How to use a digital multimeter to measure large resistance

How to use a digital multimeter to measure large resistors with a DT-830 digital multimeter to measure the resistance. When the measured resistance value exceeds 20 MΩ, the meter displays “1” indicating the over limit and cannot measure the resistance.

There are many ways to measure large resistances in excess of 20 MΩ. Here is a method that is based on the principle of parallel connection of resistances. The resistance of the large resistance being measured is measured.

The measurement method is shown in Figure 2-1. First, look for resistor R, which has a resistance value of less than 20 MΩ (requiring close to 20 MΩ, such as 18 MΩ), and connect it in parallel with the digital multimeter. This is the exact resistance of R that can be measured with a digital multimeter. Then insert the resistance to be measured into the socket X1, X2. The digital multimeter can show R and RX, and the parallel resistance R#, according to the following formula:

R#=R·RC/(R+RX), from which you can derive:

RX=R·R#/(RR#)

The resistance of the resistor RX to be measured can be found.