How to Measure High Resistance with a Digital Multimeter
The maximum range for the resistance range of a 31/2-digit and 41/2-digit digital multimeter is generally 20M Ω. For a 31/2-digit digital multimeter, different resistance ranges are used
It can only measure resistance within the range of 0.1 Ω to 19.99M Ω; For a 41/2 digit multimeter, it can only measure electricity within the range of 0.01 Ω to 19.999M Ω
Resistance. When the measured resistance Rx is ≥ 20M Ω, the instrument will display the overflow symbol "1".
Experimental results have shown that by using the "parallel resistance method" described below, the range of the 20M Ω resistance range of a 31/2-digit or 41/2-digit digital multimeter can be extended to 100M Ω.
1, Measurement method
Prepare a resistor R1 with a resistance of over ten megaohms in advance, set the digital multimeter to 20M Ω, and measure the resistance value R1, as shown in Figure 4-15 (a). Then take it
Measure the resistance Rx in parallel across R1, and then measure the total parallel resistance R, as shown in Figure 4-15 (b).
It is easy to derive (4-13) based on the calculation formula for parallel resistance
1, Measurement examples
The measured resistor is an unidentified high resistance resistor Rx, and R1 uses a resistor with a nominal resistance of 10M Ω. 20M Ω electricity using DT830 digital multimeter
In the impedance mode, the measured resistance value of R1 is 10.05M Ω. After connecting Rx in parallel with R1 and measuring with DT830, the total resistance value R is measured to be 7.70M Ω. Substitute it into equation (4-13) to obtain
to
Based on this, the nominal value of the measured resistance should be 33M Ω.
2, Measurement precautions
(1) When the resistance value of the measured resistor Rx exceeds 100M Ω, the total resistance value R after parallel connection is very close to the resistance value of the selected standard resistor R1, combined with the numerical value
The multimeter itself has an error of ± 1 word, which will increase the measurement error. Therefore, this method is not suitable for measuring resistors with a resistance greater than 100M Ω.
(2) When performing measurement operations, the measured resistor Rx should be connected in parallel with the standard resistor R1 and securely connected. If necessary, a crocodile clip can be used to fix the two.
