Walking on the road, I saw the old man lying on the ground. I quickly went up to help him. The old man looked at me and said, ‘Don’t move, young man. You’re also a worker. You go, I’ll wait.’. I was moved and quickly said, ‘Sir, there’s a parked Land Rover driver coming over soon.’. The master is also excited: you are a real young man. Why don’t you just leave and be a witness for me? After finishing, you can also buy a car to work and drive.
There are two types of power sources for PLC systems: external power sources and internal power sources.
External power supply is used to drive PLC output devices (loads) and provide input signals, also known as user power supply. The external power supply of the same PLC may have multiple specifications. The capacity and performance of the external power supply are determined by the output device and the input circuit of the PLC. Due to the filtering and isolation functions of the I/O circuit of the PLC, the external power supply has little impact on the performance of the PLC. Therefore, the requirements for external power supply are not high.
The internal power supply is the working power supply of the PLC, that is, the working power supply of the internal circuit of the PLC. Its performance directly affects the reliability of the PLC. Therefore, in order to ensure the normal operation of the PLC, there are high requirements for internal power supply. Generally, the internal power supply of PLCs adopts a switch type regulated power supply or a regulated power supply with a low-pass filter on the original side.
In situations with strong interference or high reliability requirements, isolation transformers with shielding layers should be used to power the PLC system. LC filtering circuits can also be connected in series on the secondary side of the isolation transformer. At the same time, the following issues should also be noted during installation:
1) It is best to use twisted pair connections between the isolation transformer and the PLC and I/O power supply to control serial mode interference;
2) The power line of the system should be thick enough to reduce the line voltage drop caused by the start-up of large capacity equipment;
3) When using an external DC power supply for the PLC input circuit, it is best to use a regulated power supply to ensure the correct input signal. Otherwise, it may cause the PLC to receive incorrect signals.
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