The Inconel loop fire detection system operates on which principle?

• A. Pneumatic principle
• B. Based on resistance
• C. Photoelectric cell devices
• D. Thermal expansion

Answer: (B)

The Inconel loop fire detector operates by detecting a change in electrical resistance of a heated conductor. An Inconel loop is part of a circuit that carries a set current; when a fire heats the loop, the metal’s resistance increases (metals have a positive temperature coefficient). The monitoring electronics sense this change in resistance (or the corresponding change in voltage/current for the same current) and trigger the alarm. Inconel’s ability to withstand high temperatures and oxidation makes it reliable in harsh environments like engine compartments. This is different from pneumatic systems (which use pressure changes), photoelectric cells (which sense flame light), or thermal-expansion devices (which rely on mechanical bending of a strip).