| 摘要 |
1,034,532. Protective arrangements. GENERAL ELECTRIC CO. April 8, 1964 [April 30, 1963], No. 14461/64. Headings H2H and H2K. In an arrangement for protecting an alternating current apparatus, e.g. the heating element 315 of an electric bedcover, from overtemperature conditions, a relay 313 has two coils 320, 322 with a temperature sensing element 312 connected in parallel with the coil 320 and a rectifier 314 connected across the other coil 322 to avoid noise or hum. The sensing element 312 comprises conductors 317, 319 separated by a layer 318 of a material which has a high impedance at normal temperatures and a low impedance at high temperatures. The layer 318 is in parallel with the relay coil 320 and the relay is normally sufficiently energized to maintain its contacts 323, in series with the heating element 315, closed. On overheating, current flowing through the layer 318 causes an increased voltage drop across a resistor 311 resulting in reduced energization of the coil 320, so that the relay drops out. The relay 313 may be initially closed by momentarily operating a start switch 376, a switch 362 in the heating element circuit being opened whilst the switch 376 is closed. To switch off the element 315, an " off " switch 377 is operated to short-circuit the relay coil 320. The temperature of the bedcover is normally controlled by a bimetallic control switch 340. |
