Two Methods of Measuring Resistance with Digital Multimeter
Four-wire measurement plus constant current source measurement
The four-wire measurement method mentioned above can certainly help engineers to complete the high-precision multimeter resistance measurement work, but in the four-wire measurement process, the accuracy of the constant current source current is very critical. It is recommended to use an external and more stable constant current source current.
It should be noted that the magnitude of the external constant current source current should be equal to the magnitude of the constant current source current of the digital multimeter. The external constant current source current we use is composed of a high-precision reference voltage source MAX6250, an operational amplifier and a current-expanding composite tube, as shown in Figure 2. The temperature drift of the voltage source MAX6250 is ≤2ppm/℃, and the time drift ΔVout/t=20ppm/1000h. In this measurement process, the current I should be 800μA~1mA, and R is a very low temperature drift wirewound resistor (if I=1mA, R=5kΩ), then the temperature drift and time drift of I are equivalent to the level of MAX6250.
Feeder Resistance Compensation Measurement Method
The feeder resistance compensation method is another common high-precision measurement method for measuring resistance with a multimeter. In the industrial field, if a high-precision resistance test is required, the three-wire connection method is often selected so that the measured resistance is connected to the grounding line. connect. The principle of this test method is shown in Figure 3. When using this technique for measurement, the current I is 800μA~1mA, and R is a very low-temperature drift wirewound resistor (if I=1mA, R=5kΩ), then the temperature drift and time drift of the current I are equivalent to those of MAX6250 level.
