Patent GB-890549-A (GB)
Title: Telemetering system
IPC: H02J13/00
Filed: 1960-05-18
Abstract: 890,549. Telemetering systems; measuring fluid flow. BRISTOL CO. May 18, 1960 [May 21, 1959], No. 17521/60. Class 40 (1). [Also in Groups XIX, XXIX, XXXIX and XL (c)] In a telemetering system the signals consist of a period of oscillations of one frequency followed by a period of oscillations of another frequency, selective receivers being provided to give outputs representative of the durations of the two periods respectively, and further means being included to block each receiver while the other one is receiving its signal. Transmitter (Fig. 1).-Fluid passing through a pipe 10 sets up a pressure difference at an orifice 11 which is applied to two chambers 15, 16 connected by a U-tube to vary the mercury level and turn a spindle 18 accordingly. A constant-speed motor 23 drives a disc 20 and cam 28 to lift a rider at the end of the arm 19 (Fig. 2, not shown) once per revolution and thus deflect a plate 21 outwards. This results in oscillation of a shaft 24 which by an arm 31 opens and closes contacts 33 once per revolution at times depending on the radial distance of the arm 19 from the motor shaft, which times will thus be varied by rotation of the spindle 18. The contacts 33 alter the cathode bias on a keying valve 40 which forms part of a fourstage R.C. phase-shift oscillator 41, so that a change in the impedance of the keying valve alters the frequency of oscillation. The oscillator output is passed to a phase-splitter 42 and push-pull amplifier 43 whence it is coupled to a power line 45 for transmission to a distant receiver. The output transformer has a toroidal powdered-iron core which has a low impedance to currents of power frequency to prevent such currents from modulating the signals and producing uncertainty in the time of change-over from one frequency to the other. A carrier frequency around 15 kc/s. is suitable, with a keying shift of 300-1000 c/s. alterable by plug-in replaceable units in the oscillator circuit. The transmitter circuit is in Fig. 4 (not shown). Receiver (Fig. 3).-The signal is taken off the power line 45 via a coupling network 50 consisting of three series-pairs of capacitors joined across the line, the output being taken between the centre point of one capacitor-pair and earth. Either of the other pairs may be included also, to attenuate the signal to a convenient level. The signal passes then through a high-pass R.C. filter 51 (to reduce power-frequency currents) to an amplifier 52. Thence it passes through another R.C. network, which changes by 90 degrees the phase of any residual powerfrequency currents, to a cathode-follower 54 whence feedback is taken through a further 90 degrees phase-shifter 55 back to amplifier 52 to complete the elimination of powerfrequency currents. The output of the cathodefollower 54 goes to a phase-splitter 56 from which are fed two sets of circuits each responsive to one of the two frequencies transmitted. Each circuit commences with a tuned regenerative stage 57A, 57B which passes on the frequency appropriate to its channel and rejects the other. The signal is then applied to a gated amplifier 58A, 58B whose screen-grid has its voltage removed when the other channel is receiving, so that noise in the passive channel cannot appear in the final output. The signal from 58A or 58B is further amplified and passed to a trigger circuit 63A, 63B, which controls the operation of each channel. The output stages 61A, 61B normally have positive bias on their grids and cannot pass noise voltages, which merely vary the grid current. The signal from 58A or 58B is rectified and smoothed at 60A, 60B to give a negative pulse which cuts off valve 61A or 61B, and again noise voltages cannot be passed as they are insufficient to lift the bias. A polar relay 65 has windings carrying the output currents of the valves 61A, 61B and changes over each time one receiving channel takes over from the other, the duration of each phase depending on the duration of each frequency transmitted and hence on the value of the variable being signalled. The trigger valves 63A, 63B are normally biased beyond cut-off, but are rendered conducting by a signal from 58A or 58B which is rectified in a voltagedoubler circuit and passed through a delay circuit to integrate noise pulses and reduce their amplitude. The anode voltage of the trigger valve is thus normally high, and is communicated through a voltage-sensitive neon lamp 62A or 62B to maintain a positive bias on the grid of the output stage 61A or 61B, and through a further neon lamp 64A or 64B to the screen grid of the gated amplifier 58B or 58A in the other channel. The occurrence of a signal allows the corresponding trigger valve to conduct, and the fall in anode potential unblocks the output stage and cuts off the gated amplifier in the other channel. As in the case of the transmitter, replaceable plug-in units are provided to suit the particular frequencies being transmitted. The full circuit of the receiver is in Fig. 5 (not shown). Recorder (Fig. 3). The relay 65 alternately makes and breaks the circuit to an electromagnet 71 which switches the drive from a constant-speed motor 72 to one or other of the spindles 74, 75 carrying impeller arms 76, 77. When a changeover occurs, the corresponding impeller will commence to rotate, and after a certain time will engage the corresponding arm 78 or 79 and drive it round with it. Each arm carries a pinion 80, 81 which will drive the gear member 82 and associated pen arm 84 across a chart 85. At the next changeover, the other impeller will start to rotate while the first is quickly returned to its rest position by a spring (not shown). After a certain time, therefore, the other arm and pinion will turn and drive the pen in the opposite direction. Since both pinions are permanently meshed with the gear 82, movement of each arm 78, 79 drives the other in the same angular direction so that it approaches its corresponding impeller. The time of one cycle of the cam in the transmitter is made equal to the sum of (a) the time taken for one impeller to make its excursion, and (b) the time for the other impeller to reach its arm in the position where the latter was moved by the first impeller. Thus the alternate effects of the two impellers will cause the pen to take up a definite position on the chart which will change only if the ratio of the two times (a) and (b) alters, i.e. if the original variable at the transmitter changes in value. This recorder is similar to that described in Specification 453,571.