Signal interference factor of the instrument control system - News - Global IC Trade Starts Here Free Join

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Interference, also called noise, is a signal-independent electrical signal that is inserted into or superimposed on the system power supply and signal cable. Interference can cause measurement errors and serious interference can cause equipment damage. Common interferences are as follows:

(1) Conducted interference

1) When several signal cables are transmitted together, other signals are affected due to aging and leakage of the insulating material, that is, interference is introduced in other signals.

2) In some on-site actuators, 220V power supply, sometimes equipment burnout, or human factors, causing a short circuit between the power supply and the signal cable, strong power into the weak electricity, causing greater interference and equipment damage.

3) Common mode interference due to unreasonable grounding. If both ends of the signal cable are grounded at the same time, the grounding system of the two points may have a potential difference ΔE, which may generate a large circulating current on the signal cable, superimposed on the signal current, causing the analog signal to fluctuate. Causes the card to malfunction.

4) During the operation, the acquisition signal from the card is grounded for a long time, and the ground current formed exceeds the allowable value, resulting in channel damage.

Among the above-mentioned types of conducted interference, since the state of the equipment of the instrument control system is guaranteed, the interference caused by the aging of the insulating material or the burning of the equipment is less likely, and the interference caused by the grounding is more common. It is more elusive and should be given enough attention.

(2) Capacitive inductive coupling interference

At the controlled site, there are often many signals to go through the cable trough or the cable tube to the control system. These signal cables are routed together, and there are distributed capacitances between them. These distributed capacitors are used to add interference to other signals. On the cable. In addition, alternating magnetic fluxes are generated around the alternating signal cable, and these alternating magnetic fluxes create an electromotive force between the parallel conductors, which also causes interference on the line.

(3) Interference caused by large electrical equipment

In the place where large electrical equipment starts and the switching device moves frequently, the spark generated by the start of the motor and the closing of the switch will generate a large alternating magnetic field around it. These alternating magnetic fields can either generate interference by coupling on the signal cable or by coupling high frequency interference on the power cable. If the interference exceeds the allowable range, it will also affect the operation of the system.

(4) Other factors

Lightning strikes can cause large electromagnetic interference around the system and can introduce interference through various ground lines. Static electricity is also often the killer of system equipment.