Mitsubishi PLC's interval comparison instruction ZCP - Database & Sql Blog Articles

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The ZCP instruction, or Interval Comparison Command, is used to compare the value of a source operand S3 with two other source operands S1 and S2. It then sends the result to a target operand D. This command is particularly useful in PLC programming for making decisions based on a range of values.

Here's a practical example: In an automatic shearing system, the PLC outputs Y1, Y2, and Y3 are connected to the high-speed, low-speed, and brake terminals of a variable frequency drive (VFD), respectively. When the start button X000 is pressed, the motor begins feeding and starts counting the number of revolutions. Initially, the motor runs at high speed. If the counter reaches 1000 or 1200, it switches to low speed when the counter value K falls between 1000 and 1200. Once the counter exceeds 1200, the motor engages the braking system, and the shearing action is triggered.

Here’s a sample program:

• RST: Reset instruction
• C251: High-speed counter
• ZCPP: Interval comparison pulse execution

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