Introduction to Several Methods for Measuring Resistance 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. Let's take a look together.
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 directly connected to the two ends of the constant current source.
In the process of accurately measuring resistance with a digital multimeter using the four wire measurement method, this method has two additional feeders and disconnects the connection between the voltage measurement end and the constant current source compared to the usual measurement method. Due to the disconnection between the voltage measurement terminal and the constant current source terminal, the constant current source forms a circuit with the measured resistor Rx, feeder lines RL1 and RL2. The voltage sent to the voltage measurement terminal is only the voltage at both ends of Rx, and the voltage of feeders RL1 and RL2 is not sent to the voltage measurement terminal. Therefore, the feeder resistors RL1 and RL2 have no effect on the measurement results. The feeder resistance RL3 and RL4 have an impact on the measurement, but the impact is small. Due to the input impedance of the digital multimeter being much larger than the feeder resistance, the four wire measurement method has high accuracy in measuring small resistances.
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.
