Which type of security system circuit uses devices that are all normally open when there is no abnormal condition present?

Which type of security system circuit uses devices that are all normally open when there is no abnormal condition present?

• A. Open loop circuit
• B. Closed loop circuit
• C. Double end-of-line resistor
• D. Single end-of-line resistor

Answer: (A)

Open-loop circuits are built so that the sensors are normally open when there’s no abnormal condition. The circuit isn’t complete at rest, and an event causes a sensor to close and complete the circuit, signaling the alarm. This is different from a closed-loop (normally closed) setup, where sensors are closed under normal conditions and an alarm is triggered by opening. The end-of-line resistor options are about how the loop is supervised for faults, not the normal state of the devices, so they don’t define the basic behavior of the sensors themselves.

Open-loop circuits are built so that the sensors are normally open when there’s no abnormal condition. The circuit isn’t complete at rest, and an event causes a sensor to close and complete the circuit, signaling the alarm. This is different from a closed-loop (normally closed) setup, where sensors are closed under normal conditions and an alarm is triggered by opening. The end-of-line resistor options are about how the loop is supervised for faults, not the normal state of the devices, so they don’t define the basic behavior of the sensors themselves.