Analysis and verification of nonlinear mechanism phenomenon of DC resistor divider

Author： GOZ Electric Time：2024-11-09 09:25:22 Read：10

Aiming at the nonlinear phenomenon of the resistor divider when dividing the DC low voltage, the nonlinear mechanism of the DC resistor divider was studied by using the analysis method of independent influencing factors. Through analysis and experimental verification, it was determined that the cause of the nonlinearity was the change in the output thermoelectric potential of the resistor divider caused by the change in the working current. Based on this, a nonlinear mathematical model was established and a nonlinear correction method was proposed. Using this method, the nonlinear error of ±200μV DC voltage output is less than 5nV.

Keywords: metrology; DC low voltage; resistor divider; nonlinear error; thermoelectric potential

Using precision resistors to form a resistor divider to adjust the voltage amplitude is a simple and reliable method. Since the resistor divider has the characteristics of low noise, stable performance, low temperature coefficient, high accuracy and good linearity, it is widely used in high-voltage precision measurement, weak signal amplification, standard low voltage signal generation and other occasions. In the management of aerospace materials, the performance acceptance of purchased materials is an important task. In order to accept high-sensitivity devices such as instrument amplifiers, auto-zero amplifiers and low-noise amplifiers, it is necessary to test their linearity, gain and other performance. To this end, a DC low voltage calibrator was constructed using a resistor divider constructed with precision resistors and a digital-to-analog converter. When the calibrator was used to accept high-sensitivity devices, it was found that the linearity indicators generally exceeded the standard. The test found that the resistor divider had obvious nonlinearity when outputting DC low voltage. In order to meet the requirements of aerospace quality management, a study on the nonlinear mechanism of the DC resistor divider was carried out. The nonlinear problem of the temperature measurement bridge composed of multiple resistor dividers has received widespread attention at home and abroad. The US NIST, the UK NPL, and the Chinese NIM have conducted evaluation studies on the nonlinearity of the temperature measurement bridge and proposed some hardware and software solutions. Some scholars have also conducted research on the bridge linearity evaluation method. The circuit structure of the temperature measurement bridge is relatively complex, and currently most nonlinear evaluation studies are based on the overall characteristics at the macro level. This paper analyzes the nonlinear mechanism of the resistor divider from the micro level, establishes a nonlinear model, and proposes a nonlinear correction method.

2 Nonlinear characteristic test

The test circuit shown in the digital nV meter composition diagram is used to test the linearity of the calibrator output voltage at multiple temperature points.

3 Analysis of nonlinear influencing factors

For the nonlinear problem of resistor divider in DC low voltage voltage division, the analysis method of independent influencing factors is used to determine the real cause of nonlinearity. The DC low voltage calibrator is placed in a constant temperature environment and it is found that the nonlinear phenomenon still exists, eliminating the influence of external ambient temperature factors.

In order to eliminate the nonlinear factors of the digital nV meter, multiple instruments are used to replace the KEITHLEY 2181 digital nV meter for verification, and the test results are consistent. The DAC output voltage is tested using the circuit shown in Figure 2, and it is found that the nonlinear error of the DAC is ≤0. 000 3%, eliminating the cause of nonlinearity caused by DAC.

Excluding input and output factors, it can be determined that the cause of nonlinearity is the resistor divider.

In the circuit shown in the figure, the input voltage of the resistor divider is changed, and the output voltage of the voltage divider is measured with a digital nV meter. It is found that: (1) the higher the input voltage, the greater the error of the output voltage from the theoretical value; (2) when the input voltage is 0, the error of the output voltage from the theoretical value is the smallest; (3) the error of the output voltage from the theoretical value is independent of the polarity of the input voltage; (4) when the input voltage drops rapidly from a certain value to 0, the output voltage of the voltage divider cannot return to the original zero point immediately, and it takes a period of time to slowly return to the original zero point.

Considering that when the input voltage is equal to 0, the output voltage of the passive resistor device can only be the thermoelectric potential. The thermoelectric potential is related to the temperature difference, and its polarity is independent of the working current. The temperature difference is related to the working current. Therefore, it can be determined that the factor causing the nonlinearity of the resistor divider is the working current passing through the resistor of the voltage divider. The basic mechanism of the nonlinearity of the resistor divider is: the change of the working current causes the temperature of the device to change, resulting in the change of the thermoelectric potential, which brings nonlinear error to the output voltage.

Conclusion

The resistor divider has nonlinearity when outputting low DC voltage. The fundamental reason for the nonlinearity is that the working current flows through the resistor to generate heat energy and form thermoelectric potential. The output voltage of the resistor divider is a quadratic curve. Its characteristic parameters are not significantly affected by the ambient temperature. After calculation analysis and experimental verification, it is confirmed that when the ambient temperature is in the range of 10 to 30 ℃, the input voltage is preprocessed uniformly with the nonlinear characteristics of 20 ℃. The nonlinear error of the voltage divider output in the range of ± 200 μV is less than 5 nV. Controlling and limiting the ambient temperature range can further reduce the nonlinear error.