GE 8920-PS-DC On site interface module
There are many types of PLCs commonly used in industry nowadays. For low-end PLCs, 8920-PS-DC has similar ladder diagram instructions. For mid to high end machines, such as S7-300, many programs are programmed using language tables.
A practical ladder diagram must have Chinese symbol annotations, otherwise it is difficult to read. If you can have a rough understanding of the equipment process or operation process before reading the ladder diagram, 8920-PS-DC looks relatively easy.
If conducting electrical fault analysis, 8920-PS-DC generally applies the reverse check method or reverse inference method, which is to find the corresponding PLC output relay from the fault point based on the input-output correspondence table. 8920-PS-DC starts to reverse check the logical relationship that meets its action.
The environment in industrial sites is relatively harsh, with many high and low frequency interferences. These interferences are generally introduced into the PLC through cables connected to on-site equipment. In addition to grounding measures, some anti-interference measures should be taken in the design selection and laying construction of cables:
1. Analog signals belong to small signals and are highly susceptible to external interference. Therefore, double-layer shielded cables should be used;
2. Shielded cables should be used for high-speed pulse signals (such as pulse sensors, counting codes, etc.) to prevent both external interference and low-level signal interference from high-speed pulse signals;
3. The communication cable frequency between PLCs is relatively high, and the cables provided by the manufacturer should generally be used. In cases where the requirements are not high, shielded twisted pair cables can be used;
4. Analog signal lines and DC signal lines cannot be routed in the same slot as AC signal lines;
5. The shielded cables introduced and led out from the control cabinet must be grounded and directly connected to the equipment without going through wiring terminals;
6. AC signals, DC signals, and analog signals cannot share the same cable. Power cables should be laid separately from signal cables.
The methods to solve interference during on-site maintenance include: using shielded cables on the affected lines and re laying them; Add anti-interference filtering code to the program.
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