JP6964968B2 - How to reduce noise superimposed on electrical equipment and electrical equipment signals - Google Patents

Description

The present invention relates to various electric devices and methods for reducing noise superimposed on the signals of the electric devices, and in particular, electric devices having a load in which the amount of inflowing current changes with time, and signals of such electric devices. The present invention relates to a method of reducing the noise superimposed on the electric current.

Currently, various electric devices are used in various fields. The proper operation of electrical equipment may be hindered by external noise or noise generated by itself. In order to obtain the normal operation of electrical equipment, various attempts have been made to prevent malfunction due to noise. For example, Patent Document 1 describes that noise is reduced by blunting the output waveform inside an IC that outputs a signal transmitted to a communication line.

Japanese Unexamined Patent Publication No. 2007-214643

In electrical equipment, in addition to those associated with switching of output signal levels as in Patent Document 1, for example, fluctuations in current due to fluctuations in load in the circuit of electrical equipment may be a noise source. For example, the potential of the ground line fluctuates with the fluctuation of the current flowing through the load, and as a result, the potentials of various signal lines based on this ground potential may fluctuate, resulting in malfunction. In particular, in a communication signal line that transmits and receives predetermined information due to a minute change in potential, fluctuations in the ground potential can be a major problem in accurately exchanging information. For example, in the HART protocol, which is mainly used for communication between instrumentation devices (such as between instrumentation devices or between instrumentation devices and control devices), digital signals transmitted and received by frequency shift keying (FSK) are transmitted. Since the current amplitude is _{as small as about 0.8 mA PP,} it is considered that it is easily affected by fluctuations in the ground potential.

Regarding noise due to such fluctuations in the ground potential, it is conceivable to prevent malfunction due to the influence of the noise by separating the ground which is the reference of the communication signal and the ground such as the power supply line. However, separating the ground leads to complication of the internal circuit of the electrical equipment and requires a wire or wiring pattern on the wiring board for the separated ground, and because of such wire or wiring pattern. Since it requires a lot of space, it can be a factor that hinders the miniaturization of electrical equipment. Further, the above-mentioned communication between instrumentation equipment is performed in various plants, for example, but the total number of lines connecting the instrumentation equipment installed in each building in the plant by a predetermined laying route. The extension can extend up to 1 km, which is also a problem in terms of track cost.

Further, for example, some electric devices that simply transmit and receive measurement data by a sensor by a transmission method having a relatively large noise tolerance share a reference ground for a communication signal and a ground for a power supply line. Even in these devices that share the ground line between the signal system and the power supply system, transmission of various signals may be required to improve the function, and the above-mentioned HART protocol etc. is used to multiplex the transmission signal. May need to be adopted. However, for example, in an existing device that shares a ground line between the signal system and the power supply system, if the ground is separated in order to avoid problems due to noise when adopting the HART protocol, etc., the entire electrical device can be modified or electricity can be used. It may be necessary to lay a new track between devices. In particular, for a detector that detects flammable gas, for example, it is required to comply with a predetermined safety standard that requires the provision of an explosion-proof structure, so it is not possible to change the housing structure that has been once certified as conforming. It's not easy.

The present invention has been made in view of such a problem, and it is intended to provide an electric device that operates normally without malfunction even if the internal load fluctuates, and does not require a lot of space or wiring. The purpose. Another object of the present invention is to provide an electric device capable of normally transmitting and receiving signals even if the internal load of the electric device fluctuates in a communication method sharing a ground line with a power source. Another object of the present invention is to provide a method capable of easily reducing a malfunction due to noise in an electric device having a fluctuating load unit.

The electric device according to one aspect of the present invention is supplied from a power supply unit that supplies a current at a first voltage, a first load unit in which a current from the power supply unit flows in at a current value that fluctuates with time, and a power supply unit. A constant current generation unit that causes the current to flow out at a constant current value, and a current having a magnitude corresponding to the fluctuation of the current flowing into the first load unit are configured to flow in from the constant current generation unit. It has a constant voltage generation unit that supplies a second voltage to the first load unit.

The constant current generation unit is configured to generate a constant current larger than the maximum value of the current flowing into the first load unit, and the constant voltage generation unit is configured to generate the constant current generation unit during operation of the constant current generation unit. It is preferable that the current is always flowed from the constant current generation unit.

The constant voltage generator may include a shunt regulator.

Further, it may have a communication means for transmitting and receiving a signal with reference to a ground that shares the same line as the ground of the power supply unit with an external device according to a predetermined protocol.

Further, it may have a second load section in which a current that fluctuates more slowly than the current that flows into the first load section flows in, and the second load section operates by receiving the supply of the first voltage. It may be configured as follows.

Further, it may include a detecting means for detecting the state of the surrounding environment, and may be configured so that the inflow current to the first load unit fluctuates according to the state of the detecting means.

The electric device of another aspect of the present invention includes a power supply unit that supplies a current at a first voltage, a first load unit in which a current from the power supply unit flows in at a current value that fluctuates with time, and the power supply unit. A communication means that transmits and receives a signal with reference to the ground that shares the same line as the ground with an external device according to a predetermined protocol, and a power supply unit that receives a current corresponding to fluctuations in the current flowing into the first load unit. It has a current control means for reducing fluctuations in the ground potential of the power supply unit by dividing the current from the current.

The method of the present invention is an electric device having a power supply unit and a first load unit in which a current from the power supply unit flows in at a current value that fluctuates with time. This is a method of reducing the noise superimposed on the signal of the above, in which a constant current is generated from the current supplied from the power supply unit, and a current having a magnitude corresponding to the fluctuation of the current flowing into the first load unit is constant. A constant voltage is generated by splitting the current from the current and flowing it through the split path, and a part of the constant current is supplied to the first load section, and the current flowing through the first load section and the split path is used as the power supply. It is characterized in that the fluctuation of the current flowing to the ground of the power supply unit is made smaller than the fluctuation of the current flowing into the first load unit by returning to the unit.

According to one aspect of the present invention, even if the current flowing into the first load section fluctuates, a constant current is drawn from the power supply section by the constant current generation section, and the constant current is transferred to the first load section. A current corresponding to the fluctuation of the inflow current flows into the constant voltage generation unit, and a constant voltage by the constant voltage generation unit is supplied to the first load unit. Therefore, the influence of the fluctuation of the load of the first load unit on the current flowing in and out of the power supply unit is eliminated, the ground potential is stabilized, the potential of the signal line is also stabilized, and malfunction can be prevented. Further, according to another aspect of the present invention, since the fluctuation of the ground potential of the power supply unit is reduced by the current control means, communication by the communication means sharing the ground with the power supply unit can be performed without malfunction. .. Proper communication can be performed in each of the power supply system and the signal system without providing a separate ground line. Since communication can be performed with a small number of wires without transmission errors, a communication system connecting electrical devices can be constructed using small electrical devices at low cost. It may also be possible to improve the functionality of electrical equipment while avoiding large-scale modifications.

