JPH0810239B2 - Two-wire transmitter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a two-wire type transmitter having input / output conversion characteristics of two measurement ranges.

<Prior Art> Conventionally, in order to accurately measure the amount of fluid to be measured in a wide measurement range, the measurement range is divided into two measurement ranges, measured, converted into an electrical signal, and the signal is transmitted to a receiver. There is a transmitter. In a transmitter with two such measurement ranges, power is supplied to the transmitter and DC4
In addition to the two transmission lines that transmit an output signal of ~ 20 mA, a discrimination signal line for transmitting a signal for discriminating the measurement range was required. Therefore, in a two-wire type transmitter that connects the transmitter and the receiver with only two transmission lines, only one measurement range can be measured and transmitted.

To solve this, superimpose an AC signal of a specific frequency on the output signal of 4 to 20 mA DC, determine which measurement range the output signal corresponds to according to the frequency of the AC signal, and perform two measurements. 2 configured to measure range
A wire type transmitter has been proposed (as an example of such a two wire type transmitter, there is Japanese Utility Model Laid-Open No. 56-175764).

<Problems to be Solved by the Invention> However, in such a conventional two-wire transmitter, a plurality of AC transmitters or frequency-switchable AC transmitters are required on the transmitter side, There was a problem that the circuit became complicated.

Further, since the AC oscillator consumes a large amount of power, it is difficult to apply this configuration to a transmitter such as a two-wire electromagnetic flowmeter, which has a large power consumption constraint.

Furthermore, on the receiver side, a filter that separates the output signal of 4 to 20 mA DC and the AC signal for measuring range determination, and a circuit that detects the frequency of the AC signal are required,
When the frequency of the range discrimination signal is set high, the attenuation of the discrimination signal becomes large when the transmission distance becomes long and it becomes difficult to receive.On the other hand, when the frequency is lowered, the shape of the filter becomes large, and the output signal and range discrimination There was a problem that it became difficult to separate from the signal.

<Objects of the Invention> The present invention has been made to solve the above problems, and a circuit can be configured simply, an increase in power consumption can be suppressed, and a measurement range can be accurately determined. It is an object of the present invention to provide a 2-wire type transmitter having two measurement ranges described above.

<Means for Solving Problems> The present invention has an input / output conversion characteristic corresponding to each of two measurement ranges, and the measured and input flow rate to be measured is input to one of the measurement ranges. A two-wire transmitter that converts electric power into an electric signal based on the output conversion characteristics and outputs the electric signal, and that power consumed for the conversion is supplied through two transmission lines used for electric signal transmission. Polarity determining means for determining the polarity of the voltage of the electric power and outputting a range switching signal corresponding to positive or negative of the polarity, and one of the two measurement ranges corresponding to the range switching signal from the polarity determining means. By providing range switching means for switching to the input / output conversion characteristic of the measurement range, it is possible to perform measurement in two measurement ranges and enable measurement in a wide range and forward and reverse measurement.

<Operation> In the present invention, the polarity determination means of the two-wire transmitter is
The polarity of the voltage of the supplied power is determined, and the range switching signal corresponding to the positive and negative polarities is output.

The range switching means switches the input / output conversion characteristic corresponding to each of the two measurement ranges to the input / output conversion characteristic of one measurement range corresponding to the range switching signal from the polarity determination means.

Accordingly, the input / output conversion characteristics of the 2-wire type transmitter are switched depending on whether the polarity of the voltage of the supplied power is positive or negative, and the output signal is transmitted in one of the two measurement ranges.

<Embodiment> An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit configuration diagram of a two-wire type transmitter according to an embodiment of the present invention. In the figure, SC is a transmitter, RC is a receiver, L1, L2.
Are two transmission lines that connect the transmitter SC and the receiver RC.

The transmitter SC has a detector 1 for converting a measured fluid amount, for example, a flow rate into an electric signal, and the electric signal is amplified by an amplifier A1 and converted into a digital amount by an A / D converter 2 to be a microprocessor. Input to 3.

The microprocessor 3 reads a digital amount from the A / D converter 2 at a predetermined timing based on a predetermined program, receives a range switching signal E3 from a polarity discriminating means 4 which will be described later, and a range switching means, etc. Mainly composed of a CPU that executes the processing of (1), a ROM that stores fixed information such as program data, and a RAM that stores each data related to the arithmetic processing of the CPU in a temporarily readable and writable manner. The digital amount input to the microprocessor 3 is arithmetically processed according to a predetermined range and then converted into a voltage signal E1 by the D / A converter 5.

