Patent GB-655719-A (GB)
Title: Improvements in and relating to apparatus for comparing the magnitudes of two voltages
IPC: H03K5/24
Filed: 1948-12-02
Abstract: 655,719. Voltage comparison. BRITISH BROADCASTING CORPORATION, and RUSSELL, C. GUNN-. Dec. 2, 1948, No. 31283. [Class 37] [Also in Group XL (c)] Apparatus for comparing the magnitudes of two voltages derives a third voltage therefrom which has a predetermined sign when the quotient of the first two voltages lies within a fixed range of a datum, and the opposite sign when the quotient departs from the range, the third voltage being applied to a device responsive to voltages of one sign only. In Fig. 1 direct voltages V1 and V2 are applied to terminals 10, 11 and 12, 13, interconnected with pairs of terminals 14, 16; 15, 17 and 18, 20; 19, 21 respectively. V1 and V2 are connected in series opposition to a bridge rectifier 22 and their difference voltage V1-V2 appears across the load resistance 27 in the same polarity irrespective of input sense. Resistance 28 is connected across V1 and V2 in series aiding and a voltage V1+V2/r is tapped off for connection in opposition to V1-V2   across resistance 27 in series with a half-wave rectifier 31 and a relay winding 30. The relay operates only when the voltage in series with it is finite and positive, i.e. when V1-V2<SP>V1+V2</SP>/ r  so that when V1/V2 differs from unity by more than a predetermined amount the relay contacts close and light an indicator lamp 34. V1 may be connected in opposition to a tapped fraction of V2 in a first rectifier-relay series circuit while V2 may be connected in opposition to a tapped fraction of V1 in a second similar circuit, the relays respectively operating when V2/V1 is greater or less than unity by a predetermined amount (Fig. 2, not shown). Alternatively V1 may be amplified and connected in opposition to V2 in series with a rectifier and a relay, while a tapped fraction of V1 is connected in opposition to V2 in series with an oppositely poled rectifier and the same relay, which is operated when V2 is greater, or less than, a fixed proportion of V1 (Fig. 3, not shown), V1 and V2 must be unidirectional and steady or pulsating. For comparison of alternating voltages rectifiers may be inserted between the sources and the input terminals. Fig. 4 shows an automatic transmission monitoring system for e.g. a radio transmitter in which signals are derived from two points in the system and respectively coupled to the inputs of similar overloadlimiting degenerative amplifiers 49, 52 of the kind described in Specification 653,099, [Group XL (c)]. The output circuit of the amplifier 49 comprises a transformer 55 having two secondary windings supplying full-wave recti. fier circuits which develop unidirectional voltages, proportional to the input voltage, across terminals 14, 16 and 15, 17 corresponding to those terminals in Fig. 1. Similarly, the amplifier 52 develops unidirectional voltages across terminals 19, 21 and 18, 20 proportional to its input voltage, and the remainder of the circuit functions in the same way as Fig. 1 to operate an indicating device 64 when the ratio of the two amplifier inputs lies outside a predetermined range of values. Equalizers 65, 66 are inserted in one rectifier channel of each amplifier to make the operational sensitivity of the apparatus for differences in level correspond more closely with that of the human ear. Voltage sources 69, 70 are connected through rectifiers 71, 72 to the terminals 14, 16 and 19, 21 to ensure that the voltages thereon do not fall below a predetermined magnitude, so that noise voltages mixed with one of the comparison voltages do not cause false operation. The half-wave rectifiers may be replaced by thyratrons. Specification 655,688, [Group XL (c)], also is referred to.