| 摘要 |
1,252,536. Detecting the presence of current. UNION CARBIDE CORP. May 5, 1970 [May 6, 1969], No.21466/70. Heading G1U. The presence of current above a predetermined minimum value in a cable C, Fig. 2, is detected by applying the potential drop across a small length of the cable, e.g. two feet, to an operational amplifier 25 arranged with positive feedback R7 to function as a threshold device with hysteresis. The output of the operational amplifier is rectified D5 and smoothed C3, so that either D.C. or A.C. current may be detected, and used to control a relay CR via a transistor 21. The circuit is initially set up by arranging for no current to flow in the cable, adjusting a potential divider R6 to produce a suitable output voltage from the operational amplifier, e.g. 4v., and adjusting the ratio of the feedback resistors R7, R8 to give the desired threshold voltage e.g. 4 mv. which may correspond to a current of 20A, at the input of the operational amplifier. In operation the output of the operational amplifier will normally be positive at about 4 v., and when the cable current exceeds 20A, so that the input voltage to the operational amplifier exceeds 4 mv., the operational amplifier will switch, becoming saturated in the opposite direction and producing a negative output of about 4v. |