The voltage signal E1 is input to a voltage-current conversion circuit including a differential amplifier A2, a transistor Tr2 and resistors R1 to R5. Then, the differential amplifier A2 controls the transistor Tr2 so that the voltage signal E1 and the voltage E2 generated between both ends of the current detection resistor R5 provided on the negative electrode line have a proportional relationship, and the voltage signal E1 increases. Then, the value of the voltage E2 is increased until E1 and E2 are proportionally balanced. Therefore, the currents flowing through the two transmission lines L1 and L2 are increased or decreased in proportion to E1.

The polarity discriminating means 4 comprises a transistor Tr1, a diode D1 and resistors R6 and R7 in the embodiment.
The base of is connected to the point P1 connected to the transmission line L1 via the diode D1 and the resistor R6, and the collector is connected to the output side positive line of the constant voltage circuit A3 via the resistor R7. When the transmission line L1 has a positive polarity, the transistor Tr1 is turned on and the collector output, that is, the range switching signal E3
Becomes a low level, and when the transmission line L1 has a negative polarity, the transistor Tr1 is turned off and the range switching signal E3 becomes a high level. It should be noted that the diode D1 is reverse biased when the point P1 has a negative polarity, and the emitter of the transistor Tr1
The reverse leakage current between the bases is prevented from flowing by bypassing the current detection resistor R5, so that no error occurs in the output signal of the transmitter SC.

The diode bridge D2 is a bridge rectifier for full-wave rectification, and the output terminal positive side P2 of the diode bridge D2 is always positive regardless of whether the polarity of the power supply from the transmission lines L1 and L2 is positive or negative. It is formed so as to have a sex.

The receiver RC most suitable for combination with the above-mentioned transmitter SC has the following configuration. That is, the receiver RC is the transmitter
The power supply ES for SC is provided, and the power supply ES is formed so that the voltage is supplied to the transmitter SC via the switch SW, the load resistor RL for current detection, and the two transmission lines L1 and L2. Receiver
RC is a switch SW that switches the polarity of the power supply to positive or negative.
And a setting device 6 for driving the switch SW is provided,
The switch SW and the setting device 6 constitute a polarity setting means 10.

The setter 6 amplifies the voltage signal obtained by converting the output signal of the transmitter SC (4 to 20 mA DC) by the load resistance RL with the amplifier 7 and outputs the output voltage VO, which is input to the comparators CM1 and CM2. It Comparators CM1 and CM2 have reference voltages EC1 and E, respectively.
C2 is set, the outputs of the comparators CM1 and CM2 are input to the determination circuit 8, and in response to this, the determination circuit 8 switches the switch SW to the A side or the B side and outputs a setting signal.

The reference voltages EC1 and EC2 have input / output conversion characteristics of, for example, the full scale of the first range, which is one measurement range, and the full scale of the second range, which is the other measurement range, as shown in FIG. As Q2, the output signal that switches from the first range to the second range is C1 (that is, the maximum output signal),
When the output signal for switching from the first range to the second range is C2, the reference voltage EC1 is set to a voltage corresponding to C1 and the reference voltage EC2 is set to a voltage corresponding to C2. When the switch SW is on the A side and the first range measurement is being performed, if the flow rate on the QA line decreases below Q2, the output voltage VO becomes less than the reference voltage EC2 and the comparator CM2 changes to the H level. Become. In response to this, the decision circuit 8 sets the switch SW to B
To the second side, the transmission line L1 is set to a negative polarity, and the transmitter SC is switched to the second range measurement. Also, when the switch SW is on the B side and the second range measurement is being performed,
When the flow rate on the QB line increases above Q2, the output voltage VO>
It becomes the reference voltage EC1, and the comparator CM1 becomes L level. In response to this, the determination circuit 8 switches the switch SW to the A side, sets the polarity of the transmission line L1 to be positive, and switches the transmitter SC to the first range measurement.

The output voltage VO is output to an indicator, an integrating type, etc. via a range conversion circuit (not shown) controlled by the determination circuit 8. The range conversion circuit converts the output voltage VO corresponding to the range being measured, and outputs the output voltage VO of the first range and the second range as a continuous quantity.

Next, the operation of the 2-wire type transmitter configured as described above will be described.

