What sources of electromagnetic interference in PLC control system

One, from space radiation interference
Space radiation electromagnetic (EMI) consists mainly of electrical equipment for power network, transients, lightning, radio, television, radar, high-frequency induction heating equipment, often referred to as radiation interference, its distribution is extremely complex. PLC systems in the RF field, it ***** to radiation interference, its influence through two paths; one is directly to the PLC‘s internal radiation, induced by circuit disturbance; but the radiation of PLC communication within the network, introduced by communication lines induced interference. Radiated interference and plant layout and the size of the electromagnetic fields generated by the device, in particular frequencies, generally through shielded cables and PLC local shielding and protecting high voltage discharge components.
Second, interference from the system leads to
Introduced mainly through the power and signal line, often referred to as conducted interference. This industrial field more serious interference in our country.
Third, interference from power supply
Practice has proved that the introduction of disturbance of PLC control system for a power supply failure of many, I encountered in the debugging of a project, after replacing the PLC isolated higher performance power supply, problem solved.
PLC system, the normal power supply by the power supply. Due to network coverage, will be subject to all the electromagnetic interference induced voltage on the wire and circuit. Especially within the grid changes into a switching surges, large-scale power equipment starts and stops, AC and DC rotating equipment caused by harmonics, power short-circuit transient shocks, through transmission lines to the power supply side. PLC power supply usually isolated power supply, but the institutions and the manufacturing process so that their isolation is not ideal. In fact, given the existence of distribution parameters, especially the distributed capacitance, absolute isolation is impossible.
Four, from the signal lines of interference
Connection with PLC control system signal transmission cable, other than the effective signal transmission, there will be external interference signal intrusion. This interference there are two main ways: through transmitters or shared the interference signal power supply for instruments in series, this was often ignored; the second is interference of signal lines by space radiation sensors, namely external inductive interference on the signal line, which is very serious. Introduced by signal interference can lead to I/O signals working and accuracy is greatly reduced, serious damage caused when components. For isolation system with poor performance, will also lead to mutual interference between signals, causing total system bus back, resulting in logical data changes, malfunction and crash. PLC control system I/O module is due to signal interference is introduced quite badly damaged, and the resulting system failures are many.
When he was five, from the grounding system disorder interference
Grounding is to improve the electronic equipment electromagnetic compatibility (EMC) is one of the most effective methods. Proper grounding, which can inhibit the effects of electromagnetic interference and suppression equipment issued to outside interference and error of grounding, but will introduce serious interference, the PLC system will not work properly. PLC control system of wire including system, shielding, communication and protection, and so on. Grounding system disorder interference of the PLC system is that the uneven distribution of grounding potential, ground potential difference exists between the different locations, cause a ground loop currents, impact system working properly. For example, the cable shield must be grounded if the cable shield at both ends of a and b are grounded, there is the potential difference, there is current flowing through the shield, exceptions occur when lightning strikes, ground current will be greater.
In addition, shielding, grounding wire and the Earth is likely to form a closed loop, in the presence of variable magnetic field, the shield appears in induced currents through the coupling between the shield and the core line, interference signal circuit. If systems and other ground handling messy, the circulation of potential distribution range may produce on the ground, effects of PLC logic circuit and analog circuit to work properly. PLC logic voltage interfere tolerance low, logic ground potential interference affects distribution of PLC logic operations and data storage, resulting in data corruption, that program runs or panics. Simulation of electric potential distribution will lead to decreased accuracy, caused serious distortion to the signal control and malfunction.
Six from the interference of PLC system
Primarily by system internal components and circuit interaction between electromagnetic radiation, such as logic circuits mutual radiation and its effects on analog circuits, analog and logic of interaction and components do not match each other and so on. It belongs to the PLC manufacturers electromagnetic compatibility design of the system, more complicated, as the sector cannot be changed, without much thought, but you want to select more performance or the tried and tested system.
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