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

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The ZCP (Interval Comparison) instruction is a powerful tool in PLC programming that compares the value of a source operand S3 with two other source operands S1 and S2, then sends the result to a target operand D. This function is commonly used in control systems where specific conditions must be met based on a range of values.

One practical application of this command is in an automatic shearing system. In this setup, the PLC outputs Y1, Y2, and Y3 are connected to the high-speed, low-speed, and brake terminals of an inverter, respectively. When the start button X000 is pressed, the motor begins feeding, and the counter starts counting revolutions. The motor initially runs at high speed.

If the set value of the counter is 1000 or 1200, the motor switches to low speed when the counter value K falls between 1000 and 1200. If the counter value exceeds 1200, the motor engages the brake, and the shearing action begins.

Here’s a breakdown of the program logic:

• RST: Resets the counter or specific registers.
• C251: A high-speed counter used to track the number of revolutions.
• ZCPP: Executes the interval comparison pulse, checking if the current count lies within a specified range.

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