High-precision temperature compensation voltage sampling circuit and standard electric energy meter

Abstract

The utility model discloses a voltage sampling circuit with high-precision temperature compensation. The voltage sampling circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor Rx, a resistor Ry, a resistor Ra, a resistor Rb, a resistor R6 and an operational amplifier. Compensation resistors Rx, Ry, Ra and Rb are additionally arranged in a voltage sampling loop, the primary temperature coefficient alpha and the secondary temperature coefficient beta of the compensation resistors are measured, the resistance values of the compensation resistors are determined, finally, the output voltage Uo of the voltage sampling loop meets the set precision and the temperature coefficient close to zero, and the problems that the output voltage of the voltage sampling loop is not high in precision, and the accuracy is low are solved. And the output voltage drifts along with the temperature.

Description

Technical Field

[0001] The utility model relates to the field of electric energy measurement, in particular to a high-precision temperature-compensated voltage sampling circuit and an electric energy meter. Background Art

[0002] As a standard instrument for energy meter traceability, the measurement accuracy and stability of standard energy meters are key performance indicators of standard energy meters. Measurement accuracy is an important indicator to characterize the long-term stable operation of standard energy meters. In actual use, problems such as instrument drift and stability that do not meet requirements may occur.

[0003] The voltage sampling circuit of a standard electric energy meter is a basic circuit that converts the input voltage signal into a signal that meets the working requirements of the subsequent circuit. Its accuracy and stability are key factors in achieving the performance indicators of a standard electric energy meter. The accuracy and stability of the voltage sampling circuit is a technical problem that researchers need to solve urgently.

[0004] The commonly used technical solutions for the voltage sampling circuit of the existing standard electric energy meter are as follows: Figure 2 As shown, the principle is: input high voltage signal Ui (AC 30V-500V), through the voltage divider circuit composed of resistors R1-R6, obtain a low voltage AC signal proportional to the input signal on resistor R6, this signal is followed by a low noise high impedance op amp to amplify, and then output voltage sampling signal Uo. The proportional relationship between output voltage Uo and input signal Ui is as follows:

[0005] Uo=R6 / (R1+R2+R3+R4+R5+R6) Formula 1

[0006] All resistors have different temperature coefficient characteristics, the primary temperature coefficient α and the secondary temperature coefficient β. When the resistor R is at t℃, its resistance is expressed by the temperature coefficient as:

[0007] Formula 2

[0008] In formula 2, R-actual value of resistance at temperature t℃, in Ω;

[0009] -The actual value of resistance at 20°C, in Ω;

[0010] α-first-order temperature coefficient of resistance, unit is Ω / ℃;

[0011] β - quadratic temperature coefficient of resistance, in units of .

[0012] It can be seen from Formula 2 that as the temperature changes, the resistance value of the resistor also changes, and the voltage divider value on the resistor R6 changes with the temperature.

[0013] In order to obtain a stable and accurate sampling signal proportional to the input signal, resistors R1-R6 generally use high-precision resistors, such as plastic-sealed metal foil resistors and gold-sealed metal foil resistors, with a resistance deviation of ±0.01% or ±0.05% and a temperature characteristic of ±5ppm / ℃. The normal operating temperature range of the standard meter is 10℃-40℃. Within this temperature range, the maximum change in resistance can reach ±150ppm. In extreme cases, the maximum change in the sampling voltage on the R6 resistor reaches 300ppm, which has reached the error limit (300ppm) of the temperature effect of the 0.01-level standard electric energy meter, and does not meet the index requirements of the standard electric energy meter. In addition, if it works for a long time (with a year as a cycle), the annual stability requirement of the 0.01-level standard electric energy meter requires that the basic error change does not exceed 0.01%.

[0014] In order to solve the accuracy and stability of the voltage sampling circuit of the standard electric energy meter, the following solutions are usually adopted: (1) Higher precision resistors: Use precision resistors with higher accuracy and stability to achieve voltage sampling. The disadvantage of this solution is that the cost of higher precision resistors is high, most of which are imported devices and difficult to purchase; (2) Software correction solution: After the sampling signal is sent to the post-stage A / D conversion (analog-to-digital conversion) circuit, it is converted into a digital signal by the A / D conversion chip. The electric energy metering MCU corrects the voltage sampling data by measuring the ambient temperature so that the sampling data meets the requirements of voltage division accuracy. The disadvantage of this solution is that the temperature coefficient of the resistor changes with time. After the correction parameters are set inside the electric energy metering MCU, they cannot be automatically adjusted with the long-term changes in the temperature coefficient of the resistor. When the standard electric energy meter is in long-term operation, there is still a situation where the measurement error exceeds the requirement. Utility Model Content

[0015] The purpose of the utility model is to solve the above-mentioned problems and provide a high-precision temperature-compensated voltage sampling circuit, in which a plurality of precision resistors with positive and negative temperature coefficients are connected in parallel or in series to obtain high-precision resistors with a temperature coefficient approaching zero. The temperature compensation device used in the voltage sampling circuit is designed to solve the problem that the output accuracy of the voltage sampling loop is not high and the temperature coefficient changes over time.

