| 摘要 |
<p>A fluid level control circuit has been disclosed with a safety test function. The system is specifically disclosed as a boiler water level probe of a fail safe type connected to a field effect transistor controlled amplifier having a well defined threshold of operation. A safety test switch means is provided to pull the amplifier's input down below the threshold point, but not to a shorted condition. By observing the output of the system it is possible to determine whether the fluid level detector is properly installed,and whether the amplifier has had any type of unsafe operating failure.</p> |
