bridge circuit. To the output circuit 90. The respective reference admittance value then controls the system while it is actively supplied to the bridge circuit and is independent of the other reference values, their corresponding bridge states and output signal states. It has multiple independent controllers,
All have the effect of responding to signal deviations.

FIG. 4 is a composite diagram showing the relative positions of each of the circuits FIGS. 4a-4e illustrating the details of FIG.

Referring first to FIG. 4a, the left half of the figure shows the connection to the class C power oscillator 70 and bridge circuit 72. 8.4V power is supplied to oscillator 5 via line 101, which is filtered by C201 and protected from overvoltage by D204. The inductance due to the winding 274 of the transformer 74 is 8.4 V at the emitter due to the current limiting resistor R202.
It is alternately excited by current from the collectors of transistors Q200 and Q201 connected to the power supply. Transistor
The bases of Q200 and Q201 are DC biased by winding 174 and a voltage divider composed of R203, R204 and C217 via AC positive feedback from winding 174. D201
Limits 8.4V power supply fluctuations.

The right half of FIG. 4a shows the connection of the bridge circuit including the transformer 74 to the error amplifier 80. Wire 200 extends from the high pressure side of winding 274. Wire 202 has been drawn from the center tap of winding 274. The third line 204 is shown in FIG.
Center tap and 2 as described in more detail in
It is pulled out from between the low pressure side of the next winding 274. These lines supply the voltage of the bridge to other parts of the circuit, as described below. The part of the winding I between the center tap 202 and the line 200 from the high side forms the fixed arm of the bridge circuit, and the part II between the center tap line 202 and the low side 204 is the second fixed arm of the bridge. To form An extra winding section is provided on winding 274 for adjustment. In this illustrated embodiment, the high pressure arm I
The ratio between low pressure arm II (ie between 200 and 202) and low pressure arm II (ie 200 and 202) and low pressure arm II (ie 202 and 204) is 10/3.
Line 202 is the probe measurement electrode 3 when the bridge is balanced.
The voltage is essentially the same as the voltage of 2. It has a low impedance power supply. This allows the wire 202 to be a power source for the shield 36. Line 202 branches off from line 208 at node 207. As shown in FIG. 4b, a line 208 split from the line 202 is connected to the connector 53 connected to the control unit by the shield unit 36. The second branch from line 202 goes to error amplifier 80 and is used for purposes described below.
Since the first embodiment of the present invention operates to balance the bridge for different settings to be considered, the voltage supplied to the shield or shield 36 from the bridge center via line 208 Is always equal to the voltage level of the measuring electrode 32 when the bridge is balanced. Line 210 is the output of the balanced bridge circuit and sends the output of the bridge to the error amplifier. Output line 210 is connected to ground return line 130 (FIG. 4b) via capacitor C205 to ensure that the bridge is always balanced without additional sensor inputs. C205 is connected to the bridge on the same arm as the input of the sensor 12 so that the bridge is protected even when the sensor is not connected to the bridge or when the impedance to be measured by the sensor is not detected. This returns the system to zero capacitance,
Allow the measurement to respond to zero capacitance.
Output line 210 is also connected to a center tap output branch 209 from the bridge center via a first diode D202, a second inverted D205 and a load resistor R225. The diodes D202 and D205 constitute a static protection function. The center tap branch 209 is connected to an effective ground line 130 by a pair of head-to-head Zener diodes D200 and D203. These diodes also provide static protection and true safety, and limit the voltage between shield and ground. Line 310 is drawn from error amplifier 80 and is +7.5 to 8 with respect to the voltage shielded to detector circuit 98 as described in more detail in FIG. 4b.
Powered at a voltage between V.

Referring to FIG.4b, there is shown the remainder of the circuit portion for bridge coupling to a circuit element including a sensor 12 expressing an admittance 33 responsive to a material condition and a reference admittance generator 78 and a decoder circuit 98. ing. Secondary winding
Line 200 from the “high” side of 274 is connected to junction 225. From there, one parallel line extends to the external connector 51 labeled "PAD". Variable capacitors C227, C228, C229 and C230 are also coupled to the pad potential at node 225. Single pole double throw switch a
D is in series with each of the capacitors C227-C230. The pair of switches ab and cd are both of the type CD4053.
It is implemented with two CMOS two-input multiplexers U202 and U203. The switches a to d realized by the variable capacitors C227 to C230 and U202 and U203 connected thereto are the third capacitors.
The reference admittance generator 78 shown in FIG. Each switch a-d has one output connected in parallel to node 240, the variable bridge output, and a node 224, a second output connected in parallel to the fixed bridge output, the shield potential. . Each switch a to d is a decoder circuit
Line 24 extending from NAND gates 247-250 forming part of 98
1,242,243 and 244 respectively. The shield potential line 208 is connected to the external connector via the connection point 220.
A point 222 is coupled to 53 (indicated by the symbol "SHD") and a coupling point 224 from the switch output is reached.

