OCC SACA Sensor Logic Systems 1 (C-205) Practice Test

How inversion is created in sensor logic using normally closed contact?

Place a normally closed contact in series with the coil; the coil energizes when the input is absent. Place a normally closed contact in series with the coil; the coil energizes when the input is present. Place a normally closed contact in parallel with the coil; coil energizes regardless. Use a normally open contact to achieve inversion.

Correct Answer:

Place a normally closed contact in series with the coil; the coil energizes when the input is absent.

Explanation:

Inversion in sensor logic means the output state is the opposite of the input condition. Using a normally closed contact in series with the coil does this: when the input is absent, the NC contact is closed and current can flow to energize the coil. When the input is present, the NC contact opens, cutting the current and de-energizing the coil. So the coil is ON when the input is OFF, and OFF when the input is ON, exactly the inverted behavior you want. Using a normally open contact in series would energize the coil only when the input is present (non-inverted). A normally closed contact in parallel could bypass the coil and yield unreliable results.

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