It is a block diagram which shows schematic structure of the electric device of one Embodiment of this invention. It is a circuit diagram which shows an example of the electric circuit which comprises the current control means of FIG. It is a figure which shows the appearance of the gas detector which is an example of the electric device of one Embodiment of this invention. It is a figure which shows the appearance of the gas detector which is an example of the electric device of one Embodiment of this invention. It is a figure which shows the gas detector of FIG. 3A and FIG. 3B in a state where the main body side housing and the lid side housing are separated. It is a figure which shows the fixing plate used for the gas detector of FIG. 3A and FIG. 3B. It is a figure which shows the cross section by the VI-VI line of FIG. It is a figure which shows the 1st circuit board in the state which the fixing plate shown in FIG. 4 is not attached to the lid side housing. It is a figure which shows the 2nd circuit board fixed to the fixing plate shown in FIG. It is a figure which shows the measurement result of the inflow current to the 1st load part in one Example and comparative example of this invention which has the current control means of FIG. It is a figure which shows the measurement result of the current flowing through the ground line of one Example and the comparative example of this invention under the fluctuation of the current shown in FIG. 9A. It is a figure which shows the measurement result which measured the current shown in FIG. 9A by enlarging the time axis. It is a figure which shows the measurement result which measured the current shown in FIG. 9B by enlarging the time axis.

Hereinafter, the electric device according to the embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a schematic functional block diagram of an electrical device 100 according to an embodiment of the present invention.

As shown in FIG. 1, in the electric device 100 of the present embodiment, the power supply unit 2 that supplies a current to the internal components of the electric device 100 at the first voltage V1 and the current from the power supply unit 2 with time. The ground of the power supply unit 2 is divided by dividing the current i2 corresponding to the fluctuation of the current i1 flowing into the first load unit 3 from the first load unit 3 flowing in with the current value fluctuating to and the current flowing from the power supply unit 2. It has a current control means 1 that reduces fluctuations in potential.

Here, "(current fluctuates)" means that the current changes by a change amount of a certain magnitude or more per unit time. Specifically, this "fluctuation" means that the ground potential of the power supply unit 2 fluctuates due to the change, for example, when the current control means 1 of the present embodiment is not provided, and the electric device 100 is normal. It means that the current changes rapidly enough to interfere with the operation. Also, "change over time" includes both regular and irregular changes.

In the electric device 100, electric power is supplied from the power supply unit 2 to the first load unit 3 via the current control means 1. The magnitude of the internal load of the first load unit 3 changes with time according to the operating state of the electric device 100, and the magnitude of the current flowing into the first load unit 3 changes according to the change. .. If the magnitude of the internal load changes in this way, any element of the constituent elements of the electric device 100 can be regarded as the first load unit 3. Further, the first load unit 3 may be a portion that fulfills a main function of an electric device, and is a portion that fulfills a secondary function, for example, a display unit, an operation unit, or the like, which functions as an interface with a user. May be good. The first load unit 3 includes a central processing device of the electric device 100, a storage device such as a ROM or RAM, a modem when the electric device 100 has a communication function, various sensors, a display device such as a display, and a lighting device such as an LED. Or, an input device such as a keyboard or a touch panel, and peripheral circuits thereof are exemplified.

The power supply unit 2 supplies a current to the components in the electric device 100 at the first voltage V1 based on the electric power from a commercial power source, a battery, or the like. For example, examples of the power supply unit 2 include an electric circuit constituting a linear regulator or a switching regulator that outputs a stable voltage, an integrated circuit device configured as such a regulator, and peripheral circuits thereof. Further, when the electric device 100 does not need the function of generating or stabilizing the first voltage V1, such as when a stable voltage is applied from the external power supply B at the first voltage V1, it is connected to an external electric circuit. The connection unit 101 corresponds to the power supply unit 2. Further, when the electric device 100 is operated by the electric power of the battery (not shown) set in the electric device 100, the power supply unit 2 holds the battery and sets the battery voltage in the electric device 100 as the battery is set. It may be a battery holding unit that supplies the components of the above. The connection portion 101 is a connector or coupler for connecting the external power supply B and the electric device 100, or a terminal or pad for connecting an external wire rod connected to the external power supply B to the electric device 100. good.

As described above, the current control means 1 is configured to reduce fluctuations in the ground potential of the power supply unit 2. That is, the current control means 1 is configured to divide the current supplied from the power supply unit 2 into the current i1 flowing into the first load unit 3 and the current i2 having a current value corresponding to the fluctuation of the current i1. Has been done. The current value of the current i2 is controlled by the current control means 1 so that the current value of the current i1 flowing through the first load unit 3 decreases as the current value increases, and increases as the current i1 decreases. Preferably, the current value of the current i2 is controlled so as to decrease by substantially the same amount as the amount of increase in the current i1 and increase by approximately the same amount as the amount of decrease in the current i1. The current i2 passes through the current control means 1 and flows to the ground G. By configuring the current control means 1 in this way, the fluctuation of the current taken out from the power supply unit 2 for supplying the current to the first load unit 3 becomes smaller than the fluctuation of the current i1. Further, the fluctuation of the total current obtained by adding the current returning from the first load unit 3 to the power supply unit 2 via the ground G and the current returning from the current control means 1 to the power supply unit 2 via the ground G is the current. It becomes smaller than the fluctuation of i1. That is, even if the current i1 flowing through the first load unit 3 fluctuates with time, the fluctuation of the current flowing out from the power supply unit 2 and the current flowing into the power supply unit 2 becomes smaller than the fluctuation of the current i1, and the power supply unit 2 Fluctuations in the ground potential of the above are suppressed. As a result, fluctuations in various signal lines in the electrical equipment 100 due to fluctuations in the current i1 are reduced, and malfunction of the electrical equipment 100 can be prevented.

As shown in FIG. 1, the electric device 100 of the present embodiment further includes a communication means 4. The communication means 4 transmits and receives an electric signal including desired information to and from the external device E according to a predetermined protocol. In the present embodiment, the electric device 100 is connected to the external device E by the first line L1, the second line L2, and the third line L3 with respect to signal transmission. That is, the communication means 4 is configured to transmit and receive signals by a so-called three-wire communication protocol. In the example of FIG. 1, the first line L1 is a power supply line in which power is supplied from either one of the electric device 100 or the external device E to the other, and the second line L2 transmits a signal including desired information. The signal transmission line to be transmitted, and the third line L3 is a ground line that serves as a reference for the potential of the transmitted signal.

As shown in FIG. 1, the third line L3 is connected to the ground of the power supply unit 2, and the power supply unit 2 and the communication means 4 are one of the first lines with respect to power supply and signal transmission between the external device E and the external device E. It shares 3 tracks L3. When the electric device 100 of the present embodiment does not have the current control means 1, the current flowing into the ground G fluctuates according to the fluctuation of the current i1 flowing into the first load unit 3. When the change of the current i1 is steep, the potential of the ground G fluctuates with the change of the current flowing into the ground G, and the potential of the third line L3 connected to the ground G also fluctuates. Therefore, the potential of the signal transmitted via the second line L2 with respect to the potential (ground potential) of the third line L3 fluctuates, which may hinder the normal signal transmission between the electric device 100 and the external device E. There is.

In particular, in the above-mentioned communication by the HART protocol (hereinafter, simply referred to as HART communication), since the current amplitude of the transmitted digital signal is very small, it is considered that transmission errors and malfunctions due to fluctuations in the ground potential are likely to occur. In HART communication, in order to prevent malfunctions caused by such sharing of the ground line, so-called 4-wire communication is also performed in which the ground of the power supply line and the ground of the signal transmission line are separated. However, since the 4-wire system requires two ground lines, it may be disadvantageous in terms of cost reduction and miniaturization as described above. In HART communication, so-called two-wire communication, which has fewer lines than the three-wire system, has also been put into practical use, but since the power supply line and the signal transmission line share one line, the power supply currents are compared. There is a demerit that it is limited to a small value.

