Common trouble shooting of relay
Sensing mechanism maintenance For electromagnetic (voltage, current, intermediate) relays, the sensing mechanism is an electromagnetic system. The faults of the electromagnetic system are mainly concentrated in the coil and the moving and static iron cores.
(1) Coil failure inspection and repair Coil failure usually has coil insulation damage; mechanical damage causes short circuit between turns or grounding; due to low power supply voltage, the moving and static iron cores are not closely contacted, so that the current through the coil is too large, and the coil heats up and burns. . When repairing it, rewind the coil. If the armature does not pull in after the coil is energized, it may be that the connection of the coil lead wire falls off, causing the coil to break. Weld it after checking out the dropout.
(2) Overhaul of iron core fault The main fault of iron core is that the armature cannot be sucked up after power on. This may be caused by broken coils, foreign objects between the moving and static iron cores, and low power supply voltage. It should be repaired differently. After power on, the armature is noisy. This may be caused by uneven contact surfaces between the moving and static iron cores, or oil contamination. When repairing, the coil should be removed, and its contact surface should be filed or ground; if there is grease, it should be cleaned. The high noise may be caused by short circuit or ring breakage. Just repair or replace the new short circuit ring. After the power is off, the armature cannot be released immediately. This may be caused by the moving iron core being stuck, the iron core air gap is too small, the spring is strained, and the iron core contact surface is oily. During maintenance, you should treat it differently according to the cause of the failure, or adjust the air gap to protect it at 0.02ļ½0.05MM, or replace the spring, or clean the oil with gasoline. For thermal relays, the sensing mechanism is a thermal element. The common fault is that the thermal element burns out, or the thermal element malfunctions and does not operate.
(3) The thermal element burns out. This may be caused by a short circuit on the load side, or the operating frequency of the thermal element is too high. During maintenance, the thermal element should be replaced and the setting value should be readjusted.
(4) Malfunction of thermal element. This may be caused by the fact that the setting value is too small, the action is not overloaded, or there is strong impact and vibration in the use occasion, which causes the action mechanism to loosen and trip and cause malfunction.
(5) The thermal element does not operate. This may be due to the fact that the setting value is too small and the thermal element loses its overload protection function. During maintenance, the setting current should be adjusted according to the working current of the load. Overhaul of actuators Most relay actuators are contact systems. Through its "on" and "off", to complete certain control functions. The faults of the contact system generally include contact overheating, wear, and welding. The main cause of contact overheating is insufficient capacity, insufficient contact pressure, surface oxidation or dirty, etc.; the main cause of increased wear is that the contact capacity is too small, and the arc temperature is too high to oxidize the contact metal; cause the contact The main reason for fusion welding is that the arc temperature is too high, or the contact is severely bounced. The maintenance sequence of the contacts is as follows:
(1) Open the outer cover and check the surface condition of the contacts.
(2) If the surface of the contact is oxidized, the silver contact does not need to be repaired. The copper contact can be filed with a polished file or gently scraped off the oxide layer on the surface with a knife.
(3) If the contact surface is not clean, it can be cleaned with gasoline or carbon tetrachloride.
(4) If there are burn marks on the contact surface, the silver contact does not need to be repaired, and the copper contact can be repaired with a polished file or a knife. It is not allowed to use emery cloth or sandpaper to refurbish, so as not to leave sand particles and cause poor contact.
(5) If the contacts are welded, they should be replaced. If it is caused by the contact capacity is too small, you should replace the relay with a larger capacity.
(6) If the contact pressure is not enough, the spring should be adjusted or replaced to increase the pressure. If the pressure is still insufficient, the contacts should be replaced. Maintenance of the intermediate mechanism
(1) For the air-type time relay, the intermediate mechanism is mainly an airbag. The common fault is inaccurate delay. This may be because the airbag is not tightly sealed or leaks, which shortens the action delay, or even does not delay; it may also be that the air channel of the airbag is blocked, which makes the action delay longer. When repairing, the former should be reassembled or replaced with a new airbag, and the latter should be disassembled to remove the blockage.
(2) For the speed relay, the bakelite pendulum rod belongs to the intermediate mechanism. If the motor cannot be braked and stopped during reverse braking, the bakelite pendulum may be broken. It should be replaced during maintenance.