Which of the following is a commonly detected interlock safety signal?

• A. Guards in place
• B. Operator mood
• C. Ambient noise
• D. Tool color

Answer: (A)

Interlocks are about making sure safety guards or doors are in the correct position before the machine can run. The signal an interlock provides is the status of the guard—whether it is in place and secured. In practice, a guard interlock is a switch (mechanical or door-mounted) wired to the PLC. It is often a normally closed circuit that opens if the guard is opened; when the guard stays closed, the PLC sees a safe, closed condition and allows operation. If the guard is not in place, the interlock signals the control system to stop or prevent starting, keeping the operator protected.

That’s why the option describing guards in place is the best answer: it directly represents the guard status that interlocks monitor. The other choices—operator mood, ambient noise, and tool color—don’t relate to the safety interlock signals used to verify guarding.