As described, the fixed side of the bridge is formed by winding 274, the upper and lower portions I and II forming a voltage divider. Reference admittance generator 78 capacitor
C227-C230 and connection switches ad form one arm on the variable side of the bridge. The other or “measurement” arm on the variable side of the bridge includes the admittance 33 of the sensor 12. Line 204 is coupled to return line 130, as shown in FIG. 4a. As shown in FIG. 4b,
Line 211 also couples sensor ground connection 54 to return line 130. By connecting the sensor 12 to the external connectors 52 and 54 to which the symbols “PR” and “GND” are assigned,
The materially generated admittance 33 of the sensor 12 is coupled into the bridge. Under many measurement conditions, the desired ratio of the arm ratio converter (transformer) 74 and the reference capacity C227 to
It is desirable to use a sensor that produces an admittance greater than the admittance that will balance with the maximum value of C230 (less than the capacitance of capacitor C205). For this reason, capacitors coupled back-to-back between the fixed and variable bridge outputs at junctions 220 and 240
Capacitive shunt having a C _B and C _A are provided. The current drawn from sensor 12 (ie, the measured admittance Y) is divided by CA and CB. Only CB / CA + CB times the current drawn from the sensor is measured. Usually ratios in the range of 1/1 to 1/650 are used. 1 /
For a ratio of 1, CB is very high admittance, ie a short circuit. To shift the adjustment range of capacitors C227-C230 by a fixed amount, a so-called pad capacitor 55 can be coupled between external connectors 51 and 52. Pad capacitors increase the effective reference admittance. This provides a convenient means of shifting the setting range, making the device usable for a variety of material and electrical properties, and a variety of admittance responses to material states for the full range of material states of interest. Enables the use of a sensor having The operation of the bridge 72 is shown in FIG. The winding 274 of the arm ratio converter 74 supplies the bridge reference potential on lines 200, 202 and 204 to the rest of the circuit and to the sensor 12 via terminals 51, 53 and 54, which are often subsequently referred to as "pads", "shields". Reference admittance generator 78, referred to as "" and "ground," under control of lines 241-244 from decoder 98, generates an equivalently shown effective admittance 79 (YR). The capacitors CA and CB reduce the current flowing through the admittance 33 (Y) generated by the sensor 12 to the attenuation ratio CB / (CA + CB)
Form a capacitive shunt that attenuates at, thereby coupling the apparent admittance Y * CB (CA + CB) to node 240, where the admittance of C205 (Y205) is added to the winding 274 It should be balanced with YR multiplied by the turns ratio N1 / N2 of I and II ("pad" to "shield" and "shield" to "ground", respectively). The bridge equilibrium condition is: N1 * YR = N2 (Y205 + Y (CB / CA + B))) or Y = (YR (N1 / N2) -Y205) (CA + CB) / CB Referring again to FIG. 4b. It is noted that the second contact of each switch ad is coupled to the shield potential at junction 224. Therefore, each capacitor C227
When .about.C230 is not connected in the reference balanced arm on the variable side of the bridge, it is connected in parallel to winding I of transformer 74, where it has a negligible effect. This prevents the undesirable effects that would occur if a single pole single throw switch were used. If a single pole single throw switch were used, unexpected admittance changes would occur between the open switch contacts, resulting in unexpected leakage current changes in the bridge output at 240.

Each of the switches a to d is controlled by a decoder circuit 98. The decoder circuit 12 has NAND gates 247 to 250 and a switch 25.
1 and a pair of photocouplers e and f of the type ILD-506 provided on the integrated circuit U205.
The decoder circuit 98 is coupled to the address generator 96 via a two-level address signals A ₀ and A ₁ line 260 and 261 bear. Each line 260 and 261 is a single integrated circuit
It is supplied to the separated one of the photocouplers e and f included in U205. The transistors in each coupler e and f conduct through the LEDs coupled in each line 260 and 261 when the signals on lines 260 and 261 are at an H level. Power supply line 310 extending from error amplifier circuit 80
Are coupled to the collectors of the transistors of each coupler e and f. The output of each coupler e and f are signals BA ₀ and BA _1, respectively 2 levels, respectively lines 260 and 2
According to the level of the signal A ₀ and A ₁ on 61. Signals BA ₀ and B
A ₁ is supplied to the logic network formed with single-pole double-throw switch 251 (used as an inverter) four NAND gates 247-250. Each gate 247-250 is a line 24
1 to 244 each of the reference generator switches a to d
And two switch control terminals. Such a manner distinguishing each of the four switches a~d address signals BA ₀ and BA ₁ is decoded is used to control the operation thereof switches. Although the circuit can be modified for some purposes and / or as needed, as shown, the decoder circuit is such that at any one time only one of the capacitors C227-C230 is selected and the bridge circuit is selected. The switches a to d are controlled so as to be connected to the reference arm on the variable side of the switch. The emitters of the transistors in the photocouplers e and f are coupled to the return line shield potential via load resistors R235 and R236. Return line 150 is maintained about 1 volt below the shield to select a negative bias for switches ad. This means that diode D2
"Ground" on line 130 with 06, capacitor C209 and resistor R238 to limit the peak current of diode D206.
This is achieved by half-wave rectification of the potential. R239 and C2
04 provides filtering. Power line 310 supplies a voltage between about 7.5 volts and 8 volts to the shield, and C208 and C
225 is locally filtered.

FIG. 4c schematically shows the components of the error amplifier 80 and the demodulator 82. These form a detector which provides a level of output that alters the state of the predetermined bridge condition, i.e. balance. Referring first to the error amplifier on the left side of the figure. Line 110 is about 8.DC from the power supply to the parallel resonant bandstop filter formed by L200 and C206.
Supply 4V and couple to 8.4V DC while preventing large AC current from flowing through the shield through C203.

