JP2018007135A - Signal transfer circuit and instrumentation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To transfer a signal between an input and an output in an insulation state without affecting a current signal.SOLUTION: A signal transfer circuit (5) transferring an electrical signal in an insulation state between an input and an output includes: a photocoupler (F) optically transferring an electrical signal from a light emitting diode (D) to a phototransistor (T); a limiting resistor (R) limiting a current flowing toward the light emitting diode from a power supply; and a capacitor (C) storing charges output from the power supply through the limiting resistor. Charges stored in the capacitor make the light emitting diode emit light.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a signal transmission circuit and an instrumentation device capable of transmitting a signal in a state where input and output are insulated.

  Generally, in instrumentation, a DC 4 to 20 mA current signal is used as a standard signal. The DC 4 to 20 mA current signal is a system in which 4 mA is 0% and 20 mA is 100%, and a measured value is transmitted from a linear change between 4 mA and 20 mA. An instrumentation device using a DC 4 to 20 mA current signal is supplied with power from a DC power source, for example, and outputs a measurement value measured by a sensor circuit from the control circuit to the outside using the DC 4 to 20 mA current signal. In this instrumentation device, the control circuit and the sensor circuit are signal-transmitted via an insulating signal transmission circuit so as not to receive noise from the DC power source.

As shown in FIG. 7, a signal transmission circuit 40 that transmits signals in a state where the input and output are insulated by a transformer TR has been proposed. In the signal transmission circuit 40, the electrical signal S0 is through limiting resistor R ₄₁ is input to the primary winding of the transformer TR, and output through limiting resistor R ₄₂ from the secondary winding of the transformer TR. The secondary winding side of the transformer TR, the diode D ₄₁ for removing a reverse voltage generated by the transformer TR is provided. In the transformer TR, only the rising of the electrical signal on the input side and the rising high frequency component are transmitted to the output side as the short pulse signal S3. The pulse width of the short pulse signal S3 is adjusted by the pulse width changing circuit 41, and the electric signal S0 is restored on the output side.

  In the signal transmission circuit 40 described above, it is possible to insulate by using the transformer TR, but the transformer TR has a problem that its component outer shape is large and expensive. For this reason, signal transmission circuits using inexpensive and small photocouplers and photoMOS relays have also been proposed. In a signal transmission circuit using a photocoupler, an input signal is converted into light by a light emitting diode in the photocoupler, and this light is received by a phototransistor in the photocoupler, so that the signal is isolated between the input and output. It is possible to communicate. A configuration in which a photocoupler is applied to a signal transmission circuit is described in Patent Document 1, for example.

JP 2008-028589 A

  By the way, in order to turn on an insulating signal transmission element such as a photocoupler or a photoMOS relay, it is necessary to pass a current of 0.5 to 10 mA to the light emitting diode. Since the DC4 to 20 mA current signal also serves as power supply, when the current is consumed by the light emitting diode, the current value consumed by the light emitting diode is added to the current value transmitted by the DC4 to 20 mA current signal. As described above, the current signal of DC4 to 20 mA represents the current value of 4 mA to 20 mA as the measured value of 0% to 100%, so that when the consumption current is added, the accurate measured value cannot be transmitted to the outside. There was a problem.

  The present invention has been made in view of such points, and an object of the present invention is to provide a signal transmission circuit and an instrumentation device capable of transmitting signals in an insulated state between input and output without affecting a current signal. One.

  The signal transmission circuit of the present invention is a signal transmission circuit for transmitting an electrical signal in a state where the input and output are insulated, a signal transmission unit for optically transmitting a signal from a light emitting element to a light receiving element, and a light source from the light emitting element And a capacitor for storing the electric charge output from the power source through the limiting resistor, and the light emitting element is caused to emit light by the electric charge stored in the capacitor. .

  According to the present invention, the capacitor serves as an internal power source, the light emitting element of the signal transmission unit emits light, and an optical signal is transmitted with the light emitting element and the light receiving element insulated. When the light emitting element emits light, current from the power source is not consumed, but electric charge stored in the capacitor is consumed. For this reason, the influence of the current consumption of the light emitting element on the current signal that also serves as the power supply from the power source can be suppressed. Even if the voltage drops due to the consumption of the capacitor charge, the current flowing from the power source into the signal transmission circuit is limited by the limiting resistor, so that the influence on the current signal is suppressed. Therefore, the signal can be transmitted in an insulated state between the input and output without affecting the current signal.

