Question

In a ladder logic diagram, what is the exact signal state of an output coil if its associated normally-open input contact is closed, but the rung is preceded by an XIO (Examine If Open) instruction that is also currently closed?

Accepted Answer

The output coil will be de-energized, or &#x27;OFF,&#x27; because the rung lacks logical continuity. In ladder logic, an XIO (Examine If Open) instruction acts like a safety sensor that checks if a bit is at a zero state; if the bit is currently closed (meaning it is at a one state), the XIO instruction evaluates as false and breaks the flow of power to the rest of the rung. Think of an XIO instruction as a &#x27;normally closed&#x27; switch that physically opens its contacts when energized, blocking the signal from reaching anything downstream. Even though your normally-open input contact is closed—which usually allows signal flow—the signal is blocked upstream by the XIO instruction, preventing it from ever reaching the output coil.

In a ladder logic diagram, what is the exact signal state of an output coil if its associated normally-open input contact is closed, but the rung is preceded by an XIO (Examine If Open) instruction that is also currently closed?

The output coil will be de-energized, or 'OFF,' because the rung lacks logical continuity. In ladder logic, an XIO (Examine If Open) instruction acts like a safety sensor that checks if a bit is at a zero state; if th....

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In a ladder logic diagram, what is the exact signal state of an output coil if its associated normally-open input contact is closed, but the rung is preceded by an XIO (Examine If Open) instruction that is also currently closed?

The output coil will be de-energized, or 'OFF,' because the rung lacks logical continuity. In ladder logic, an XIO (Examine If Open) instruction acts like a safety sensor that checks if a bit is at a zero state; if th....

Community Answers