Patent GB-688239-A (GB)
Title: Improvements in self-balancing, self-standardizing measuring systems
IPC: G05B11/01
Filed: 1951-03-14
Abstract: 688,239. Electric telemetering system. LEEDS & NORTHRUP CO. March 14, 1951 [March 14, 1950], No. 6186/51. Class 40 (i). The self-balancing, self-standardizaing receiver of a telemetering system transmitting signals whose frequency is proportional to the magnitude to be indicated, comprises a filter 10 for passing signals within the required frequency band brought to a constant level, a pulse converter 11 producing pulses at the same frequency as the signal, terminated in a rectifier 21 which gives a D.C. voltage proportional to the frequency of the input signal, and a motor-driven indicator-recorder 12, where the D.C. voltage is balanced. against a fixed D.C. voltage, facilities being provided for periodically checking and adjusting the sensitivity of the apparatus, and a time-delay network 14 to disconnect the recorder for the checking period and for the duration of the switching transients. The bandpass filter 10 consists of two. valves 15, 16 preceded by tuned networks 68, 76 coupled for negative feedback, thereby providing a constant output voltage with the required frequency range. The pulse converter 11 comprises a first wave shaping stage 18 producing a square wave, which is differentiated at 90, 91 to provide a pulse input to a second wave shaping stage 19 producing pulses whose average value is independent of the converter input shape. These are followed by an amplifier 20 and rectifier 21. Measuring circuit 12. The D.C. output of the converter 11 is compared with a voltage from a measuring network including the potentiometer 23, fed from a stabilized power supply 13, any unbalance voltage being converted to A.C. at supply frequency by a vibrating reed converter 24, amplified at 25 and fed to a two-phase motor 26 which moves the slider of potentiometer 23 to. restore balance. Standardizing arrangement. A series of switches at various parts of the circuit are operated at the required instants by the movement of an arm 40 (Fig. 2) controlled by a cam 42 and notched disc 43 driven by a constantly running motor 37, which may also drive the record sheet 51. When the cam 42 and disc 43 allow the arm 40 to fall, switches S1-S4 are operated to standardizing position, and the drum 35, carrying an adjusting slidewire 31 of the measuring network, is allowed to be driven by the balancing motor 26. Switch Sl replaces the output of filter 10 by a standard volttage from the A.C. supply, and S2 disconnects the normal balancing slide-wire 23, whereupon the rotation of the unbalance motor 26 will effect adjustment of slide-wire 31. Time delay network. A thyratron 54 normally energizes a relay winding 53 to close motor switch S5, but coincidental with the operation of switches S1, S2, two further switches S3, S4 short-circuit the bias for the grid of the thyratron for a short period, to deenergize the relay winding 53 and switching from measuring to standardizing and vice veisa. A further switch S7 prevents the temporarily stop the motor 26. This occurs in operation of motor 26 during standardization if the supply frequency is outside predetermined limits, being operated by a control cam 67 connected to the movable element of a frequency meter 66.