The contact resistance can be measured by the voltage profile of the multimeter, that is, in the case of power on, use the multimeter pen to check the two sides of the contact, the range will change from large gradually to small. If the measured voltage drop is large, indicate that the contact resistance is large, and if the voltage drop is zero, indicate that the contact is good. In addition, can also be measured by the resistance profile in the case of power outages, but it must be noted that contact resistance is relevant to the plus pressure to armature. Therefore, after breaking the connection of contacts, the contact resistance should be measured in the case of coil power on.
In general, should regularly remove the arc extinguishing chamber, and check and clean contact to prevent the fault occur .In addition, for the electric appliance that work in the harsh environment (such as acid, alkali, salt and steam), it is advisable to choose the sealing, with glass cover, and should adopt appropriate protective measures.