[0016] The technical solution adopted by the utility model is as follows:

[0017] A high-precision temperature-compensated voltage sampling circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor Rx, a resistor Ry, a resistor Ra, a resistor Rb, a resistor R6 and an operational amplifier, wherein the resistor R1, the resistor R2, the resistor R3, the resistor R4 and the resistor R5 are connected in series in sequence, Rx and Ry form a first parallel resistor Rp1, Ra and Rb form a second parallel resistor Rp2, one end of the first parallel resistor Rp1 is connected to the resistor R5, and the other end is respectively connected to one end of the second parallel resistor Rp2 and a non-inverting input end of the operational amplifier, the other end of the second parallel resistor Rp2 is connected to one end of the resistor R6, the other end of the resistor R6 is grounded, the inverting input end of the operational amplifier is connected to the output end, one end of the resistor R1 and the other end of the resistor R6 form an input signal Ui, and the output end of the operational amplifier and the ground form an output voltage Uo.

[0018] Preferably, the input signal is AC 30V-500V.

[0019] Preferably, the resistors R1 , R2 , R3 , R4 , R5 , R6 , Rx, Ry, Ra and Rb are made of high-precision resistors.

[0020] Preferably, the resistors R1 , R2 , R3 , R4 , R5 , R6 , Rx , Ry , Ra and Rb are plastic-sealed metal foil resistors or gold-sealed metal foil resistors.

[0021] The utility model also provides a standard electric energy meter, which comprises the above-mentioned high-precision temperature-compensated voltage sampling circuit.

[0022] Preferably, the standard electric energy meter is a 0.01-level standard electric energy meter.

[0023] Due to the adoption of the above technical solution, the beneficial effects of the utility model include:

[0024] By adding compensation resistors Rx, Ry, Ra, and Rb to the voltage sampling loop, measuring the primary temperature coefficient α and the secondary temperature coefficient β of the compensation resistor, and determining the resistance value of the compensation resistor, the output voltage Uo of the voltage sampling loop finally meets the set accuracy and temperature coefficient close to zero, thus solving the problem of low output voltage accuracy of the voltage sampling loop and output voltage drift with temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a circuit schematic diagram of a high-precision temperature-compensated voltage sampling circuit of the utility model;

[0026] Figure 2 It is a circuit schematic diagram of a voltage sampling circuit in the prior art. DETAILED DESCRIPTION

[0027] The utility model is described in detail below in conjunction with the accompanying drawings.

[0028] In order to make the purpose, technical solution and advantages of the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model, rather than to limit the utility model.

[0029] Figure 1 This is a circuit schematic diagram of a high-precision temperature-compensated voltage sampling circuit of the utility model. Figure 1 As shown, a high-precision temperature-compensated voltage sampling circuit includes a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor Rx, a resistor Ry, a resistor Ra, a resistor Rb, a resistor R6 and an operational amplifier, wherein the resistor R1, the resistor R2, the resistor R3, the resistor R4, and the resistor R5 are connected in series in sequence, Rx and Ry form a first parallel resistor Rp1, Ra and Rb form a second parallel resistor Rp2, one end of the first parallel resistor Rp1 is connected to the resistor R5, and the other end is respectively connected to one end of the second parallel resistor Rp2 and the in-phase input end of the operational amplifier, the other end of the second parallel resistor Rp2 is connected to one end of the resistor R6, the other end of the resistor R6 is grounded, the inverting input end of the operational amplifier is connected to the output end, one end of the resistor R1 and the other end of the resistor R6 form an input signal Ui, and the output end of the operational amplifier and the ground form an output voltage Uo.

[0030] In the present invention, parallel resistors Rx and Ry are added to the series circuit R1-R5, and parallel resistors Ra and Rb are connected in series to R6. By connecting resistors in parallel, we can get: Rp1=Rx / / Ry, Rp2=Ra / / Rb. By connecting resistors in series, we can get: Rs1=R1+R2+R3+R4+R5, Rs2=R6.

[0031] In the range of 10℃-40℃, the resistance value of resistor Rs1 is measured, and its primary temperature coefficient α1 and secondary temperature coefficient β1 can be obtained by calculation; the resistance value of resistor R6 is measured, and its primary temperature coefficient α2 and secondary temperature coefficient β can be obtained by calculation.

