Mitsubishi PLC control system design to save input / output point skills - Database & Sql Blog Articles

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In engineering design, there are often cases where the control system signal is too much and the plc input point is not enough, and adding hardware requires additional investment. How to use existing equipment to process as many data points as possible is a question worth exploring.
(1) Method of reducing the number of input points required a. The group input automatic program and the manual program are not executed at the same time. It is conceivable to superimpose these two signals and input them into the PLC according to different control state requirements.
b. Contact merge input, such as a two-ground start, three-stop relay - contactor control. When the PLC control circuit is used, the three ground stop buttons can be connected in series with one input point, and the two ground start buttons are connected to one input point, so that the number of input points occupied is greatly reduced. The functions implemented are exactly the same.
c. Make full use of the internal function of the PLC. Use the transfer instruction to connect a switch to an input as a manual/automatic mode changeover switch.
Manual and automatic operations can be distinguished by using a branch instruction. With the counting command or the shift register, the start and stop of the single button can also be realized by the alternate output command.
(2) Method of reducing the number of required output points a. The load with the same on-off state can be paralleled to the same output end point if the output point power of the PLC allows, that is, one output end point has multiple loads.
b. When there are m BCD code displays showing PLC data, the BCD display can occupy 4 output terminals in parallel, that is, one output point has multiple loads.
c. Some control logic is simple, but does not participate in the work cycle, or the appliance that must be started before the start of the work cycle can be controlled without PLC.