A Self-Calibrated Method to Measure the Load Effect of the Resistor

Abstract

Since 1999, quantum Hall resistance (QHR) has been widely used as the primary standard of resistance in national metrology institutes (NMIs). The standard resistors can trace to the QHR standard by Cryogenic Current Comparator (CCC) bridge or Direct Current Comparator (DCC) bridge. In the calibration, the current applied to resistor should be a certain value. However, in most industrial applications, the current applied to the resistor is not the same as the one used in the calibrated procedure. Due to the temperature change from the resistor’s self-heating with current, the value of the resistor will also change, which is called load effect. Besides, the load effect is also determined by the environment temperature. Thus in many precise measurements, the load effect or power coefficient of the resistor should be considered and evaluated. So far, there is not an instrument can be used to measure the load effect of a resistor directly. Lack of a standard resistor with known load effect is also a problem. Here, a self-calibrated method is proposed to get the load coefficient of a resistor at different temperature. A series of 500 ohm resistor components with the same temperature coefficient is used to form a 100 ohm resistor and a 20 ohm resistor by series-parallel connection. A DCC bridge is used to compare two resistors at 1 volt and 0.5 volt alternately. The power change of 500 ohm component in 20 ohm resistor is 4 times of that in 100 ohm resistor. Thus the ratio change is mainly from the change of the 20 ohm resistor and the load coefficient can be got with this approach. The 100 ohm resistor is put in an oil bath with fixed temperature, and the 20 ohm resistor is put in another oil bath, which temperature is changed to get the load coefficient of the 20 ohm resistor at different temperature. Measurement results show that the load coefficient of the 20 ohm resistor is at 1E-9 level when the oil bath is set at 23.5 degree. Then it can be used as a reference to measure the load coefficient of other resistors.