GB502881A - Improvements in and relating to amplifying systems - Google Patents

Abstract

502,881. Current and voltage measurements: BRITISH THOMSON-HOUSTON CO., Ltd. June 18, 1937, No. 17046. Void. Convention date, June 19, 1936. [Class 37] [Also in Groups XL and XXXVIII] Varying direct voltages are amplified and indicated by connecting the voltage source in series with a galvanometer and a balancing- resistance, the galvanometer being arranged to vary the light falling on a photo-cell in the grid circuit of a valve, the anode circuit of which includes the balancing-resistance and the indicating or recording instrument. As shown in Fig. 1, the source of voltage is a thermopile T which is connected in series with a resistance R1 and a galvanometer coil G. When the voltage source T varies, the coil G is disturbed and varies the amount of light passing from a lamp L to a photo-electric cell P. The voltage on the grid of a valve V is thus varied, and the plate current through the resistance R1 rises or falls intil the consequent voltage across the resistance R1 balances the new voltage of the source T. The voltage is indicated or recorded by a meter A in the plate circuit of the valve. To prevent selfoscillation, a condenser C is connected across the photo-cell resistance so as to prevent rapid changes in grid voltage. In the modification shown in Fig. 2, the meter A and resistance R1 are connected in one diagonal of a bridge the arms of which comprise resistances D, E, F and the valve V, the other diagonal being occupied by the supply source. The balance circuit G, T, T is connected as one diagonal of a second resistance bridge B, with a source H in the other diagonal. One resistance arm W is temperature-dependent, and is subjected to the same temperature variations as the cold junctions of the thermopile T with the object of balancing out the effects of variations in room temperature.