Cause Analysis and Solution of Numerical Jumping When Digital Multimeter Measures The Resistance Value of Motor

Cause Analysis and Solution of Digital Multimeter Value Jumping

Cause Analysis and Solution of Digital Multimeter Value Jumping

In the process of motor maintenance and inspection, it is a common method to measure the resistance value of motor winding with digital multimeter. However, sometimes the digital multimeter will encounter the problem of numerical jumping when measuring, and can not obtain stable measurement results, which brings trouble to judge. This paper will analyze the reasons of numerical jumping when the digital multimeter measures the resistance value of the motor from many angles, and give the corresponding solutions.

The motor has not completely stopped running 

When the motor stops, due to the remanent magnetic action of the rotor, the induction voltage will pulsate in the motor winding. This induced voltage interferes with the measurement of the digital multimeter, causing the value to jitter. To solve this problem, the motor spindle can be fixed before measurement to ensure that the motor is completely stopped.

Electromagnetic interference impact digital multimeter

Nearby electrical equipment, power lines, etc. May generate electromagnetic fields, that interfere with the winding of the motor and cause it to appear induced voltage. In order to reduce the impact of electromagnetic interference, shielding measures can be taken to isolate the motor from the source of interference. At the same time, when measuring, you can choose to operate in a relatively good electromagnetic environment.

Digital Multimeter
Digital Multimeter

In addition, the characteristics of the digital multimeter itself may also cause the value to jitter. Some digital multimeters have an automatic shift function, which automatically selects the appropriate gear during measurement. This process can cause readings to be unstable and require waiting for some time before accurate measurements. In addition, the resistance of the motor is usually small, and if the surface of the terminal is  in poor contact, it will also cause the resistance value to jump. Therefore, before measuring, make sure that the pen is in good contact and clean the terminal.

In view of the above problems, we can take some solutions to improve the accuracy of measurement. First, you can choose to use a pointer multimeter for measurement. The pointer type multimeter has the advantages of stable indication and easy operation, although the accuracy is relatively low, it can meet the basic judgment needs of the motor resistance value in most cases. Secondly, if conditions permit, the measurement can be carried out by electric bridge. Bridge measurement has high accuracy and stability, especially suitable for the precise measurement of motor resistance.

Solutions in practice

In practice, we can also take some additional measures to reduce the measurement error according to the specific situation. For example, the motor UVW can be short-circuited before measurement and the motor shaft can be turned several times to consume the remaining magnetic field in the motor. This reduces the effect of remanence on the measurement results. In addition, during the measurement process, the environment should be kept stable.

Generally speaking, the reasons for the numerical jump when the digital multimeter measures the resistance value of the motor may involve many aspects, including the state of the motor, electromagnetic interference, and the characteristics of the measurement tool itself. In order to obtain accurate measurement results, we need to take appropriate solutions and measures according to the specific situation. At the same time, in the measurement process, you should also be careful and patient to ensure that every step of the operation is correct.


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