可编程控制器中定时器精度分析

Analysing the Accuracy of Timer in Programmable Controller

讨论可编程控制器（ＰＬＣ）中定时器的误差，提出减少误差的方法． 通过理论分析和实验证实，定时器的误差有两种：第１ 种是由于定时器动作条件造成的，可能的最大值为１ 个扫描周期，这种误差是不可避免的；第２ 种误差是由于指令执行先后造成的，可能的最大值为２ 个扫描周期，这种误差可以通过合理安排指令的次序而尽量减少． 当定时器时间设定值很小时，相对误差可能很大，控制精度将明显下降．

A discussion is devoted to the error of timer in programmable controller and the method is proposed to cut down the error.As confirmed by theoretical analysis and experiment,there exist two kinds of errors in the timer.The first one with one scanning cycle as its possible maximum is due to condition under which the timer operates,it is unavoidable.The second one with two scanning cycles as its possible maximum is due to the order of instruction execution,it can be reduced as far as possible by reasonably arranging the order of instructions.When the time set point of the timer is very small,relative error may be great and control accuracy will be obviously decreased.