Patent GB-696009-A (GB)
Title: Improvements in or relating to telemetering apparatus
Inventor: LEWIS GEORGE ANDREW
IPC: G08C15/12
Filed: 1951-10-26
Abstract: 696,009. Electric telemetering systems. SHORT BROS. & HARLAND, Ltd. Oct. 26, 1951, No. 25106/51. Addition to 660,270. Class 40 (i) [Also in Groups XL(b) and XL(c)] General arrangement. In a pulse telemetering system of the type described in the parent Specification, plural measurement voltages are sequentially connected to a translator by a cyclically operating electronic selector switch unit comprising a series of individual switching circuits in which one of a multivibrator triggered pair of stabilized switching valves is normally conducting and the other is normally non-conducting and has its grid energized by a corresponding measurement voltage; the multivibrators operating in succession to trigger the corresponding switching valves whereby a train of synchronizing pulses corresponding to each multivibrator operation and a train of information pulses corresponding in magnitude to the respective measurement voltages controlling the individual switching circuits are derived, the first switching circuit receiving a known datum voltage and the second a known fullscale voltage. The operation of each multivibrator triggers the next until the completion of a cycle, at which the first multivibrator is triggered to repeat the process, and the pulse trains energize and synchronize an electronic translator wherein the saw tooth voltage from a cyclically charging and discharging condenser on the grid of a normally non-conducting valve is compared with the successive information pulses on the grid of a normally conducting valve and the valves suddenly exchange functions when the two grid signals are equal, to develop a train of pulses whose durations are proportional to the magnitudes of the corresponding measurement voltages; which pulses are positively and negatively clamped and shaped and then modulate a transmitter whose signals are received on plural diversity receivers producing outputs combined in an electronic converter, which separates the incoming pulses, converts them into voltages proportional to the measurement voltages to be telemetered, and displays the several resultant voltages on the screen of a C.R. oscillograph synchronized to the operation of the transmitter switching multivibrators so as to show vertical spaced lines of lengths dependent on the respective measurement voltages, or alternatively bright spots representing' the tops of said lines. For operation in aircraft the multiple selector switch, power supply, translator, and transmitter are constructed as individual units for rack mounting and interconnection by multiple plug and socket connectors so arranged that a plurality of selector switch units may be associated with the same translator and transmitter, whereby the individual switching circuits of the whole range of selector switch units. operate in sequence and recommence a new cycle after operation of the final switching circuit; thus enabling a large range of different phenomena to be successively telemetered. Electronic selector switch unit. This comprises (Fig. 2) a plurality (e.g. 11) of single stroke doubletriode multivibrators 2a, 2b; 4a, 4b ; . . . . 20a, 20b; 22a, 22b, in which the b valves normally conduct, associated with corresponding triodepentode switching circuits 1a, 1b; 3a, 3b ; . . .19a, 19b; 21a, 21b; wherein the a valve normally conducts, and the b valve is normally cut off by the bias developed in the common cathode resistance. The triodes la, 3a ... 19a, 21a have a common anode load R9 and the pentodes 1b, 3b ... 19b, 21b have a common anode load Ra + Rb, while the suppressor grid of valve 1b is clamped to a 12v. negative voltage on line S11, and the suppressors of valves 3b ... 19b, 21b are supplied with voltages on terminals 34 derived from e.g. the plural strain gauges of an aircraft. A master multivibrator Ma, Mb initiates each switching cycle by a positive pulse through condenser Cl to the grid of valve 2a, and through condenser G2, cathode follower Fb and interconnected lines S12, S16 to the common cathode of-valves 22a, 22b. Valve 2a then conducts and 2b cuts off for a time dependent on the values of R5, R3, C3 (the time constant of the multivibrator 2a, 2b being slightly, and that of 22a, b being considerably, longer than those of the remainder). The multivibrator then reverts to normal, having generated a timed negative pulse across R5, applied through C4 to the grid of valve la, which cuts off and allows 1b to conduct for the duration of the pulse. When 2b resumes its normal cut off condition, a positive pulse is taken from its cathode through condenser C5 to trigger the grid of the a valve of the succeeding multivibrator 4a, 4b which operates similarly to open the switching circuit 3a, 3b ; and the sequence continues until all the eleven switching circuits have operated in turn. The master positive pulse of the succeeding switching cycle is applied to the cathode of the last multivibrator 22a, band operates to change the multivibrator over to its normal condition and close the last electronic switching circuit 21a, 21b simultaneously with the restarting pulse of the succeeding cycle on the grid of 2a. The output line OS connected to the anodes of the pentodes 1b, 3b, ... 