Millivolt readings - Drop-out (another alternative)

Millivolt readings - Drop-out (another alternative)

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

Answer: (A)

The main idea is how a millivolt flame-sensing circuit keeps a gas valve open. In these systems, the valve relies on a tiny millivolt signal from the flame to stay energized. The dropout value is the minimum signal required to hold that valve open. If the flame weakens and the millivolt signal falls below that threshold, the valve drops out and the gas flow shuts off for safety. Here, about 12 millivolts is the threshold at which the circuit no longer holds the valve open, so that reading reflects the dropout point. Values higher than that could still keep the valve open if the flame were stronger, while a much smaller value like 4 millivolts would typically be insufficient to reliably hold the valve open.

The main idea is how a millivolt flame-sensing circuit keeps a gas valve open. In these systems, the valve relies on a tiny millivolt signal from the flame to stay energized. The dropout value is the minimum signal required to hold that valve open. If the flame weakens and the millivolt signal falls below that threshold, the valve drops out and the gas flow shuts off for safety. Here, about 12 millivolts is the threshold at which the circuit no longer holds the valve open, so that reading reflects the dropout point. Values higher than that could still keep the valve open if the flame were stronger, while a much smaller value like 4 millivolts would typically be insufficient to reliably hold the valve open.