CN220896675U - Isolation type conversion circuit for industrial instrument current signal - Google Patents
Isolation type conversion circuit for industrial instrument current signal Download PDFInfo
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- CN220896675U CN220896675U CN202322421978.2U CN202322421978U CN220896675U CN 220896675 U CN220896675 U CN 220896675U CN 202322421978 U CN202322421978 U CN 202322421978U CN 220896675 U CN220896675 U CN 220896675U
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Abstract
The present disclosure provides an isolated conversion circuit for industrial meter current signals, the circuit comprising: the device comprises a signal input conversion unit, a negative feedback isolation unit and a voltage output driving unit; wherein the signal input conversion unit is configured to convert an input current signal into a transition voltage signal; the negative feedback isolation unit is configured to convert the transition voltage signal into an isolated current signal through photoelectric conversion; the voltage output driving unit is configured to convert the isolated current signal into a voltage signal for output. According to the circuit, the negative feedback isolation unit is matched with photoelectric conversion to realize isolation conversion between a current signal and a voltage signal, so that the anti-interference capability and stability of the circuit are improved, and the signal linear conversion precision is ensured.
Description
Technical Field
The disclosure relates to the technical field of industrial instrument signal transmission, in particular to an isolated conversion circuit of an industrial instrument current signal.
Background
The industrial instrument field widely uses 4-20mA current signals to transmit analog signals, and a receiving end needs to convert the linear current signals into corresponding voltage signals so as to carry out further processing application.
The common 4-20mA current signal is converted into a voltage circuit, non-isolated conversion is usually adopted, the current signal and the conversion circuit are commonly grounded, the anti-interference treatment measures of input and output signals are simple, when a strong interference signal appears, the instability of the output signal is increased, the accuracy of a measurement result is affected, and in addition, the safety of the measurement circuit is easily threatened when a current signal loop breaks down.
Disclosure of utility model
The embodiment of the disclosure aims to provide an isolation type conversion circuit for industrial instrument current signals, which is used for solving the problems of low circuit reliability and low anti-interference capability in the prior art.
The embodiment of the disclosure adopts the following technical scheme: an isolated conversion circuit for industrial meter current signals, comprising: the device comprises a signal input conversion unit, a negative feedback isolation unit and a voltage output driving unit; wherein the signal input conversion unit is configured to convert an input current signal into a transition voltage signal; the negative feedback isolation unit is configured to convert the transition voltage signal into an isolated current signal through photoelectric conversion; the voltage output driving unit is configured to convert the isolated current signal into a voltage signal for output.
In some embodiments, the signal input conversion unit includes at least: the first end of first inductance is connected with the first signal input end, the second end of first inductance is connected with the first end of first resistance, the first end of second inductance is connected with the second signal input end, the second end of second inductance is connected with the second end of first resistance, the first end of first resistance is used as the output end of the signal input conversion unit, the second end of first resistance is also connected with the isolation ground, and the first capacitance is connected with the first resistance in parallel.
In some embodiments, the signal input conversion unit further comprises: a fuse connected in series between the first end of the first inductor and the first signal input end; and the bidirectional transient suppression diode is connected in parallel with two ends of the first resistor.
In some embodiments, the negative feedback isolation unit includes at least: the first operational amplifier, the linear optocoupler, the second resistor, the third resistor and the third capacitor; the first pin and the second pin of the first operational amplifier are connected with an isolation ground, the third pin of the first operational amplifier is connected with the second resistor in series and then is connected with the output end of the signal input conversion unit, the fourth pin of the first operational amplifier is connected with the first end of the third resistor and the first pole of the third capacitor, and the fifth pin of the first operational amplifier is connected with an isolation power supply; the second end of the third resistor is connected with the first pin of the linear optocoupler, the second pin of the linear optocoupler is connected with an isolation power supply, the third pin of the linear optocoupler is connected with the second pole of the third capacitor and the third pin of the first operational amplifier, the fourth pin of the linear optocoupler is connected with the isolation ground, the fifth pin of the linear optocoupler is connected with the analog ground, and the sixth pin of the linear optocoupler is connected with the voltage output driving unit.
In some embodiments, the negative feedback isolation unit further comprises: the first electrode of the second capacitor is connected with the first pin of the first operational amplifier, and the second electrode of the second capacitor is connected with the fifth pin of the first operational amplifier.
