CN108051641A - For the measuring circuit of measuring loop resistance - Google Patents

Abstract

The invention provides a measuring circuit for measuring loop resistance, which belongs to the field of micro-resistance measurement. The measuring circuit includes a test power supply, a loop resistance, a sampling circuit, a microcontroller, a voltage amplifier, an A/D converter, and an instrument amplifier. Combined with the connection relationship of each device in the above measurement circuit, by using the dynamic zero calibration method to measure the voltage and current of the loop resistance, when the test power is off, the voltage and current of the loop resistance are measured for the first time, and the voltage and current record will be obtained. is the zero point; when the test power supply is started, the voltage and current of the loop resistance are measured for the second time, and the obtained voltage and current minus the voltage and current as the zero point are divided by the magnification to obtain the accurate voltage and current, and then It is not affected by the temperature drift of the amplifier, making the measurement results accurate.

Description

Measuring circuit for measuring loop resistance

technical field

The invention belongs to the field of micro-resistance measurement, in particular to a measurement circuit for measuring loop resistance.

Background technique

When measuring loop resistance, due to the influence of temperature, service conditions, environment and other factors, the amplifier has the problem of temperature drift. Among them, the accuracy of the amplifier directly affects the measurement results.

At present, in order to accurately measure the voltage and current of the loop resistance, an extremely low offset voltage and expensive amplifier is used, but the amplifier is still affected by external factors and still has the problem of temperature drift, which leads to deviations in the measurement results.

Contents of the invention

In order to solve the shortcomings and deficiencies in the prior art, the present invention provides a measurement circuit that measures the voltage and current of the loop resistance by adopting a dynamic zero calibration method, and is not affected by the temperature drift of the amplifier, and improves the accuracy of the test results.

In order to achieve the above-mentioned technical purpose, the present invention provides the measurement circuit that is used for measuring loop resistance, and described measurement circuit comprises test power supply, is connected with loop resistance, sampling circuit, microcontroller on the described test power supply, the output of described loop resistance connected to the sampling circuit, the output of the sampling circuit is connected to a voltage amplifier, the output of the voltage amplifier is connected to an A/D converter, and the output of the A/D converter is connected to the micro A controller, the other output end of the loop resistance is connected with an instrumentation amplifier, the output end of the instrumentation amplifier is connected with the A/D converter, and the gain control end of the instrumentation amplifier is connected with a microcontroller.

Optionally, the sampling circuit includes a sampling resistor, and the sampling resistor is a four-terminal resistor.

Optionally, the voltage amplifier has an inverting input terminal and a non-inverting input terminal, and the sampling resistor is provided between the inverting input terminal and the non-inverting input terminal.

Optionally, a feedback resistor Rf is provided between the inverting input terminal of the voltage amplifier and its own output terminal, and the inverting input terminal of the voltage amplifier is grounded through the current limiting resistor R0.

Optionally, the instrumentation amplifier has a non-inverting input terminal and an inverting input terminal, and the loop resistance is provided between the non-inverting input terminal of the instrumentation amplifier and the inverting input terminal of the instrumentation amplifier.

Optionally, the A/D converter has at least two input terminals.

Optionally, a relay is provided between the test power supply and the microcontroller.

The beneficial effects brought by the technical scheme provided by the invention are:

Combined with the connection relationship of each device in the above measurement circuit, by using the dynamic zero calibration method to measure the voltage and current of the loop resistance, when the test power is off, the voltage and current of the loop resistance are measured for the first time, and the voltage and current record will be obtained. is the zero point; when the test power supply is started, measure the voltage and current of the loop resistance for the second time, subtract the voltage and current as the zero point from the obtained voltage and current, divide it by the magnification to obtain the accurate voltage and current, and then It is not affected by the temperature drift of the amplifier, making the measurement results accurate.

Description of drawings

In order to illustrate the technical solution of the present invention more clearly, the accompanying drawings that need to be used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. Ordinary technicians can also obtain other drawings based on these drawings on the premise of not paying creative work.