C203 provides a shield hero impedance path from the output of L200-C206 and filters DC to the shield until it approaches the AC potential of the shield. R205 and C231 provide an additional filter, creating a positive voltage on line 310 for the shield between 7.5 VDC and 8.5 VDC, but at substantially the same alternating voltage as the shield. Line 310 supplies power to the bridge as described above. Line 310 also extends through line 320 to error amplifier 80 and to demodulator 82, and an optical isolator U206 for demodulation for feedback from feedback circuit 20 (see FIG. 3).
Provides power supply for Type 4N25. The bridge output signal from point 240 is passed through block capacitor 207 on line 210 to the base of transistor Q202 in the error amplifier. The base of transistor Q202 is also coupled through resistor R215 from the voltage divider center formed by series resistors R240 and R206 between power supply line 310 and shield line 209. Resistor networks R240, R215 and R206 are connected to transistor Q20.
2 is biased in the active area. The collector of Q202 is coupled to power line 310 through a resistor R207 and capacitor C210 connected in parallel. The emitter of Q202 is coupled to shield line 209 through resistors R208 and R210 in series with bypass capacitor C211 and resistor R211 connected in parallel, the second transistor Q203 being controlled by the first transistor Q202. . Q203 base is R207, C
It is coupled to the collector junction of 210 and Q202.

C210 greatly attenuates frequencies higher than the signal frequency to avoid parasitic oscillation. The emitter of Q203 is also coupled to power line 310 through the parallel of emitter bypass capacitor 213 and resistor R212. The collector of Q203 provides the output to demodulator 82 through capacitor C214 and R213 and R210
Feedback to the emitter of Q202 through a voltage divider formed by and a resistor R208. In addition, feedback from Q203 to Q202 is C212, D207, D208, R241, D213, D214,
Supplied by a multi-stage diode switch feedback consisting of D215, D216, R209 and R208. The DC return for the collector current of Q203 is provided by R230, L201 and C232. L201 and C232 resonate in parallel near the signal frequency, allowing the amplifier to have a high load impedance and thus having a high gain. L201
And C232 provide a low load impedance outside the frequency range of interest, thus reducing the amplifier gain for the signal outside that region. L201 also allows the output to swing below the negative supply rail, thus extending the dynamic range of the amplifier.

Error amplifier 80 provides amplification over a wide dynamic range of inputs to greatly simplify the design of demodulator 82 while reducing the dynamic range of its output.
The multi-stage diode switch feedback network of FIG. 4c provides three levels of feedback to the emitter of Q202, and thus the three levels of gain are shown graphically in FIG. While the bridge network output level is very low (± 0.5 millivolts or less than 1 millivolt peak-to-peak), no diodes are conducting and the gain is set to 1000 by the ratio of resistors R213 and R210. . Near the bridge balance, a 1/4 millivolt peak-to-peak change in bridge output voltage level is required to operate the unit. Bridge output signal level between 1.0 and 1 peak-to-peak
When between 1.3 millivolts, diodes D207 and D208 conduct. This adds the feedback from resistors R241 and R209 through R208 and R210 to the feedback from R213 through R210. This increase in resistance reduces the increase gain from 1000 to 195. The bridge output signal level is peak-to-
When the peak exceeds 11.3 millivolts, the diode D213-2
16 also conducts, bypassing R241 and further reducing the increased gain to 99. At the maximum possible input signal (approximately 52.6 millivolts peak-to-peak), it is 7.08V peak-to-peak for an effective total gain of 135 output levels. The reduction in dynamic gain provided by the diode network in the error amplifier requires a device that maintains both amplitude and phase information and resolves susceptance changes as small as 300 micro Siemens in the presence of conductive signals as large as 14,000 micro Siemens. to enable. This is equivalent to detecting a 450 picofarad capacitor when there is a 70 ohm resistor.

Amplifier U201, type CA3080, is provided for demodulating the susceptance component from the bridge output signal. Amplifier U2
01 gain input (pin 5) is connected to resistor R214 and diode
It is coupled to capacitor C214 through D212. C214
Is a DC block capacitor that allows only the AC portion of the error amplifier output to pass. The line between the output of D212 and the gain input of amplifier U201 is also coupled to shield line 209 through capacitor C219. The voltage divider network is
A resistor R216 connected in series between the power supply line 310 and the shield line 209, diodes D211 and D209, and a resistor R2
17 and diode D217. diode
D210, resistor R216, input resistor R214 and diode D212,
It forms a bias current that is conducted in a chain from the divided output to the gain input of amplifier U201.

One AC reference signal is substantially in phase with the shield-to-ground voltage and between the inverting or non-converting input of amplifier U201 having a network including resistors R218-R222 and capacitors C215, C216, C218 and C223. To be generated. C218
And the C215 play a fundamentally important role in guiding the AC components from the bridge input. C223 smoothes the voltage obtained between R218 and R219.

If the reference AC signal generated during the inverted or unconverted input of U201 is in phase with the bridge output signal passing through capacitor C214, the output current of U201 will be equal to the reference signal generated between the inverted or unconverted input. Includes a DC component that is proportional to the product of the gain control current (depending on the bridge output signal) and the in-phase component. When the phase of the bridge output signal is sufficiently different from the phase of the reference signal, the in-phase component is small and, as a result, DC is correspondingly reduced. Like this
Only the susceptance component of the bridge output that is in phase with the reference signal causes a net DC output. With proper selection of component values, the demodulation is made to also respond to the conductive component of the bridge output. This is important in enabling a device that compensates for admittance that interferes with the measurement of required material conditions, as described, for example, in US Patent No. 3,746,975 to Maltby.