It is a block diagram of the instrumentation apparatus of this Embodiment. It is a circuit diagram of the signal transmission circuit of a comparative example. It is a figure which shows the change of the electric current value of DC4-20mA current signal of a comparative example. It is a figure which shows an example of the signal transmission circuit of 1st Embodiment. It is a figure which shows the relationship between the short pulse signal of 1st Embodiment, and the drive voltage of a photocoupler. It is a figure which shows an example of the signal transmission circuit of 2nd Embodiment. It is a figure which shows an example of the conventional signal transmission circuit.

  Hereinafter, instrumentation equipment to which the signal transmission circuit of the present embodiment is applied will be described. FIG. 1 is a block diagram of the instrumentation device of the present embodiment. FIG. 2 is a circuit diagram of a signal transmission circuit of a comparative example.

  As shown in FIG. 1, the instrumentation device 1 is connected to a DC power source (power source) 2, and is supplied with a DC 4 to 20 mA current signal from the DC power source 2, and is measured with a DC 4 to 20 mA current signal. Is output to the outside. The instrumentation device 1 is provided with a control circuit 3 that controls the instrumentation device 1, a sensor circuit 4 that measures a measurement target, and a signal transmission circuit 5 that transmits a signal between the control circuit 3 and the sensor circuit 4. Yes. The signal transmission circuit 5 optically transmits the signal in a state where the control circuit 3 on the input side and the sensor circuit 4 on the output side are electrically insulated so that the control circuit 3 and the sensor circuit 4 are not affected by noise. ing.

  In the instrumentation device 1 configured as described above, an electric signal is input from the control circuit 3 to the signal transmission circuit 5, and the sensor circuit 4 is driven by the electric signal input through the signal transmission circuit 5. Then, the measurement value is acquired from the sensor circuit 4 by the control circuit 3, and the measurement value is output from the control circuit 3 to the outside with a DC 4 to 20 mA current signal that is also used for power supply. The DC 4-20 mA current signal is a standard signal for instrumentation, and 4 mA is 0%, 20 mA is 100%, and the measured value is transmitted using a linear change in current value from 4 mA to 20 mA. It is a signal for transmission.

Meanwhile, as shown in the comparative example of FIG. 2, those using photocoupler F ₃₁ inexpensive and compact as a general signal transmission circuit 30 has been proposed. The input power line L ₃₁ is connected to the anode of the light emitting diode D ₃₁ of the photocoupler F ₃₁ via the limiting resistor R _31, and the input line L ₃₂ of the electric signal S 0 is connected to the cathode of the light emitting diode D ₃₁ . . Moreover, the phototransistor pull-up resistor _{R 32} power line _{L 33} of the output side via the collector of _{T 31} of the photo coupler _{F 31} is connected, the emitter of the phototransistor _{T 31} is grounded to the ground _{G 31.} The connection point _{P 31} of the collector of the pull-up resistor _{R 32} and the phototransistor _{T 31} is connected to the output line _{L 34} of the electrical signal S0.

In the signal transmission circuit 30, for example, an electrical signal S0 input side when switched to Low from High, the power source voltage V0 of the input side is emitted are applied to the light emitting diode _{D 31} through a limiting resistor _{R 31.} When light in the base of the phototransistor T ₃₁ by light-emitting diode D ₃₁ strikes, the collector of the phototransistor T ₃₁ - emitter is conductive, the output-side power source voltage VE of the output side is short-circuited to ground G ₃₁ Is switched from High to Low. Thus, ON / OFF of the light emitting diode _{D 31} is switched in response to an electrical signal S0 from the input terminal, the electrical signal S0 by phototransistor _{T 31} is switched in accordance with the light emission of the light-emitting diode _{D 31} is signal transduction Is done.

3, in the comparative example signal transfer circuit 30, in order to turn ON the photo coupler _{F 31,} it is necessary to flow a current of about 0.5~10mA the light emitting diode _{D 31.} Therefore, the light emitting the diode 10mA at _{D 31} is the current consumption, the current 10mA is added to the current value carried in DC4~20mA current signal which also serves as a power supply may flow. For example, when the light emitting diode D ₃₁ emits light while outputting a current signal of 4 mA, the light emitting period T of the light emitting diode D ₃₁ is 10 mA in addition to the base current (current consumed by other circuits in the apparatus). The added current is output. Thus, since the current value of the DC4~20mA current signal is varied by the current consumption of the light emitting diode D _31, it is impossible to transmit precise measurements.

