Full dynamic range high-precision resistance measurement structure and measurement method thereof

Abstract

This invention discloses a high-precision resistance measurement structure with full dynamic range, wherein the resistor to be measured, R, is in the structure. t Two long wires are connected to the two ends of the resistor; one end of the reference resistor R1 is connected to the resistor R to be measured. t One end of the wire is connected, and its circuit node is X. The resistor to be measured is R. t A long wire at the other end is connected to a reference resistor R2. Circuit nodes M, X, and Y are sequentially connected to the first three-input single-output switch, and circuit nodes X, Y, and N are sequentially connected to the second three-input single-output switch. The outputs of the two switches are connected to the inputs of instrumentation amplifier A. The output of the instrumentation amplifier is connected to a single-input dual-output switch, the output of which is connected to the non-inverting input of instrumentation amplifier B and the input of a voltage holder, respectively. The output of the voltage holder is connected to the inverting input of instrumentation amplifier B. The advantage of this measurement structure is that it can perform high-amplification measurements, and the output voltage swing can range from zero to the supply voltage.

Description

Technical fields:

[0001] This invention relates to long-distance resistance measurement technology, high-resolution resistance measurement technology, high-accuracy resistance measurement technology, and full dynamic range resistance measurement technology, specifically to a high-precision resistance measurement structure and method with full dynamic range, which can be widely used in the field of long-distance, high-resolution, high-accuracy, and full dynamic range resistance measurement. Background technology:

[0002] Achieving long-distance, high-resolution, and high-accuracy resistance measurement is of significant practical importance for scientific research and industrial control. Existing high-resolution resistance measurement methods primarily utilize Wheatstone bridge temperature measurement. However, this circuit structure cannot eliminate the influence of factors such as thermoelectric potential and wire resistance. Furthermore, as the resistance value deviates from the bridge's equilibrium position, the circuit's resolution gradually deteriorates, exhibiting significant nonlinear characteristics. Another method, a four-wire resistance measurement method excited by a constant current source, can mitigate the influence of thermoelectric potential and wire resistance. However, the output voltage range of this circuit structure does not start from zero voltage. Limited by the operating voltage, this circuit cannot perform high-amplification resistance measurements. This means that high-resolution resistance measurement requires a higher-bit analog-to-digital converter (ADC), and most of the ADC's dynamic range is outside the actual resistance measurement range, resulting in a significant waste of the ADC's dynamic performance. Currently, no technology similar to this invention has been found in publicly available literature. Summary of the Invention:

[0003] The main purpose of this invention is to solve the problems of low resolution in resistance measurement over long distances and the significant waste of the dynamic range of the subsequent analog-to-digital converter. It utilizes a high-precision resistance measurement structure with full dynamic range to reduce the errors introduced by temperature difference thermoelectric potential and wire resistance in long-distance applications. This structure and measurement method also reduce the influence of factors such as offset voltage, gain error, and long-term drift of the instrumentation amplifier in voltage measurement, thereby realizing resistance measurement scenarios with high resolution, high accuracy, and full dynamic range that can be applied over long distances.

[0004] The entire resistance measurement structure consists of two reference resistors R1 and R2, and one resistor to be measured, R. t The circuit consists of two instrumentation amplifiers A and B, two three-input single-output switching switches forming a switching group, a single-input dual-output switching switch, and a voltage holding circuit; the resistor to be measured is R. t Two long wires are connected to each end of the resistor; one end of the reference resistor R1 is connected to the resistor R to be measured. t A long wire connects to the circuit at one end, with the circuit node being X, and the resistor to be measured is R. tA long wire at the other end is connected to a reference resistor R2, with its circuit node being Y. The other end of the reference resistor R1 has a circuit node M, and the other end of the reference resistor R2 has a circuit node N. Circuit nodes M, X, and Y are sequentially connected to the first three-input single-output switch, and circuit nodes X, Y, and N are sequentially connected to the second three-input single-output switch. The output terminals of the two switches are connected to the input terminals of instrumentation amplifier A. The output terminal of the instrumentation amplifier is connected to a single-input dual-output switch, and the output terminal of this switch is connected to the non-inverting input terminal of instrumentation amplifier B and the input terminal of a voltage holder, respectively. The output terminal of the voltage holder is connected to the inverting input terminal of instrumentation amplifier B. A schematic diagram of the invention is shown below. Figure 1 As shown.

[0005] When this high-precision resistance measurement structure with full dynamic range is connected to a long wire for resistance measurement, its circuit structure model is simplified to: Figure 1 As shown, r and E are the wire resistance and thermoelectric potential of the long wire, respectively.

