GB1150664A - A Frequency Meter - Google Patents

Abstract

1,150,664. Frequency discriminators. COMMISSARIAT A L'ENERGIE ATOMIQUE. 22 April, 1966 [22 April, 1965], No. 58438/68. Divided out of 1,150,663. Heading H3A. In a frequency meter, the A.C. signal whose frequency is to be determined is converted into a signal consisting of unidirectional pulses of the same frequency which are supplied to one input of a trigger circuit whose output is supplied with current from the time of arrival of one of the unidirectional pulses and until it receives a control pulse, derived from the output of a frequency divider, on a second input. The frequency divider is supplied with pulses of a higher predetermined frequency via a switch so connected to the output of the trigger circuit that it is held in its conductive state while the above output is supplied with current. The output of the divider is also supplied to an integrating current to provide an indication of the frequency of the original signal. A signal c, e.g. from a n.m.r. magnetometer as described and claimed in Specification 1,150,663, whose frequency is to be determined, is shaped by trigger circuit 23. The resulting rectangular pulses are then rectified and differentiated in circuit 24 to provide unidirectional pulses e which are fed to the trigger circuit 38 to open a gate 31 and allow reference pulses from a thermostated quartz clock 29 to pass through a differentiating circuit 50-52 to a frequency divider 34. The output m of frequency 204À8 kH2 from the clock is squared by Schmitt trigger circuit 30 and differentiated by a circuit 48-49. Once gate 31 has been opened, the divider 34 counts 1024 pulses before a signal is transmitted through differentiating circuit 53- 54 to an input 40 of the trigger circuit 38, which stops current flowing through the output 41 to block gate 31. Gate 31 is next opened by the arrival of the following pulse e at input 39. The output pulses from the frequency divider, corresponding to 1024 pulses K, are integrated by a circuit 42, 43 to give a direct voltage V 1 , proportional to the frequency to be measured. To reduce noise and thereby increase sensitivity, the measurement of the frequency is obtained from the difference between two voltages V 1 , V 2 , the latter being obtained by integration of the signal at output 37 of the divider 34. This difference voltage is supplied to a recorder (not shown), after filtering of the desired band, through an amplifier (not shown).