The DC resistance of the motor winding is an important part of the motor. Measuring this parameter is an important part of the motor test. By analyzing the measured resistance value, it is possible to preliminarily determine whether the number of turns, the wire diameter, the number of windings, the wiring method and the wiring quality of the motor windings of the tested motor have reached the design or predicted requirements, and whether there is a winding between the windings and the turns. Serious short circuit problems, etc. The DC resistance of the group is also a parameter necessary for the calculation of the loss and the calculation of the temperature rise. Therefore, the measurement test of the winding DC resistance must select a meter with higher precision, and be careful and careful, so that the measured data has higher accuracy.
When measuring the DC resistance of the winding in the motor test, the DC resistance measuring instrument is generally used to directly measure the value; the voltmeter and the ammeter can also be used to simultaneously measure the DC current passing through the winding and the voltage across the winding, and then use Ohm's law to find the value. The method of measuring the DC resistance of the winding, the method is simply referred to as "voltage current method". Ms. Participation today will briefly summarize the problems that are easy to occur in the testing process.
1. Common types of DC resistance measuring instruments
●DC resistance bridge
The most common instrument for measuring the DC resistance of a motor winding is a DC resistance bridge. There are two types of commonly used DC resistance bridges, one is called single-arm bridge, also known as Wheatstone bridge; the other is called double-arm bridge, also known as Kelvin bridge. The "arm" here refers to the connection between the bridge and the resistance to be measured. The single arm is a connection at each end; the two arms are two wires at each end. One-arm bridge is used to measure resistance above 1Ω; double-arm bridge is used to measure resistance of 1Ω and below; compared with single-arm bridge, double-arm bridge has the advantage of basically eliminating the error caused by the resistance of the lead-in wiring .
●Digital display electronic DC resistance measuring instrument
Digital electronic DC resistance measuring instruments are also commonly used, and their appearance specifications are many. This table-only working principle is based on the "voltage-current method" mentioned above. Compared with the DC resistance bridge, it has the advantages of convenient use and quick reading. It has the advantage of high precision within a certain measurement range; the disadvantage is that the stability is relatively poor. When using this type of watch only, it should be noted that the current to the winding should not exceed 10% of the rated current of the winding, and the energization time should be as short as possible to avoid the heating of the winding affecting the measurement accuracy.
2. Common mistakes made during the use of DC bridges
(1) Using a single-arm bridge to measure small resistance, the accuracy of the measurement is not met, resulting in inaccurate measurement, and the problem of uneven resistance cannot be found. This type of problem often occurs in manufacturers who repair motors.
(2) When the power supply battery is low, the stability of the bridge is not good, and the measurement data is large and small, and the measurement imbalance is prone to occur.
(3) The gear position selection is unreasonable, which leads to the limit swing of the hands, which easily leads to the burnout of the bridge.
(4) The power supply was not turned off in time, and the battery was instantaneously depleted due to the contact of the measuring terminals.
(5) When the head and tail end of a certain phase of the motor are reversed, it cannot be found by the bridge, and can only be found in the later inspection test.
