Patent GB-602996-A (GB)
Abstract: 602,996. Frequency measurements. GRAVES, A., DAWES, T. J., and ALLTOOLS, Ltd. Nov. 15, 1945, No. 30606. [Class 37] [Also in Group XXXVIII] In an apparatus for the detection and measurement of radiation, a Geiger - Miiller counter tube is connected to an integrating circuit through an impulse lengthener of adjustable time constant. In the embodiment shown, the cathode 2, of Geiger-M³ller counter tube 1, is connected to the grid of valve 3, which with its associated circuit elements constitutes an extinguishing unit of the Neher-Harper type for tube 1. In'this the valve 3 is normally biassed to cut-off, but on tube 1 becoming conducting; in response to the incidence of radiation, the valve 3 passes current and the voltage drop across resistor 5 extinguishes tube 1 and the valve 3 becomes again non-conducting. The provision of variable grid-bias to valve 3 by potentiometer 6 permits the use of counter tubes with.varying characteristics and effects the elimination of weak or unwanted signals. The output of valve 3 is passed through condenser 7 to the multivibrator comprising valves 8, 9, which are respectively an amplifier normally biassed. to conduct and a power valve biassed beyond cut-off. With switch S at the left-hand position, the anode of valve 9 is connected to H.T. supply line 14 through the mechanical counter 17 and at the right-hand position, through the resistor 20 of the same resistance as coil 17. Switch S2 connects the anode of valve 9 with the grid of valve 8 through one or other of condenser 23a, 23b. Switches S1, S2 move together and in the position shown the multivibrator is adjusted to give long pulses which operate the mechanical counter. With the switch arms S, S2 at their other contacts, the condenser 23b is in circuit, and being smaller than condenser 23a, conditions the multivibrator for the production of short pulses which are received by an integrating circuit in place of the counter. The integrating circuit comprises a valve 29, the anode current of which passes through meter 30 and the grid of which is connected to the moving contact of potentiometer 32, connected across the tank circuit comprising condenser 31 in parallel with resistors R1, R2, R3, R4 selected by switch S3 as the rate of reception of pulses changes. Condenser 27 and rectifier 28 protect the grid of valve 29 from the potential of line 14. With no impulses from the multivibrator to the grid of valve 29, the current through the valve is a maximum and the meter 30 gives a full scale reading which with the application of impulses' to the grid, is reduced corresponding to the integral thereof. In a further embodiment, not shown, the counter is dispensed with and a stylus is incorporated in place of the meter 30 which operates on a chart moved in synchronism with the spectrometer table. It is stated that the operation of the multivibrator may be regulated by resistors instead of alternative condensers and that scaling units may be employed to reduce the number of pulses fed to the counter or integrator. The embodiment described in the Provisional Specification incorporates two amplifying valves before the multivibrator, a double triode, and the counting 'device is associated with a separate power valve. A phase-reversing valve links the multivibrator to. the integrating circuit.