How does a multimeter measure large value resistors? Precautions for measuring large resistance with multimeter
How to measure large resistance with a multimeter, the method and examples of measuring large resistance with a multimeter, and the precautions for measuring large resistance with a multimeter. When measuring a resistance with a resistance value greater than 100MΩ, the measurement error will increase a lot. This point should be noted.
Multimeter to measure large value resistors
The maximum range of the resistance range of the 31/2-digit and 41/2-digit digital multimeters is generally 20MΩ.
For a 31/2-digit digital multimeter, using different resistance ranges can only measure resistance within the range of 0.1Ω～19.99MΩ; for a 41/2-digit digital multimeter, it can only measure resistance within the range of 0.01Ω～19.999MΩ resistance. When the measured resistance Rx≥20MΩ, the meter will display the overflow symbol "1".
Experiments have proved that the range of the 20MΩ resistance range of a 31/2-digit or 41/2-digit digital multimeter can be extended to 100MΩ by using the following "parallel resistance method".
1. Measurement method
Prepare a resistance R1 of more than ten megohms in advance, turn the digital multimeter to the 20MΩ range, measure the resistance value R1, then connect the measured resistance Rx in parallel to both ends of R1, and then measure the total parallel resistance R.
2. Measurement example
The resistance to be tested is a high-resistance resistor Rx with an unknown mark, and R1 selects a resistor with a nominal resistance value of 10MΩ. Using the 20MΩ resistance file of the digital multimeter, the measured resistance value of R1 is 10.05MΩ.
After connecting Rx and R1 in parallel, measure again, and the total resistance value R=7.70MΩ is measured. Substitute into formula (4-13) to get
Judging from this, the nominal value of the measured resistance should be 33MΩ.
3. Precautions for measurement
1. When the resistance value of the measured resistance Rx exceeds 100MΩ, the total resistance value R after parallel connection is very close to the resistance value of the selected standard resistance R1, and the digital multimeter itself has an error of ±1 character, which will increase the measurement error. big.
Therefore, this method is not suitable for measuring resistances greater than 100MΩ.
2. During the measurement operation, the measured resistance Rx and the standard resistance R1 should be connected in parallel and firmly connected. If necessary, the two can be fixed with crocodile clips.
