Position Sensor Check

1. What the Program Does

This example checks two position sensors for agreement. When Position_A and Position_B differ, XOR activates the diagnostic output Sensor_Mismatch.

The diagram illustrates checking a pair of sensors that should normally report the same value.

Position_A XOR Position_B → Sensor_Mismatch

2. Example Signals

3. Main Logic

XOR produces TRUE when its inputs differ:

Sensor_Mismatch = Position_A XOR Position_B

Both FALSE or both TRUE produce no mismatch. One TRUE and one FALSE produce a mismatch.

4. Truth Table

5. Testing in the Simulator

• Leave both inputs FALSE: no mismatch.
• Activate only Position_A: Sensor_Mismatch becomes TRUE.
• Activate both inputs: the mismatch clears.
• Clear Position_A while Position_B stays TRUE: the mismatch returns.

6. What to Watch For

XOR detects a difference but does not explain its cause. Real diagnostics often add messages identifying each sensor's state and the duration of the mismatch.

Add a TON timer if brief transitions should not immediately activate an alarm.