The DC component of the output of amplifier U201 is filtered by C200 and transistors Q204 and Q205 and associated resistors R223, R232,
Amplified by R226, R227 and R229 and capacitors C220, C222 and C224. The amplifier operates as a switch that drives the junction 315 high or low. Amplifier U201
Is coupled to the base of transistor Q204 through resistor R223. R223, together with C222, is provided to further filter the output of amplifier U201. The resistor R232 and the capacitor C224 are connected to the power line 31
Coupled in parallel between 0 and the collector of Q204. R232
And the output of C224 is coupled to the base of second transistor Q205. Resistor R227 is coupled from power supply line 310 through the capacitor C222 to the emitter of Q204 to the output of resistor R223. Load resistors R226 and R229 return current from Q204 and Q205 to shield line 209, respectively. Joint 315
Is fed back to the base of the transistor Q204 through the capacitor C220 and output to the capacitor C221 through the resistor R228. Demodulator output voltage is line
On 330, it is conveyed to the output amplifier 84. R228 and C221 prevent any AC current in line 330 from being returned to output amplifier 84 back to the base of Q204.

The positive feedback to the demodulator 82 is a 4N25 type optical isolator U2
It is further provided from the feedback circuit 20 via 06 (see FIG. 3). A resistor R224 is provided between the output of the optical coupler U206 and the non-inverting input of the amplifier U201 to introduce controlled hysteresis at the switching point of the demodulator. The load resistance R233 also
It is coupled between the output of the optical coupler U206 and the shield line 209. Optical coupler U206 is driven by the output from transistor Q206. Voltage supply line 99 from power supply 58 supplies power to Q206. The base of the transistor Q206 is the feedback circuit 20.
(See FIG. 3).

Referring now to FIG. 4d, a circuit coupled to output amplifier 84 is shown. This circuit is an integrated circuit of type CD4007
With U108, the integrated circuit includes an array of six transistors coupled between a +12 volt power supply line 100 and a ground return 190. The resistors R110 to R111 and the capacitor C106 provide a bias function and a filtering function of the demodulator output. Zener diodes D110 and D111 and capacitors C107-109 provide protection of the digital components coupled to the +12 volt line 100, overvoltage and spike voltage of the +12 volt power supply to the output amplifier, and local filtering.

The output of amplifier 84 is a bi-level or ethical level signal that swings between bi-level or 12 volts and ground. Especially,
The output signal of the output amplifier is carried to the data input of a latch 86 which forms part of the feedback circuit 20 of the system.

Referring now to FIG. 4e, the components of feedback circuit 20, controller 22, and output circuit 90 are shown. In the center of the bottom of the drawing, capacitors C105 and C110, resistors R108 and R112
And three of the six inverters 401, 402, 402 for the CMOS Schmitt inverter of type CD40106
The clock circuit 92 of FIG. 3 is obtained by the well-known three-inverter type multivibrator formed by 403.

A 40 Hz square wave is generated by a clock circuit and
It is sent to the input of a CMOS decimal counter (ie, a frequency divider) 94 on 93. The frequency divider divides the 40 Hz signal by 10, “5” and “7”
Output two signals 50 ms apart. One signal, which occurs 125 ms after the start of the counting cycle, is sent through another inverter 404 to the non-writable pin of latch 86. A second to generate 175 milliseconds in the cycle
Is sent to the clock input of an address signal generator 96 formed by a CMOS dual flip-flop chip of type CD4013. Each of the flip-flops 96 has a line 196
And 296, the two address signals A ₀ and A ₁ are output. The address signal is two of the three address lines of the octal latch 86.
It is sent to the book and to the address line of a CMOS multiplexer 88 of type CD4053. The signals on address lines 196 and 296 are also sent to the bases of transistors Q103 and Q102, respectively. The emitters of these transistors are connected to the decoder circuit 98
In the dual optical isolator device U205 (see FIG. 4b), the oscillating current signals on the lines 260 and 261 are sent to the optical isolators e and f, respectively. Load resistance R200 and R201 (4b
(Refer to the figure) means that the LEDs of the optical isolators e and f
Restore current to 90. First (125 millisecond) counter signal to the octal latch 86, a "high" state also "low" state address lines A ₀ and A ₁ with the address storage element of the output signal of the power amplifier Have them write in Latch 86 therefore has adjustable capacitors C227 through C2
The output amplifier signal of the bi-level characteristic is stored for each of the 30 in turn so that it is coupled to the bridge. After 50 milliseconds, the second (175 millisecond) counter signal causes the address signal generator 96 to increment the address and switch the new capacitor to the bridge. The system waits for one second to stabilize the current state of the output amplifier signal before it is again written to another storage element in the latch.
Only 2/10 will be given. For each of the four lines 486-489, the latch 86 outputs a two-level state of the system for each of the four set points controlled by each of the four capacitors C227-C230. Address lines 196 and 296
The multiplexer 88, which is controlled to select the latch output signal corresponding to the particular capacitor C227-C230 currently switched to the variable side of the bridge, and
Output to the base of Q206. The output of transistor Q206 is passed through optical coupler U206. As described above with respect to the demodulator circuit, the output of optical coupler U206 is sent to the demodulator amplifier for positive feedback. An optical coupler U206 and an assembly U205 having optical couplers e and f are provided to electrically isolate the error amplifier and demodulator components of the bridge from feedback and controller circuits for inherent stability considerations. I have. If desired, other conventional means such as transformers can be provided for the same function.