Therefore, the signal transmission circuit 5 of this embodiment is the charges output from the power accumulated in the temporarily capacitor C _{11 (see} FIG. 4), the light emitting diode D ₁₁ using the charge stored in the capacitor C ₁₁ (Refer to FIG. 4) is caused to emit light. Accordingly, to suppress the influence of current consumption by the light emission of the light emitting diode _{D 11} for DC4~20mA current signal. Furthermore, even if the voltage drops by the consumption of electric charge of the capacitor C _11, by limiting a current limiting resistor R ₁₁ flowing from the power supply to the signal transmission circuit 5 _(see FIG. 4), effect on DC4~20mA current signal Is suppressed.

  The signal transmission circuit according to the first embodiment will be described below. The signal transmission circuit according to the first embodiment is a circuit that transmits a signal in a state where the input and output are insulated by a single photocoupler. The signal transmission circuit according to the first embodiment is used when an electric signal having a constant pulse width is transmitted. FIG. 4 is a diagram illustrating an example of the signal transmission circuit according to the first embodiment. FIG. 4 is a simplified circuit diagram for explaining the present embodiment, and it is assumed that the signal transmission circuit normally includes a configuration.

As shown in FIG. 4, the signal transmission circuit 5 is provided with a photocoupler (signal transfer unit) F ₁₁ encapsulating the light emitting diode D ₁₁ and the phototransistor T ₁₁ in the package, the light emitting diode D ₁₁ and the phototransistor T ₁₁ , the input side and the output side are electrically insulated. Power line _{L 11} of the input side of the signal transmission circuit 5 is grounded to the ground _{G 11} through the limiting resistor _{R 11} and capacitor _{C 11.} The connection point _{P 11} of the limiting resistor _{R 11} and capacitor _{C 11} is connected to the anode of the light emitting diode _{D 11} through a limiting resistor _{R 12.} The input line L _{12 for the} electric signal S 0 is connected to the cathode of the light emitting diode D ₁₁ via a monostable multivibrator (signal conversion unit) 11.

Power line L ₁₃ of the output side of the signal transmission circuit 5 is connected to the collector of the phototransistor T ₁₁ via a pull-up resistor R _13, the emitter of the phototransistor T ₁₁ is grounded to the ground G _12. The connection point _{P 12} of the collector of the pull-up resistor _{R 13} and the phototransistor _{T 11} is connected to the output line _{L 14} of the electric signals S0 through a pulse width changing circuit (signal restorer) 12. In the signal transmission circuit 5, the signal from the input lines _{L 12} to the photocoupler _{F 11} is input, are optically signaled from the light emitting diode _{D 11} photocoupler _{F 11} to the phototransistor _{T 11} to the output line _{L 14} A signal is output.

In the signal transmission circuit 5, a current flows through the limiting resistor R ₁₁ through the power line L ₁₁ of the input side, the charge output from the power supply through the limiting resistor R ₁₁ is stored in the capacitor C _11. By temporarily stored charge in the capacitor C _11, the light emitting diode D ₁₁ is emitted. Thus, the capacitor _{C 11} during light emission of the light-emitting diode _{D 11} is used as the internal power supply, the current consumption of the light emitting diode _{D 11} to the current value of DC4~20mA current signal is not to be added. Thus, the influence of the transmission of measured values with DC4~20mA current signal when the light-emitting diode _{D 11} is suppressed.

