GB781167A - Measuring electrical potentials - Google Patents

Abstract

781,167. Photo-electric measurement. HILGER & WATTS, Ltd. Sept. 3, 1954 [Sept. 3, 1953], No. 24397/53. Class 40 (3). [Also in Group XXXVI] Apparatus for measuring a voltage comprises a double triode comparator circuit producing an output voltage, dependent in magnitude on the difference between the unknown voltage and a voltage increasing or decreasing from a fiducial valve at a known rate, which holds open a diode bridge switching circuit, energized from an A.C. supply circuit to excite an amplifier, phasesensitive rectifier and counter, until the output voltage is zero at equality between the unknown and comparison voltages, so that the switching circuit is closed and the counter stops at a value representing the unknown voltage. For measuring a photomultiplier voltage V integrated across a condenser C in the spectrochemical analysis apparatus described in Specification 727,410, there is provided a double triode V1 whose anodes are connected to a positive H.T. supply, grids are respectively connected to the voltage V and to a comparison voltage VR decreasing at a known time rate from a known initial value, and cathodes K1, K2 are connected to the negative H.T. supply over equal load resistances. The voltage between the cathodes is connected across the first diagonal of a comparison bridge comprising four diodes V3 to V6, whose second diagonal is excited with an alternating voltage at frequency f from transformer T1. Voltage VR initially greater than V is derived from the anode of a pentode V2 connected in an integrating circuit of the kind described in Specification 580,527, [Group XL], in which on arrival of a starting pulse at the suppressor grid the voltage VR linearly diminishes with elapsed time. When VR > V, the diode bridge is unbalanced to develop a voltage at frequency f across the second diagonal, which is transformer coupled to an amplifier, a phase-sensitive rectifier and a counter, which is started at the instant at which the fall in VR commences, and arrested at the instant at which V = VR and the difference therebetween is about to change sign. Then the voltage difference between the cathodes K1 and K2 is zero, the diode bridge is balanced, and the alternating voltage supplied to the counter chain is zero. It is stated that the rate of change of VR may be controlled by a further voltage in terms of which V is measurable.