Each of the four output lines from addressable latch 86 is coupled to an output circuit 90a-90d, respectively. These output circuits are the same as conventional ones. Therefore, only the 90a component will be described. All components are of the first inverter 407 of the type CD40106.
a to 407d and one of the second inverters 408a to 408d.
It has one. The switches SW100-1 to SW100-4 are provided to select either the output from the latch for "high" level failsafe switching or the output from the first inverter 407 for "low" level failsafe switching. ing. The output of switch 64 is the second inverter
Around it is routed via 408 to a plurality of conventional delay module connections. The output from one of these connections is connected to transistors Q104-Q1 connected in the illustrated embodiment.
Sent to the base of 07. Each transistor is connected LE
D is controlled to drive D103-D106, respectively, while energizing the coil of a conventional two pole, two throw relay. Relay K1
Each of 00 to K103 has two sets
It has three contacts (not shown for simplicity).
The line 99 from the power supply 58 provides approximately 20 volts (DC), and relays K100-K103, opto-isolators U205 and U206, transistors Q102-Q107 and Q207, as well as transistors Q102 and Q1.
Used to energize LED D108 installed on the line that supplies current to 03. Diode D108 is "high"-"low"-corresponding to the current flowing through transistors Q102 and Q103 under the control of address signal generator U103.
Switching from "low" to "off" sequentially.

Referring again to FIG. 4d, the circuit configuration of the power supply 58 is depicted in FIG. 4d. This power supply 58 is traditional. 3-wire AC power source 57 (shown in FIG. 2)
Is converted to a 28 VRMS tapped by transformer T100, rectified by diodes D103 and D104, stored in capacitor C101, and has a pulsating DC voltage of about +20 volts for the circuitry connected to line 99. Is supplied. Resistor / diode network is R100, R101, R1
02, R999, D101, D107; constituted by D102, D109, the transistor Q100 to the line 100 is almost +
Provides a 12 volt DC voltage and also includes transistor Q101
From the line 101 to the line 160.

FIG. 7 illustrates some timing and control signals used in the system in connection with the output signal. The top line is 40Hz output from clock 92 in FIG.
Are shown. The count output signals “5” and “7” of the divider / counter are also
It is drawn to show signals that go high at 125 msec. And 175 msec. The analog output of the demodulator is initially at a low level. Both address signals A0 and A1
Are initially at a high level and coincide with the first set point. When signal "5" outputs a high level, latch 86 sets the output amplifier to output (possibly low level) to the first storage element, and the first reference admittance / first set point output signal RLY0.
Is output. When the signal "7" outputs a high level, the AO signal goes low and matches the second reference admittance connected to the variable side of the bridge network. That capacitor will cause the analog output of the demodulator to go high. Before the signal "5" goes high again, the stable state is maintained. The high level output of the demodulator is stored in the second storage element of the latch, causing the output signal RLY1 to go high. When "7" output from the divider / counter 94 goes high again, the AO signal goes high, triggering the A1 signal low and connecting the third signal to the bridge network.
Matches the capacitor of This process is the third and fourth
Will be repeated for the first capacitor and then started again for the first capacitor.

Having described the first preferred embodiment according to the present invention,
Variations of the preferred embodiment, including the context for the second embodiment described below, will be apparent to those skilled in the art. For example, other oscillators, bridges, error amplifiers, and output amplifiers may be provided. As a demodulator,
Other traditional phase sensitive detection circuits may be provided. Further, other known circuit configurations can be substituted for the feedback circuit 20 and the control circuit 22 described above. For example, in a two-point monitor system, the address generator may be able to be configured with one flip-flop, and may be able to eliminate the overall decoder circuitry as previously described. Further, while multiple capacitor and switch chains are described for the preferred admittance generator, other circuits or devices for automatically generating different capacitor or admittance chains may be replaced as appropriate. Absent.

FIG. 9 is a diagram showing blocks of main functional elements of the second embodiment according to the present invention. An AC or DC external power source 557 is coupled to a power source 558 for supplying power to a portion of the circuit configuration in a suitable configuration. The oscillator 570 is
Connected to transformer 574 for boost bridge 572.
Transformer 574 may include a portion of oscillator 570. Bridge 572 includes a reference admittance generator 578 coupled to the material response sensor by junctions 551-553 and coupled to clock 592. Clock 592 activates reference admittance generator 578 to perform a predetermined sequence of admittance values, which in this embodiment are also automatically and repeatedly changing bridge parameters. Although the bridge output is coupled to the error amplifier 580, the output of the bridge 572 is typically included because it is too small to reliably perform further processing. The output of error amplifier 580 is coupled to a demodulator 582 to extract useful information from the amplified bridge output signal. Demodulator 582 is preferably a phase sensitive detector, the output of which may be responsive to the bridge output produced by conductance, susceptance, or a combination thereof. The output of the demodulator 582 is coupled to an output circuit 584 to generate one or more outputs 525 related to the monitored material condition based on the demodulated and amplified bridge output. Desirably, demodulator 582 or output means 584 includes positive feedback to provide a clear output state despite the continuous variability of system inputs.

The details of the schematic diagram of the second preferred embodiment according to the present invention are shown in FIGS. 10a to 10d, which are aligned as shown in FIG. 10 to constitute a complete schematic diagram.

