1、 PLC QUESTION PLC which should pay attention in the application is specially the control device which serves for the industrial production, usually does not need to take any measure, may use directly in the industry environment. But, when the production environment is too bad, the electromagnetic in
2、terference is special intense, or installs uses improper, cannot guarantee PLC the normal operation, therefore should pay attention to the following question in the use. First, installment and wiring (1) The power line, the pilot wire as well as the PLC power line and the I/O line should distinguish
3、 the wiring, between the insulating transformer and PLC and I/O should use the double rubberized wire connection. (2) PLC should be far away from the strong jamming source like electric welding machine, the high efficiency silicon rectifier unit and the large-scale power equipment, cannot install wi
4、th the high-pressured electric appliance in the identical switch cabinet. (3) The input and output of PLC are best separate the line, the switch quantity and the simulation quantity must separate the placing. The simulation quantity signals transmission should use the shielded wire, the shielding la
5、yer should an end or the both sides earth, and the earth resistance should be smaller than the shielding layer resistance 1/10. (4) The PLC elemental area and the expansion unit as well as functional modules ties cable should lie alone, prevents the outside signal the disturbance. (5) The exchange o
6、utput line and the direct-current output line do not use the identical root electric cable, the output line to be far away from the high tension line and the power line as far as possible, avoids parallel. Second, I/O end wiring 1. Input wiring (1) inputs the wiring not to surpass 30 meters generall
7、y. But if the environment disturbance is small, when the loss of voltage is not big, the input wiring may suitable long. (2)Inputs/the output line not to be able to use the identical root electric cable, the input/output line to be separated. (3)Uses the normally opened contact form to connect the i
8、nput end as far as possible, causes the establishment the trapezoidal chart to be consistent with the relay schematic diagram, is advantageous for reading. 2. Outgoing junction (1) The out-put wiring divides into the independent output and the public output. In not group, may use the different type
9、and the voltage class output voltage. But can only use the identical type, the identical voltage class power source in the identical groups output. (2) Because the PLC output element is sealed on the print circuit wafer, and connects to the terminal strip, if will connect output elements load short
10、circuit, will burn down the print circuit wafer, therefore, application fuse protection output element. (3)Uses when the relay outputs, withstands inductive loads size, will affect relays service life, therefore, time use inductive load the selective relay working life must be long. (4) The PLC outp
11、ut load possibly has the disturbance, must therefore take the measure to control, if direct-current outputs after flow guarantees protects, the exchange output anti- accommodates the absorbing circuit, the transistor and the bidirectional thruster output by-passed resistor protection. Third, outside
12、 security electric circuit to guarantee that the overall system can under the secure state the reliable work, avoids, because the external power supply breaks down, PLC to present the heavy economic loss which and the person casualty exceptionally, the disoperation as well as outputs by mistake crea
13、tes, PLC the outside should install the essential protection circuit. (1) Stops the electric circuit anxiously. Regarding can cause the user to cause the damage the dangerous load, besides performs in the control procedure to consider, but also exterior should design the emergency stop electric circ
14、uit, causes when PLC breaks down, can cause the injury load power source reliably to shut off. (2)Fragment. The forward and reverse revolution and so on reversible operations control system must establish the exterior electric appliance interlock protection； the reciprocation moves and rises and fal
15、ls motion the control system, must establish the exterior spacing protection circuit. (3)The programmable controller has self-checking functions and so on surveillance timer, when inspects exceptionally, outputs completely the closure. But when programmable controller CPU breakdown cannot control th
16、e output, therefore, regarding can cause the user to cause the damage the dangerous load, to guarantee that the equipment moves under the secure state, must design the external circuit to protect. (4) Power source load protection. If the PLC power source breaks down, the interruption interval is sho
17、rt in 10 seconds, PLC works not affected, if the power source interrupt surpasses 10 second or the power source drops surpasses the permissible value, then the PLC stop work, all output also separates； when the power source restores, if RUN input connection, then operates carries on automatically. T
18、herefore, to establish the essential current limiting protection circuit to some easy over-loadings input device. (5) Significant breakdown warning and protection. Regarding easy to have heavy accidents place, to guarantee the control system when the heavy accident occurs still the reliable warning
19、and the protection, should have with the significant breakdown the contacting signal to output through the external circuit, caused the control system to move under the safe condition. Fourth, PLC earth the good earth is guaranteed that the PLC reliable work the important condition, may avoid the he
20、terogametic the voltage surge harm. PLC meets the grounding and machines ground terminal docking, meets the grounding the cross-sectional area should not to be smaller than 2mm2, the earth resistance is smaller than 100； If must use the expansion unit, its ground point should accept after checking w
21、ith the elemental area earth in the same place. In order to suppress adds in the power source and the input end, out-ports disturbance, should joins the special-purpose grounding to PLC, the ground point should with the power equipment (for example electrical machinery) the ground point separate； If
22、 cannot meet this kind of requirements, must achieve with the other equipment public earth, forbids to establish contacts the earth with other equipment. The ground point should approach PLC as far as possible. Fifth, the redundant system and hot backup system in profession in and so on petroleum, c
23、hemical industry, metallurgy certain systems, the request control device has the extremely high reliability. If the control system breaks down, will create the production suspension, the raw material massive wastes or the equipment trouble, will create the enormous economic loss to the enterprise. B
24、ut depends on the enhancement control system hardwares reliability to satisfy the above request is only not enough, because the PLC itself reliable enhancement has certain limit. Uses the redundant system or the hot backup system can solve the above problem quite effectively. (1) Redundancy control
25、system in redundancy control system, entire PLC control system (or in system most important part, if the CPU module) of two set of identical system composition. Two CPU module use same user program multi-tasking, one is advocates CPU, another is spare CPU； advocates the CPU work, but the spare CPU o
26、utput is forbidden, when advocates CPU breaks down, spare CPU automatic investment movement. This cut process is controlled by the redundancy processing unit RPU, the switching time in 13 scanning periods, the I/O systems cut is also completes by RPU. (2) Hot backup system in the hot backup system,
27、two CPU with the communication connection connects in together, which is at circular telegram condition .When the system presents the breakdown, advocates CPU informs spare CPU to make the spare CPU work. This cut process is not too generally quick, but its structure is simpler than the redundant system.
