【正文】 acility control applications. However, there is some confusion because so many possibilities exist. To help eliminate this confusion, let39。s 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 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 position. Two CPU module use same user program multitasking, one is advocates CPU, another is spare CPU。 the reciprocation moves and rises and falls motion the control system, must establish the exterior spacing protection circuit. (3)The programmable controller has selfchecking functions and so on surveillance timer, when inspects exceptionally, outputs pletely the closure. But when programmable controller CPU breakdown cannot control the 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 short 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。s transmission should use the shielded wire, the shielding layer 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 module39。 5, maintenance process and technical requirements (1) measure voltage, use a digital voltmeter or accuracy of 1% of the multimeter, measure (2) the power rack, CPU board can only be removed when the main power cut off。 (2) To protect the ponents and the template does not function no fault damage, must be protection devices and serious preparations for antistatic。 Second, the provisions of cleaning equipment on a regular basis (1) every six months or a quarter of the PLC to clean, cut off power to the PLC power supply to the power rack, CPU board and input / output board in turn be removed to purge, clean and then in turn installed in situ, will all link to resume evacuation call and start the host PLC. PLC box carefully sweeping health。 (4) connected to the power supply rack power cord clear line number in mind and remove the link location, then remove the power rack and rack screws connected, power rack can be removed。 (6) pluggable template, to be more careful, gently, and the goods shipped out of static electricity。s service life, therefore, time use inductive load the selective relay working life must be long. (4) The PLC output load possibly has the disturbance, must therefore take the measure to control, if directcurrent output39。 If must use the expansion unit, its ground point should accept after checking with the elemental area earth in the same place. In order to suppress adds in the power source and the input end, outport39。t prehend the internal structure and operation orders of the interruption pletely also, we do a very small example to explain. Each equipment always will not forget a button, it also is at we meet the urgent circumstance use of, which is nasty to stop the button. When we meet the Human body trouble and surprised circumstances we as long as press it, the machine stops all operations immediately, and wait for processing the over surprised empress recover the operation again. Nasty stop the internal I/ O of the internal CPU of the button conjunction PLC to connect up, be to press button an exterior to trigger signal for CPU, the CPU carries on to the I/ O to examine again, being to confirm to have the exterior to trigger the signal, CPU protection the spot breaks off procedure counts the machine turn the homologous exterior I/ O automatically in the procedure to go to also, be exterior interruption procedure processing plete, the procedure counts the machine to return the main procedure to continue to work. Have 1:00 can what to explain is we generally would nasty stop the button of exterior break off to rise to the tallest Class, thus guarantee the safety. When we are work a work piece, giving the PLC a signal, counting PLC inner part the machine add 1 to pute us for a day of workload, a count the machine and can solve problem in brief, certainly they also can keep the data under the condition of dropping the electricity, urging the data not to throw to lose, this is also what we hope earnestly. The PLC still has the function that the high class counts the machine, being us while accept some dates of high speed, the high speed that here say is the data of the in all aspects tiny second class, for example the bar code scanner is scanning the data continuously, calculating highspeed signal of the data processor DSP etc., we will 外文翻譯（ 原文 ） 11 adopt the high class to count the machine to help we carry on count. It at the PLC carries out the procedure once discover that the high class counts the machine to should of interruption, will let go of the work on the hand immediately. The trapezoid diagram procedure that passes by to weave the distance again explains the high class for us to carry out procedure to count machine would automatic performance to should of work, thus rise the Class that the high class counts the machine to high one Class. You heard too many this phrases perhaps: crash, the meaning that is mostly is a workload of CPU to lead greatly, the internal resources shortage etc. the circumstance can39。固定式 PLC 包括CPU 板、 I/O 板、顯示面板、內(nèi)存塊、電源等，這些元素組合