First, when the switch SW of the receiver RC is on the A side, the transmission line L1
When the polarity of is positive, the power supply voltage is supplied to the transmitter SC. Therefore, a positive voltage is applied to point P1 of the transmitter SC, the transistor Tr1 is turned on, and the range switching signal E3 of the polarity discriminating means 4 becomes low level. The detected flow rate is output as an electric signal in the detector 1, and further converted into a digital amount by the A / D converter 2.

Then, as shown in the flow chart of FIG. 2, the microprocessor 3 starts after the initial set operation according to the control program, and at step 100, the digital amount is read from the A / D converter 2. Next, the process proceeds to step 110 and the range switching signal E
If 3 is low level, step is judged when the judgment is YES.
In step 120, the digital amount is calculated using the coefficient corresponding to the first level. Then, in step 140, the calculated digital amount is output to the D / A converter 5.

On the other hand, when the switch SW of the receiver RC switches to the B side,
The polarity of the transmission line L1 becomes negative, and a negative voltage is applied to point P1. Then, the transistor Tr1 is turned off, and the range switching signal E3 of the polarity discriminating means 4 becomes high level.

When the range switching signal E3 becomes high level, the determination of step 110 in the microprocessor 3 becomes NO, the process proceeds to step 130, and the digital amount is calculated by the coefficient corresponding to the second range. Then, in step 140, the calculated digital amount is output to the D / A converter 5. When the process of step 140 is completed, the process returns to step 100 and the above process is repeated.

For the input / output of the above-mentioned microprocessor 3, if the full scale of the first range and the second range in the input / output conversion characteristics of FIG.
When 0M ³ / H, the output signal becomes 20mA of full scale, and in the 2nd range, when 20M ³ / H, the output signal becomes 20mA of full scale.
It becomes mA. Therefore, when the digital amount calculated by the microprocessor 3 in the first range at step 120 is a value equivalent to 50 M ³ / H, the digital amount output to the D / A converter 5 at step 140 is an output signal equivalent to 20 mA. Is the value of. See also step 130
When the digital amount calculated in the second range is a value equivalent to 20 M ³ / H, the digital amount output to the D / A converter 5 in step 140 is a value equivalent to 20 mA. In addition, the above steps 110, 120,
The processing of 130 corresponds to the range switching means 20 of the present invention.

The digital amount input to the D / A converter 5 is the voltage signal E1.
After being converted to, the signal is output from the transistor Tr2 as an output signal of DC4 to 20 mA to the receiver RC via the transmission lines L1 and L2.

In the receiver RC, the output signal of the transmitter SC is the load resistance.
It is converted into a voltage signal by RL and input to the setting device 6. The setting device 6 outputs the setting signal when the flow rate decreases to Q2 or less (the output signal is C2 or less) during the measurement of the first range with the switch SW on the A side, and switches the switch SW to the B side for transmission. Line L1
Switch the polarity of to negative. Also, when the switch SW is on the B side and the flow rate increases above Q2 (the output signal is above C1) during the measurement of the second range, a setting signal is output, the switch SW is switched to the A side, and the polarity of the transmission line L1 Switch to positive. As a result, in the transmitter SC, the measurement range is switched and measurement is performed as described above.

In Fig. 3, the full-scale Q2 of the flow rate is in the second range.
I showed an example of switching to the 1st range when reaching Q2.
For example, the measurement range may be changed with a value of 90% of an arbitrary ratio or with a value of 90% of an arbitrary ratio with respect to 20 mA of the output signal. It is also possible to add hysteresis to the switching of the measurement range.

Further, when the flow rate of the forward flow and the reverse flow is measured by using the detectors for the forward flow and the reverse flow, the present invention can be used to measure the forward flow in the first range and the reverse flow in the second range. Is. Fig. 4 exemplifies the switching between the forward flow and the reverse flow of the flow rate. The full scale of the first range is, for example, +50 M ³ / H of the positive flow Q1, and the full scale of the second range is the reverse flow.
This is the case when Q2 is selected as −50 M ³ / H. In FIG. 4, when the output signal becomes 4 mA or less during the measurement in the first range, the setter 6 switches the switch SW to the B side, so that the transmitter SC becomes the second range of the backflow measurement. For the measurement of the reverse flow, the A / D converter 2 may be a known method corresponding to both the forward and reverse directions.