In some embodiments, the voltage output drive unit includes at least: a second operational amplifier, a fifth capacitor and a fourth resistor; the first pin and the second pin of the second operational amplifier are connected with an analog ground, the third pin of the second operational amplifier is connected with the output end of the negative feedback isolation unit, the fourth pin of the second operational amplifier outputs a voltage signal and is connected with the first pole of the fifth capacitor, the fifth pin of the second operational amplifier is connected with a working power supply, the second pole of the fifth capacitor is connected with the third pin of the second operational amplifier, and the fourth resistor is connected with the fifth capacitor in parallel.
In some embodiments, the voltage output drive unit further comprises: and the first pole of the fourth capacitor is connected with the first pin of the second operational amplifier, and the second pole of the fourth capacitor is connected with the fifth pin of the second operational amplifier.
In some embodiments, the first resistance is a low temperature drift chip resistor with 0.1% precision and 1/4W power; the first inductor and the second inductor are chip patch inductors.
In some embodiments, the model number of the linear optocoupler is HCNR200 or HCNR201; the first operational amplifier is an LMV321 rail-to-rail output operational amplifier.
In some embodiments, the second operational amplifier is an LMV321 rail-to-rail output operational amplifier.
The beneficial effects of the embodiment of the disclosure are that: the negative feedback isolation unit is matched with photoelectric conversion to realize isolation conversion between current signals and voltage signals, so that the anti-interference capability and stability of the circuit are improved, and the signal linear conversion precision is ensured.
Drawings
For a clearer description of one or more embodiments of the present description or of the solutions of the prior art, the drawings that are necessary for the description of the embodiments or of the prior art will be briefly described, it being apparent that the drawings in the description that follow are only some of the embodiments described in the description, from which, for a person skilled in the art, other drawings can be obtained without inventive faculty.
FIG. 1 is a schematic diagram of an isolated switching circuit for industrial meter current signals according to an embodiment of the disclosure;
Fig. 2 is a circuit diagram of one embodiment of an isolated conversion circuit for an industrial meter current signal in an embodiment of the present disclosure.
Detailed Description
In order to enable a person skilled in the art to better understand the technical solutions in one or more embodiments of the present specification, the technical solutions in one or more embodiments of the present specification will be clearly and completely described below with reference to the drawings in one or more embodiments of the present specification, and it is obvious that the described embodiments are only some embodiments of the present specification, not all embodiments. All other embodiments, which can be made by one or more embodiments of the present disclosure without inventive faculty, are intended to be within the scope of the present disclosure.
The industrial instrument field widely uses 4-20mA current signals to transmit analog signals, and a receiving end needs to convert the linear current signals into corresponding voltage signals so as to carry out further processing application.
The common 4-20mA current signal is converted into a voltage circuit, non-isolated conversion is usually adopted, the current signal and the conversion circuit are commonly grounded, the anti-interference treatment measures of input and output signals are simple, when a strong interference signal appears, the instability of the output signal is increased, the accuracy of a measurement result is affected, and in addition, the safety of the measurement circuit is easily threatened when a current signal loop breaks down.
In order to solve the above-mentioned problems, the disclosed embodiments provide an isolated conversion circuit mainly used for converting 4-20mA current signals to output linear voltage signals, fig. 1 shows a schematic structural diagram of the isolated conversion circuit in this embodiment, which mainly includes a signal input conversion unit 10, a negative feedback isolation unit 20 and a voltage output driving unit 30 that are coupled in sequence, wherein the signal input conversion unit 10 is configured to convert the input current signals into transition voltage signals, the negative feedback isolation unit 20 is configured to convert the transition voltage signals into isolated current signals through photoelectric conversion, and the voltage output driving unit 30 is configured to convert the isolated current signals into voltage signals for output, so as to realize conversion between the linear current signals and the voltage signals.
