Method 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 complete the high-precision multimeter resistance measurement work. However, in the four-wire measurement process, the accuracy of the constant current source current is very critical. It is recommended to use an external more stable constant current source current.
It should be noted that the magnitude of the applied constant current source current should be equal to that of the digital multimeter constant current source current. 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, R is the extremely low temperature drift wirewound resistance (if I=1mA, R=5kΩ), the temperature drift and time drift of I are equivalent to the level of MAX6250.
