| 摘要 |
A thermostat has two separate switches operated by one differential expansion actuator, a thermostatic switch 4 for controlling the temperature of fluid such as water in a tank and a thermal cut-out switch 5 to turn off a heater if the thermostatic switch fails. An assembly comprising the switches is attached to the end of an elongate actuator 3 comprising actuator members having different thermal expansion coefficients, such as a tube 7 attached to a rod 8 at its distal end. Changes in temperature can cause relative movement of the actuator members 7,8 which act separately on the switches to change their state at different thresholds, The temperature threshold may be adjustable using dial 19 for the thermostatic switch, which can automatically reset while the cut-out switch may require manual reset using push pin 33. A four-terminal thermostat (fig 6) can be adapted to replace a two-terminal thermostat by an adaptor (fig 8,70) that short-circuits two of its terminals such as the element terminals, (fig 8, 53,54) , the power supply terminals (fig 9, 51,52) or pilot light terminals (fig 10, 63,64). The adaptor can be insulated hand have male or female connectors.
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