Also, limiting resistor _{R 11} is the current flowing from the power source to the light emitting diode _{D 11,} limits to the size that does not affect the DC4~20mA current signal. Thus, without the current flowing into the signal transmission circuit 5 becomes too large through the power line L ₁₁ during light emission of the charging or light emitting diode D ₁₁ of the capacitor C _11, transmission of measurement values using the DC4~20mA current signal The influence on is suppressed. The resistance value R _L1 of the limiting resistor R ₁₁ at this time is represented by the following equation (1), where the power supply voltage on the input side is V 0, and the maximum value of the current that does not affect the DC 4 to 20 mA current signal is I _amax. expressed. In the case of V0 = 5 V and I _amax = 0.1 mA, R _L1 ≧ 50 kΩ.
Formula (1)
R _L1 ≧ V0 / I _amax

Also, limiting resistor _{R 12} is the current flowing from the capacitor _{C 11} to the light emitting diode _{D 11,} limits to the size required for the light emission of the light-emitting diode _{D 11.} The resistance value R _L2 of the limiting resistor R ₁₂ at this time is the maximum driving voltage of the photocoupler F ₁₁ (the maximum voltage at the connection point P ₁₁ between the limiting resistor R ₁₁ and the capacitor C ₁₁ ) V1 _max , and the light-emitting diode D ₁₁ is caused to flow. When the current is IF, it is expressed as the following formula (2). In the case of V1 = 5 V and IF = 10 mA, R _L2 = 500Ω.
Formula (2)
R _L2 = V1 _max / IF

Monostable multivibrator 11 is applied to the cathode of the light emitting diode D ₁₁ an electrical signal S0 is converted to a short pulse signal S1 in synchronization with the rising or falling of the electrical signal S0. By signal level of the short pulse signal S1 is switched to Low from High, the light emitting diode _{D 11} are applied forward voltage, the light emitting diode _{D 11} and a current flows from the capacitor _{C 11} to the light emitting diode _{D 11} emits light. At this time, the pulse width of the short pulse signal S1, since it is set to the light emitting diode D ₁₁ in the charge stored in the capacitor C ₁₁ below the light emitting period available, the light emitting diode only the charge stored in the capacitor C ₁₁ it can emit D _11.

In photocoupler _{F 11,} the short pulse signal S1 is transmitted to the phototransistor _{T 11} is converted into light emission of the light-emitting diode _{D 11.} The phototransistor T ₁₁ receives light from the light emitting diode D ₁₁ , and thus a base current flows and conducts between the collector and the emitter. At this time, the collector of the phototransistor T ₁₁ has the power source voltage VE on the output side through a pull-up resistor R ₁₃ is applied, the collector voltage Collector - varies by conduction between the emitter. As the collector voltage fluctuates in synchronization with the short pulse signal S1 on the input side, the short pulse signal S1 on the output side is extracted from the fluctuation of the collector voltage and transmitted.

  The pulse width changing circuit 12 adjusts the pulse width of the short pulse signal S1 on the output side to restore the electric signal S0 having a constant pulse width. That is, the short pulse signal S1 is converted into an electric signal S0 having a constant pulse width that falls in synchronization with the signal level of the short pulse signal S1 changing from High to Low. As described above, the signal transmission circuit 5 of the first embodiment is used for signal transmission of an electric signal having a constant pulse width. For this reason, it is possible to transmit the electric signal S0 having a constant pulse width between the input and output by transmitting either the rising or falling timing of the electric signal by the short pulse signal S1.

In the signal transmission circuit 5 thus configured, when the electric signal S0 is input to the input line L _12, the electrical signal S0 by the monostable multivibrator 11 is converted into a short pulse signal S1. By signal level of the short pulse signal S1 is switched to Low from High, the light emitting diode _{D 11} emits light by the charge stored in the capacitor _{C 11.} The collector of the phototransistor T ₁₁ in synchronization with the light emission of the light-emitting diodes D ₁₁ - emitter is turned on, variations in the collector voltage is taken as the short pulse signal S1. Then, when the electrical signal S0 is restored by the pulse width changing means 12 from the short pulse signal S1, the electrical signal S0 is a signal transmitted in a state where the insulation between input and output by the photo coupler F _11.

At this time, since the light-emitting diode _{D 11} only the charge stored in the capacitor _{C 11} emits light, it does not affect the DC4~20mA current signal. By electric charge of the capacitor C ₁₁ is used for light emission of the light emitting diode D _11, the voltage of the capacitor C ₁₁ is current flows into the signal transmission circuit 5 from the outside decreases, the current is limited by the limiting resistor R ₁₁ Thus, the influence on the DC4 to 20 mA current signal can be suppressed. Because the input and output using a photocoupler F ₁₁ is insulated, as compared to the configuration in which isolation between input and output by using a transformer, a signal transmission circuit 5 can be formed at low cost and compact.