Fig. 1 is the structural representation of the measuring circuit that is used for measuring loop resistance provided by the present invention;

Fig. 2 is a circuit connection diagram of a measuring circuit for measuring loop resistance provided by the present invention.

Detailed ways

In order to make the structure and advantages of the present invention clearer, the structure of the present invention will be further described below in conjunction with the accompanying drawings.

Embodiment one

The invention provides a measurement circuit for measuring loop resistance, the measurement circuit includes a test power supply, a loop resistance, a sampling circuit, and a microcontroller are connected to the test power supply, and the output end of the loop resistance is connected to the sampling circuit, the output end of the sampling circuit is connected with a voltage amplifier, the output end of the voltage amplifier is connected with an A/D converter, and the output end of the A/D converter is connected with the microcontroller; the loop The other output end of the resistor is connected with an instrumentation amplifier, the output end of the instrumentation amplifier is connected with the A/D converter, and the gain control end of the instrumentation amplifier is connected with a microcontroller.

In implementation, as shown in FIG. 1 , in order to avoid deviations in measurement results caused by low-voltage offsets and temperature drifts in amplifiers used to measure voltage and current. Therefore, the dynamic zero calibration method is used to measure the voltage and current of the loop resistance, and the loop resistance is measured twice. For the first measurement, the microcontroller is turned off the test power supply. When the test power supply is turned off, the sampling circuit collects the value of the loop resistance. Analog current, the collected analog current is transmitted to the voltage amplifier, and the voltage amplifier amplifies the analog current by a preset multiple, and then the amplified analog current is converted into a digital current by the A/D converter, and the digital current is converted into a digital current. The measured current is transmitted to the microcontroller, and the microcontroller reads the digital current and records the digital current as zero.

At the same time, the instrumentation amplifier collects the analog voltage of the loop resistance. Since the A/D converter has a preset reading range, when the analog voltage collected by the instrumentation amplifier is not within the preset reading range of the A/D converter, the instrumentation amplifier will The collected voltage is transmitted to the microcontroller through the gain control terminal, so that the microcontroller can amplify the analog voltage by a preset multiple through the gain control terminal, and then the amplified analog voltage is converted into a digital voltage by the A/D converter , the microcontroller reads the digital voltage and records the digital voltage as zero.

For the second measurement, the microcontroller starts the test power supply. When the test power supply is in the starting state, the test power supply outputs a current greater than 100A. The sampling resistor collects the analog current of the loop resistance, and outputs the analog current to the voltage amplifier. The voltage amplifier amplifies the analog current by a preset multiple, and then the amplified analog current is converted into a digital current by the A/D converter. The microcontroller reads the digital current and subtracts the digital current as the zero point. Divide the measured current by the preset multiple to get the precise digital current.

At the same time, the instrumentation amplifier measures the analog voltage of the loop resistance. Since the A/D converter has a preset reading range, when the analog voltage collected by the instrumentation amplifier is not within the preset reading range of the A/D converter, the instrumentation amplifier will The collected voltage is transmitted to the microcontroller through the gain control terminal, so that the microcontroller can amplify the analog voltage by a preset multiple through the gain control terminal, and then the amplified analog voltage is converted into a digital voltage by the A/D converter , the microcontroller reads the digital voltage, subtracts the digital voltage as the zero point from the digital voltage, and divides it by a preset multiple to obtain an accurate digital voltage.

Since the temperature drift of the amplifier changes slowly, the voltage and current of the loop resistance need to be measured twice each time. When the test power is turned off, the voltage and current of the loop resistance are measured for the first zero calibration, and the voltage and current will be obtained. Record it as the zero point; when the test power supply is started, measure the voltage and current of the loop resistance for the second time, subtract the voltage and current as the zero point from the obtained voltage and current, and divide it by the magnification to obtain the accurate voltage and current. Furthermore, it is not affected by the temperature drift of the amplifier, and the accuracy of the measurement result is improved.

Optionally, the sampling circuit includes a sampling resistor, and the sampling resistor is a four-terminal resistor.

