Method of measuring resistance with digital multimeter - four-wire measurement method
In the process of measuring resistance with a digital multimeter, technicians often use the four-wire measurement method in order to improve the accurate test of small resistances less than 100Ω. The so-called four-wire measurement method is to separate the two current lines of the constant current source current flowing into the resistance R under test and the two voltage lines of the voltage measuring end of the digital multimeter, so that the voltage of the measuring end of the digital multimeter is no longer between the two ends of the constant current source. Direct voltage, its operating principle is shown in Figure 1.
Principle of digital multimeter measuring resistance _ how to measure resistance with digital multimeter _ steps to measure resistance with digital multimeter
It can be seen from the test schematic diagram given in Figure 1 that in the process of using the four-wire measurement method to complete the accurate test of the resistance of the digital multimeter, this method has two more feeders than the usual measurement method, which disconnects the voltage Connect the measuring end to both ends of the constant current source. Since the voltage measurement terminal is disconnected from the constant current source terminal, the constant current source forms a loop with the measured resistance 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 voltages of the feeders RL1 and RL2 are not sent to the voltage measurement terminal. Therefore, the feeder resistances RL1 and RL2 have no effect on the measurement results. The feeder resistances RL3 and RL4 have influence on the measurement, but the influence is very small. Since the input impedance of the digital multimeter is much larger than the feeder resistance, the four-wire measurement method has high accuracy for measuring small resistances.
