Patent GB-680945-A (GB)
Title: Improvements in or relating to electrical measuring circuits
Inventor: GARFIELD WILLIAM LITTERY
IPC: G08C19/00
Filed: 1950-06-30
Abstract: 680,945. Voltage measurement; frequency measurement. STANDARD TELEPHONES & CABLES, Ltd. June 30,1950, No. 16393/50. Class 37. In an electric subtraction circuit the difference between a first variable direct voltage and a second variable direct voltage controls the frequency of an A.C. generator in the same sense as the difference voltage, which A.C. output energizes a frequency-sensitive converter to develop the second direct voltage varying in the same sense as the A.C. output, whose frequency is therefore maintained characteristic of the value of the first direct voltage. Fig. 1 shows a telemetering system wherein an unknown direct voltage on line 8 is compared in a subtraction circuit 7 with a direct voltage from a frequency-sensitive converter 5, Fig. 3 (not shown), connected to the output of a variable frequency relaxation oscillator 1, Fig. 2 (not shown). The difference voltage is fed back over line 2 to control the frequency of the oscillator so that at equilibrium the frequency has a value corresponding to the unknown voltage, and is transmitted over line 4 to a similar converter at a remote point, whose output is measured by a D.C. instrument indicating the unknown voltage. Any type of frequency-variable relaxation oscillator may be used, while the transmitter and receiver converters may be of the same type having a non- linear-response, or differing types having a linear response. In a modification (Figs. 4, 5) the voltage to be measured is applied over line 8 to one end of a potentiometer network R14, R15, R16 and the frequency of a relaxation oscillator comprising a thyratron V5 and a constant current pentode V4 is controlled by a direct difference voltage applied over connection 2 to the grid of V4 from the slider of potentiometer R15. The saw-tooth output is differentiated by C4, R3, R4 to positive-going pips corresponding to the flybacks, which trigger the suppressor grid of the pentode V6 of a phantastron circuit, whose anode and control grid are interconnected by a condenser, and respectively connected through diodes D3, D4 to voltage taps on the bleeder chain R5, R6, R7, R8, R4. The control grid is also connected to the H.T. line through R9, and the circuit generates constant size, constant width pulses at the frequency of the incoming pips across the cathode resistance R10 of V6, which are smoothed by R12, R13, C6 and C7 to develop a direct voltage linearly related to the frequency of the relaxation oscillator which is applied to the other end of the difference potentiometer so that the frequency is controlled in correspondence with the voltage to be measured. The difference potentiometer is balanced with regard to earth by the variable resistance R17 connected between H.T. - and the junction of R14, R15. A positive-going train of pulses in antiphase with that on the cathode appears on the screen of V6, and may key a radio transmitter for transmission to the receiving station, at which the pulse input after amplification and pulse shaping is applied as a train of negativegoing pips to the cathode of diode D5 of a phantastron circuit similar to that in Fig. 4, comprising a pentode V7 and diodes D5, D6, which is anode triggered to produce a train of negative-going constant size constant width pulses on the cathode of V7 which are smoothed by R19, R20, C8, C9 to a direct voltage corresponding to the unknown voltage at the transmitting end, and applied to a balanced valve voltmeter circuit comprising two cathodeloaded triodes V8a, V8b having a meter M connected between the cathodes. The signal is fed to the grid of V8a, and the circuit balance is adjustable by a positive bias on the grid of V8b.