Patent GB-688443-A (GB)
Title: Improvements in or relating to smoothing circuits
IPC: G05D1/02
Filed: 1951-06-14
Abstract: 688,443. Radio navigation; valve amplifier circuits. BENDIX AVIATION CORPORATION. June 14, 1951 [June 17, 1950], No. 14127/51. Classes 40 (vi) and 40 (vii). In a circuit for removing undesirable H.F. components from the input data signal of an automatic control system, containing spurious irregularities and interference, to give a steady signal containing the required data from which interference is eliminated without time lag, the input signal is applied to an integrating low-pass filter network of long time constant passing a smoothed interference-free signal, whose resultant time lag referred to the input signal is connected by passing it through a phase advancing rate circuit whose time-constant is equal to or longer than that of the integrating low-pass filter circuit, to produce a resultant smoothed output signal voltage in phase with or leading in phase, the original input signal. An amplitude modulated A.C. aircraft control signal from a radio navagation system is coupled through transformer 1 and triode amplifier 9 to the parallel grids of discriminator triodes 27, 29, whose anodes are energized from A.C. source 47 in phase with the modulated signal frequency, through heater elements 41, 43 of a thermal time delay tube 45 of the kind described in Specification 603,610, [Group XXXVI], having a time constant of, e.g., 2 minutes. Thermally-responsive resistors 49 51 in heat exchange relationship with the respective heaters are connected as variable arms of a bridge energized from A.C. source 47, and the bridge unbalance signals energize the primary of a feed-back transformer 13 whose secondary is connected in series with the secondary of transformer 1 in the grid return of triode 9. The discriminator tubes are biased so that for zero signal the resistors 49, 51 have equal values at the middle of their normal thermal range to balance the bridge, and the input control signal (which may assume either of two 180 degrees displaced phase conditions) unequally heats the resistors in accordance with its phase sense to unbalance the bridge and develop a filtered integrated voltage across the secondary of transformer 13, having a time lag referred to the input signal but free from irregularities and interference. This voltage is connected through the secondary of feed-back transformer 61 to the grid of triode amplifier 65 energizing the grids of discriminator triodes 73, 75, which supply the heaters 77, 79 of a thermal time delay tube 81 whose thermally responsive resistors are connected in a bridge circuit as described above to energize the primary of transformer 61 when unbalanced by a time lagging integrated input signal. The time delay tube 81 has a time constant equal to or longer than that of the time delay tube 45, and the resultant voltage on the grid of tube 63 is the difference betweer the integrated time lagging input voltage and the feed-back voltage and is equivalent to a rate signal in phase with or leading the original input signal but free from interference; which signal may operate rudder or aileron control servo systems over lead 91 as described in Specification 679,560. The system is operable from D.C. signals if the transformers are substituted by magnetic amplifiers, e.g. of the kind described in Specification 647,961, [Group XXXIX].