SCADAPack 474: Logic Blocks for Pulse Counting and DI-Based Reset

This article explains how to implement a pulse counting mechanism using SCADAPack 474 logic, leveraging a soft counter and a digital input (DI) for reset functionality. The logic is designed to work with physical I/O constraints, where the external counter retains its value and cannot be reset to zero.

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Connections

• Pulse Input: Connect the pulse signal to PIO_SP474_CI1, which acts as the physical counter input.
• Soft Counter: Use a SoftCounter variable to track the pulse count logically.
• Reset Input: Connect a digital input to PIO_SP474_DI1, which will be used to trigger a logical reset.

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Key Logic Operations

1. Copy Counter Value to SoftCounter
   The current value from PIO_SP474_CI1 is copied to SoftCounter.VALUE during each scan cycle.

2. Reset Temporary Counter Value
   A MOVE block resets tempCounterValue when required.

3. Trigger-Based Reset Using DI1
   When PIO_SP474_DI1 transitions from high to low (falling edge), the value of PIO_SP474_CI1 is loaded into tempCounterValue. This simulates a reset by establishing a new reference point.

4. Calculate Difference and Update SoftCounter
   The logic compares PIO_SP474_CI1.VALUE with tempCounterValue using GT, LT, and EQ blocks.
   Based on the comparison, a SUB_UDINT block calculates the difference and updates SoftCounter.VALUE.

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Working Principle

Since the physical counter (PIO_SP474_CI1) cannot be reset, the logic uses a reference value (tempCounterValue) to simulate a reset. The SoftCounter reflects the number of pulses counted since the last reset trigger, calculated as:

The below image shows a screenshot of the counter working principle.

This approach ensures accurate pulse tracking while respecting the hardware limitations of SCADAPack I/O.

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