Patent GB-660270-A (GB)
Title: Improvements in or relating to telemetering apparatus
Inventor: LEWIS GEORGE ANDREW
IPC: G08C15/12
Filed: 1948-07-19
Abstract: 660,270. Telemetering. SHORT BROS. & HARLAND, Ltd. Aug. 18, 1949. [July 19, 1948] No. 19306/48. Class 40 (i). [Also in Groups XL (b) and XL (c)] In a telemetering device, plural input voltages representing quantities to be measured are developed e.g. by strain gauges and sequentially selected by an electronic switch, A (Fig. 1) for application to a translating device B, producing a train of pulses which correspond in length to the input voltages and modulate a radio transmitter C. A receiver D demodulates the signals and clips the resultant pulses, while a converter E produces voltages proportional to the inputs which may be displayed on an oscilloscope F, or sequentially routed to a plurality of meters H by an electronic selector switch G, to indicate the quantities to be measured. The indications of position, speed, and altitude meters in aircraft, the control signals for pilotless aircraft or missiles, or information regarding odds and share prices may be similarly transmitted. The channel of communication may be radio, line, waveguide, acoustic, or optical transmission. The transmitter selector switch comprises (Fig. 2A) a plurality of multivibrators (e.g. 5), VIA, V1B-V5A, V5B, in which the B valves normally conduct, and are associated with pentodes V1C-V5C whose suppressor grids are normally biassed to cutoff by the voltage drop across the anode resistors of the respective B valves. Positive voltages from 4 strain gauges are respectively fed to the control grids of V1C-V4C and a larger bias voltage to that of V5C. When switch S1S2. is in position M a free running multivibrator V6E, F is started and sequentially pulses the grids of V1A and V5B through V7, so that initially V1A conducts instead of V1B for a short time interval during which V1C conducts. Then V1B again conducts and V1A cuts off, thus pulsing the grid of V2A to conduct, allowing V2C to conduct, and cutting off V1B, so that the multivibrators change over successively. Since V5A, B has a longer time constant than the others of the chain it does not return to normal operation until pulsed from V6E, F at the same time as V1A is pulsed to restart the cycle. Valves V1C-V5C thus cyclically conduct and the successive pulses of voltage proportional to the strain gauge voltages and to the bias voltage on the grids appearing on the common anode line are amplified and fed to the grid of valve 26 in parallel with a maximum voltage limiter 26h-26j. Valves 25, 26 have valve 27 as a common cathode impedance and a load resistance 28 in the anode of valve 26. A series of pulses from the cathode line 10 of the multivibrator chain, and synchronous with the successive changeovers of the latter is transformer coupled to the pulse-shaping amplifier 51-54 which applies a train of square negative pulses of known length to the grid of a time base valve 55, normally shunting a condenser 22 which is charged over resistance 23 from the H.T. line. Each resultant negative going pulse initially cuts off valve 25 and renders valve 26 conducting, and the condenser 22 charges up until its voltage equals the signal on the grid of valve 26. Valve 26 then cuts off and 25 conducts so that a negative pulse applied to the input of the pulse-shaper 71-73 has a duration proportional to the strain gauge value to be telemetered and modulates a known radio transmitter Fig. 2B (not shown) having a thermionic relay circuit whereby speech modulation overrides telemetering modulation. To transmit the indication of one strain gauge exclusively, switch S1S2 is placed in the appropriate position to bias the B valve of the selected multivibrator to cutoff and release the appropriate C valve, which develops anode signals proportional to the associated. strain gauge indication. The free running multivibrator V8EF is also started to supply a train of square positive pulses to valve 55, to initiate a train of square pulses of length representing the indication of the appropriate strain gauge. At the receiver (Fig. 3) the signals are demodulated and the negative pulses pass through a clipping amplifier to successively cut off a valve 43 shunting a condenser 44 which is charged from the H.T. line through resistance 45 to a voltage representing the length of each pulse and thus the successive strain gauge indications to be telemetered which is amplified and appears on terminal 48. The pulses are also applied to a similar valve 49 shunting a charging condenser 44a, whose sawtooth voltage is applied to' drive conducting the normally cutoff valve 80 on the larger voltage pulses derived from the 5th or synchronising multivibrator, to synchronise over terminal 49a an oscilloscope displaying the various strain gauge indications, which may be photographically recorded. The receiver mav incorporate a multiple electronic distributor switch (Fig. 4, not shown), similar to that used in the transmitter, wherein five multivibrators change-over in a cycle initiated by the receiver synchronising pulse, to successively render conducting five gate valves whose grids are supplied in parallel with the receiver output signals, and whose anode currents operate measuring instruments corresponding to the strain gauges at the transmitter. On closure, the anode voltage pulse of each gate valve triggers the succeeding multivibrator. Servomotor controls for pilotless aircraft or guided missiles may replace the measuring instruments.