19b, 21b of the electronic switching circuits thus develops a sequence of signal voltages, sdccessively representing the datum voltage supplied to switching pentode 1b and the several inputs supplied to switching pentodes 3b ... 19b, 21b, which is connected through cathode follower Ca (whose time constant is reduced by degeneration from its cathode to a tap on the anode resistance Ra, Rb of the switching pentodes) and condenser C7 to the high cathode load R12 of cathode follower Cb. At the beginning of each switching cycle a clamp pulse from the anode of 2b through cathode follower Fa, condenser C10 and resistance R8 positively pulses the grid of clamp valve Cb which is earthed through a rectifier W1 permitting only negative excursions, so that so long as the first switching circuit is operative the cathode voltage of Cb is held to a fixed datum determined by the rectifier W1, while thereafter it represents successively the input voltages to be' telemetered, and is amplified in Aa, Ab to supply the output line S17. The clamp pulse on the cathode of valve Fa also appears on terminals 19, while the operation of the successive multivibrators 2a, b ... 22a, b develops a train of synchronizing pulses on line S18 to control the succeeding translator unit. Switch 40 is operable: to disable the controlling multivibrator Ma, Mb, while switch 41 is operable to select a particular switching circuit for continuous measurement by moving arm 41 from contact 42 to any contact 1-10 corresponding to the switching circuits 2-11. Relay 44 releases to open contacts 45, 46, 47, disable the master multivibrator Ma, Mb, and rearrange the switching multivibrator 4a, 4b for free running under control, of. the biasing potentiometer R10, R11. The selector switch places -12v. bias from line S11 on to the grid of the a valve of the selected switching circuit, so that the b. valve operates merely as an amplifier for the voltage on its control grid, energizing the .output line OS as before. Operation of the multivibrator 4a, 4b when measurement is continuous on a particular input develops the translator synchronizing train on line S18. the degree of overlap between successive switching circuits is adjustable by R9, and R7a, b are adjustable to minimise the effect of temperature and voltage variations on the system. Further similar selector switch units may be added on to give a greater range of switchable inputs under the control of the master multivibrator of the first unit, all the remaining master multivibrators being disabled by switch 40. Lines S13 and S14 are interconnected in all units except the last to connect R13 in parallel with the last multivibrator 22a, 22b to shorten its time constant to that of the preceding units. Lines S12 of all units are connected to line S16 of the last unit, and line S16 of each unit is connected to line S22 of the succeeding unit. On arrival of an initiating pulse from the master multivibrator, the switching circuits of the first unit are operated in turn and a pulse from line S16 to S22 initiates the operation of the second unit, and so 'on, until after all switching circuits have operated the arrival of the next pulse from the master multivibrator initiates operation of the first switching circuit of the first unit and simultaneously over terminals S12, S16 restores the last switching circuit of the last stage to its original condition. Any particular input may be switchably selected for continuous measurement as described above. In a modified selector switch of lower gain Fig. 3 (not shown) intended to handle larger voltage inputs, the first switching circuit receives a signal representing datum zero input, the second a signal representing full-scale input, and the succeeding ten respond sequentially to corresponding input signals to be telemetered. Both valves of each switching circuit are triodes and the datum level clamp circuit and signal output amplifiers are eliminated, while otherwise the system operates as described with reference to Fig. 2. Translator unit. The sequential output signals on terminal S17 are connected through line T17 of the translator (Fig. 4) to the grid of the positively biased cathode follower Cx whose cathode is condenser coupled to the cathode of cathode follower Cy, the grid of which is clamped to a positive datum value by rectifier W2 biased from potentiometer R15, R16, and pulsed over line T19, S19 from the selector switch (Fig. 2) when the first switching stage thereof is operated, so that the cathode of Cy develops a datum voltage when the first switching circuit operates, and subsequently in the cycle develops a sequential plurality of voltage pulses represent