[0032] In order to achieve a temperature coefficient of the voltage divider value of resistors R1-R6 close to zero temperature coefficient within a temperature range of 10°C-40°C, it is necessary to design and screen the resistance values ​​and temperature coefficients of matching resistors Rx, Ry, Ra, and Rb. The utility model sets the resistance values ​​and temperature coefficients of matching resistors through the following scheme, with the purpose of making the parallel resistor Rp1 of Rx and Ry a resistor with a temperature coefficient opposite to that of the resistor formed in series with R1-R5. The parallel resistor Rp2 of Ra and Rb is a resistor with a temperature coefficient opposite to that of R6. By selecting the temperature coefficients of matching resistors Rx and Ry, Ra and Rb, the temperature coefficient of the final measurement result is close to zero.

[0033] Assume that the resistance value Rp1 and temperature coefficient of compensation resistors Rx and Ry are , ; Resistance Rp2 and temperature coefficient of compensation resistors Ra and Rb , , so that the following formula holds:

[0034] Formula 3

[0035] Formula 4

[0036] Formula 5

[0037] Formula 6

[0038] Since Rs1, α1, Rs1, β1, α2, and β2 have been designed and measured and are determined values, the temperature coefficient can be determined by formula 3 to formula 6. , , , The product of the values ​​of Rp1 and Rp2.

[0039] The resistance values ​​of resistors Rx, Ry, Ra and Rb are determined according to the following formula:

[0040] Rp1 / Rs1<0.01% Formula 7

[0041] Rp2 / Rs2<0.01% Formula 8

[0042] Where Rp1=Rx / / Ry, Rp2=Ra / / Rb; Rs1=R1+R2+R3+R4+R5, Rs2=R6. Under the conditions of formula 7 and formula 8, the fine adjustment of the output voltage by the compensation resistors Rp1 and Rp2 reaches 0.01%.

[0043] Under the condition of satisfying Formula 3 to Formula 6, the resistance values ​​of resistors Rx, Ry, Ra, and Rb are set, and the resistance temperature coefficients are screened so that the final compensated total resistance after series-parallel connection is within the range of 10°C-40°C, and the primary temperature coefficient and the secondary temperature coefficient are close to zero, so that the accuracy of the voltage sampling output voltage Uo meets the accuracy requirements of the voltage divider ratio, thereby solving the problems of output voltage accuracy and temperature drift of the resistance voltage divider sampling loop.

[0044] Optionally, the input signal is AC 30V-500V.

[0045] Optionally, high-precision resistors are used for the resistors R1 , R2 , R3 , R4 , R5 , R6 , Rx, Ry, Ra, and Rb.

[0046] Optionally, the resistors R1 , R2 , R3 , R4 , R5 , R6 , Rx , Ry , Ra and Rb are plastic-sealed metal foil resistors or gold-sealed metal foil resistors.

[0047] The utility model also provides a standard electric energy meter, which comprises the above-mentioned high-precision temperature-compensated voltage sampling circuit.

[0048] Optionally, the standard electric energy meter is a 0.01-level standard electric energy meter.

[0049] The principles and implementation methods of the present invention are described in this article using specific embodiments. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, the present invention can also be improved and modified without departing from the principle of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A high-precision temperature-compensated voltage sampling circuit, characterized in that: The invention comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor Rx, a resistor Ry, a resistor Ra, a resistor Rb, a resistor R6 and an operational amplifier, wherein the resistor R1, the resistor R2, the resistor R3, the resistor R4 and the resistor R5 are connected in series in sequence, Rx and Ry form a first parallel resistor Rp1, Ra and Rb form a second parallel resistor Rp2, one end of the first parallel resistor Rp1 is connected to one end of the resistor R5, the other end of the first parallel resistor Rp1 is respectively connected to one end of the second parallel resistor Rp2 and a non-inverting input end of the operational amplifier, the other end of the second parallel resistor Rp2 is connected to one end of the resistor R6, the other end of the resistor R6 is grounded, the inverting input end of the operational amplifier is connected to the output end, one end of the resistor R1 and the other end of the resistor R6 constitute an input signal Ui, and the output end of the operational amplifier and the ground constitute an output voltage Uo.

2. The high-precision temperature-compensated voltage sampling circuit according to claim 1, characterized in that: The input signal is AC 30V-500V.

3. The high-precision temperature-compensated voltage sampling circuit according to claim 2, characterized in that: High-precision resistors are used as the resistor R1 , the resistor R2 , the resistor R3 , the resistor R4 , the resistor R5 , the resistor R6 , the resistor Rx, the resistor Ry, the resistor Ra, and the resistor Rb.

4. The high-precision temperature-compensated voltage sampling circuit according to claim 3, characterized in that: The resistor R1 , the resistor R2 , the resistor R3 , the resistor R4 , the resistor R5 , the resistor R6 , the resistor Rx , the resistor Ry , the resistor Ra and the resistor Rb are plastic-sealed metal foil resistors or gold-sealed metal foil resistors.

5. A standard electric energy meter, characterized in that: A high-precision temperature-compensated voltage sampling circuit comprising any one of claims 1 to 4.

6. The standard electric energy meter according to claim 5, characterized in that: The standard electric energy meter is a 0.01-level standard electric energy meter.

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