| 摘要 |
<p>1,111,747. Electric control systems. DANFOSS A/S. July 13, 1966 [July 13, 1965], No. 31510/66. Heading G1N. A bridge circuit 1, having a temperature sensitive resistor 4 and an adjustable resistance 5 in one branch, and resistors 6, 8 linked by a potentiometer 7 in the other branch, is rebalanced by a motor 17 which drives the pointer 9 of potentiometer 7 and also a controlled member such as a valve (not shown), the potentiometer 7 being shunted by a manually variable resistor 10 and by a variable impedance circuit including a transistor 20, whereby the range of control of the bridge is continuously and automatically variable. The output of the bridge from points 9, 11 is amplified at 12 and according to its polarity operates a relay 13 or a relay 14 to drive the single phase A. C. motor 17 in one or other direction. When initial bridge rebalance is achieved, both contacts 15, 16 of the relays 13, 14 are unoperated, and supply A. C. energization from 18 to a heater 22 associated with a negative temperature coefficient resistor 21 in the base circuit of the transistor 20. Consequently the net shunt resistance across the potentiometer 7 is reduced and increases the range of control of the bridge and the motor is re-operated to effect a finer adjustment of bridge balance. The sequence of operation continues until the bridge is finally balanced, with the only error remaining being the threshold voltage of the relays. The apparatus is intended to avoid overshoot without using integral feedback or the like.</p> |
