| 摘要 |
1,120,365. D.C. level detectors. BUDAPESTI RADIOTECHNIKAI GYAR. 14 Oct., 1966 [15 Oct., 1965], No. 46114/66. Heading H3P. Information can be transmitted along telephone lines by means of a variable level D.C. superimposed on the audio frequencies. A detector for detecting when the D.C. level lies within precise narrow limits comprises a potential divider formed by R1 and R2 the voltages across which are opposed by a potential source stabilized by a Zener diode D3 connected to two points on the divider through respective diodes D1, D2 and secondary windings of a transformer Tr1 energized from a reference A.C. source. At low input currents through R1 and R2 both diodes are cut off; at a precise value of input current determined by the circuit constants D1 conducts and thereby allows the reference A.C. to pass to transformer Tr2 and produce an A.C. output at terminals 3 and 4; and at a precise higher value of the input current both diodes conduct and the anti-phase voltages in the secondary windings of Tr1 cancel each other, and there is then no output from Tr2. |
