| 摘要 |
<p>The temperature of a semi-conductor gas sensor 8 (Fig. 1) is controlled by a circuit Fig. 2 including a heater 6 and an NTC temperature sensor 7 in a bridge circuit. The desired temp. is pre-set on a pot 15 and deviation therefrom results in bridge output to an operational amplifier 19. A feedback circuit to the amplifier input including a capacitor 21, causes the amplifier to produce an oscillatory output, eg at 1 KHZ. Thereby a transistor 20 is controlled so as to apply current pulses through heater 6 with a mark/space ratio dependent upon the amount of temperature deviation. <IMAGE></p> |
