What is the millivolt reading for drop-out condition?

What is the millivolt reading for drop-out condition?

• A. 30 mv
• B. 15 mv
• C. 2 mv
• D. 0 mv

Answer: (C)

The key idea is that the gas valve in a thermoelectric safety system must be held open by a minimum millivolt signal from the thermocouple. When the flame is hot, the thermocouple generates voltage; as the flame or heat source diminishes, that voltage falls. There comes a low threshold where there isn’t enough energy to keep the valve energized—that point is the drop-out condition. About 2 millivolts is the typical threshold at which the valve releases and the gas shuts off. So, a reading of around 2 mV represents the drop-out level, meaning any further drop would cause the valve to de-energize. Values like 30 mV or 15 mV are well above the drop-out threshold and would keep the valve open, while 0 mV would indicate no signal at all and would correspond to complete loss of operation rather than the defined drop-out point.

The key idea is that the gas valve in a thermoelectric safety system must be held open by a minimum millivolt signal from the thermocouple. When the flame is hot, the thermocouple generates voltage; as the flame or heat source diminishes, that voltage falls. There comes a low threshold where there isn’t enough energy to keep the valve energized—that point is the drop-out condition. About 2 millivolts is the typical threshold at which the valve releases and the gas shuts off.

So, a reading of around 2 mV represents the drop-out level, meaning any further drop would cause the valve to de-energize. Values like 30 mV or 15 mV are well above the drop-out threshold and would keep the valve open, while 0 mV would indicate no signal at all and would correspond to complete loss of operation rather than the defined drop-out point.