[0006] The method of using this invention is as follows:

[0007] 1. Connect circuit nodes M and N to the power supply, and compare the series-connected reference resistor R1 and the resistor to be measured R. t Power is supplied through a reference resistor R2, and the current flowing through them is I. S ;

[0008] 2. Set up a switching group, with node M connected to the non-inverting input of instrumentation amplifier A and node X connected to the inverting input of instrumentation amplifier A. Then, set the switching switch to connect the output of instrumentation amplifier A to a voltage holder. Let the output voltage of instrumentation amplifier A at this time be U. A1 After the voltage holder stabilizes, set up a switching group. Connect node X to the non-inverting input of instrumentation amplifier A and node Y to the inverting input of instrumentation amplifier A. Then, set up a switching switch to connect the output of instrumentation amplifier A to the non-inverting input of instrumentation amplifier B. Let the output voltage of instrumentation amplifier A at this time be U. A2 The output voltage of instrumentation amplifier B is U. B1 ;

[0009] 3. Set up a switching group, with node X connected to the non-inverting input of instrumentation amplifier A and node Y connected to the inverting input of instrumentation amplifier A. Then, set the switching switch to connect the output of instrumentation amplifier A to a voltage holder. Let the output voltage of instrumentation amplifier A at this time be U. A3After the voltage holder stabilizes, set up a switching group. Connect the Y node to the non-inverting input of instrumentation amplifier A and the N node to the inverting input of instrumentation amplifier A. Set up the switching switch to connect the output of instrumentation amplifier A to the non-inverting input of instrumentation amplifier B. Let the output voltage of instrumentation amplifier A at this time be U. A4 The output voltage of instrumentation amplifier B is U. B2 ;

[0010] 4. Set up a switching group, connecting the Y node to the non-inverting input of instrumentation amplifier A and the N node to the inverting input of instrumentation amplifier A. Then, set the switching switch to connect the output of instrumentation amplifier A to a voltage holder. Let the output voltage of instrumentation amplifier A at this time be U. A5 After the voltage holder stabilizes, set up a switching group. Connect node M to the non-inverting input of instrumentation amplifier A and node X to the inverting input of instrumentation amplifier A. Set up the switching switch to connect the output of instrumentation amplifier A to the non-inverting input of instrumentation amplifier B. Let the output voltage of instrumentation amplifier A at this time be U. A6 The output voltage of instrumentation amplifier B is U. B3 ;

[0011] 5. The resistance to be measured, R t The formula for calculating the resistance is as follows:

[0012]

[0013] When using this invention, similar wires and welding methods should be selected as much as possible, so that the resistances of different wires are approximately equal, denoted uniformly as r. The thermoelectric potentials of the temperature difference on the wires are also almost equal, denoted uniformly as E. Since the subsequent stage uses an instrumentation amplifier to acquire the voltage of the reference resistor and the resistor under test, its input impedance is generally at the GΩ level, so the voltage loss on the wire resistance r can be ignored. At the same time, since the temperature field distribution of each wire on the resistor under test is basically the same, the thermoelectric potential E can be ignored. Let the gain drift errors of instrumentation amplifiers A and B be α respectively. A α B The amplifier gain factors are A A A B The amplifier output offset voltages are ΔU A , ΔU B ; The current flows through the reference resistor R1 and the resistor to be measured R t The current in the reference resistor R2 is denoted as I. S The output offset voltage of the voltage holder is ΔU0. According to the method of use described in this invention, the following equations are obtained:

[0014]

[0015] It can be deduced that:

[0016]

[0017] According to the above formula, the influencing factors such as gain drift error of the instrumentation amplifier, output offset voltage, and output offset voltage of the voltage holder are all eliminated. After simplification, the formula for calculating the resistance value of the resistor to be measured is obtained:

[0018]

[0019] It is worth noting that if the reference resistor R1 and the resistor to be measured R t If the resistance value is similar to that of the reference resistor R2, then the output voltage U of the instrumentation amplifier B will be... B1 U B2 U B3 The ability to approach zero voltage means that instrumentation amplifier B can be configured with a relatively large gain. The overall gain of this circuit structure is A. A A B .

[0020] The beneficial effect of this method is that it reduces the influence of thermoelectric potential, wire resistance, output offset voltage, gain drift error, etc. in voltage measurement. By using the voltage holder design, the voltage difference at the input terminal of instrumentation amplifier B is lowered, making it possible to set its high amplification factor. It realizes the circuit output from zero to the power supply voltage, makes full use of the dynamic range of the subsequent analog-to-digital converter, avoids performance waste, and thus realizes resistance measurement that can be applied to long distance, high resolution, high accuracy, and full dynamic range. Attached image description:

[0021] Figure 1 This is a schematic diagram of a high-precision resistance measurement structure with full dynamic range.

