Mitsubishi PLC timing analysis - Solutions - Huaqiang Electronic Network

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The timers of the Mitsubishi FX series plc are divided into a general-purpose timer with no power-down retention capability and an integrated timer with power-down retention capability. The counted clock pulses can be divided into 1ms, 10ms, 100ms timers. The operation of the timer can be described as follows: When the timing condition of the timer is satisfied, after the coil is driven, the timer starts to count, the timing time is up, and the contact action. The PLC is programmed according to the cyclic scan mode. A cyclic scan cycle can be divided into five stages: internal processing, communication service, input refresh, program execution and output refresh. Since these five phases are executed in a time-sharing manner when the PLC is in the RUN operating mode. Therefore, this scanning method will have a certain impact on the timing accuracy of the PIC. The accuracy of the timing precision timing is related to the scheduling of the program, and is also related to the timing input signal (timing condition) and the exact time at which the timer is timed. The accuracy of the timer is analyzed below for the limit case. 1.1 The contact of the timer is after the coil. Here we assume that the input of the timer (corresponding to Figure 1) turns ON just after the PLC has completed the input refresh. We know that the PLC inputs in one scan cycle. It is only scanned once, so the timer does not work during the program execution phase of this scan cycle, and only waits until the next scan cycle. This produces an error of one scan cycle. Again, we assume that the exact timing of the timer completion is after the coil instruction of the ladder timer has been executed, that is, after the OUTTo instruction is executed.