| 摘要 |
<p>703,758. Control systems for consumption apparatus. BRITISH THOMSON-HOUSTON CO., Ltd. Dec. 4, 1950 [Dec. 20, 1949], No. 29619/50. Class 38 (4). [Also in Group XXXVIII] In a circuit arrangement, such as that described in Specification 696,369, wherein a layer 6 of normally insulating organic material disposed between two conductors 5, 7 conducts at an elevated temperature to effect switching of a supply to a load such as an electrically heated blanket 2 thereby to provide overheat protection, the present invention provides an additional member 22 responsive to temperature and/or humidity change and connected into the bridge circuit controlling the supply switching relay 15 whereby to increase the degree of temperature or humidity or both at which the load is switched out. As shown, the additional member 22 is a thermistor in heat exchange relationship with a cycling control heating resistor 11, and is serially connected in the bridge circuit with a capacitor 17 which resonates with an inductor 18 to provide the relay operating voltage. At the temperature point in the blanket at which conduction across the layer 6 would otherwise unbalance the bridge to relay drop-out point, the decreased resistance of member 22, consequent upon heating by resistor 11, offsets the unbalance of the bridge until a predetermined higher temperature is reached, at which the relay will drop out. Partly to counteract increased conduction of the layer 6 due to humidity thereof, the member 22 is shunted by a humidity compensator 26 which has a similar effect on the bridge. The compensator may comprise one conductor in the form of tube, spaced from the other, axially disposed therein, by material having similar hygroscopic characteristics to the layer 6. Alternatively the members 22, 26 may be disposed in the blanket 2, or the former may be connected in series or in parallel with the relay coil 16 ; or it may comprise a positive temperature coefficient resistor shunting capacitor 17, or may be constituted by making the signal wire 5 of negative temperature coefficient of resistance material. In controls responsive purely to humidity, the compensator 26 only is provided to elevate the point at which the relay drops out.</p> |
