"Safety relay" is not "relay without fault", but can act regularly when fault occurs. Finder safety relay has a forced guide contact structure (or other protection methods), which can also ensure safety in the case of contact melting, which is completely different from general relays.
When the contact of the ordinary intermediate relay is fused or the movable spring is damaged, both the normally open contact and the normally closed contact may become closed at the same time, resulting in the danger of the control circuit. The finder safety relay has a forced guide contact. After the normally open contact and normally closed contact are welded, the finder safety relay itself can detect the welding of the contact. Using the finder safety relay can avoid the dangerous situation caused by the welding of the relay contact. It uses the welding detection function provided by the forced guide contact in the finder safety relay circuit to establish redundancy and self-monitoring functions.
Finder safety relay is often used in the design of safety circuit to confirm the safety input of the machine for control. For example, when the emergency stop is released, the machine cannot be restarted suddenly. If the safety circuit of the machine fails, the power supply of the machine can be stopped.
Here we give an example of the application of finder safety relay in the dual circuit design protection of robot safety door in industrial automation, that is, by opening the safety door guardrail, the robot is controlled to stop. After the safety door is closed, just press the reset button to connect the robot safety door return circuit.
Working process: when the safety door is closed, the normally closed contact of the safety switch is closed, the input channel of the finder safety relay is closed, and the channel indicators Ch.1 and ch.2 are on. Therefore, the normally open contacts 13/14 and 23/24 of the robot are closed, the double circuit of the robot safety door is closed, and the robot is allowed to operate. When the safety door is opened, the safety switch is triggered, its normally closed contact is disconnected, and the input channel of the finder safety relay is in the open state. Therefore, its normally open contact 13/14 is disconnected, the double circuit of the robot safety door is disconnected, and the robot is controlled to stop.
When the operation needs to be started after the safety door is closed, it needs to be reset through the button first, and the auxiliary contact of the finder safety relay can be connected only after the safety conditions are met. If both channel 1 and channel 2 are in the closed circuit, the safety normally open contacts 13-14, 23-24 and 33-34 are closed, and the auxiliary normally closed contacts 41-42 are open; The LED lights of both channels are on (green); Transistor output y31-y32 is closed. If channel 1 and channel 2 are disconnected, the safety normally open contacts 13-14, 23-24 and 33-34 are disconnected, the auxiliary normally closed contacts 41-42 are closed, the LED lights of both channels are closed, and the transistor output y31-y32 is disconnected.