Fig. 2 shows an embodiment of an isolated switching circuit for industrial meter current signals. Specifically, the signal input conversion unit 10 mainly includes a first resistor R1, a first capacitor C1, a first inductor L1, and a second inductor L2, where a first end of the first inductor L1 is connected to the first signal input terminal in+, a second end of the first inductor L1 is connected to the first end of the first resistor R1, a first end of the second inductor L2 is connected to the second signal input terminal IN-, a second end of the second inductor L2 is connected to the second end of the first resistor R1, the first end of the first resistor R1 is used as an output end of the signal input conversion unit 10, a second end of the first resistor R1 is also connected to an isolated ground ISO5VGND, and the first capacitor C1 is connected IN parallel to the first resistor R1. At this time, a 4-20mA current signal is connected to the input terminal IN+ and IN-, and forms a loop through the first inductor L1, the first resistor R1 and the second inductor L2, the loop is converted into a corresponding transition voltage signal on the first resistor R1, the inductors L1 and L2 are used for filtering high-frequency interference IN a signal loop, and the first capacitor C1 is used for removing coupling interference.
Further, the signal input conversion unit 10 further includes a fuse F1 connected IN series between the first end of the first inductor L1 and the first signal input terminal in+ and a bidirectional transient suppression diode VD1 connected IN parallel across the first resistor R1. The fuse F1 in this embodiment may be a self-recovery current-limiting 40mA chip fuse, to prevent the circuit from being damaged due to excessive input current, and the bidirectional transient suppression diode VD1 may be a bidirectional TVS tube, to limit the voltage across the first resistor R1, so as to prevent the damage to the subsequent circuit caused by abrupt voltage change of the input signal.
It should be noted that, during actual connection, the bidirectional transient suppression diode VD1 is connected in parallel to the front end of the first resistor R1 for protection, and the first capacitor C1 is connected in parallel to the rear end of the first resistor R1 for interference filtering. In addition, the first inductor L1 and the second inductor L2 can be realized by adopting chip inductors, and the first resistor R1 is realized by adopting high-precision and low-temperature drift chip resistors with the precision of +/-0.1 percent and the power of 1/4W.
Referring to fig. 2, the negative feedback isolation unit 20 of the present embodiment may mainly include a first operational amplifier U1, a linear optocoupler U2, a second resistor R2, a third resistor R3, and a third capacitor C3; the first pin 1 and the second pin 2 of the first operational amplifier U1 are connected to an isolated ground ISO5VGND, the third pin 3 of the first operational amplifier U1 is connected in series with the second resistor R2 and then connected to the output end of the signal input conversion unit 10 (i.e., the first end of the first resistor R1), the fourth pin 4 of the first operational amplifier U1 is connected to the first end of the third resistor R3 and the first pole of the third capacitor C3, and the fifth pin 5 of the first operational amplifier U1 is connected to an isolated power supply ISO5V; the second end of the third resistor R3 is connected with the first pin 1 of the linear optocoupler U2, the second pin 2 of the linear optocoupler U2 is connected with the isolation power supply ISO5V, the third pin 3 of the linear optocoupler U2 is connected with the second pole of the third capacitor C3 and the third pin of the first operational amplifier U1, the fourth pin 4 of the linear optocoupler U2 is connected with the isolation ground ISO5VGND, the fifth pin 5 of the linear optocoupler U2 is connected with the analog ground AGND, and the sixth pin 6 of the linear optocoupler U2 is connected with the voltage output driving unit 30; a Light Emitting Diode (LED) is connected between a first pin 1 and a second pin 2 in the linear optocoupler U2, a first photodiode (PD 1) is connected between a third pin 3 and a fourth pin 4 of the linear optocoupler U2, and a second photodiode (PD 2) is connected between a fifth pin 5 and a sixth pin 6 of the linear optocoupler U2.
In the negative feedback isolation unit 20, the voltage (transition voltage signal) on the first resistor R1 is input to the 3 rd pin of the first operational amplifier U1 through the second resistor R2, the voltage is output by the 4 th pin of the first operational amplifier U1 after amplification, the light emitting diode LED inside the high-linearity optocoupler U2 is driven to light through the third resistor R3, the first photodiode PD1 is turned on when being illuminated, a photoelectric conversion feedback signal is provided for the first operational amplifier U1, the output end voltage of the 4 th pin of the first operational amplifier U1 is continuously adjusted, and the linear optocoupler U2 forms a linear relation between the input current signal and the output current signal according to the current transmission ratio; the third resistor R3 is a current limiting resistor, and the third capacitor C3 is a negative feedback capacitor of the first operational amplifier U1, and is used for eliminating and preventing self-oscillation of the operational amplifier and filtering interference signals.