  Here, a change in the driving voltage of the photocoupler with respect to the short pulse signal will be described with reference to FIG. FIG. 5 is a diagram illustrating a relationship between the short pulse signal and the driving voltage of the photocoupler according to the first embodiment. Here, description will be made with reference to FIG. 4 as appropriate.

As shown in FIG. 5, the Low period Tl of the short pulse signal S1, charge current to the light emitting diode _{D 11} is stored in the capacitor _{C 11} flows from the capacitor _{C 11} is consumed, the limiting resistor and a capacitor _{C 11 R 11} The driving voltage V1 at the connection point P ₁₁ (see FIG. 4) rapidly decreases. Although the driving voltage V1 than the power supply voltage V0 is a current flows from the power supply to the signal transmission circuit 5 by reduction are current limited by the limiting resistor R _11. The High period T2 of the short pulse signal S1, the light emitting diode D ₁₁ is no current flowing off the charge output from the power supply through the limiting resistor R ₁₁ is stored in the capacitor C _11, the subsequent short pulse The drive voltage V1 gradually increases until the signal becomes low.

As described above, in the signal transmission circuit 5 according to the first embodiment, the capacitor C ₁₁ serves as an internal power source, the light emitting diode D ₁₁ of the photocoupler F ₁₁ emits light, and the light emitting diode D ₁₁ and the phototransistor T _11. The signal is optically transmitted in a state of being insulated from each other. The time of light emission of the light emitting diode D ₁₁ instead of the current from the power supply is consumed, the charge stored in the capacitor C ₁₁ is consumed. Therefore, it is possible to suppress the influence of the current consumption of the light emitting diode _{D 11} for DC4~20mA current signal. Further, even if the voltage drops by the consumption of electric charge of the capacitor C _11, since the current flowing from the power supply to the signal transmitting circuit 5 is limited by the limiting resistor R _11, it is suppressed effect on DC4~20mA current signal . Therefore, it is possible to transmit a signal with the input and output insulated without affecting the DC4 to 20 mA current signal.

  Next, a signal transmission circuit according to a second embodiment will be described. The signal transmission circuit according to the second embodiment is a circuit that transmits a signal with a plurality of photocouplers insulated from input and output. The signal transmission circuit according to the second embodiment can transmit an electric signal having a variable pulse width by individually transmitting the rising and falling edges of the electric signal by a plurality of photocouplers. FIG. 6 is a diagram illustrating an example of a signal transmission circuit according to the second embodiment. FIG. 6 is a simplified circuit diagram for explaining the present embodiment, and it is assumed that the signal transmission circuit normally includes a configuration. In the second embodiment, the description of the same configuration as that of the first embodiment is omitted.

As shown in FIG. 6, the signal transmission circuit 20 includes first and second photocouplers F ₂₁ and F ₂₂ , and the first and second photocouplers F ₂₁ and F ₂₂ are connected to the input side. The output side is electrically isolated. The power supply line L ₂₁ on the input side of the signal transmission circuit 20 is grounded to the ground G ₂₁ via the limiting resistor R ₂₁ and the capacitor C ₂₁ . The connection point P ₂₁ between the limiting resistor R ₂₁ and the capacitor C ₂₁ is connected to the anodes of the first and second light emitting diodes D ₂₁ and D ₂₂ via the limiting resistor R ₂₂ . The electric signal input line L ₂₂ is connected to the first and second light emitting diodes D ₂₁ and D ₂₂ via the first and second monostable multivibrators (first and second signal converters) 21 and ₂₂ . Connected to the cathode.

The first power supply line L ₂₃ on the output side of the signal transmission circuit 20 is connected to the collector of the first phototransistor T ₂₁ via the first pull-up resistor R _23, and the emitter of the first phototransistor T ₂₁ . It is grounded to the ground _{G 22.} The second power supply line _{L 24} of the output side is connected to the collector of the second phototransistor _{T 22} via a second pull-up resistor _{R 24,} the emitter of the second phototransistor _{T 22} on the ground _{G 23} Grounded. The connection points P ₂₁ and P ₂₂ between the first and second pull-up resistors R ₂₃ and R ₂₄ and the collectors of the first and second phototransistors T ₂₁ and T ₂₂ are flip-flops (signal restoration units), respectively. 23 is connected to the output line L ₂₅ of the electric signal through 23.

