| 摘要 |
In a conventional type of thermostat the temperature-sensing element, usually in the form of a bimetal strip, acts against a resiliently loaded switch contact, tending to move that contact to switch-open position against the action of the spring loading thereof. In most instances as the bimetal changes its shape progressively in accordance with changes in temperature, the force exerted thereagainst by the switch contact that it is tending to open will increase, thereby making the bimetal strip work harder and harder as the temperature changes, and in any event the force against which the bimetal works is comparatively great. These are sources of inaccuracy. To eliminate them an additional temperature-sensitive element is provided, one which normally is comparatively inactive on the switch. However, when a temperature is reached which is close to the desired operating temperature of the switch, that element becomes active on the switch with a force which is not strong enough in and of itself to move the switch to open position. Hence the element, when active, will act to assist the bimetal, thereby enabling the bimetal to work against a relatively low opposing force and thus increasing the accuracy with which the bimetal can control the opening and closing of the switch.
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