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The sequential start and stop control circuit is a common method used in industrial automation to manage the operation of multiple devices in a specific order. This system ensures that one device starts only after another has been activated, and it also controls the shutdown sequence so that the main device stops before the auxiliary one. As shown in the schematic diagram, the control logic involves contactors (KM1 for the auxiliary device and KM2 for the main device) and thermal relays (FR1 and FR2) for overload protection.
When the system is powered on by closing the circuit breaker QF, the process begins. By pressing the SB2 button, the coil of KM1 becomes energized, which closes its main contacts, allowing the auxiliary device to start. At the same time, the normally open auxiliary contact of KM1 provides self-locking, ensuring the contactor remains engaged.
Once the auxiliary device is running, the SB4 button can be pressed to energize the coil of KM2, starting the main motor. The normally open contact of KM2 also provides self-locking, maintaining the connection. Additionally, an auxiliary contact from KM2 is connected across SB1, preventing the auxiliary device from being stopped prematurely.
To stop the system, pressing SB3 will de-energize KM2, cutting off power to the main motor. However, the auxiliary device (KM1) will continue to run until the overcurrent relay FR1 activates, which then cuts off the entire control circuit, stopping both devices.
Common issues may arise during operation. For instance, if KM1 fails to self-lock, it could be due to incorrect wiring of its auxiliary contacts. Another issue might be that KM2 starts before KM1, indicating a problem with the control circuit connections. If KM1 can be stopped before the main device, it suggests a miswired contact or a faulty connection. Lastly, if SB1 does not work, it could mean that the wrong auxiliary contacts are being used to control the stop function.
By understanding these components and their interactions, engineers can effectively troubleshoot and maintain such systems, ensuring smooth and safe operation of motor-driven equipment.