Teach you how to cleverly use a multimeter to measure large-value resistors
The maximum range of the resistance range for 31/2-digit and 41/2-digit digital multimeters is generally 20M Ω. For 31/2-digit digital multimeters, using different resistance ranges 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 resistance within the range of 0.01 Ω to 19.999M Ω. 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.
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 connect the measured resistor Rx in parallel across R1, and measure the total parallel resistance R, as shown in Figure 4-15 (b).
Measurement examples
The measured resistor is an unidentified high resistance resistor Rx, and R1 uses a resistor with a nominal resistance of 10M Ω. Using the 20M Ω resistance range of the DT830 digital multimeter, the measured resistance of R1 is 10.05M Ω. After connecting Rx in parallel with R1 and measuring with DT830, the total resistance value is R=7.70M Ω.
(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. In addition, the digital 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.