In the present embodiment, as described above, the current control means 1 suppresses fluctuations in the ground potential of the power supply unit 2 due to fluctuations in the current flowing into the first load unit 3, so that even in so-called 3-wire HART communication. , A signal can be appropriately transmitted between the electric device 100 and the external device E without causing a transmission error or a malfunction. The communication protocol by the communication means 4 of the present embodiment is not limited to the 3-wire HART communication, and may be a 2-wire or 4-wire HART communication. In addition, Modbus Protocol, FOUNDATION Fieldbus, Profibus, Ethernet (registered trademark), and the like are exemplified as communication protocols by the communication means 4. However, in the present embodiment, the communication means 4 is configured to perform HART communication by a three-wire system in that a signal can be appropriately transmitted and received with a small number of lines even if the signal has a minute amplitude. , More informative.

Further, according to the present embodiment, an electric device in which one ground line is shared between the ground of the power supply line and the ground of the signal transmission line and signal transmission is performed by a transmission method that is relatively resistant to noise is used as the ground line. Without increasing the number, it is possible to switch so that a transmission method that is easily affected by noise but has high transmission performance can be used. While avoiding large-scale remodeling of electrical equipment and expansion of transmission lines between electrical equipment, it is possible to easily improve the functionality of signal transmission. In particular, this embodiment is useful when the structure of the housing of the electric device cannot be easily changed in terms of conformity with safety standards.

The communication means 4 is composed of hardware such as an integrated circuit device and an electric circuit composed of individual components, which are configured to transmit and receive electric signals between the external device E and the electric device 100. Further, the communication means 4 may include software such as a program in which an instruction for causing the integrated circuit device to perform a predetermined process is written. Further, the communication means 4 includes signal conversion (conversion between an analog signal and a digital signal, signal level conversion, etc.), signal amplification, signal synthesis and decomposition, which are necessary for communication with the external device E. And / or may include integrated circuit devices and electrical circuits configured to modulate and demodulate the signal. For example, the communication means 4 defines a communication control IC composed of a microcomputer, an ASIC, or the like programmed to perform signal processing necessary for signal transmission with the external device E, and a signal inside the electric device 100 as a predetermined protocol. It is composed of a modem IC configured to modulate the signal format and demodulate from such a signal format, and peripheral circuits of these ICs. In particular, when the communication means 4 performs HART communication, the communication means 4 uses FSK for a communication control IC that controls communication according to the HART protocol, a modem for HART communication, and a signal consisting of an analog current of 4 to 20 mA. It may include an electric circuit configured to superimpose a modulated digital signal.

The electric device 100 is a device that receives electric power from a commercial power source, a battery, or the like and performs a predetermined function, and may be an electric device for any purpose of industrial use or consumer use, and the use thereof is not particularly limited. .. For example, the electric device 100 includes a control device for an automobile, a communication device, a control device for constructing various control systems constructed in a plant, and a detection for monitoring the surrounding environment as described later. It may be any of various electric devices such as vessels, so-called white goods and other household electric appliances. Therefore, the electric device 100 may have an arbitrary function depending on the application. Therefore, in addition to the first load unit 3, the electric device 100 is a part that fulfills a specific function according to its application, and includes one or more load parts into which the current from the power supply unit 2 flows. You may have.

In the example shown in FIG. 1, the electric device 100 has a second load unit 5 in addition to the first load unit 3. The second load unit 5 is configured such that the current flowing through the second load unit 5 fluctuates more slowly than the current flowing into the first load unit 3. For example, during the normal operation of the electric device 100, the second load unit 5 is such that a current whose magnitude does not change so rapidly as the ground potential of the power supply unit 2 fluctuates, or a current having a substantially constant magnitude flows in. It is configured in. That is, it is considered that the risk of transmission error in communication between the electric device 100 and the external device E and the malfunction of the electric device 100 due to the current supplied from the power supply unit 2 to the second load unit 5 is low. Therefore, the second load unit 5 is connected so as to operate by receiving the supply of the first voltage V1 from the power supply unit 2 without going through the current control means 1. With such a configuration, the second load unit 2 receives a current corresponding to the current supply capacity of the power supply unit 2, that is, a current having a sufficiently large size so that a part of the current is not divided by the current control means 1. Can be supplied to. Further, even if the current control means 1 is accompanied by a voltage drop, the first voltage V1 supplied from the power supply unit 2 can be supplied to the second load unit 5 as it is. Therefore, a larger amount of electric power can be supplied to the second load unit 5.

As described above, the electric device 100 may be a detector or an alarm that monitors the surrounding environment in which the electric device 100 is installed and detects that the surrounding environment is in a specific state. Such detectors and alarms include gas detectors that detect the presence of a specific type of gas at a predetermined concentration or higher, smoke detectors, fire alarms, and crime prevention that detects the intrusion of people. Examples thereof include alarms for electric devices (however, detectors and alarms by the electric device 100 are not limited to these). For example, in a plant or the like, a monitoring system consisting of a plurality of detectors is constructed, and the detectors installed at a plurality of locations or the central control device (master) and each detector (slave) are described above. Signals are transmitted and received by HART communication. In this embodiment, the electric device 100 is a detector or alarm that performs such HART communication in that a signal with a small amplitude can be appropriately transmitted and received with a small number of lines. , Especially beneficial. In addition, energy management systems called HEMS (Home Energy Management System) are beginning to spread not only in plants but also in ordinary households, and other detectors that monitor energy consumption are available. It is also expected to send and receive signals to and from detectors and home appliances. This embodiment is considered to be useful in that even when the electric device 100 is such a detector for general household use, transmission errors and the like are unlikely to occur.

When the electric device 100 is a detector or the like, the electric device 100 may have detection means (not shown) such as various sensors according to the detection target. Examples of such a sensor include a gas sensor that detects carbon monoxide (CO) gas, methane gas (CH ₄ ), a temperature sensor consisting of a thermistor, a humidity sensor, a smoke sensor, and the like (however, the sensors include these). Not limited to). Such a sensor mainly outputs an electric signal according to a detection state, or changes the impedance of an electric circuit inside the sensor. Therefore, when a current is supplied to the detection means, for example, from the power supply unit 2, the magnitude of the current flowing into the detection means varies depending on the detection state. A detection means such as a gas sensor may be included in the first load unit 3. However, even when the current flowing into the detection means changes according to the detection state, the physical environment around the electric device 100 is usually changed so rapidly that the ground potential of the electric device 100 fluctuates. It is thought that it will not be done. Therefore, a detection means (not shown) may be included in the second load unit 5. Further, the detection means (not shown) may be connected to the power supply unit 2 or the current control means 1 separately from the first load unit 3 and the second load unit 5.

When the electric device 100 is a detector as described above, not only the inflow current to the detection means but also the inflow current to the first load unit 3 and the second load unit 5 depends on the detection state of the detection means (not shown). Can fluctuate. For example, if the first load unit 3 is a display device and is configured to display the detection result by the detection means as described above, the display state may change according to the detection state of the detection means. When the first load unit 3 is a digital display 29 (see FIG. 3A) described later, the number of lighting segments changes according to the detection state of the detection means, and the inflow current to the first load unit 3 fluctuates. .. Further, in this case, even if the change in the surrounding physical environment detected by the detection means is gradual, the display state of the digital display 29 changes in an extremely short time, for example, a transition time of 2 milliseconds (one). Or multiple segments can change from on to off and vice versa). Therefore, the inrush current to the first load unit 3 may change so rapidly that the ground potential of the power supply unit 2 fluctuates according to the detection state of the detection means. However, in the present embodiment, since the current control means 1 is provided, the fluctuation of the ground potential of the power supply unit 2 is reduced. Therefore, it is possible to prevent malfunction of the electric device 100.

