How to Perform Resistance Measurement with a Digital Multimeter?
In the process of using a multimeter to measure resistance, engineers sometimes need to accurately measure small resistances less than 100 Ω, which often requires the use of techniques that can improve measurement accuracy. This article summarizes three common techniques for measuring resistance with a multimeter for technical personnel.
Four line measurement method
In the process of using a digital multimeter to measure resistance, technicians often use the four wire measurement method to improve the accuracy of testing small resistors less than 100 Ω. The so-called four wire measurement method is to separate the two current wires of the constant current source current flowing into the measured resistor R and the two voltage wires of the digital multimeter voltage measurement end, so that the voltage at the measurement end of the digital multimeter is no longer the direct voltage at both ends of the constant current source.
Four line measurement with added constant current source measurement
The four wire measurement method mentioned earlier can certainly help engineers complete high-precision multimeter resistance measurement work. However, in the four wire measurement process, the accuracy of the constant current source current is crucial. It is recommended to use an external, more stable constant current source current here.
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 we use consists 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 voltage source MAX6250 is ≤ 2ppm/℃, and the time drift Δ Vout/t=20ppm/1000h. In this measurement process, the current I should be taken as 800 μ A to 1mA, and R is the extremely low temperature drift wire winding resistance (if I=1mA, R=5k Ω). At this time, 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 high-precision resistance testing is required, the three wire connection method is often chosen to connect the measured resistance to the grounded wire. The principle of this testing method is shown in Figure 3. When using this technique for measurement, the current I is taken as 800 μ A to 1mA, and R is the extremely low temperature drift wire winding resistance (if I=1mA, R=5k Ω). At this time, the temperature drift and time drift of the current I are equivalent to the level of MAX6250.