The capacitor C ₂₁ stores the charge output from the power source, and the first and second light emitting diodes D ₂₁ and D ₂₂ emit light by the charge temporarily stored in the capacitor C ₂₁ . Thus, the first capacitor _{C 21} during light emission of the second light-emitting diodes _{D 21, D 22} is used as an internal power supply. Further, the limiting resistor R ₂₁ limits the current flowing into the signal transmission circuit 20 through the power supply line L ₂₁ when the capacitor C ₂₁ is charged or when the first and second light emitting diodes D ₂₁ and D ₂₂ emit light. For this reason, the influence of the consumption current of the first and second light emitting diodes D ₂₁ and D _{22 on} the DC 4 to 20 mA current signal is suppressed.

In the signal transmission circuit 20 configured as described above, when an electric signal is input to the input line L ₂₂ , the electric signal S 0 is input to the first and second monostable multivibrators 21 and 22. In the first monostable multivibrator 21, the electric signal S0 is converted into a first short pulse signal S1 synchronized with the falling edge of the electric signal S0, and in the second monostable multivibrator 22, the electric signal S0 is It is converted into a second short pulse signal S2 synchronized with the rising edge of the electric signal S0. The pulse widths of the short pulse signals S1 and S2 are set to be equal to or shorter than a period during which the first and second light emitting diodes D ₂₁ and D ₂₂ can emit light with the electric charge stored in the capacitor C ₂₁ .

By first short pulse signal S1 is switched to Low from High, the first light emitting diode _{D 21} emits light by the charge stored in the capacitor _{C 21,} a first phototransistor T from the first light-emitting diode _{D 21 21} receives the first short pulse signal S1. Similarly, the second short pulse signal S2 that switches to Low from High, the second light emitting diode _{D 22} emits light by the charge stored in the capacitor _{C 21,} the second light-emitting diodes _{D 22} second second short pulse signal S2 is transmitted to the phototransistor _{T 22.} The flip-flop 23 restores the electrical signal S0 from the first and second short pulse signals S1 and S2.

  In this case, in the flip-flop 23, the signal level is lowered by the first short pulse signal S1, the signal level is raised by the second short pulse signal S2, and the electric signal S0 is restored. That is, the electric signal is cleared when the signal level of the first short pulse signal S1 becomes Low, and the electric signal is set when the signal level of the second short pulse signal S2 becomes Low. Thus, by transmitting the falling and rising timings of the electric signal S0, the electric signal S0 can be transmitted with the input and output insulated even when the pulse width of the electric signal S0 is indefinite. Is possible.

As described above, also in the signal transmission circuit 20 of the second embodiment, the DC 4 to 20 mA current signal generated by the light emission of the first and second light emitting diodes D ₂₁ and D ₂₂ is the same as in the first embodiment. The impact is suppressed. Even if the pulse width of the electric signal S0 is variable, the signal can be transmitted with the input and output insulated.

In the first and second embodiments described above, the photocouplers F ₁₁ , F ₂₁ , and F ₂₂ are illustrated as signal transmission units, but the present invention is not limited to this configuration. The signal transmission unit may be configured to optically transmit an electrical signal from the light emitting element to the light receiving element. For example, a photo MOS relay including a light emitting diode and a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is used. May be.

  In the first and second embodiments described above, monostable multivibrators 11, 21, and 22 are exemplified as the signal conversion unit, but the present invention is not limited to this configuration. The signal conversion unit may be configured to convert an electric signal into a short pulse signal synchronized with the rising or falling of the electric signal, and can be converted into a short pulse signal using, for example, a differentiation circuit.

  In the first embodiment described above, the pulse width changing circuit 12 is exemplified as the signal restoration unit. In the second embodiment, the flip-flop 23 is exemplified as the signal restoration unit. It is not limited to the configuration. The signal restoration unit may be configured to restore an electric signal from a short pulse signal transmitted from the light emitting element to the light receiving element.

  Moreover, the instrumentation apparatus 1 of this Embodiment should just be an instrumentation apparatus provided with the signal transmission circuit of this invention, for example, the vehicle detector which detects the presence or absence of the vehicle in a parking lot, or the approach of the vehicle to a gate May be used.

  Moreover, although each embodiment of the present invention has been described, as another embodiment of the present invention, the above embodiments may be combined in whole or in part.