In practice, there are many types of sampling circuits, a typical sampling circuit is a sampling resistor, and the sampling resistor is used to collect the current of the loop resistance. The sampling resistor in this embodiment is a 0.75mΩ four-terminal resistor made of low-temperature bleached manganese-copper material, and the maximum sampling current is 100A. As shown in Figure 2, the sampling resistor R1 has four output terminals, which are the first output terminal, the second output terminal, the third output terminal, and the fourth output terminal, and the first output terminal of the sampling resistor R1 is connected through the loop resistor R2 The input terminal of the test power supply, the second output terminal of the sampling resistor R1 is connected to the other input terminal of the test power supply, the third terminal of the sampling resistor R1 is connected to the non-inverting input terminal of the voltage amplifier U1, and the fourth terminal of the sampling resistor R1 is connected to the voltage amplifier U1 The sampling resistor R1 collects the analog current of the loop resistor R2 through the first output terminal and the second output terminal, and the sampling resistor R1 transmits the collected analog current to the voltage amplifier through the third terminal and the fourth terminal U1.

Optionally, the voltage amplifier has an inverting input terminal and a non-inverting input terminal, and the sampling resistor is provided between the inverting input terminal and the non-inverting input terminal.

In practice, in order to obtain the current of the loop resistance, according to the above, the sampling resistor R1 is used to collect the analog current of the loop resistance R2, therefore, a sampling resistor is provided between the inverting input terminal and the non-inverting input terminal of the voltage amplifier U1 R1, and then the voltage amplifier U1 obtains the analog current through the inverting input terminal and the non-inverting input terminal, and amplifies the obtained analog current by a preset multiple.

Optionally, a feedback resistor Rf is provided between the inverting input terminal of the voltage amplifier and its own output terminal, and the inverting input terminal of the voltage amplifier is grounded through the current limiting resistor R0.

In practice, the voltage amplifier U1 is a non-inverting voltage amplifier. The closed-loop gain of the voltage amplifier U1 is determined by connecting the feedback resistor Rf and the current limiting resistor R0 between the inverting input terminal and the output terminal. The input signal Ui is added to the voltage amplifier U1. At the non-inverting input terminal, the phase of the output voltage Uo is the same as that of the output signal Ui, the closed-loop amplification factor A=1+Rf/R0, the voltage amplifier amplifies the analog current by a preset multiple, so that the amplified analog current is converted in A/D within the reading range of the device, and then the A/D converter converts it into a digital quantity. Wherein, according to measurement requirements, the value range of the preset multiple is 1 to 1000 times.

Optionally, the instrumentation amplifier has a non-inverting input terminal and an inverting input terminal, and the loop resistance is provided between the non-inverting input terminal of the instrumentation amplifier and the inverting input terminal of the instrumentation amplifier.

In practice, in order to obtain the analog voltage of the loop resistance, since the instrumentation amplifier is different from the voltage amplifier, the instrumentation amplifier can directly obtain the voltage of the loop resistance. And the acquired analog voltage of the loop resistance is amplified by a preset multiple. As shown in Figure 2, the non-inverting input terminal and inverting input terminal of the instrumentation amplifier U2 are respectively connected to both ends of the loop resistor R2, the voltage reference terminal REF of the instrumentation amplifier U2 is grounded, and the gain control terminal A1/A0 of the instrumentation amplifier U2 is connected to the micro controller.

Among them, the instrumentation amplifier U2 is a special differential amplifier with ultra-high input impedance, extremely good common-mode suppression ratio, low input offset, and low output impedance, which can amplify those signals under common-mode voltage. It is a closed-loop gain component with a differential input and an output relative to a reference terminal. The two differential input terminals of the instrumentation amplifier U2 are applied with input signals, and its gain can be preset internally, or can be preset by the user through pins internally or through an external gain resistor isolated from the input signal.

Optionally, the A/D converter has at least two input terminals.

