Which millivolt reading corresponds to 'Open circuit (another alternative)'?

Which millivolt reading corresponds to 'Open circuit (another alternative)'?

• A. 27 mv
• B. 13 mv
• C. 4 mv
• D. 28 mv

Answer: (D)

Open circuit means no current is drawn from the source, so the meter shows the source’s full electromotive force. In millivolt gas valve systems, the thermopile or sensing device typically produces about 25–30 millivolts when unloaded. The reading closest to that unloaded voltage is 28 millivolts, which matches the expected open-circuit value. The other numbers would indicate some load on the source or a weak/conditioned output rather than the true open-circuit EMF. So, 28 millivolts best represents the open-circuit reading.

Open circuit means no current is drawn from the source, so the meter shows the source’s full electromotive force. In millivolt gas valve systems, the thermopile or sensing device typically produces about 25–30 millivolts when unloaded. The reading closest to that unloaded voltage is 28 millivolts, which matches the expected open-circuit value. The other numbers would indicate some load on the source or a weak/conditioned output rather than the true open-circuit EMF. So, 28 millivolts best represents the open-circuit reading.