APPLIANCE HAVING A SAFETY STRING

摘要

A gas-fired appliance is disclosed that includes a gas valve powered by a power source. A plurality of switching units, each responsive to a condition of the applianc e, are arranged in series between the gas valve and the power source. Each switching unit includes an emitter, such as an emitter of an optocoupler, that is used to monitor the opened or closed status of a switch in the switching unit. When at least one switch opens, power to the g as valve is reduced preventing the gas valve from operating. However, because this reduced power is provided to each subsequent switching unit, each optocoupler can be monitored regardless of the opened or closed status of previous switching units. As such, one or more open switches can be detected simulataneously.