[0022] Figure 2 This is a circuit model diagram of a high-precision resistance measurement structure with full dynamic range in a long-distance measurement environment. Detailed implementation method:

[0023] According to the instruction manual, the full dynamic range high-precision resistance measurement structure consists of two reference resistors R1 and R2, and one resistor to be measured, R. t The circuit consists of two instrumentation amplifiers A and B, two three-input single-output switching switches forming a switching group, a single-input dual-output switching switch, and a voltage holding circuit; the resistor to be measured is R. t Two long wires are connected to each end of the resistor; one end of the reference resistor R1 is connected to the resistor R to be measured. t A long wire connects to the circuit at one end, with the circuit node being X, and the resistor to be measured is R. tA long wire at the other end is connected to the reference resistor R2, with its circuit node being Y. The other end of the reference resistor R1 has a circuit node of M, and the other end of the reference resistor R2 has a circuit node of N. Circuit nodes M, X, and Y are connected to the first three-input single-output switch in sequence, and circuit nodes X, Y, and N are connected to the second three-input single-output switch in sequence. The output terminals of the two switches are connected to the input terminals of instrumentation amplifier A. The output terminal of the instrumentation amplifier is connected to a single-input dual-output switch, and the output terminal of this switch is connected to the non-inverting input terminal of instrumentation amplifier B and the input terminal of a voltage holder, respectively. The output terminal of the voltage holder is connected to the inverting input terminal of instrumentation amplifier B.

[0024] The values ​​of the reference resistors and the amplification factor of the instrumentation amplifier depend on the actual resistance measurement range. For example, in a design to measure the resistance of a PT1000 type platinum resistance thermometer, assuming the actual resistance measurement range is 900Ω to 1000Ω, then let the reference resistors R1 = 900Ω and R2 = 1000Ω, the operating voltage be 5V, and the circuit nodes M and N be connected to a 0.5mA constant current power supply. Then the maximum amplification factor of the instrumentation amplifier A is: The maximum voltage difference at the input of instrumentation amplifier B occurs at U B3 At a voltage of 0.5V, the maximum amplification factor of instrumentation amplifier B is 5 / 0.5 = 10, resulting in an overall amplification factor of 100 for this circuit structure. If a 16-bit analog-to-digital converter is used for voltage acquisition in the subsequent stage, a voltage change of 0.0015Ω can be identified without any wasted dynamic range. The resistance measurement performance of this circuit structure is superior to that of a reference resistance ratio measurement structure based on a constant current source, using the same constant current source, the same instrumentation amplifier, the same type of platinum resistance thermometer, and the same type of reference resistor. The specific performance improvement depends on the actual device performance.

Claims

1. A high-precision resistance measurement structure with full dynamic range, comprising two reference resistors R1 and R2, and one resistor to be measured R t The system comprises two instrumentation amplifiers A and B, a switching switch group consisting of two three-input single-output switching switches, a single-input dual-output switching switch, and a voltage holder, characterized in that: The resistor to be measured R t Two long wires are connected to each end of the resistor; one end of the reference resistor R1 is connected to the resistor R to be measured. t A long wire connects to the circuit at one end, with the circuit node being X, and the resistor to be measured is R. t A long wire at the other end is connected to the reference resistor R2, with its circuit node being Y. The other end of the reference resistor R1 has a circuit node of M, and the other end of the reference resistor R2 has a circuit node of N. Circuit nodes M, X, and Y are connected to the first three-input single-output switch in sequence, and circuit nodes X, Y, and N are connected to the second three-input single-output switch in sequence. The output terminals of the two switches are connected to the input terminals of instrumentation amplifier A. The output terminal of the instrumentation amplifier is connected to a single-input dual-output switch, and the output terminal of this switch is connected to the non-inverting input terminal of instrumentation amplifier B and the input terminal of a voltage holder, respectively. The output terminal of the voltage holder is connected to the inverting input terminal of instrumentation amplifier B.