Furthermore, FIG. 5 is an example in which the measurement states of FIG. 3 and FIG. 4 are combined, and the full scale of the first range is a positive flow Q1, for example, +50 M ³ / H, and the full scale of the second range is a reverse flow. Q2 For example, it can be applied when selecting -20M ³ / H for measurement.

The fluid layer to be measured detected by the transmitter SC may be various process variables such as temperature, differential pressure, and flow velocity.

<Operation and Effect of the Invention> As described above, the two-wire transmitter of the present invention has the input / output conversion characteristics corresponding to each of the two measurement ranges, and the measured and input measured fluid amount is divided into two. Based on the input / output conversion characteristics of one of the measurement ranges, it is converted into an electric signal and output, and the power consumed for the conversion is supplied through two transmission lines used for transmission of the electric signal. In the wire-type transmitter, the transmitter discriminates the polarity of the voltage of the supplied power by the polarity setting means for switching and setting the polarity of the voltage of the power supplied to the transmitter on the receiver side, and the polarity is positive or negative. Since the configuration includes polarity determining means for outputting a range switching signal corresponding to, and range switching means for switching the input / output conversion characteristic to the input / output conversion characteristic of the measurement range corresponding to the range switching signal from the polarity determining means, it is 2 Wire system Since it is possible to automatically switch between the two measurement ranges, it is possible to accurately perform measurement in a wide measurement range, and it is possible to automatically switch between the two measurement ranges.

Furthermore, since independent measurement ranges can be selected for forward and reverse measurement of the fluid to be measured and forward and reverse of the fluid to be measured, it is possible to maximize its function as a two-wire transmitter.

Further, when the polarity setting means for automatically switching between the two measurement ranges is provided on the receiver side as described above, only the polarity determining means and the range switching means are required on the transmitter side.
The transmitter can be constructed simply and inexpensively. Moreover, the increase in power consumption due to the function added to the transmitter is extremely small, and it is most suitable for application to a transmitter with a large power consumption constraint such as a two-wire electromagnetic flowmeter.

Furthermore, unlike the conventional two-wire transmitter, there is no difficulty in attenuating the superimposed AC signal (measurement range discrimination signal) due to a long transmission distance and separation of the output signal and the AC signal,
It is possible to accurately determine the range of the output signal.

In addition, by setting the first range and the second range to the same setting, the same output signal can be obtained regardless of the connection polarity of the transmission line, and therefore it is not necessary to consider the polarity when connecting the transmission line, The effect that the installation work can be performed easily and quickly is achieved.

When the 2-wire transmitter of the present invention is combined with the conventional receiver and power supply device without the polarity switching function, the 2-wire transmitter of the present invention is an input / output device corresponding to each of two measurement ranges. Since it has conversion characteristics and is equipped with a polarity determination means,
Either the input / output conversion characteristic can be switched by changing the wiring of the transmission line or reversing the polarity of the power source inserted in the transmission line. Therefore, when the time for switching the measurement range is known in advance, it is effective even if it is buried in the ground or the transmitter is installed in a place where people cannot easily approach.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a two-wire type transmitter according to an embodiment of the present invention, FIG. 2 is a flow chart showing the arithmetic processing of the range switching means of the microprocessor, and FIG. FIG. 4 is a diagram illustrating output conversion characteristics, and FIG. 4 is a diagram illustrating an example in which input / output conversion characteristics are applied to forward flow and reverse flow.
The figure is a diagram showing an example in which the input / output conversion characteristics are applied in combination with two measurement ranges of forward flow and reverse flow. 4 ... Polarity determination means, 6 ... setting device, 10 ... polarity setting means, 20 ... range switching means, SW ... switch, SC ... transmitter, RC ... receiver.

Claims (1)

[Claims] 1. An electric signal having an input / output conversion characteristic corresponding to each of two measurement ranges, wherein the measured and input fluid amount to be measured is based on the input / output conversion characteristic of one of the measurement ranges. It is a two-wire type transmitter that converts the power into two and outputs it, and the power consumed for the conversion is supplied through two transmission lines used for the transmission of electric signals, and the polarity of the voltage of the supplied power is determined. A polarity discriminating means for outputting a range switching signal corresponding to positive and negative polarities, and an input / output conversion characteristic of one of the two measuring ranges corresponding to the range switching signal from the polarity discriminating means. A two-wire transmitter, comprising: a range switching means for switching to.