Explain the purpose and functionality of the EXAMINE OFF instruction.
What will be an ideal response?
When the N.C. symbol is programmed in a ladder diagram, the processor views it as a request to examine the address of the contact for an OFF condition. Any address that is actually OFF becomes logically true and power can flow. If an N.C. contact has an input address and the real-world input device is open, or OFF, the processor sets the bit to 0, or OFF. As the EXAMINE OFF instruction is looking for an OFF condition, a bit set to 0, or OFF, is a true condition and there would be logic continuity, so power can flow through the contact. If the input device had been closed, or ON, the bit would be set to 1, or ON. The EXAMINE OFF instruction can only be logically true when an OFF condition exists. Any bit set to 1 is viewed as an ON condition which makes an EXAMINE OFF (N.C.) contact false and no power can flow.
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