Patent GB-1015074-A (GB)
Title: Improvements in or relating to frequency measuring devices
Inventor: SALVI ANTOINE
IPC: G01R23/00
Filed: 1962-06-14
Abstract: 1,015,074. Frequency measuring. COMMISSARIAT A L'ENERGIE ATOMIQUE. June 14, 1962 [July 12, 1961], No. 22943/62. Heading G1U [Also in Division H3] Apparatus for measuring the frequency F of oscillations a (Fig. 1) produced by an oscillator 1 e.g. a magnetic resonance maser oscillator for measuring variations in the earth's magnetic field comprises an oscillator unit 2 producing oscillations b 1 , b 2  of known frequency F 1 , F 2  respectively, a double mixer-unit 3 producing beat oscillations c 1 , c 2  of frequency f 1 =F-F 1 , f 2 =F 2 -F respectively, a waveform-shaping unit 4 converting oscillations c 1 , c 2  into complementary negative square pulses d 1 , d 2 , a generator 5 converting pulses d 1 , d 2  to saw-tooth pulses e 1 , e 2 , and a comparator unit 6 for determining the difference between the amplitudes E 1 , Eg of pulses e 1 , e 2  and hence frequency F, the variations in said amplitudes being proportional to variations in frequencie f 1 ,f 2  respectively. Comparator 6 comprises two variable potential dividers (Fig. 6, not shown) which are connected to a differential galvanometer and adjusted to produce at least approximately zero deflection in the galvanometer, the settings of the dividers and the deflection in the galvanometer providing an indication of the frequency F. When E 1 -E 2 =O, frequency F=<SP>1</SP>/ 2 (F 1 +F 2 ). Unit 2 (Fig. 2) comprises a quartz oscillator 11 producing sinusoidal oscillations g, a frequency divider 12 e.g. an astable multivibrator, producing rectangular pulses h of frequency F 0  e.g. 42.576 c/s, a generator 13 producing saw-tooth pulses i, two sets of circuits 14 1 , 14 2  selectable by ganged switches and which are tuned to successive harmonics n of frequency F 0 , and an amplifier, which includes a double triode 19, delivering oscillations b 1 , b 2  at its output terminals 21 1 , 21 2 , the frequencies of b 1 , b 2  being F 1  = n 1 F 0 , F 2  = n 2 F o  respectively, where n 2  - n 1  is a constant e.g. 10, established by appropriate tuning of circuits 14 1 ,14 2 . The double mixer-unit 3 comprises two identical channels each including a double-triode 22 (Fig. 3) to which oscillations a, b 1  (or a, b 2 ) are applied at grids 23, 25 as shown, a low-pass filter network 28 for frequency f 1  (or f 2 ), and an amplification stage which comprises a pentode 31 and has sufficient gain to permit adequate clipping of oscillation c 1  (or c 2 ) in the next stage of the apparatus. Unit 4 comprises two identical channels each including a double triode 37 (Fig. 4) and peak limiting circuits comprising diodes 36a, 37b, 39a, 39b which provide two stages of clipping of oscillation c 1  (or c 2 ) so that substantially rectangular pulses j 1 are received by a further double-triode 41 in a bi-stable multi-vibrator network. Rectangular pulses k 1 , produced by the multivibrator are applied to a differentiating circuit 43 and a negative pulse selecting circuit which includes diodes 44, 45 so that negative pulses m are received by a further multivibrator network comprising a double triode 46, the output of which has the form of complementary negative pulses na,nb. The final stage of each channel is formed by an amplifier comprising a double-triode 51 to convert pulses na,nb to pulses da, db, which are indicated by d 1  or d 2  in Fig. 1. Each of two identical channels in generator 5 comprises pentodes 60a, 60b (Fig. 5) which are rendered alternately conducting and non-conducting (one conducting whilst the other is non-conductive) by negative pulses da, db at terminals 59a, 59b acting through diodes 62a, 62b the pentodes being balanced by a voltage-stabilizing glow-lamp 60 and bridge 60c. Capacitors 55a, 55b are thereby alternately charged and discharged through the respective pentodes so that triangular pulses ca, cb are received by an OR circuit comprising silicon diodes 64a, 64b and a saw-tooth voltage c 1  (or c 2 ) is obtained by mixing of pulses ea, eb. The amplitudes E 1 , Eg of pulses e 1 , e 2 , can be varied by operation of a rheostat 65 in each channel. The galvanometer and potential dividers in comparator 6 may be calibrated in "gammas", one gamma being equal to 10<SP>-5</SP> oerstad.