Millivolt readings - Drop-out (alternative)

Millivolt readings - Drop-out (alternative)

• A. 12 mv
• B. 27 mv
• C. 4 mv
• D. 28 mv

Answer: (A)

In millivolt flame-sensing systems, the gas valve stays open as long as the flame-generated voltage feeds the valve’s solenoid. Drop-out happens when that voltage falls below the minimum needed to keep the valve energized. For many alternative (millivolt) controls, this dropout threshold is about 12 millivolts. So a reading around 12 mv represents the point where the flame is just sufficient to keep the valve open; any weaker flame would cause the valve to drop out and the gas to shut off. Higher readings like 27–28 mv indicate a healthy flame well above the dropout point, while a reading as low as 4 mv would suggest the system is already at or below the dropout level or has a fault. Hence, 12 millivolts is the correct dropout reading for this scenario.

In millivolt flame-sensing systems, the gas valve stays open as long as the flame-generated voltage feeds the valve’s solenoid. Drop-out happens when that voltage falls below the minimum needed to keep the valve energized. For many alternative (millivolt) controls, this dropout threshold is about 12 millivolts. So a reading around 12 mv represents the point where the flame is just sufficient to keep the valve open; any weaker flame would cause the valve to drop out and the gas to shut off. Higher readings like 27–28 mv indicate a healthy flame well above the dropout point, while a reading as low as 4 mv would suggest the system is already at or below the dropout level or has a fault. Hence, 12 millivolts is the correct dropout reading for this scenario.