In some embodiments, the negative feedback isolation unit 20 further includes a second capacitor C2, as shown in fig. 2, where a first pole of the second capacitor C2 is connected between the first pin 1 of the first operational amplifier U1 and the fifth pin 5 of the first operational amplifier U1, and is used as a high-frequency bypass capacitor of the first operational amplifier U1 to implement more stable operation of the first operational amplifier U1. In actual implementation, the first operational amplifier U1 may be an LMV321 rail-to-rail output operational amplifier, and the linear optocoupler U2 may be a precise linear isolation optocoupler, and the corresponding model may be selected to implement HCNR200 or HCNR 201.
With further reference to fig. 2, the voltage output driving unit 30 of the present embodiment mainly includes: the second operational amplifier U3, the fifth capacitor C5 and the fourth resistor R4, where the first pin 1 and the second pin 2 of the second operational amplifier U3 are connected to the analog ground AGND, where the first pin 1 may be connected to the same analog ground AGND with the fifth pin 5 of the linear optocoupler U2, the third pin 3 of the second operational amplifier U3 is connected to the output end of the negative feedback isolation unit 20 (i.e. connected to the sixth pin 6 of the linear optocoupler U2), the fourth pin 4 of the second operational amplifier U3 outputs the voltage signal VOUT and is connected to the first pole of the fifth capacitor C5, the fifth pin 5 of the second operational amplifier U3 is connected to the working power source VCC5V, the second pole of the fifth capacitor C5 is connected to the third pin 3 of the second operational amplifier U3, and the fourth resistor R4 is connected in parallel to the fifth capacitor C5.
In the voltage output driving unit 30, the isolated current signal generated by the negative feedback isolation unit 10 is converted into a voltage signal by the second operational amplifier U3 and the fourth resistor R4 to be used in a subsequent circuit (not shown). Specifically, the fourth resistor R4 is connected in parallel with the fifth capacitor C5, and is connected in parallel to the 3 rd pin and the 4 th pin of the second operational amplifier U3, the fourth resistor R4 controls the gain of the second operational amplifier U3, adjusts the ratio of the converted input voltage and the converted output voltage, and the fifth capacitor C5 is a negative feedback capacitor of the second operational amplifier U3, so as to limit the amplification frequency bandwidth of the second operational amplifier U3, reduce the high-frequency gain, prevent and eliminate self-oscillation, and reduce the noise influence.
In some embodiments, the voltage output driving unit 30 further includes a fourth capacitor C4, referring to fig. 2, a first pole of the fourth capacitor C4 is connected to the first pin 1 of the second operational amplifier U3, a second pole of the fourth capacitor C4 is connected to the fifth pin 5 of the second operational amplifier U3, and the fourth capacitor C4 is used as a high-frequency bypass capacitor of the second operational amplifier U3, so as to eliminate noise interference in a power supply loop, reduce high-frequency internal resistance of a power supply, and make the U3 operate more stably. In addition, the second operational amplifier U3 may be implemented by an operational amplifier of the same type as the first operational amplifier U1, for example, an LMV321 rail-to-rail output operational amplifier.
In practical implementation, when the working power supplies of the first operational amplifier U1 and the second operational amplifier U3 are both 5V, and the resistance value of the first resistor R1 is 250 ohms, a proper resistance value is selected for R4, so that when the input end has a current signal in the range of 4-20mA, the output end VOUT can obtain an isolated voltage signal of 1-5V.
According to the isolation type conversion circuit for the industrial instrument current signal, through optimizing the filter circuit design and focusing on element selection, various protection and stable working measures are arranged in the circuit, so that the circuit can work stably and reliably, and more accurate conversion voltage data is provided for an external circuit or an ADC (analog-to-digital converter). The circuit of the embodiment has strong anti-interference capability, high reliability and safety, wide range of low-voltage power supply conversion output voltage and ensures the signal linear conversion precision.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present disclosure, and not for limiting the same; although the present disclosure has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present disclosure.
