Patent GB-546754-A (GB)
Title: An improved means for enabling a direct-current voltage proportional to a frequency to be obtained
IPC: G01R23/02
Filed: 1941-02-01
Abstract: 546,754. Frequency measurements. TRIGGS, W. W. (Akt.-Ges. Brown, Boveri, & Cie). Feb. 1, 1941, No. 1340. [Class 37] For generating a direct voltage proportional to frequency two elements, one of which is saturable, are connected in series opposition and an impedance is connected in series so that proportionality between frequency and voltage is independent of the amplitude of the alternating voltage. In the arrangement shown in Fig. 4, two pentodes 10, 11 are fed in push-pull from a transformer 12, the primary of which is excited by the voltage the frequency of which is to be determined. In the plate circuit of each pentode is the primary of a transformer 16, 17 having a saturated magnetic circuit and a transformer 15 the core of which does not become saturated, these being connected in opposition. The transformer 16, 17 may be wound on a common core. The secondary windings of the transformers 15, 16, 17 are connected in series in the plate circuit of a rectifier valve 18. A resistance 19 is connected between the filament of the valve 18 and the mid-point of the secondary winding of the transformer 15. The valves 10, 11 supply currents of almost rectangular wave-form to the primary windings of the transformers 15, 16, 17 because the amplitude of the driving voltage of the grids is high, and the system gives compensated impulses on each of the anodes of the valve 18 in succession. The compensating impulse given by the unsaturated transformer 15 is spread out by means of a condenser 21 and resistance 20 connected across the secondary winding. A measuring instrument (not shown) having a moving system with considerable inertia is connected in series with the resistance 19. This measures the mean value of the current and therefore indicates the frequency. A filtered D.C. voltage for supplying other appliances may be obtained by connecting across the resistance 19 a filter comprising a resistance 22 and a condenser 23. Fig. 5 shows a modification for use in tele-measuring receivers giving indications between two particular frequencies and having means for adding or subtracting measurements. A first receiving device comprises a saturated transformer 30 and an unsaturated transformer 31 in series with a rectifier 32, a high resistance 33, a measuring instrument 34, and a totalizing instrument 35. A second receiving device, in parallel with the first comprises a saturated transformer 36 and an unsaturated transformer 37, a rectifier 38, and a measuring instrument 39. A current corresponding to the minimum frequency to be measured flows through a source 40 and resistance 41 and passes through the instruments 34, 35 in the opposite direction to the current i proportional to the frequency to be measured. In the second receiver the current of minimum frequency is compensated for by a resistance 42. Gas-filled valves may be substituted for the pentodes shown in Fig. 4. Instead of using an unsaturated transformer for compensating for voltage variation, a condenser discharging through a resistance may be employed.