  The embodiments of the present invention are not limited to the above-described embodiments, and various changes, substitutions, and modifications may be made without departing from the spirit of the technical idea of the present invention. Further, if the technical idea of the present invention can be realized in another way by technological advancement or other derived technology, the method may be used. Accordingly, the claims cover all embodiments that can be included within the scope of the technical idea of the present invention.

  In the embodiment of the present invention, the configuration in which the present invention is applied to the signal transmission circuit of the instrumentation device has been described. However, the present invention can also be applied to the signal transmission circuit of other devices.

The feature points in the above embodiment are organized below.
The signal transmission circuit described in the above embodiment is a signal transmission circuit that transmits an electrical signal in a state where the input and output are insulated from each other, and includes a signal transmission unit that optically transmits a signal from a light emitting element to a light receiving element, and a power source. A limiting resistor for limiting a current flowing toward the light emitting element; and a capacitor for storing a charge output from the power supply via the limiting resistor, and causing the light emitting element to emit light by the charge stored in the capacitor. Features.

  According to this configuration, the light emitting element of the signal transmission unit emits light with the capacitor serving as an internal power source, and an optical signal is transmitted with the light emitting element and the light receiving element insulated. When the light emitting element emits light, current from the power source is not consumed, but electric charge stored in the capacitor is consumed. For this reason, the influence of the current consumption of the light emitting element on the current signal that also serves as the power supply from the power source can be suppressed. Even if the voltage drops due to the consumption of the capacitor charge, the current flowing from the power source into the signal transmission circuit is limited by the limiting resistor, so that the influence on the current signal is suppressed. Therefore, the signal can be transmitted in an insulated state between the input and output without affecting the current signal.

  Further, in the signal transmission circuit described in the above embodiment, a signal conversion unit that converts an electric signal into a short pulse signal synchronized with the rising or falling of the electric signal and inputs the signal to the light emitting element; A signal restoration unit that restores an electrical signal from the short pulse signal transmitted to the light receiving element, and the pulse width of the short pulse signal is equal to or shorter than a period during which the light emitting element can emit light with the charge stored in the capacitor. According to this configuration, since the light emitting element can emit light only with the electric charge stored in the capacitor, the influence of light emission of the light emitting element on the current signal can be suppressed.

  Further, in the signal transmission circuit described in the above embodiment, the signal restoration unit restores the electric signal by adjusting the pulse width of the short pulse signal. According to this configuration, by restoring an electrical signal having a constant pulse width from a short pulse signal, it is possible to transmit an electrical signal having a constant pulse width between the input and output.

  Further, in the signal transmission circuit described in the above embodiment, the signal transmission unit optically transmits a signal from the first light emitting element to the first light receiving element, and a second light emitting element. And a second signal transmission unit for optically transmitting a signal to the second light receiving element, and the signal conversion unit converts the electrical signal into a first short pulse signal synchronized with a falling edge of the electrical signal. A first signal conversion unit that converts the electrical signal into a second short pulse signal that is synchronized with the rising edge of the electrical signal, and the signal restoration unit includes the first signal conversion unit. The signal level is lowered by the first short pulse signal transmitted from the light emitting element to the first light receiving element, and the second short pulse signal transmitted from the second light emitting element to the second light receiving element. The electrical signal is restored by raising the signal level, and the first short The pulse width of the pulse signal is equal to or shorter than the period during which the first light emitting element can emit light with the electric charge stored in the capacitor, and the pulse width of the second short pulse signal is the electric charge stored in the capacitor. The period is shorter than the period during which the second light emitting element can emit light. According to this configuration, the electrical signal with variable pulse width can be transmitted by individually transmitting the falling edge of the electrical signal using the first short pulse signal and the rising edge of the electrical signal using the second short pulse signal. it can.

  In the signal transmission circuit described in the above embodiment, the signal transmission unit is a photocoupler including a light emitting diode as the light emitting element and a phototransistor as the light receiving element. According to this configuration, the signal transmission circuit can be formed using an inexpensive and small photocoupler.

  Further, in the signal transmission circuit described in the above embodiment, the limiting resistor limits the current supplied to the capacitor to a magnitude that does not affect the DC4 to 20 mA current signal. According to this configuration, it is possible to reliably suppress the influence of the current consumption in the light emitting element on the DC4 to 20 mA current signal.

