Patent GB-762795-A (GB)
Abstract: 762,795. Electric indicating systems. HEWITTIC. April 30, 1954 [May 20, 1953], No. 12670/54. Class 40 (1). [Also in Group XXXVI] In a telemetering system, direct voltages proportional to the quantities to be measured are successively connected by a step by step selector switch to a transmission line which at the receiver applies such voltages in sequence to charge a condenser, which intermediately of the arrival of each successive voltage is discharged by a relay to deflect a ballistic measuring instrument whose oscillation period is of the same order as that of the condenser discharge time constant and whose pointer at its maximum excursion is electromagnetically caused to record its deflection by means of a stylus and printing ribbon on a travelling strip; the selector switch, the discharge relay and the recording electromagnet being successively energized by a timing switch driven by a constant speed motor at the receiver so that the unknown quantitites are recorded in sequence on the ribbon. Fig. 1 shows a telemetering system in which respective voltages (derived, e.g. from potentiometers) representing quantities to be measured at the transmitter are connected to contacts m-s of selector switch 5 stepped by electromagnet 9 with voltage impulses from the receiver over line 6 and the selected voltages are successively connected over line pair 7 to charge condenser 16 which after each charge is discharged by operation of relay 17 into moving coil 16 in a magnetic field, which impulses a spring-loaded'needle 11 to swing over a moving recording strip 12. The deflection time constant of the instrument is of the same order as the discharge time constant of the condenser, and at its maximum deflection coil 24 is energized to depress the needle against the recording strip through a multicolour ink ribbon 13 to produce a mark thereon; the ribbon being then stepped by electromagnet 10 to record the next deflection in a different colour. A rotary switch 14 driven by a. constant speed motor 15 successively closes contacts 19, 20, 21 to energize relay 17, electromagnet 24, and electromagnet 10 together with electromagnet 9 to discharge condenser 16, record the maximum deflection, and shift the ink ribbon simultaneously with selection of the next measurement in proper sequence; the time interval between condenser discharge and deflection recording being equal to the period of damped swing of the needle to its maximum deflection. Relay 17 may have double contacts operative to completely disconnect condenser 16 from lines 7 and reconnect it to coil 23, and a second selector switch 4 operated by electromagnet 8 may be switchably connected to lines 7 alternatively to selector switch 5 for the measurement of a further range of quantities. Fig. 2 shows a modified receiver circuit independently recording the several transmitter voltages wherein condenser 16 on energization of relay 17 by closure of contacts 19 by rotary switch 14 is discharged through a selector switch 27 into a selected one of a range of blocked needle moving coil recording elements 30 to 33 corresponding to the several quantities to be telemetered while the previous closure of contacts 20 has energized through a selector switch 28 synchronous with switch 27, the corresponding release electromagnet 40 to 43 of the recording element so that its maximum needle deflection is recorded. Finally, closure of contacts 21 energizes line 6 and electromagnet 29 to step the transmitter selector switch and selector switches 27, 28 to a position appropriate to the next quantity to be recorded. The opening of contacts 20 is delayed by known device 50 so that the needle of the selected recording element remains free until it reaches its maximum deflection and recording is made.