Which flame sensing relay technique relies on ionized hot gases conducting electricity in the flame?

Which flame sensing relay technique relies on ionized hot gases conducting electricity in the flame?

• A. Ionization detector
• B. UV sensor
• C. Flame rod
• D. Thermocouple

Answer: (C)

Ionized hot gases in a flame create a conductive path that lets electricity flow between electrodes, and a flame rod uses this conduction to prove flame presence. A small probe is placed in the flame and wired into the control circuit; when the flame is burning, the ions in the flame carry current, which the relay detects to keep the gas valve open. If the flame goes out, ionization drops, current falls to zero, and the control shuts off fuel to prevent unburned gas from accumulating. This direct ionization-based sensing is the principle behind the flame rod method. In contrast, a UV sensor detects flame by its ultraviolet light, and a thermocouple senses temperature rather than flame existence via ionization.

Ionized hot gases in a flame create a conductive path that lets electricity flow between electrodes, and a flame rod uses this conduction to prove flame presence. A small probe is placed in the flame and wired into the control circuit; when the flame is burning, the ions in the flame carry current, which the relay detects to keep the gas valve open. If the flame goes out, ionization drops, current falls to zero, and the control shuts off fuel to prevent unburned gas from accumulating. This direct ionization-based sensing is the principle behind the flame rod method. In contrast, a UV sensor detects flame by its ultraviolet light, and a thermocouple senses temperature rather than flame existence via ionization.