  In addition, the instrumentation device described in the embodiment includes the signal transmission circuit described above, a control circuit that inputs an electric signal to the signal transmission circuit, and an electric signal that is input via the signal transmission circuit. A sensor circuit for driving, and outputs a measured value of the sensor circuit using an electrical signal of DC 4 to 20 mA. According to this configuration, it is possible to accurately transmit a measurement value transmitted with a DC 4 to 20 mA current signal to the outside.

  As described above, the present invention has an effect that signals can be transmitted between the input and output without affecting the current signal, and in particular, the power supply is limited by the DC 4 to 20 mA current signal. It is useful for signal transmission circuits and instrumentation devices that transmit signals.

DESCRIPTION OF SYMBOLS 1 Instrumentation equipment 3 Control circuit 4 Sensor circuit 5, 20 Signal transmission circuit 11 Monostable multivibrator (signal conversion part)
12 Pulse width change circuit (signal restoration part)
21 1st monostable multivibrator (1st signal converter)
22 2nd monostable multivibrator (2nd signal converter)
23 Flip-flop (signal restoration unit)
C ₁₁ , C ₂₁ capacitor D ₁₁ light emitting diode (light emitting element)
D ₂₁ first light emitting diode (first light emitting element)
D ₂₂ Second light emitting diode (second light emitting element)
F ₁₁ photocoupler (signal transmitting portion)
F ₂₁ first photocoupler (first signal transmission unit)
F ₂₂ second photocoupler (second signal transmission unit)
R ₁₁ , R ₂₁ limiting resistor T ₁₁ phototransistor (light receiving element)
T ₂₁ first phototransistor (first light receiving element)
T ₂₂ second phototransistor (second light receiving element)

Claims (7)

A signal transmission circuit for transmitting an electrical signal in a state where the input and output are insulated,
A signal transmission unit for optically transmitting a signal from the light emitting element to the light receiving element;
A limiting resistor for limiting a current flowing from the power source toward the light emitting element;
A capacitor for storing electric charges output from the power source via the limiting resistor,
A signal transmission circuit, wherein the light emitting element is caused to emit light by electric charge stored in the capacitor. A signal converter that converts the electrical signal into a short pulse signal synchronized with the rise or fall of the electrical signal and inputs the short pulse signal; and
A signal restoration unit that restores an electrical signal from a short pulse signal transmitted from the light emitting element to the light receiving element;
2. The signal transmission circuit according to claim 1, wherein a pulse width of the short pulse signal is equal to or shorter than a period during which the light emitting element can emit light with the charge stored in the capacitor.   The signal transmission circuit according to claim 2, wherein the signal restoration unit restores an electric signal by adjusting a pulse width of a short pulse signal. The signal transmission unit optically transmits a signal from the first light emitting element to the first light receiving element, and optically transmits a signal from the second light emitting element to the second light receiving element. A second signal transmission unit,
The signal converter converts a first signal converter that converts an electric signal into a first short pulse signal that is synchronized with the falling edge of the electric signal; and a second short signal that is synchronized with the rising edge of the electric signal. A second signal converter for converting into a pulse signal,
The signal restoration unit lowers the signal level with a first short pulse signal transmitted from the first light emitting element to the first light receiving element, and from the second light emitting element to the second light receiving element. The electrical signal is restored by raising the signal level with the transmitted second short pulse signal,
The pulse width of the first short pulse signal is equal to or shorter than a period during which the first light emitting element can emit light with the charge stored in the capacitor, and the pulse width of the second short pulse signal is stored in the capacitor. 3. The signal transmission circuit according to claim 2, wherein the second light-emitting element has a period during which the second light-emitting element can emit light with a constant charge.   5. The signal transmission circuit according to claim 1, wherein the signal transmission unit is a photocoupler including a light emitting diode as the light emitting element and a phototransistor as the light receiving element.   6. The signal transmission circuit according to claim 1, wherein the limiting resistor limits a current supplied to the capacitor to a magnitude that does not affect a DC4 to 20 mA current signal. . A signal transmission circuit according to any one of claims 1 to 6;
A control circuit for inputting an electric signal to the signal transmission circuit;
A sensor circuit that is driven by an electric signal input via the signal transmission circuit,
An instrumentation device that outputs a measured value of the sensor circuit using an electric signal of DC 4 to 20 mA.

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