As shown in FIG. 1, in the present embodiment, the current control means 1 includes a constant current generation unit 11 and a constant voltage generation unit 12. The constant current generation unit 11 is configured to cause the current supplied from the power supply unit 2 to flow out from the constant current generation unit 11 at a constant current value. That is, the constant current Ic flows out from the constant current generation unit 11. Further, as will be described later, the constant current generation unit 11 is configured so that the constant current Ic1 flows in from the power supply unit 2 by being combined with the constant voltage generation unit 12.

The constant voltage generation unit 12 supplies the second voltage V2, which is a constant voltage, to the first load unit 3. Further, the constant voltage generation unit 12 is configured such that the current i2 having a magnitude corresponding to the fluctuation of the current i1 flowing into the first load unit 3 flows in from the constant current generation unit 11. That is, the constant voltage generation unit 12 converts the current from the power supply unit 2 (specifically, the current flowing out from the constant current generation unit 11) into the current i1 and the current i2 in the above description of the current control means 1. It has the function of splitting the current. Therefore, the constant voltage generation unit 12 is configured such that the current i2 decreases as the current value of the current i1 flowing through the first load unit 3 increases, and the current i2 increases as the current i1 decreases. Since the constant current Ic flows out from the constant current generation unit 11, the constant voltage generation unit 12 is configured to decrease (increase) the current i2 by substantially the same amount as the increase (decrease amount) of the current i1. ..

By providing the current control means 1 including the constant current generation unit 11 and the constant voltage generation unit 12 as shown in FIG. 1, the current flows out from the power supply unit 2 to supply the current to the first load unit 3, and then The current returned to the power supply unit 2 via the ground G can be made substantially constant without being affected by the fluctuation of the load of the first load unit 3. Therefore, the fluctuation of the ground potential can be suppressed extremely highly, and the malfunction of the electric device 100 and the signal transmission error between the electric device 100 and the external device E can be almost certainly prevented.

FIG. 2 shows an example of a specific electric circuit constituting the constant current generation unit 11 and the constant voltage generation unit 12. In the example of FIG. 2, the constant current generator 11 is composed of an operational amplifier U3, a reference voltage generator U2, a P-channel field effect transistor (hereinafter, simply referred to as a “transistor”) Q1, and resistors R1 to R6. ing. The reference voltage generator U2 is not particularly limited as long as it generates a constant voltage at a predetermined voltage value. FIG. 2 shows an example in which a shunt regulator that outputs a constant reference voltage Vr2 to the reference voltage output terminal U2r with respect to the anode terminal is used as the reference voltage generator U2. The reference voltage output terminal U2r and the cathode terminal are connected so that the potential difference between the cathode terminal and the anode terminal is a constant voltage (reference voltage) Vr2.

The resistors R1, R2 and R3 are connected in series, the non-inverting input terminal of the operational amplifier U3 is connected to the connection line between the resistor R1 and the resistor R2, and the anode terminal of the reference voltage generator U2 is the resistor R2 and the resistor R3. It is connected to the connection line. One end R1a of the resistor R1 opposite to the resistor R2 is connected to the drain terminal of the transistor Q1 together with the cathode terminal of the reference voltage generator U2, and one end of the resistor R3 opposite to the resistor R2 is connected to the ground G.

The output terminal of the operational amplifier U3 is connected to the gate terminal of the transistor Q1 via the resistor R4, and the resistor R5 is connected between the gate terminal of the transistor Q1 and the ground G. One end of the resistor R6 is connected to the drain terminal of the transistor, and the other end of the resistor R6 is connected to the inverting input terminal of the operational amplifier U3. The constant current Ic1 flows into the source terminal of the transistor Q1 from the power supply unit 2 (see FIG. 1), and the constant current Ic flows out from the other end of the resistor R6.

A commercially available operational amplifier can be used as the operational amplifier U3. The transistor Q1 is also not particularly limited as long as it has a rated drain current exceeding the constant current Ic1. The resistance values of the resistors R1 to R3 and R6 are appropriately selected according to the desired constant current Ic and the magnitude of the reference voltage Vr2 of the reference voltage generator U2. A resistor having a small tolerance of resistance value is advantageous in that the variation of the constant current Ic is reduced. Further, the resistance values of the resistors R4 and R5 can be appropriately selected so that an appropriate gate voltage is applied to the transistor Q1. Although not shown, the positive power supply terminal of the operational amplifier U3 is connected to the power supply voltage supply line, and the negative power supply terminal or the GND terminal is connected to the ground G. Preferably, the positive power supply terminal of the operational amplifier U3 is connected to a power supply voltage supply line that supplies a voltage higher than the first voltage V1 supplied by the power supply unit 2.

In the example of FIG. 2, the constant voltage generation unit 12 is composed of a shunt regulator U1 and resistors R7 to R9. The shunt regulator U1 is configured to output a constant reference voltage Vr1 to the reference voltage output terminal U1r with respect to the anode terminal. The resistors R7, R8 and R9 are connected in series, and the cathode terminal of the shunt regulator U1 is connected to one end of the resistor R7 opposite to the resistor R8, and the resistor R6 of the constant current generator 11 and the operational amplifier U3. It is connected to the connection line with the inverting input terminal of. The reference voltage output terminal U1r of the shunt regulator U1 is connected to the connection line between the resistor R8 and the resistor R9, and the anode terminal of the shunt regulator U1 is connected to the ground G together with one end opposite to the resistor R8 of the resistor R9. ..

The shunt regulator U1 has an accuracy of a reference voltage Vr1 capable of generating a second voltage V2 with a desired accuracy, and has a sufficient current capacity for the inflowing current i2 according to the fluctuation of the current i1. There is no particular limitation. For example, when a constant current Ic of 60 mA is supplied from the constant current generation unit 11, the constant current Ic is preferably 100 mA or more so that all the constant current Ic can flow even when the current i1 to the first load unit 3 is almost zero. A shunt regulator with cathode current capacity is selected.

The resistance values of the resistors R7 to R9 are appropriately selected according to the desired second voltage V2 and the magnitude of the reference voltage Vr1 of the shunt regulator U1. A resistor having a small tolerance of resistance value is advantageous in that the variation of the second voltage V2 is reduced. Two resistors R7 and R8 connected in series are used, but if the desired resistance value and tolerance can be satisfied, one resistor is the cathode terminal of the shunt regulator U1 and the reference voltage output terminal U1r. It may be connected in between. Further, a variable resistor may be connected instead of one or both of the resistor R7 and the resistor R8. Further, a bypass capacitor may be connected to any part of the circuit constituting the constant current generation unit 11 and the constant voltage generation unit 12.

