PLC and man-machine interface field application in anti-jamming - how to do

PLC controller, man-machine interface to the anti-disturbance challenges of field applications, is complex and detailed. Anti-jamming design is a very complicated systematic project, involving specific input and output devices and the environment in the industrial field requires consideration of various factors, we must according to the actual situation, from the aspects such as reduce the interference sources, to cut off the way to conduct a comprehensive consideration, make full use of all kinds of anti-interference measures to carry out the design of the programmable controller, man-machine interface. Can really improve the programmable controller, man-machine interface HMI field application of anti-jamming capability, to ensure the safe and stable operation of the system.

1 PLC controller software anti-interference measures because of the complexity of electromagnetic interference and hardware anti-jamming measures are not enough, only want to use software anti-interference technology of PLC controller to cooperate, to further improve the reliability of the system. Using digital filter and plastic power frequency sampling, timing calibration reference point potential and other measures, effectively eliminate periodic interference, to prevent potential drift. USES the information redundancy technology, designs the corresponding software logo; Using indirect jump, set the software protection, etc. The switch input signal, for example, with the method of time delay timer read for many times, is an effective and consistent reconfirm to improve the reliability of the software.

2 right choice location, perfect grounding system good is vital to ensure reliable PLC controller work, to avoid accidental voltage surge, also can inhibit the interference. Perfect grounding system is one of the important measures for PLC controller resistance to electromagnetic interference.

PLC controller belong to the low level control device, direct grounding method should be adopted. In order to curb on power supply and input, the output interference, should give special PLC controller connected to ground, ground should be separated from power equipment of the ground. If not meet this requirement, must also be common ground with other equipment, and other equipment series grounding is prohibited. Pick up location should be as close to PLC controller.

centralized arrangement of the PLC controller is suitable for parallel point grounding method, cabinet put oneself in another's position of each device center ground to separate grounding line to extremely. Dispersion of PLC controller controller, series one-point earthing methods should be adopted. Grounding pole grounding resistance is less than 2 Ω, very best buried in 10 ~ 15 m away from buildings in the distance, and the PLC controller of by site must with high voltage equipment location are separated by more than 10 m. If you want to use extension units, the ground should be connect together with the contact of the basic unit, the site.

signal grounding, shield should be against the side of the signal grounding; Signal source is not grounded, should be grounded in the PLC controller side. Signal lines in the middle joint, shielding layer should be firmly connected and insulating treatment, the shield should be connected well. Select the appropriate is located in the single point grounding, avoid multipoint earthing.

3 with good performance of power, inhibition of power grid is introduced into the power of the interference to PLC controller of power supply, the power line power supply should be adopted, directly from the mistress of the low voltage transformer room online using private power supply. Selects the isolation transformer and transformer capacity should be bigger than actual need 1. 2 to 1. About five times, still can add filter in front of the isolation transformer. For transmitter and common signal instrument power supply should choose several times with the isolation and shielding, distributed capacitance and leakage inductance of the technology of the distributor.

4 correct selection of cable, and implementation of eliminating space radiation interfere with the correct selection of cable, and implementation of elimination of programmable controller, man-machine interface of space radiation interference.

of the different types of signals respectively by different cable transmission, adopting away from technology, signal cable, according to the transmission signal type layered signal lines of the same type used twisted way. It is forbidden to use the same cable of different wire transmit power source and the signal at the same time, avoid close to parallel signal wire and power cable laying, increases the Angle between the cable, in order to reduce electromagnetic interference. To reduce the number of power cable, especially the frequency conversion device feed cable radiation, electromagnetic interference from interference on the way to block the invasion of the interference, shielded power cables must be used.

5, PLC controller input and output channels of anti-interference measures input module of the filter can reduce the differential mode interference between the line of the input signal. In order to reduce common-mode interference between input signal and the earth, PLC controller should be good grounding. Input with inductive load, the input signal for communication, can be on both ends of the load and capacitance and resistance, and succeeded flow diode for dc input signals. In order to prevent the parasitic capacitance between the input signal, and the other line parasitic or coupling between the induction electromotive force, generated by the RC surge absorber can be used.

output of ac inductive load, can be on both ends of the load in parallel RC surge absorber; If for dc load, can fly-wheel diode in parallel, also should as far as possible close to the load. For the occasion of switch output, can use surge absorber or thyristor output module. In addition, using the output point concatenated intermediate relay or photoelectric coupling measures, can prevent the PLC controller output point, direct access to the electrical control circuit in the electrical is completely isolated.

6 equipment selection in choosing equipment, the first thing to understand domestic PLC manufacturers give anti-interference index, such as the common mode rejection ratio and differential mode rejection ratio, compression ability, allowed in the electric field strength, and high frequency magnetic field environment, work, etc. , should choose to have higher anti-interference ability of products, such as adopting the floating technology, high performance programmable controller, man-machine interface HMI.

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