Patent GB-578818-A (GB)
Title: Improvements in instruments for measuring the frequency of an electrical oscillation
IPC: G01R23/00
Filed: 1944-05-01
Abstract: 578,818. Frequency measurements. GENERAL ELECTRIC CO., Ltd., and PHILLIPS, F. C. F. May 1, 1944, No. 8134. [Class 37] In a frequency meter of the type described in Specification 567,572, in which the digits are separately determined by beating with a standard oscillation of appropriate frequency and passing the difference frequency to the next stage, the indicating member associated with the set of standard oscillation carries the numerals 0 to 9 in duplicate and two elements such as lamps which displays one of these numerals and are alternately operable according to whether the stage has called for inversion or not. The apparatus shown is appropriate to the first stage of a series of generally similar stages in an instrument adapted to measure frequencies up to 100 kc/s. The first stage is provided with an additional section constituting a preliminary stage in which if the incoming frequency is less than 50 kc/s it is changed to a frequency exceeding this value by combining it with a frequency of 100 kc/s. This preliminary section has two positions JA, JB at which the frequency to be measured can be introduced by a plug. If the oscillation is introduced at JA it is applied to the primary of a transformer T1, the secondary of which is tuned by a condenser 2, operated by a dial 1, and feeds through an amplifier 17 a detector 18, which can be fed simultaneously through an amplifier 20. The detector output is fed to an indicator 3 which indicates when the direct voltage is a maximum. The detector 18 is fed through the amplifier 20 from the secondary of a transformer T2, the primary of which is fed from a multivibrator 15. This secondary can be tuned by any one of six condensers, selected by the switch 14, so that the fifth to the tenth harmonic of the multivibrator can be selected for application to the amplifier 20. The difference frequency from the detector 18 is applied to the second stage through a lead 19. If the incoming oscillation is introduced at JB it is applied to a modulator 21, the output of which feeds the primary of the transformer T1. The modulator 21 is also supplied with an oscillation of 100 kc/s selected by a series-tuned circuit 22, 23. The tuning dial 1 indicates the frequency on a scale 5 against fiduciary marks 4, 6. An indicator dial 16 is associated with the selector switch 14 and rotary reversing switches S. It bears in duplicate the numerals 0 to 9, any one of which can be selectively illuminated by one or other of lamps NL, IL. When the input is introduced at JA the contacts JA1 are closed and the lamp NL lights, whereas when the input is introduced at JB the lamp IL is lighted through the contacts JB1. The dials 1, 16 are lettered from A to K and the dial 16 is set with the letter opposite the mark 13 corresponding to the letter opposite the marks 4, 6 wheel resonance is indicated by the indicator 3. The selector switch 14 then selects the appropriate frequency from the multivibrator and one of the lamps NL. IL displays the first digit of the incoming frequency. The last two or three digits may be evaluated by the direct-reading means described in Specification 567,571, preferably modified as described in Specification 578,819.