The operation of the constant current generation unit 11 and the constant voltage generation unit 12 shown in FIG. 2 will be described. The reference voltage Vr2 of the reference voltage generator U2 is applied to both ends of the series circuit of the resistors R1 and the resistors R2 connected between the cathode terminal and the anode terminal of the reference voltage generator U2. Therefore, a potential difference is generated between one end R1a and the other end R1b of the resistor R1 at a constant voltage obtained by dividing the reference voltage Vr2 by the resistors R1 and R2. Further, the voltage Vin of the other end R1b of the resistor R1 is input to the non-inverting input terminal of the operational amplifier U3. A negative feedback circuit is formed in the operational amplifier U3 by the resistor R4, the transistor Q1 and the resistor R6. Therefore, the gate voltage of the transistor Q1 is controlled so that the voltage of the other end R6b of the resistor R6 connected to the inverting input terminal of the operational amplifier U3 becomes substantially the same as the voltage Vin. In other words, the current flowing through the resistor R6 is controlled at both ends of the resistor R6, which is connected to one end R1a of the resistor R1 and one end R6a, so that a potential difference is generated at the same constant voltage as between both ends of the resistor R1. A constant current Ic flows through a certain resistor R6. This constant current Ic is supplied to the first load unit 3 and the constant voltage generation unit 12. The magnitude of the constant current Ic can be easily adjusted by selecting the reference voltage Vr2 and the resistance values of the resistors R1, R2 and R6.

In the constant voltage generation unit 12, the shunt regulator U1 generates a second voltage V2 based on the reference voltage Vr1 and the resistance values of the resistors R7 to R9. That is, the cathode current of the shunt regulator U1 is controlled so that the voltage of the cathode terminal of the shunt regulator U1 becomes Vr1 × (1+ (R7 + R8) / R9), and the constant voltage second voltage V2 composed of this cathode voltage Will be generated. In the formula, R7, R8 and R9 indicate the resistance value of each resistor, respectively. The magnitude of the second voltage V2 can be easily adjusted by selecting the reference voltage Vr1 and the resistance values of the resistors R7 to R9.

As described above, the constant current Ic is supplied from the constant current generation unit 11, while the current i1 flowing through the first load unit 3 fluctuates with time. In the example of FIG. 2, the cathode current is adjusted by the shunt regulator U1 so that a second voltage V2 having a constant voltage is generated. Therefore, the current i2, which is the difference between the constant current Ic and the current i1 to the first load unit 3, is diverted to the shunt regulator U1 side as a cathode current so that the second voltage V2 is kept constant, and the ground G It is returned to the power supply unit 2 via. Even if the current i1 to the first load unit 3 fluctuates, the current i2 corresponding to the fluctuation is diverted by the shunt regulator U1. As a result, the constant current generation unit 11 can continue to flow the constant current Ic without being affected by the fluctuation of the load of the first load unit 3. Further, since the constant voltage generation unit 12 generates a constant voltage second voltage V2, the voltage at one end R1a of the resistor R1 and the cathode terminal of the reference voltage generator U2 become substantially constant. Therefore, the current flowing through the reference voltage generator U2 and the resistor R1 is also substantially constant, and the current Ic1 flowing from the power supply unit 2 into the constant current generation unit 11 is also substantially constant. As a result, fluctuations in the current flowing out of the power supply unit 2 and the current flowing into the power supply unit 2 are suppressed, the ground potential of the power supply unit 2 is stabilized, and malfunction of the electric device 100 can be prevented.

It should be noted that preferably, the constant current generation unit 11 is configured to generate a constant current Ic larger than the maximum value of the current i1 that fluctuates with time, and the constant voltage generation unit 12 operates the constant current generation unit 11. The inside is configured so that the current i2 always flows in from the constant current generation unit 11. By doing so, it is possible to prevent the ground potential of the power supply unit 2 from fluctuating over the entire range of change of the current i1. However, the constant current Ic generated by the constant current generation unit 11 does not necessarily have to be larger than the maximum value of the current i1. For example, the constant current Ic may be substantially the same as the maximum value of the current i1, and may be smaller than the maximum value of the current i1 as long as it does not interfere with the operation of the first load unit 3. For example, even if the fluctuation of the ground potential due to the fluctuation of the current i1 in the region near the maximum value where the frequency of occurrence is low cannot be completely suppressed, the electric device 100 may not malfunction in the normal operation. Further, by reducing the constant current Ic, the power consumption of the electric device 100 may be reduced.

Next, a method of reducing noise superimposed on the signal of the electric device according to the embodiment of the present invention will be described with reference to FIGS. 1 and 2.

In the method of the present embodiment, in the electric device 100 having the power supply unit 2 and the first load unit 3 in which the current from the power supply unit 2 flows in at a current value that fluctuates with time, the ground potential of the power supply unit 2 fluctuates. This is a method of reducing the noise superimposed on the signal on the internal electric circuit. In the method of the present embodiment, a constant current Ic is generated from the current supplied from the power supply unit 2, and a current i2 having a magnitude corresponding to the fluctuation of the current i1 flowing into the first load unit 3 is diverted from the constant current Ic. A constant voltage (second voltage) V2 is generated, a part of the constant current Ic is supplied to the first load unit 3, and the current i1 and the current i2 flowing through the first load unit 3 are supplied to the power supply unit 2. By returning the current, the fluctuation of the current flowing to the ground of the power supply unit 2 is made smaller than the fluctuation of the current flowing into the first load unit 3. By reducing the fluctuation of the current flowing through the ground of the power supply unit 2, the ground potential of the power supply unit 2 is stabilized, and the noise superimposed on the signal on the electric circuit of the electric device 100 is reduced.

The constant current Ic can be generated by, for example, a constant current generation circuit including a reference voltage generator U2, an operational amplifier U3, and resistors R1 to R6 as shown in FIG. Since the operations of the reference voltage generator U2, the operational amplifier U3, and the resistors R1 to R6 are as described above, the description thereof will be omitted again.

For the diversion of the current i2 having a magnitude corresponding to the fluctuation of the current i1 flowing into the first load unit 3 from the constant current Ic, for example, a shunt regulator U1 and resistors R7 to R9 as shown in FIG. 2 are used. Can be done. The shunt regulator U1 generates a constant voltage (second voltage V2) determined by the reference voltage Vr1 and the resistance values of resistors R7 to R9 between the cathode terminal of the shunt regulator U1 and the anode terminal connected to the ground G. NS. In other words, the shunt regulator U1 diverts the current i2 having a magnitude corresponding to the fluctuation of the current i1 flowing through the first load unit 3 from the constant current Ic, whereby the second voltage V2 is maintained at a substantially constant value. NS. The shunted current i2 is passed through a shunt path leading from the cathode terminal to the anode terminal of the shunt regulator U1.

The current i1 flowing through the first load section 3 and the current i2 flowing through the shunt regulator U1 which is a diversion path connect the low potential side of the first load section 3 and the anode terminal of the shunt regulator U1 to the ground G. Is returned to the power supply unit 2 via the ground G. When the current i1 and the current i2 divided by the magnitude corresponding to the fluctuation of the current i1 flow through the ground G, the fluctuation amount of the current flowing through the ground G is changed by the fluctuation of the current i1 flowing into the first load unit 3. It can be smaller than the amount. As a result, it is possible to reduce the noise superimposed on the signal on the electric circuit in the electric device 100 due to the fluctuation of the ground potential of the power supply unit 2.

Preferably, while the constant current Ic is being generated, a part of the constant current Ic is always diverted to a diversion path such as the shunt regulator U1. That is, it is preferable to generate a constant current Ic larger than the maximum value of the current i1 that fluctuates with time. As described above, it is possible to prevent the ground potential of the power supply unit 2 from fluctuating over the entire range of change of the current i1.