FIG. 10a depicts a power supply and oscillator circuit of a second preferred embodiment according to the present invention. The power supply 558 is formed by receiving a DC input between its terminal + IN and the common terminal. Capacitor CI filters AC noise present at the input of the power supply, diode D2 is provided to protect the reverse polarity, and diode D3 is provided to protect the circuit against excessive input voltage. . As a result, the unregulated supply potential is designated as B + with respect to the common terminal. A voltage regulator connected to B + generates a regulated voltage at 8.4 volts as follows. Resistor R2 supplies current to Zener diode D1 to stabilize the voltage buffered by emitter follower transistor Q1 tied to a voltage of 8.4 volts. resistance
R1 provides current limit and diode D10 is regulated
Provides overvoltage protection on the 8.4 volt line.

The oscillator, including transformer T1, is energized by an 8.4V power supply. With the exception of the transformer T1, the oscillator is the same as that described in the first embodiment, so its operation will not be discussed further. Transformer T1 differs from transformer 74 in that the shield potential is obtained from an independent winding rather than from above the secondary winding. This is desirable to minimize the source impedance of the shield source and not to vary the ridge output with respect to the shield load, so that the system can be used in various forms of material conductivity and sensor location, these are the shield and It shows high conductance between ground electrodes. An oscillator generates three alternating potentials from a general point of view. These are denoted OSC +, shield, and OSC- with the opposite phase of OSC +.

The oscillator output is coupled to the bridge circuit shown in FIG. 10b. The depicted bridge is of the type shown in FIG. 8b, i.e. the signal appearing at the measuring electrode has a relatively low source impedance in the important material state and the effective material admittance Y ₁
And generated admittance divider consisting of Y _3. The bridge contains a clock consisting of integrated circuit U2, type CD4060. U2 includes three inverters connected to C13, R13 and R14 as monostable multivibrators. U2 further includes a binary divider connected to the multivibrator to generate a clock output denoted as Q. The period of the clock output Q is such that the system can properly respond to any input that appears within a half period of the clock and is much longer than the response time of the remaining circuits. Because the clock can modulate the system output under certain input conditions, such modulation creates one output state of the system of the second embodiment, which is to select the clock period, so that the modulation is It occurs at a frequency that can be sensed. Applicant has discovered that the frequency of 2H _z is adapted for these purposes in the system according to the second embodiment. Clock output Q is used to operate switch U3a, which forms U3, half of type CD4053, the effects of which are described below.

The bridge shields the midpoint of the source at those junctions
Includes an admittance divider consisting of C14 and C17, with an open circuit voltage between OSC +. This source is connected to one end of C20, the other end is the bridge output, and is connected to one input of error amplifier 580. The coupling between the input and the measurement electrode terminal 52 is based on C21. Thus, in the terminology of FIG.
C21 forms an admittance element 514. The bridge thus balances when the current flowing through C20 is equal to the onset of admittance of C21 and the difference between the shield voltage and the measurement electrode voltage.

The bridge further includes C19 connected between OSC + and the common terminal of SPDT switch U3a. In the position shown, the switch connects the switch termination of C19 to the associated insensitive shield. In other positions, the switch sets C19 to C
Connect in parallel with 14, thus adding the admittance and turning it into a current source through a balanced C20. This in turn creates a shield voltage difference that requires equilibrium in the measuring electrodes, and thus changes the material state that must be present in equilibrium.
In this way, different material state set points are established at each part of the clock cycle. If it is desired that the particular system have the required changing capacity of the measuring electrode voltage for equilibrium in order to adapt to different sensor arrangements and / or different material conditions, bridge elements such as C14 and / or C19 May be made variable. Further, the set points may be adjusted independently by switching C14 and C19 to the bridge independently. Further, as noted, the different set points may be made by analog variable bridge elements, such as voltage variable capacitors, using the clock used to change the control input.

R15 and C22 are included between the control bridge outputs and linearize the bridge gain.

Bridge 572 further includes means for proper system operation testing by simulating a material condition of interest, in this case, the submitted container 40. The test means includes a second switch U3b, the common terminal of which is connected to OSC- through C18. As shown, the switch connects C18 to the shield with no associated effect. In other locations, C18 is connected to a junction of C14 and C17 sufficient to produce a bridge output corresponding to a high material condition (by appropriate choice of component values). Thus, when C18 is connected to C41 and C17, the generated output corresponding to a high level indicates that most of the system is functioning.

U703 is connected to a positive shield-reference supply shown at +7.7 and made in the circuit as described below, and to a negative shield-reference supply shown at -7V. −7v power supply is rectified by OSC + and OSC− by D6 and D5 and C16
Made by filtering by R16 limits the current flowing from -7V. These power supplies are also connected to U2.

Switch control C18 allows operation by a circuit adapted for manual or automatic external switch control. The circuit is
Includes a light-separator U5 that has a near radio frequency potential and allows operation by the ground-reference circuit of the switch. U5,
Type 4N23a may include an input LED connected to a positive power supply potential through a current limiting resistor R3. The LED cathode is connected to the test point, which when connected together,
Allows current to flow to the conductor through the LED based on U5 phototransistor. The control input of test switch U3b, which is normally connected to +7.7 potential and kept high through R21, is pulled down to -7V potential by the conduction of a phototransistor, and C35 attenuates noise on the test line operating the LED. .

