Patent GB-977391-A (GB)
Title: Apparatus for transmitting to a distance the value of a variable quantity
IPC: G01R21/133
Filed: 1961-02-14
Abstract: 977,391. Voltage power measurement. ELECTRICITE DE FRANCE. Feb. 14, 1961 [Feb. 17, 1960], No. 5434/61. Addition to 871, 544. Heading G1U. [Also in Divisions G4, H3 and H4] The integrator-comparator circuit of the parent Specification for converting a voltage U to be measured, Fig. 2, into a sawtooth waveform A of frequency (f) proportional to the magnitude of U, and comprising a capacitor 2 which is repeatedly charged by the source U over a resistor 1 until it reaches a reference voltage V when a transistor 3 conducts to energize a relay 4 to discharge the capacitor, is modified by the provision of a further resistor 16 over which further charging current may be fed to the capacitor to vary the substantially linear relationship (f being sufficiently large) between U and f. A further voltage k U may be injected into the circuit at X 3 , X 4  to compensate for the "dead-time" of the relay, as shown mathematically in the Specification. The voltage U may be derived from a potentiometer, Fig. 5 (not shown) connected across the battery 18, Fig. 2, the potentiometer slider being moved in accordance with the variable being measured. For telemetering purposed, Fig. 1, (not shown), the sawtooth wave A in converted into a rectangular pulse train to modulate a carrier which after filtering and amplification is transmitted by line or radio. At the receiver the pulse train is demodulated, differentiated and rectified to operate a counter or other indicator. Power measurement, Fig. 4. Voltage E A  and current I fed over respective transformers 26, 25 are combined in a ring modulator 22 (including silicon diodes 24,) the output U of which is E A .I, cos # (where # is the phase angle). The circuit shown is connected at X 1 .. X 4  to the integratorcomparator circuit, Fig. 2, in lieu of that portion thereof to the left of line XX. The reference voltage Eg for supplying the charging resistor 16 and potentiometer 17, Fig. 2, is derived from the voltage transformer 26 over a rectifier bridge 28 and further bridge 29, and the "dead-time" correction voltage k U is derived from the current transformer 25 over rectifier bridge 27. Transmitter, Figs. 7a, 7b, 8. Here U may be of either polarity, a rectifier 41 ensuring that only negative charges are applied to capacitor 2. The relay 4 is replaced by a transistor 43, feeding a monostable multivibrator 44a, 44b and two transistors 45, 46. The arrangement is that during charging of capacitor 2, transistor 43 conducts, 44a is blocked, transistor 44b conducts and transistors 45, 46 are blocked. When the charge on capacitor 2 corresponds to the reference voltage, transistor 3 conducts, transistor 44a conducts and 44b is therefore cut off and transistor 45 conducts, capacitor 2 discharging through this transistor (waveform A). At the end of the discharge, transistor 46 becomes conductive and, through diode 47 returns multivibrator 44a, 44b to its initial state. The pulses A 1  at 48 are then differentiated by 49, 50 to form peaks A 2 , A 3 , Fig. 8, and applied to a further multivibrator 52a, 52b to obtain at 53 a signal B which modulates the carrier from oscillator 54, consisting of the transistor and tuned coupled circuits 55a, 55b. The signal modulated carrier is then amplified at 57, 60 and transmitted over lines 10. Receiver, Figs. 9A, 9B, 10. Comrpises a filter 11 to which the input C 1  from the transmitter is applied, amplified at 62, 63, and demodulated at 65, 66, the output C2 being transformed by a bistable Schmitt multivibrator 67a, 67b into rectangular pulses B<SP>1</SP>, which are then differentiated and rectified to produce pulses G in circuits 70a, 71a, 72a and 70b, 71b, 72b. The pulses G are amplified in stages 74, 75, and then counted, or, as shown, a current proportional to their frequency is produced as follows. They are first transformed into amplitude and duration modulated pulses L by applying them to the tuned primary of transformer 76 the secondary of which supplies signals K at 77 which are amplified and limited in duration by transistor 78 in conjunction with a Zener diode 79 and by transistors 80, 81, and in amplitude by a further Zener diode 82. The pulses L at 83 are applied to the bases of shunt transistors 84, 85 and the collector current of transistor 84, 85 is applied to a circuit comprising an A.C. branch consisting of a potentiometer 91 and meter 92. The amplitude of the collector current is compensated for variations due to variations in the transistor characteristics by a correction circuit including transistors 87, 88 which provides correcting pulses to the bases of transistors 84, 85.