The method for reducing the noise superimposed on the signal of the electric device of the present embodiment is not limited to the method using the circuit shown in FIG. The method of the present embodiment is carried out by using an arbitrary circuit capable of generating a constant current Ic and capable of dividing the current i2 corresponding to the fluctuation of the current i1 flowing through the first load unit 3 from the constant current Ic. Can be done.

Next, taking the case where the electric device 100 is a gas detector for detecting flammable gas or toxic gas, which has a 3-wire HART communication function, as an example, the structure of the electric device according to the embodiment of the present invention. An example will be described.

3A and 3B show the appearance of the gas detector 200, which is an example of the electric device of the present invention. FIG. 3A shows a front view seen from the side opposite to the surface to be the installation surface side when the gas detector 200 is installed, and FIG. 3B is a bottom view seen from the upper and lower sides of FIG. 3A. As shown in FIGS. 3A and 3B, the gas detector 200 has a housing 20 composed of a main body side housing 21 and a lid side housing 22. The main body side housing 21 constitutes a portion of the housing 20 on the installation surface side. The main body side housing 21 and the lid side housing 22 are engaged by the hinge portion 23 and are connected by four housing fixing screws 24. The gas detector 200 includes a detection unit 25 including a gas sensor that detects the gas to be detected, and the gas detector 200 and an external power source (not shown) are electrically mounted on the side surface of the main body side housing 21. A cable insertion portion 26 for inserting a connecting cable (not shown) is provided.

The gas detector 200 has four switches 27 for adjusting the gas detector 200 that can be operated from the outside with a stick-shaped operation tool on the front surface 22a, and three LED indicators that indicate the operating state of the gas detector 200. It has 28. Further, the gas detector 200 is provided with a lighting element having 8 segments per digit, including a dot display indicating a decimal point, which is provided so as to be visible from the front surface 22a side through the opening 22b of the lid side housing 22. It is equipped with a 4-digit digital display 29 for displaying.

FIG. 4 shows each housing viewed from the side that becomes the internal side of the gas detector 200 when the main body side housing 21 and the lid side housing 22 are separated from each other. ing. In FIG. 4, the hinge portion 23, the detection portion 25, and the cable insertion portion 26 shown in FIGS. 3A and 3B are not shown. As shown in FIG. 4, the main body side housing 21 and the lid side housing 22 have recesses 21c and 22c, respectively, and the first circuit board 31 is arranged in the recesses 22c of the lid side housing 22. A third circuit board 33 is arranged in the recess 21c of the main body side housing 21. The first circuit board 31 and the third circuit board 33 are electrically connected by a plurality of cables 30a. The cable 30a and the first circuit board 31 are connected via the connector 35 (in FIG. 4, the main body side housing 21 and the lid side housing 22 are shown in a state where the connector 35 is not connected. ).

The first circuit board 31 is fixed to the lid-side housing 22 with two first circuit board fixing screws 39. Although not shown, a second circuit board 32 (see FIG. 6) is arranged on the lid-side housing 22 so as to overlap the first circuit board 31, and the first circuit board 31 is partially excluded. It is covered with a fixing plate 34 of the second circuit board 32. The four corners of the fixing plate 34 are fixed to the lid-side housing 22 by four plate fixing screws 41. The second circuit board 32 is fixed to the fixing plate 34 with two second circuit board fixing screws 44.

The fixing plate 34 is formed of a rectangular plate as a whole, as shown in FIGS. 5 (a) and 5 (b), respectively, in a plan view and a front view thereof. It has a side end portion 342 composed of a portion in the vicinity of each of the two sides. The main body portion 341 and the side end portion 342 are connected so as to form a step between them, and the fixing plate 34 is viewed from the edge side without the side end portion 342 in FIG. 5 (b). As shown in, it has a convex shape as a whole. The main body 341 is provided with two through holes 34d for the second circuit board fixing screw, and the side end 342 is provided with four through holes 34e for the plate fixing screw. Further, the fixing plate 34 is provided with three notches 34a, 34b and 34c.

Referring to FIG. 4 again, in addition to the connector 35, the first circuit board 31 is provided with a terminal portion 38 electrically connected to a predetermined node of the electric circuit configured in the first circuit board 31. ing. Although the terminal portion 38 is formed by the connector in FIG. 4, it may be a conductor pad formed on the conductor layer of the first circuit board 31 or the like. The terminal portion 38 is provided, for example, for inspecting an electric circuit configured on the first circuit board 31 and writing information to a storage element (not shown) mounted on the first circuit board 31. In the example of FIG. 4, the connector 35 is exposed in the notch 34a of the fixing plate 34, and the terminal portion 38 is exposed in the notch 34b. Therefore, the connector 35 can be easily inserted and removed while the fixing plate 34 is fixed to the lid-side housing 22, and writing to the storage element can be performed via the terminal portion 38.

An external cable connector 36 to which a plurality of external cables 30b for connecting to an external power supply or the like are connected is mounted on the third circuit board 33. The external cable 30b is inserted into and fixed to the external cable connector 36 at an angle to the component mounting surface of the third circuit board 33. Although not shown, on the third circuit board 33, in addition to the external cable connector 36, a protection circuit for protecting the electric circuit in the gas detector 200 from an external surge voltage or the like may be mounted. The external cable 30b is introduced into the main body side housing 21 through the cable insertion portion 26 (see FIG. 3A). An O-ring 37 is provided around the recess 21c of the main body side housing 21.

FIG. 6 shows a cross-sectional view taken along the line VI-VI of FIG. 4 of the lid-side housing 22 on which the first circuit board 31 and the like are arranged. As shown in FIG. 6, a counterbore surface 22e is provided on the outer peripheral portion of the recess 22c of the lid-side housing 22 at a position recessed from the bonding surface 22d with the main body-side housing 21 (see FIG. 3B). The first circuit board 31 is placed on the counterbore surface 22e and fixed to the lid-side housing 22 with the first circuit board fixing screw 39. Further, the fixing plate 34 of the second circuit board 32 is fixed to the counterbore surface 22e with the plate fixing screw 41 via the spacer 40. The second circuit board 32 is fixed to the fixing plate 34 via the spacer 42 with the second circuit board fixing screw 44. That is, the second circuit board 32 is arranged on the opposite side (main body side housing 21 side) of the counterbore surface 22e of the first circuit board 31 so as to overlap the first circuit board 31. With such an arrangement, a small gas detector 200 can be configured with respect to the occupied area on the installation surface.

The digital display 29 is mounted on the bottom surface (upper and lower surfaces of FIG. 6) of the recess 22c of the first circuit board 31. The digital display 29 is mounted at a position corresponding to the opening 22b of the lid-side housing 22 so that the display can be visually recognized from the outside of the gas detector 200.

