2) Interference from lead wire outside the system
Introduce through the power and signal line mainly, is usually called and conducted interfering. This kind of interference is relatively serious at the industrial scene of our country.
3) Interference from power
Practice has proved , interference introduced because of the power causes situations of PLC control system trouble a lot of, I meet in debugging in some project, is it isolate performance high PLC power to change, the problem is solved .
Normal power supply power, PLC of system supply power by the electric wire netting. Because the electric wire netting is widely covered, it will be interfered the voltage of reaction and circuit on the circuit electromagnetically by all space. Change of electric wire netting, enter switch operate wave well up, large-scale electric equipment is it park, is it is it move in harmony wave, electric wire netting that device cause short out the attitude is bludgeoned into etc. temporarily to spread direct to pay to get up especially, it is through it is the original since transmission line of electricity last power. PLC power usually adopts and isolates the power, but its organization and manufacturing engineering factor make its isolating unsatisfactory. In fact, because of distributing the existence of the parameter especially distribution capacity, it is impossible to isolate definitely.
4) Come from the interference that the signal thread introduces
All kinds of signal transmission lines connected with PLC control system, besides transmitting all kinds of effective information, always there will be outside interfering signals that will be invaded. This interference has two kinds of ways mainly: Supply power or share through changer power supply power a bunch of electric wire netting entered, signal of instrument interfere, this is often ignored; second, the signal line is influenced by space electromagnetic radiation reaction, namely the external inductive interference on the line of signal, this is very serious. Is it is it can cause I/O signal work by signal unusual measuring precision reduce greatly to interfere to introduce, will cause the components and parts to damage when being serious. For isolating the system with bad performance, will cause the mutual interference among the signals, cause the backset current of the systematic bus altogether, because logic data changing, work up by mistake and system halted. PLC control system cause by the fact that the signal introduces I/O mould piece is it count quite serious to damage, being caused situations of the systematic trouble by this is a lot of too.
5) Interference while coming from the earth system confusedly
Earth to improve electronic equipment electromagnetic effective means of compatibility one of. Correct earth, can suppress the equipment to send out and interfere outwards not only can suppress the electromagnetic influence that interfere but also; And wrong earth, can introduce serious interfering signal instead , make PLC to be system unable to work normally .
6) The ground wire including systematic ground , shielding , exchanging of PLC control system and protect the ground etc..Earth whether all connect the place electric potential misdistributions mainly to interference, PLC of system, different to connect person who have electric potential difference under place, person who cause cycle electric current, influence the system to work normally. For example cable shielding layer must one point ground, if cable shielding layer both ends A, B ground, person who store in electric potential difference, there is electric current that flows through the shielding layer, when the unusual state takes place and is struck by lightning, the ground wire electric current will be bigger.
In addition, the shielding layer , earth connection and earth may be formed and closed the cycle, under changing the function of the magnetic field , will present the reaction electric current in the shielding layer, pass the coupling between the shielding layer and core line , the return circuit of interfering signal. If with deal with confusion by other earth systematically, ground circulation produced might is it vary the electric potential distribute to produce at ground wire, influence the normal work of the logical circuit and simulation circuit in PLC. Logic voltage that PLC work interfere tolerance to be relatively low, logic distribution of electric potential interfere apt to influence logic operation and datum of PLC store, lead to the fact the confusion of the data , procedure run and fly or system halted. Simulation distribution, ground of electric potential is it measure precision drop, it causes to be distorted and missing movements seriously to whom signal observe and control to result
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