Which number is appropriate to measure the quality of the AC contactor coil and the ohm block of the multimeter
The size of the contactor is different, and the parameters are also different, in other words, the resistance value of the coil is also different. Under normal circumstances, it is tens of ohms to tens of thousands of ohms. You can test it with different ohm gears of the multimeter. As long as it is convenient for you to read the value yourself.
Normally, the coils of the contactor are either shorted or open. It's not very good to judge good or bad. Our usual detection method is to take a contactor that is exactly the same size as the contactor to be tested. By comparing the resistance of the two, you can judge whether the coil is good or bad. Because if there is a short circuit between the turns of the coil, the resistance value will only change a little, and it cannot be judged by simple measurement with a multimeter.
If the multimeter has 200 ohms, use 200 ohms to measure first, and if the measurement exceeds 200 ohms, use 1000 ohms or 2000 ohms to measure. The above is the domestic multimeter measurement method. It would be fine if Fluke directly switched to the ohm gear
How to check the air switch with a multimeter
Let's take this 3P circuit breaker as an example. We first turn the circuit breaker to the off position, and use a multimeter to measure whether the three circuits are connected. It is good if they are not connected. Then push it to the open position, measure the continuity, if it is good, if it is not, it is bad.
Due to the low precision of ordinary multimeters, they can only be used as auxiliary tools at ordinary times. It cannot be used as a device to issue specific data. Therefore, there is a certain error in using a multimeter to detect whether the air switch is good or bad. However, ordinary households do not have special instruments. It is also very good to have a multimeter to measure voltage, current or resistance.
The air switch has two automatic protection functions of overload protection and short circuit protection. In addition, it can also connect the breaking circuit and play the role of isolating the power supply. We cannot check the overload protection and short circuit protection functions with a multimeter, and a large current generating device is used to detect overload performance in the laboratory. Short-circuit performance requires the use of transformers, short-circuit impedance, and data acquisition systems to complete the detection. But at home, you can use a multimeter to check whether the contacts are consistent with the position indicated by the handle. Sometimes the air switch is energized and operated for a long time, or the contacts will be welded after a fault occurs. Even if the handle is in the open position during welding, one pole or several poles of the contacts will be in the on state. At this time, use the resistance gear of the multimeter. The status of the contacts can be checked.
In the same way, if the mechanism fails or breaks a large short-circuit current, the contacts may not be able to connect the circuit. We turn the handle of the air switch to the closed position, and when there is no electricity on the load side of the switch. You can also use a multimeter to measure the voltage on the load side, or measure the resistance after removing it. To determine whether the contact is connected to the circuit.