A board-to-board type connector 43a is mounted on the first circuit board 31, and a board-to-board type connector 43b that fits into the connector 43a is mounted on the second circuit board 32. When the first circuit board 31 is attached to the lid-side housing 22, and then the second circuit board 32 is fixed to the lid-side housing 22 via the fixing plate 34, the connector 43a and the connector 43b are coupled. Will be done. At this time, if the first circuit board 31 is not fixed at an accurate position with respect to the lid-side housing 22, the connector 43a and the connector 43b cannot be properly coupled. However, referring to FIG. 4 again, in the present embodiment, the first circuit board fixing screw 39 is exposed in the notches 34a and 34c. Therefore, the first circuit board fixing screw 39 can be turned even when most of the first circuit board 31 is covered with the fixing plate 34 on which the second circuit board 32 is attached. That is, the first circuit board 31 may not be fixed to the lid-side housing 22 at the time when the fixing plate 34 is attached to the lid-side housing 22. For example, after connecting the connector 43a and the connector 43b in advance, the first circuit board 31 and the fixing plate 34 can be fixed to the lid-side housing 22. Alternatively, for example, the connector 43a and the connector 43b can be coupled while being aligned with each other in a state where the first circuit board 31 is temporarily fixed to the lid side housing 22, that is, in a state where the first circuit board 31 is movable. can. After that, the first circuit board 31 can be completely fixed by tightening the first circuit board fixing screw 39, and the fixing plate 34 can be further fixed to the lid side housing 22.

FIG. 7 shows the first circuit board 31 in the recess 22c of the lid-side housing without the fixing plate 34 shown in FIG. 4 attached. The first circuit board 31 is provided with a connector 35, a connector 43a, and a terminal portion 38, and a predetermined electric circuit constituting the gas detector 200 is formed. In the example of FIG. 7, the power supply unit 2 and the second load unit 5 are formed on the first circuit board 31. Further, as described above, the digital display 29 (see FIG. 6), which can be the first load unit 3 (see FIG. 1) of the electric device of the present embodiment, which is the gas detector 200, is a recess of the first circuit board 31. It is mounted on the bottom surface side surface of 22c (the surface opposite to the surface shown in FIG. 7).

On the other hand, in the gas detector 200, which is an example of the electric device of one embodiment, the current control means 1 is provided on the second circuit board 32 as shown in FIG. 8 (FIG. 8 shows FIG. 4). The second circuit board 32 attached to the fixing plate 34 in a state where the fixing plate 34 shown in the above is inverted in the left-right direction is shown in FIG. 4). For example, the shunt regulator U1 shown in FIG. 2, the reference voltage generator U2, the operational amplifier U3, the transistors Q1, and the resistors R1 to R9 are mounted on the second circuit board 32. Further, on the second circuit board 32, among the communication means 4 shown in FIG. 1, a HART communication control unit 4a including a control required for performing HART communication and an electric circuit for modulating and demodulating a signal is provided. It is formed.

As shown in FIGS. 7 and 8, in the gas detector 200, the power supply unit 2 is formed on the first circuit board 31, and the current control means 1 provided on the second circuit board 32 receives a current from the power supply unit 2. Is supplied. The current flowing out from the current control means 1 returns to the first circuit board 31 side and flows into the first load unit 3 (see FIG. 1) including the digital display 29 (see FIG. 6). As described above, the current control means 1 suppresses fluctuations in the ground potential due to fluctuations in the current to the first load unit 3. The HART communication control unit 4a, which controls HART communication by a three-wire system that is easily affected by fluctuations in the ground potential, is formed on the second circuit board 32 together with the current control means 1. That is, the portion responsible for HART communication and the portion responsible for suppressing fluctuations in the ground potential so that normal 3-wire HART communication can be performed are the substrates on which other components of the electric circuit of the gas detector 200 are formed. (First circuit board 31) and another board (second circuit board 32) are collectively formed. Therefore, by adding the second circuit board 32, the HART communication function can be added to the existing gas detector that does not have the HART communication function without significantly changing the existing part.

In the example of FIG. 8, the connector 45 provided for inspecting the electric circuit configured on the second circuit board 32 and writing information to a storage element (not shown) mounted on the second circuit board 32. Is mounted on the edge of the second circuit board 32. The mating surface of the connector 45 with the connector on the other side is directed to the side of the second circuit board 32. Therefore, even when the fixing plate 34 is fixed to the lid-side housing 22 (see FIG. 4), the connector on the other side of the connector 45 is inserted into and removed from the side of the second circuit board 32 into the connector 45 to store the storage element. You can write to. The power supply unit 2 and the second load unit 5, the current control means 1 and the HART communication control unit 4a shown in FIGS. 7 and 8 are simply the first circuit board 31 or the second circuit board. It merely indicates that it is formed on 32, and is not intended to indicate its size or its exact position on each circuit board.

Example 1
A current control means 1 including a constant current generation unit 11 and a constant voltage generation unit 12 shown in FIG. 2 is added to a gas detector (manufactured by New Cosmos Electric Co., Ltd .: KD-12B) to reduce fluctuations in the ground potential. I investigated the effect. The gas detector had a digital display 29 and an LED indicator 28 as shown in FIG. 3A (however, it did not have a HART communication function). The state of the digital display 29 and the LED indicator 28 is changed over time, and a power source is used for fluctuations in the current i1 flowing through the first load unit 3 (see FIG. 1) including the digital display 29 and the LED indicator 28. The fluctuation of the current flowing through the ground of the part 2 (see FIG. 1) was examined.

In this survey, the power supply unit of the gas detector KD-12B was disconnected, and a Texas Instruments switching regulator IC: LM2501 evaluation board was connected as the power supply unit 2, and the power supply unit 2 was connected to a voltage of 24V from an external power supply. Was supplied. The power supply unit 2 was set to a switching frequency of 500 kHz and an output voltage of 3.6 V. That is, in this embodiment, the first voltage V1 (see FIG. 1) was 3.6V. Renesas Electronics' μPC1093 was used as the shunt regulator U1, and resistors R7 to R9 were selected so that the second voltage V2 was 3.18V. A Texas Instruments shunt regulator TLV431A was used as the reference voltage generator U2, and the reference voltage generator U2 had a reference voltage Vr2 of 1.24V as a TYPE value. OPA170 from Texas Instruments and RQ5E035AT from ROHM were used as the operational amplifier U3 and the transistor Q1, and resistors R1 to R3 and R6 were selected so that the constant current Ic was 57.4 mA.

For each current measurement, only the most significant digit of the digital display 29 with 8 segments x 4 digits is turned on every 8 milliseconds, and the three LED indicator lights 28 are turned on for a cycle of 1 second and the duty ratio is 50%. I went while blinking with. The current i1 to the first load unit 3 was measured by inserting a 0.5 Ω resistor between the current control means 1 and the first load unit 3 and measuring the voltage drop due to this resistor. .. Similarly, the current flowing through the ground line was measured by inserting a 20Ω resistor into the ground line between the external power supply and the power supply unit 2 and measuring the voltage drop thereof. Each current was measured using an oscilloscope.

9A and 10A are the measurement results of the current i1 to the first load unit 3, and FIGS. 9B and 10B are the measurement results of the current of the ground line. Here, FIGS. 9A and 9B observe the oscilloscope time axis setting as 5 seconds per division, and FIGS. 10A and 10B expand the time axis setting to 0.1 seconds per division. It was observed. Further, in FIGS. 9B and 10B, the reference numeral ig indicates the current of the ground line measured in this embodiment, and the reference numeral ix is a comparative example in which the current control means 1 is not added, which is measured for comparison. It shows the current of the ground line. Since there is no difference in the current to the first load unit 3 between this embodiment and the comparative example, only one current waveform (current i1) is shown in FIGS. 9A and 10A.

