GE SD-108542-SD-108542-M2-021-900015-95CMS1211-0479
work environment
(1) Temperature PLC requires an ambient temperature of 0~55oC. During installation, it should not be placed under elements with large heat, and the surrounding ventilation and heat dissipation space should be large enough.
(2) Humidity To ensure the insulation performance of PLC, the relative humidity of air should be less than 85% (non condensing).
(3) The vibration shall keep the PLC away from strong vibration sources and prevent frequent or continuous vibration with vibration frequency of 10~55Hz. When vibration is unavoidable in the use environment, damping measures must be taken, such as damping rubber.
(4) The air shall be free of corrosive and flammable gases, such as hydrogen chloride, hydrogen sulfide, etc. For the environment with more dust or corrosive gas in the air, PLC can be installed in the control room or control cabinet with good sealing.
(5) The power supply PLC has certain ability of resisting power line interference. In the environment with high reliability requirements or serious power interference, isolation transformer with shielding layer can be installed to reduce the interference between the equipment and the ground. Generally, PLC has DC 24V output to the input. When external DC power supply is used at the input end, DC regulated power supply shall be selected. Due to the influence of ripple, ordinary rectifier and filter power supply is easy to make PLC receive error information.
2. Interference in control system and its source
Field electromagnetic interference is one of the common factors that easily affect the reliability of PLC control system. It is called to solve the problem first, find out the problem, and then propose the solution to the problem. Therefore, it is necessary to understand the source of on-site interference.
(2) Main sources and ways of interference in PLC system
A. Strong current interference
The normal power supply of PLC system is supplied by the power grid. Due to the wide coverage of the power grid, it will be subject to all spatial electromagnetic interference and induce voltage on the line. In particular, changes in the power grid, surges in the operation of knife switch, start and stop of large power equipment, harmonics caused by AC and DC drives, and the instantaneous impact of short circuit in the power grid are all transmitted to the power supply through the transmission line.
B. Interference in the cabinet
High-voltage electrical appliances, large inductive loads and disordered wiring in the control cabinet are easy to cause a certain degree of interference to the PLC.
C. Signal line interference
All kinds of signal transmission lines connected to the PLC control system will always be invaded by external interference signals in addition to transmitting various effective information. There are two main ways of such interference: one is the power grid interference connected in series by the transmitter power supply or the power supply of the shared signal instrument, which is often ignored; The second is that the signal line is subject to the inductive interference of space electromagnetic radiation, that is, the external inductive interference of the signal line, which is very serious. The interference introduced by the signal will cause the I/O signal to work abnormally, and the measurement accuracy will be greatly reduced, which will seriously affect the measurement accuracy
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