Referring to FIG. 10c, the error amplifier and demodulator of the second embodiment are shown, along with the generator circuit for the + 7.7V power supply. The error amplifier and the demodulator form a detector that provides a two-level output that changes the predetermined bridge condition, ie, the state of equilibrium. Since these circuits correspond exactly to the circuits of the first embodiment shown in FIG. 4c, they are simply described. The main difference is that control feedback and multi-breakpoints limiting the circuit of FIG.
This is not shown in the figure.

L1, C23, R17, C24 and C25 form a filter whose input is 8.4V with respect to its reference and whose output has a +
7.7V. This + 7.7V power supply operates the error amplifier and demodulator and is used for the aforementioned bridge.

The output of the bridge, which is the voltage with respect to the guard potential, is the first
, And a second transistor Q6. The output of this bridge is connected to the base of Q5, which is biased through R18 and R19. The AC emitter load for Q5 is R3
4, the direct current is controlled by R23 and R23
Is bypassed by C29 at the operating frequency. The collector load is provided by R20 and C26, which provides a gain roll-off for stability. Its output at the collector of Q5 is connected to the base of Q6, which includes a resistor R27 at its emitter to establish a DC operating level and a capacitor C27 to establish an AC emitter load. The collector load of Q6 is formed by R24 and an LC circuit consisting of L2 and C30, which is a parallel resonant circuit at the operating frequency. This load is a secondary at high and low frequencies for stability.
The gain of the stage is rolled off, allowing the output to swing below the negative supply voltage with increasing dynamic range. The overall feedback is provided by R34 and R22, but when the output is increased sufficiently to conduct D8 and D28, R22 is shunted and the increased gain of the amplifier is reduced. This increases the dynamic range of the error amplifier.

The demodulator 582 of FIG. 10c is different from that of FIG. 4c in that the diodes D209 to D212 are removed from the bias circuit for setting the gain of the transconductance operational amplifier U4.
The only difference is that in the first embodiment, the elements R224, R233, and U206 that establish the feedback condition associated with the output state when a particular parallel parameter was last selected are removed. Instead, in the second embodiment, a single feedback resistor is connected from the outputs of switches Q7 and Q8 of the two transistors to the non-inverting input of U4.
The feedback form of the first embodiment may also be used, but generally the level and coating thickness are not likely to be close enough to cause the setpoint feedback cancellation interaction to occur. It is not necessary for status monitoring. The output of demodulator 582 is a two-state signal at the junction of R12 and C12, which is pulled high when Q8 conducts and low when Q8 does not conduct.

The output circuit of the second embodiment is shown in FIG. 10d and basically consists of an amplifier formed by U1, a type CD4007, and an open collector output transistor Q2. The output of the demodulator is connected to a voltage divider and low-pass filter circuit consisting of R4, R5, and C2, which is connected to the gate of the n-channel transistor in U1 and thereby the AC component of the output of the protection scaled demodulator. And ensures that the high and low levels of the output of the demodulator substantially completely turn the transistor on and off, respectively. R6 limits transistor drain current, transistor is CMOS
Connected to the gate of the inverter to provide a low impedance two-level output. This output is connected to the base of the output transistor Q2 via the current limiting resistor R7.
Q2 gives the output of an open collector system. If necessary, an unused inverter may be used to provide the opposite system output.

The transfer function of the whole system of the second embodiment is shown in FIG. As described above with respect to FIGS. 12 and 10b, the system automatically responds, for example, in response to a sensor coated with a material of interest thickness and in response to a sensor completely immersed in a full tank. And it can be made to repeatedly change its set point. Each of these set points are expressed as t _c and t _f on the X-axis. The thickness of the low-level state less than t _c of the coating, the output of the bridge regardless of the state of the switch U3a is high, constantly outputs a high. Coating at lower than exceeded and t _f a t _c, if the tank is not filled, the the output of the look-bridge goes high, C14 and C19 are both circuit when the C14 is switched into the circuit Goes low when switched. Thus, the output oscillates at the clock frequency between high and low and is effectively modulated by the clock. When the thickness of the coating is greater than t _f or the sensor is covered with material, the output of the bridge goes low, regardless of the state of switch Ua3, and the output of the system is therefore low. Thus, the system of the second embodiment provides a single output with three possible output states. An advantage of the tri-state output signal is that a single display means, such as an LED, can display the three output states by assuming off, flashing, and full states. The three-state output provided essentially by the output of the demodulator or provided by the output circuit can be converted to another form of three-state output or to a separate two-state output for two set points. Is understood. For example, a circuit for detecting the oscillation output can be provided, in which case the level output is at a low level and the film output is at a high level.

13a and 13b show a circuit for generating an output which is a function of one or more set points of the first embodiment. FIG. 13a shows a circuit used in conjunction with the split output of the first embodiment to generate a combined output of the type generated by the second embodiment. This circuit has an input t _c and t _f, which are supplied from the output pair of the latch 86 of the 4e Figure, these are high until the excess coating thickness and filled containers set point, respectively. The output 534 of the OR gate 530 until it exceeds the set point t _c is high, the output 534 input t _c is low, according to the clock input. The output 536 of the AND gate 532 is OR gate 530 as long as it does not exceed the set point t _f and as long as t _f is high.
According output 534, the input t _f becomes low, the output 536 goes low. Thus, output 536 provides a transfer function similar to that shown in FIG. 11 and can be used to drive an open collector output transistor or other suitable device as in FIG. 10d.

Figure 13b shows the one state when the input is between the set point t _c and t _f, shows the circuit used to provide an output 542 indicating another state when all other conditions . Output t
XOR 540 connected to the _c and t _f is provides this functionality, and its output, t _f output connected to a suitable output device.