2. A measurement method based on the full dynamic range high-precision resistance measurement structure described in claim 1; characterized in that... The method is as follows: First, connect circuit nodes M and N to the power supply, and then connect the series-connected reference resistor R1 and the resistor to be measured R. t Power is supplied through a reference resistor R2, and the current flowing through them is I. S Then, set up a switching group, connecting node M to the non-inverting input of instrumentation amplifier A and node X to the inverting input of instrumentation amplifier A. Set the switching switch to connect the output of instrumentation amplifier A to a voltage holder. Let the output voltage of instrumentation amplifier A at this time be U. A1 After the voltage holder stabilizes, set up a switching group. Connect node X to the non-inverting input of instrumentation amplifier A and node Y to the inverting input of instrumentation amplifier A. Then, set up a switching switch to connect the output of instrumentation amplifier A to the non-inverting input of instrumentation amplifier B. Let the output voltage of instrumentation amplifier A at this time be U. A2 The output voltage of instrumentation amplifier B is U. B1 Set up a switching group, with node X connected to the non-inverting input of instrumentation amplifier A and node Y connected to the inverting input of instrumentation amplifier A. Then, set up a switching switch to connect the output of instrumentation amplifier A to a voltage holder. Let the output voltage of instrumentation amplifier A at this time be U. A3 After the voltage holder stabilizes, set up a switching group. Connect the Y node to the non-inverting input of instrumentation amplifier A and the N node to the inverting input of instrumentation amplifier A. Set up the switching switch to connect the output of instrumentation amplifier A to the non-inverting input of instrumentation amplifier B. Let the output voltage of instrumentation amplifier A at this time be U. A4 The output voltage of instrumentation amplifier B is U. B2 Set up a switching group, with the Y node connected to the non-inverting input of instrumentation amplifier A and the N node connected to the inverting input of instrumentation amplifier A. Then, set the switching switch to connect the output of instrumentation amplifier A to a voltage holder. Let the output voltage of instrumentation amplifier A at this time be U. A5 After the voltage holder stabilizes, set up a switching group. Connect node M to the non-inverting input of instrumentation amplifier A and node X to the inverting input of instrumentation amplifier A. Set up the switching switch to connect the output of instrumentation amplifier A to the non-inverting input of instrumentation amplifier B. Let the output voltage of instrumentation amplifier A at this time be U. A6 The output voltage of instrumentation amplifier B is U. B3 Finally, the current resistance value of the resistor to be measured is calculated; the specific measurement method is as follows: Connect circuit nodes M and N to the power supply, and compare the series-connected reference resistor R1 and the resistor under test R. t Power is supplied through a reference resistor R2, and the current flowing through them is I. S ; Configure a switching group, connecting node M to the non-inverting input of instrumentation amplifier A and node X to the inverting input of instrumentation amplifier A. Then, configure the switching switch to connect the output of instrumentation amplifier A to a voltage holder. Let the output voltage of instrumentation amplifier A at this time be U. A1 After the voltage holder stabilizes, set up a switching group. Connect node X to the non-inverting input of instrumentation amplifier A and node Y to the inverting input of instrumentation amplifier A. Then, set up a switching switch to connect the output of instrumentation amplifier A to the non-inverting input of instrumentation amplifier B. Let the output voltage of instrumentation amplifier A at this time be U. A2 The output voltage of instrumentation amplifier B is U. B1 ; Configure a switching group, with node X connected to the non-inverting input of instrumentation amplifier A and node Y connected to the inverting input of instrumentation amplifier A. Then, configure the switching switch to connect the output of instrumentation amplifier A to a voltage holder. Let the output voltage of instrumentation amplifier A at this time be U. A3 After the voltage holder stabilizes, set up a switching group. Connect the Y node to the non-inverting input of instrumentation amplifier A and the N node to the inverting input of instrumentation amplifier A. Set up the switching switch to connect the output of instrumentation amplifier A to the non-inverting input of instrumentation amplifier B. Let the output voltage of instrumentation amplifier A at this time be U. A4 The output voltage of instrumentation amplifier B is U. B2 ; Configure a switching group, with the Y node connected to the non-inverting input of instrumentation amplifier A and the N node connected to the inverting input of instrumentation amplifier A. Then, configure the switching switch to connect the output of instrumentation amplifier A to a voltage holder. Let the output voltage of instrumentation amplifier A at this time be U. A5 After the voltage holder stabilizes, set up a switching group. Connect node M to the non-inverting input of instrumentation amplifier A and node X to the inverting input of instrumentation amplifier A. Set up the switching switch to connect the output of instrumentation amplifier A to the non-inverting input of instrumentation amplifier B. Let the output voltage of instrumentation amplifier A at this time be U. A6 The output voltage of instrumentation amplifier B is U. B3 ; The resistance to be measured, R t The formula for calculating the resistance is as follows: 。

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