PLC自动提高控制系统可靠性的方法
一、控制系统可靠性降低的主要原因
虽然工业控制机和可编程控制器本身都具有很高的可靠性，但如果输入给PLC的开关量信号出现错误，模拟量信号出现较大偏差，PLC输出口控制的执行机构没有按要求动作，这些都可能使控制过程出错，造成无法挽回的经济损失。影响现场输入给PLC信号出错的主要原因有：1、造成传输信号线短路或断路（由于机械拉扯，线路自身老化，连接处松脱等），当传输信号线出故障时，现场信号无法传送给PLC，造成控制出错。2、机械触点抖动，现场触点虽然只闭合一次，PLC却认为闭合了多次，虽然硬件加了滤波电路，软件增加微分指令，但由于PLC扫描周期太短，仍可能在计数、累加、移位等指令中出错，出现错误控制结果。3、现场变送器，机械开关自身出故障，如触点接触不良，变送器反映现场非电量偏差较大或不能正常工作等，这些故障同样会使控制系统不能正常工作。影响执行机构出错的主要原因有：
(毕业设计) 1、控制负载的接触不能可靠动作，虽然PLC发出了动作指令，但执行机构并没按要求动作。2、控制变频器起动，由于变频器自身故障，变频器所带电机并没按要求工作。3、各种电动阀、电磁阀该开的没能打开，该关的没能关到位，由于执行机构没能按PLC的控制要求动作，使系统无法正常工作，降低了系统可靠性。要提高整个控制系统的可靠性，必须提高输入信号的可靠性和执行机构动作的准确性，否则PLC应能及时发现问题，用声光等报警办法提示给操作人员，尽快排除故障，让系统安全、可靠、正确地工作。
PLC automatic control system to improve the reliability
1. The main reasons for the lower control system reliability
Although the main reason for the decline in industrial control system reliability and control aircraft PLC itself has high reliability But if the input signal to the PLC Switch mistakes analog signal larger deviations, Output PLC control by the implementing agencies do not require action, which will enable control of mistakes The economic losses caused irreparable. PLC wrong signal to the scene affect the importation of the main reasons are: 1. Signal transmission line caused a short circuit or open circuit (due to mechanical shearing, their aging lines connecting dislocation). When the signal transmission line failure, the signal can not be transmitted to the scene PLC, the controlling mistakes. 2, the mechanical contact tremble, although close contact one scene, but that closed several PLC, Although the increase in the filter circuit hardware, software differential increased orders, but because PLC scan cycle is too short, it was possible to count, add up. Displacements orders mistake, error control results. 3, the transmitter site and switches their own fault, such as contact connections and Transmitter site reflects the normal work of non-electricity or larger deviations. These same fault control system will not function properly. Impact of implementing agencies to identify two main reasons: one, the contact is not reliable load control actions Although PLC issued a direct action, but did not request executive body movements. 2, starting inverter control, inverter own fault, no converter required to bring the electrical work. 3, various electrical valve did not open the solenoid valve is opened, the customs clearance can not place As the implementing agency did not require action by the PLC control, the system''s normal work, the system''s reliability.
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