Claims (10)
1. An isolated conversion circuit for industrial instrument current signals, comprising:
the device comprises a signal input conversion unit, a negative feedback isolation unit and a voltage output driving unit; wherein,
The signal input conversion unit is configured to convert an input current signal into a transition voltage signal;
the negative feedback isolation unit is configured to convert the transition voltage signal into an isolated current signal through photoelectric conversion;
The voltage output driving unit is configured to convert the isolated current signal into a voltage signal for output.
2. The isolated switching circuit of claim 1, wherein the signal input switching unit comprises at least:
the first end of first inductance is connected with the first signal input end, the second end of first inductance is connected with the first end of first resistance, the first end of second inductance is connected with the second signal input end, the second end of second inductance is connected with the second end of first resistance, the first end of first resistance is used as the output end of the signal input conversion unit, the second end of first resistance is also connected with the isolation ground, and the first capacitance is connected with the first resistance in parallel.
3. The isolated switching circuit of claim 2, wherein the signal input switching unit further comprises:
A fuse connected in series between the first end of the first inductor and the first signal input end;
and the bidirectional transient suppression diode is connected in parallel with two ends of the first resistor.
4. The isolated switching circuit of claim 1, wherein the negative feedback isolation unit comprises at least:
the first operational amplifier, the linear optocoupler, the second resistor, the third resistor and the third capacitor; wherein,
The first pin and the second pin of the first operational amplifier are connected and isolated, the third pin of the first operational amplifier is connected with the second resistor in series and then is connected with the output end of the signal input conversion unit, the fourth pin of the first operational amplifier is connected with the first end of the third resistor and the first pole of the third capacitor, and the fifth pin of the first operational amplifier is connected with an isolated power supply;
The second end of the third resistor is connected with the first pin of the linear optocoupler, the second pin of the linear optocoupler is connected with an isolation power supply, the third pin of the linear optocoupler is connected with the second pole of the third capacitor and the third pin of the first operational amplifier, the fourth pin of the linear optocoupler is connected with the isolation ground, the fifth pin of the linear optocoupler is connected with the analog ground, and the sixth pin of the linear optocoupler is connected with the voltage output driving unit.
5. The isolated switching circuit of claim 4, wherein the negative feedback isolation unit further comprises:
The first electrode of the second capacitor is connected with the first pin of the first operational amplifier, and the second electrode of the second capacitor is connected with the fifth pin of the first operational amplifier.
6. The isolated switching circuit of claim 1, wherein the voltage output drive unit comprises at least:
A second operational amplifier, a fifth capacitor and a fourth resistor; wherein,
The first pin and the second pin of the second operational amplifier are connected with an analog ground, the third pin of the second operational amplifier is connected with the output end of the negative feedback isolation unit, the fourth pin of the second operational amplifier outputs a voltage signal and is connected with the first pole of the fifth capacitor, the fifth pin of the second operational amplifier is connected with a working power supply, the second pole of the fifth capacitor is connected with the third pin of the second operational amplifier, and the fourth resistor is connected with the fifth capacitor in parallel.
7. The isolated switching circuit of claim 6, wherein the voltage output drive unit further comprises:
And the first pole of the fourth capacitor is connected with the first pin of the second operational amplifier, and the second pole of the fourth capacitor is connected with the fifth pin of the second operational amplifier.
8. The isolated switching circuit of claim 2, wherein the first resistor is a low temperature drift chip resistor with a precision of ± 0.1% and a power of 1/4W;
the first inductor and the second inductor are chip patch inductors.
9. The isolated switching circuit of claim 4, wherein the linear optocoupler is model HCNR200 or HCNR201;
the first operational amplifier is an LMV321 rail-to-rail output operational amplifier.
10. The isolated switching circuit of claim 6 wherein the second operational amplifier is an LMV321 rail-to-rail output operational amplifier.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202322421978.2U CN220896675U (en) | 2023-09-06 | 2023-09-06 | Isolation type conversion circuit for industrial instrument current signal |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202322421978.2U CN220896675U (en) | 2023-09-06 | 2023-09-06 | Isolation type conversion circuit for industrial instrument current signal |
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| CN220896675U true CN220896675U (en) | 2024-05-03 |
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| CN202322421978.2U Active CN220896675U (en) | 2023-09-06 | 2023-09-06 | Isolation type conversion circuit for industrial instrument current signal |
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- 2023-09-06 CN CN202322421978.2U patent/CN220896675U/en active Active
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