As shown in FIG. 9A, the magnitude of the current i1 to the first load unit 3 changes in a cycle P1 of about 1 second in accordance with the blinking cycle (1 second) of the LED indicator lamp 28. .. Further, as shown in FIG. 10A, which is the result of measurement by enlarging the time axis, the current i1 has a cycle P2 of about 8 milliseconds in accordance with the change of the display state of the digital display 29 having a cycle of 8 milliseconds. The size of is fluctuating. That is, in FIG. 9A, the current i1 is painted black and drawn in a band shape, but the current i1 finely fluctuates in a cycle of about 8 milliseconds according to the amount of current flowing through the digital display 29, and the LED. It fluctuates in a cycle of about 1 second according to the amount of current flowing through the indicator lamp 28. Note that FIGS. 10A and 10B show measurement results for 0.2 seconds (time from t1 second to (t1 + 0.2) seconds) when the LED indicator lamp 28 is in the lit state. Further, in FIG. 9A, since the LED indicator lamp 28 is always lit after the time T1, the current i1 does not fluctuate in a 1-second cycle. Further, since the current i1 also flows to the components of the gas detector other than the digital display 29 and the LED indicator lamp 28, the current i1 continues to flow without dropping to the zero level in FIGS. 9A and 10A.

In a situation where the current i1 to the first load unit 3 fluctuates as shown in FIGS. 9A and 10A, in the comparative example, as shown in FIG. 9B, the current ix of the ground line fluctuates as shown in FIG. 9B. It fluctuates in a cycle of 1 second, and further fluctuates in a cycle of 8 milliseconds as shown in FIG. 10B. On the other hand, in this embodiment, as shown by the reference numerals ig in FIGS. 9B and 10B, the current ig of the ground line flows at a substantially constant current value without being affected by the fluctuation of the current i1. I understand. Therefore, the potential of the signal line in the gas detector does not fluctuate due to the fluctuation of the current flowing through the digital display 29 or the like, and the normal operation of the gas detector can be obtained. Further, in the above-mentioned HART communication, a standard for ground level fluctuation of 2.2 mVrms or less is defined in the frequency band of 500 Hz to 10 kHz when the load resistance is 500 Ω, but in this embodiment, the ground level fluctuation is defined. Is approximately 0 mVrms, and the HART communication standard can be satisfied by using the current control means 1 of the embodiment illustrated in FIG.

1 Current control means 2 Power supply unit 3 1st load unit 4 Communication means 4a HART communication control unit 5 2nd load unit 11 Constant current generation unit 12 Constant voltage generation unit 21 Main unit side housing 22 Lid side housing 28 LED indicator light 29 Digital display 31 1st circuit board 32 2nd circuit board 33 3rd circuit board 34 Fixing plates 34a, 34b, 34c Notches 39 1st circuit board fixing screw 41 Plate fixing screw 43a Connector on the 1st circuit board 43b Connector on the second circuit board 100 Electrical equipment 200 Gas detector B External power supply E External equipment G Ground i1 Current flowing into the first load unit i2 Current flowing through the current control means Ic Constant current flowing out from the constant current generator ig Ground line current ix of the embodiment of the present invention Ground line current of the comparative example L1 1st line L2 2nd line L3 3rd line U1 Shunt regulator U2 Reference voltage generator U3 Computational amplifier V1 1st voltage V2 2nd voltage

Claims (10)

The power supply unit that supplies the current at the first voltage, the first load unit that causes the ground potential of the power supply unit to fluctuate due to the time-dependent fluctuation of the inrush current from the power supply unit, and the supply of the first voltage. It is a detector that is equipped with a detection means that detects the state of the surrounding environment and operates by receiving it, and detects that the surrounding environment is in a specific state.
The first load unit is configured so that the inflow current fluctuates according to the detection state of the detection means.
A constant current generator that causes the current supplied from the power supply unit to flow out at a constant current value,
A constant voltage generation unit that is configured so that a current having a magnitude corresponding to a fluctuation of the current flowing into the first load unit flows in from the constant current generation unit and supplies a second voltage to the first load unit. Have more
A detector in which the fluctuation of the potential generated in the ground of the power supply unit due to the fluctuation of the inrush current of the first load unit is reduced by the constant current generation unit and the constant voltage generation unit. The constant current generation unit is configured to generate a constant current larger than the maximum value of the current flowing into the first load unit, and the constant voltage generation unit is configured to generate the constant current generation unit during operation of the constant current generation unit. The detector according to claim 1, wherein a current is always flowed from the constant current generation unit. The detector according to claim 1 or 2, wherein the constant voltage generator includes a shunt regulator. Further, any one of claims 1 to 3 having a communication means for transmitting and receiving a signal with reference to a ground sharing the same line as the ground of the power supply unit with an external device according to a predetermined protocol. The detector described in the section. Further, it has a second load unit into which a current that fluctuates more slowly than the current that flows into the first load unit flows in.
The detector according to any one of claims 1 to 4, wherein the second load unit is configured to operate by receiving the supply of the first voltage. The constant current generation unit includes a transistor having a source terminal into which a current from the power supply unit flows, a first resistor connected between the drain terminal of the transistor and the constant voltage generation circuit, and the first resistance. It includes an operational amplifier in which a negative feedback circuit including a resistor and the transistor is formed, and a second resistor connected between the non-inverting input terminal and the drain terminal of the operational amplifier.
The detector according to any one of claims 1 to 5 , wherein the potential difference between the non-inverting input terminal and the drain terminal is constant. The power supply unit that supplies the current at the first voltage, the first load unit that causes the ground potential of the power supply unit to fluctuate due to the time-dependent fluctuation of the inrush current from the power supply unit, and the supply of the first voltage. It is a detector that is equipped with a detection means that detects the state of the surrounding environment and operates by receiving it, and detects that the surrounding environment is in a specific state.
The first load unit is configured so that the inflow current fluctuates according to the detection state of the detection means.
A communication means for transmitting and receiving a signal with reference to a ground that shares the same line as the ground of the power supply unit with an external device according to a predetermined protocol.
By diversion of the current corresponding to the fluctuation of the current flowing into the first load section from the current from the power supply section, the potential generated in the ground of the power supply section due to the fluctuation of the inflow current of the first load section. A detector further comprising a current control means for reducing fluctuations and supplying a second voltage to the first load unit. The detector according to any one of claims 1 to 7 , wherein the first load unit includes a display device showing a detection result in the detector. The power supply unit that supplies the current at the first voltage, the first load unit that causes the ground potential of the power supply unit to fluctuate due to the time-dependent fluctuation of the inflow current from the power supply unit, and the supply of the first voltage. In a detector having a detection means for detecting the state of the surrounding environment, which receives and operates, the ground of the power supply unit due to the fluctuation of the inflow current to the first load unit according to the detection state of the detection means. It is a method of reducing the noise superimposed on the signal of the detector due to the fluctuation of the potential.
A constant current is generated from the current supplied from the power supply unit to generate a constant current.
A constant voltage is generated by diverting a current having a magnitude corresponding to the fluctuation of the current flowing into the first load section from the constant current and flowing it through the divergence path, and a part of the constant current is used as the first load. Supply to the department
A detector that returns the current flowing through the first load unit and the diversion path to the power supply unit so that the fluctuation of the current flowing to the ground of the power supply unit is smaller than the fluctuation of the current flowing into the first load unit. A method of reducing the noise superimposed on the signal of. The method for reducing noise superimposed on a signal of the detector according to claim 9 , wherein a part of the constant current is always diverted into the divergence path during generation of the constant current.

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