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Precautions for selection and use of PLC output type
2023-12-08
At present, there is a common feature in customer sites where relay problems often occur in the market: the output point with fault has a fast action frequency, and the driven loads are all inductive loads such as relays, solenoid valves or contactors, and there is no absorption protection circuit. Therefore, it is recommended that
Pay attention to the following points when selecting and using types:
1. Pay attention to the load capacity.
The output port must comply with the allowable maximum current limit to ensure that the thermal limit of the output port is within the allowable range. The service life of the relay is related to the load capacity. When the load capacity increases, the contact life will be greatly reduced, so special attention should be paid.
2. Pay attention to the nature of the load,
The inductive load will generate instantaneous high voltage at the moment of opening and closing, so the load capacity may not be large on the surface, but in fact, the load capacity is large, and the life of the relay will be greatly shortened. Therefore, when driving the inductive load, the absorption protection circuit should be connected at both ends of the load. In particular, the protection circuit must be added when the working frequency is relatively high. From the customer's use, the improvement effect after adding the absorption protection circuit is very obvious. According to the characteristics of capacitance, if the capacitive load is directly driven, the impulse surge current will be generated at the moment of conduction. Therefore, in principle, the output port should not be connected to the capacitive load. If necessary, ensure that the impulse surge current is less than the maximum current in the specification.
3. Be sure to pay attention to the action frequency.
When the action frequency is high, it is recommended to select the transistor output type. If you want to drive large current at the same time, you can use the transistor output mode to drive the intermediate relay. When controlling the stepping motor/
servo system
, or for high-speed output/PWM wave, or for nodes with high operation frequency, only transistor type can be used
PLC
The output types of the expansion module and the main module are not required to be the same. Therefore, when there are many system points and different functions, the main module expanded transistor output of the relay output or the transistor output main module expanded relay output can be considered to achieve the best coordination.