In practice, there are many types of A/D converters. In this embodiment, the A/D converter is 16-bit AD7656, specifically 6 A/D conversion channels, and only two channels are used here. As shown in Figure 2, the V1 input terminal of the A/D converter U3 is connected to the output terminal OUT of the instrumentation amplifier U2, the V2 input terminal of the A/D converter U3 is connected to the output terminal of the voltage amplifier U1, and the A/D converter U3’s The ground terminal is grounded, and the CONVST startup terminal of the A/D converter U3, the /RD read control line terminal, and the DB8~DB15 data bus terminal are connected to the microcontroller, wherein the A/D converter U3 receives the instrumentation amplifier U2 through the V1 input terminal to amplify After the analog voltage, the A/D converter U3 converts the received analog voltage into a digital voltage, and the digital voltage is read by the microcontroller; the A/D converter U3 receives the voltage amplifier through the V2 input terminal The amplified analog current by U1 converts the amplified analog current into a digital current, so that the microcontroller can read the digital current.

Optionally, a relay is provided between the test power supply and the microcontroller.

In practice, the microcontroller controls the startup and shutdown of the test power supply by controlling the relay. The relay includes coils and contacts. When the microcontroller disconnects the coil and contacts of the relay, the test power supply is turned off. When the microcontroller When the coil and contacts of the relay are closed, the test power is started.

There may also be other devices with switching functions between the test power supply and the microcontroller, which will not be repeated here.

The invention provides a measuring circuit for measuring loop resistance. The measuring circuit includes a test power supply, a loop resistance, a sampling circuit, a microcontroller, a voltage amplifier, an A/D converter, and an instrument amplifier. Combined with the connection relationship of each device in the above measurement circuit, by using the dynamic zero calibration method to measure the voltage and current of the loop resistance, when the test power is off, the voltage and current of the loop resistance are measured for the first time, and the voltage and current record will be obtained. is the zero point; when the test power supply is started, measure the voltage and current of the loop resistance for the second time, subtract the voltage and current as the zero point from the obtained voltage and current, divide it by the magnification to obtain the accurate voltage and current, and then It is not affected by the temperature drift of the amplifier, making the measurement results accurate.

The serial numbers in the above embodiments are for description only, and do not represent the sequence of the components during assembly or use.

The above description is only an embodiment of the present invention, and is not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention Inside.

Claims (7)

1. for the measuring circuit of measuring loop resistance, the measuring circuit includes experiment power supply, which is characterized in that the experiment Loop resistance, sample circuit, microcontroller are connected on power supply, the output terminal of the loop resistance is connected with the sampling electricity Road, the output terminal of the sample circuit are connected with voltage amplifier, and the output terminal of the voltage amplifier is connected with A/D conversions Device, the output terminal of the A/D converter are connected with the microcontroller, and another output terminal of the loop resistance is connected with instrument Amplifier, the output terminal of the instrument amplifier are connected with the A/D converter, and the gain control end of the instrument amplifier connects It is connected to microcontroller.

2. the measuring circuit according to claim 1 for measuring loop resistance, which is characterized in that the sample circuit bag Sampling resistor is included, the type of the sampling resistor is four terminal resistances.

3. the measuring circuit according to claim 2 for measuring loop resistance, which is characterized in that the voltage amplifier The sampling electricity is equipped with inverting input and in-phase input end, between the inverting input and the in-phase input end Resistance.

4. the measuring circuit according to claim 1 for measuring loop resistance, which is characterized in that the voltage amplifier Inverting input and the output terminal of itself between be equipped with feedback resistance Rf, the inverting input of the voltage amplifier is through current limliting Resistance R0 is grounded.

5. the measuring circuit according to claim 1 for measuring loop resistance, which is characterized in that the instrument amplifier With in-phase input end and inverting input, the in-phase input end of the instrument amplifier and the reverse phase of the instrument amplifier are defeated Enter and be equipped with the loop resistance between holding.

6. the measuring circuit according to claim 1 for measuring loop resistance, which is characterized in that the A/D converter At least there are two input terminals.

7. the measuring circuit according to claim 1 for measuring loop resistance, which is characterized in that the experiment power supply with Relay is equipped between the microcontroller.