Although the second output is shown as a two set point system, it will be appreciated that it can be modified to provide more set points. For example, the bridge may be provided with an additional switch and connected at an additional admittance element for the duty cycle specific to each admittance element. In this case, the output between the highest and lowest set points is modulated by the clock component over those beyond each set point.

It will also be appreciated that it is generally possible to interchange the circuit blocks of the second embodiment with the circuit blocks of the first embodiment appropriately and to replace them with other equivalents. Would.

While a single-sensor system adapted to monitor both level and coating disclosed herein has the advantage that the coating is measured and conveniently implemented in the actual sensor used to monitor the level, It will further be appreciated that equivalent results can be obtained with a pair of single setpoint monitoring systems other than those described. That is, a pair of single set point systems, each with its own sensor, can be properly positioned within the container, assuming that the coating is uniformly accumulated on the interior surface of the container. is there. Switching occurs when the set point in one of the systems exceeds a predetermined thickness of the coating, and the set point in the other one of the systems determines when the coating is completely formed. Switching can be adjusted to occur.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Peterson, Stephen Earl. United States, Pennsylvania 19025, Dresser, West Windway 204 (56) References JP-A-51-26063 (JP, A) JP-A-51 -63653 (JP, A) JP-A-61-292021 (JP, A) JP-A-57-4519 (JP, A) JP-A-54-107361 (JP, U) JP-A-62-156836 (JP, U) US Patent 3650994 (US, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01F 23/00-25/00

Claims (18)

(57) [Claims] 1. A substance monitoring system, comprising: a sensor disposed in a container containing a fluid substance, wherein the sensor has a thickness corresponding to a level of the substance in the container and a thickness of the coating of the substance on the sensor. A sensor for generating a corresponding sensor signal; and a reference signal having a value that varies among a plurality of reference signal values including a reference signal value representing a substance level set point and a reference signal representing a sensor film thickness set point. A reference generator, and an output signal generation circuit connected to the sensor and the reference generator, the output signal generating circuit comparing the sensor signal and the reference signal to generate a response output signal, and the output signal is: A first state representing a high substance level for the substance level set point, a second state representing a low substance level for the substance level set point, and And a third state indicating that the thickness of the quality of the coating exceeds the sensor coating thickness set point, with at least three different states, material monitoring system. 2. The system of claim 1, wherein said sensor includes a substantially planar material sensing surface. 3. The substance monitoring system according to claim 1, wherein said sensor is an admittance sensor. 4. The output signal generation circuit includes a bridge.
The substance monitoring system according to claim 1. 5. The substance monitoring system according to claim 1, wherein said output signal generation circuit includes a switch for changing said reference signal value when driven. 6. The substance monitoring system according to claim 1, wherein said reference generator includes a switch for changing said reference signal value when driven. 7. The substance monitoring system according to claim 6, further comprising a switch controller connected to said switch, wherein said switch controller automatically and repeatedly drives said switch. 8. A method for monitoring a fluid material in a container, comprising: arranging a sensor in the container, driving the sensor to respond to a level of the fluid material in the container, and to monitor the fluid on the sensor. Generating a sensor signal according to the thickness of the coating of the substance, generating a level reference signal representing the substance level set point and a film thickness reference signal representing the sensor film thickness set point, and converting the sensor signal and the reference signal. Comparing and generating an output signal comprising one selected from at least three different states according to the result of said comparing step, wherein two of said states are representative of a level of a substance with respect to said substance level set point, A method of monitoring a fluid material in a container, wherein one of the states represents a thickness of a material coating on the sensor relative to the sensor film thickness set point. 9. The step of disposing the sensor comprises disposing the sensor having a flat surface in the container.
9. The method of claim 8, including thereby causing said substantially planar surface to be substantially the same as an interior surface of said container. 10. The method of claim 8, wherein driving the sensor comprises applying a radio frequency signal to the sensor. 11. The method of claim 8, wherein said step of disposing a sensor comprises disposing an admittance sensor in said container. 12. The method according to claim 8, wherein the step of generating the reference signal includes driving a switch that selects one of the reference signals for comparison in the comparing step.
The method described in the section. 13. The method of claim 12, wherein said step of generating a reference signal comprises automatically and repeatedly driving said switch. 14. The comparing step includes providing a bridge that compares the sensor signal with the reference signal.
The method according to claim 8. 15. A fluid material in a container using an instrument system including a sensor disposed in the container and an instrument connected to the sensor to provide a level output signal indicative of a level of the material in the container. In the level monitoring process, the sensor is made to be coated with a substance, and the coating of the substance on the sensor affects the performance of the instrument to generate a level output signal that accurately represents the level of the substance. The method of operating the instrument system comprising: detecting a coating of a substance on the sensor within the instrument; generating a coating output signal indicative of the coating of the substance on the sensor; A method of operating an instrument system that distinguishes it from a level output signal. 16. The method according to claim 15, wherein said output signal indicative of said coating is indicative of a thickness of said coating on said sensor. 17. The method of claim 16, wherein the output signal indicative of the coating indicates whether the thickness of the coating on the sensor exceeds a coating thickness set point. 18. The method according to claim 18, wherein the instrument generates an output signal having one of at least three predetermined states, and the step of generating an output signal representative of the coating generates an output signal having one of the predetermined states. 16. The method of claim 15, comprising: