Tips for using a multimeter to measure the quality of contactor coils
Low voltage coils are generally in the milliohm range and cannot be accurately measured with a multimeter (with significant errors), requiring a dedicated direct resistance tester. However, it cannot be concluded that the coil is good just because the measured value is the same or similar to the design value. Sometimes, the insulation damage between turns or layers of the coil cannot be measured with a multimeter, and a frequency doubling tester such as a third harmonic generator set is needed to detect the fault point.
Measure the coil with a digital multimeter in ohms range below 2K to see if the coil is open circuit. If it is open circuit, it indicates that the coil is damaged.
Measure normally closed and normally open using a multimeter with an ohm range of 200. If the auxiliary contacts are not connected and the contacts are not in good contact, the measured resistance will be high. Indicating poor contact of the contacts, if the auxiliary contacts are connected to a load, the voltage will not reach the rated voltage when measuring the voltage.
Measure each normally open and normally closed terminal with a multimeter to see if it is normal. It is difficult to measure the coil with a multimeter, and the best way is to directly apply the rated voltage to test the operation.
How to measure capacitance with a multimeter?
1. Take out the multimeter and first find the capacitor range. The capacitor range on the multimeter is usually marked with an F prompt.
2. Then confirm if the needle is inserted incorrectly and if it needs to be replaced. For example, the multimeter below needs to change these two probes.
3. Select the capacitance range, and if you do not know the size of the capacitor to be tested, you can choose the maximum range.
Place the probe at both ends of the capacitor
Before measuring a capacitor, remember to discharge it first. The discharge method is also very simple. Simply short-circuit the two ends of the capacitor. It is best to connect a resistor to a capacitor with a large capacity. Just connect the probe to both ends of the capacitor. Remember not to touch both electrodes with your hands at the same time, otherwise the measurement result will be inaccurate. If the measurement goes smoothly, you can directly read the capacity of this capacitor on the display screen.
How to roughly measure the capacitance of a capacitor with a pointer multimeter. Prepare several capacitors with small errors and commonly used capacities, such as 0.1uf, 0.47uf, 1uf, 2.2uf, 4.7uf, 10uf. Measure the two pins of the capacitor alternately using 1K (or 10K) resistor settings, and record the amplitude of the pointer swing to create a reference table. When measuring the capacitance of a capacitor in the future, solder it off the circuit board and use a pointer multimeter to measure alternately. By comparing the pointer swing amplitude with the reference table, the capacitance of the capacitor can be roughly determined.
