Patent GB-1049851-A (GB)
Title: Improvements in or relating to measurement of electrical capacity
Inventor: HAMBERGER GERHART LOTHAR
IPC: G01R27/26
Filed: 1961-08-16
Abstract: 1,049,851. Electric selective signalling. SANGAMO WESTON Ltd. Nov. 15, 1962 [Aug. 16, 1961], No. 29608/61. Heading G4H. [Also in Division G1] In Fig. 3, a capacitor Cx to be measured is charged over switches R1, R2, R3 from a constant voltage source over transistor T1 controlled by transistor T3, while transistor T2 controls the discharge of Cx through moving coil movement 11. Switching voltages at terminals 1, 2 open transistors T3, T1 when terminal 1 is - ve and terminal 2 is +ve, and open transistor T2 on reversal of the polarity; the remaining transistors being cut off in each case. Opening transistor T1 and closing T2 charges Cx with the movement 11 inoperative, and when fully charged transistor T2 is opened and T1 closed to discharge Cx through the movement, which assumes a deflection representing the charge of the capacitance. A relay (not shown) is operated to change over switch contacts R1, R2, R3 whereby Cx is disconnected and a smaller capacitor Cq connected, to be charged through the movement 11 by again opening T1 and closing T2, so that the deflection is reduced by one step. The control voltage on 1, 2 is reversed, so that T1 is closed and T2 opened, to discharge Cq. The process is sequentially repeated by successive reversals of the control voltage until the deflection of the movement is zeroized, and a count of the discharges of Cq on a binary or other pulse counter measures the charge on Cx and represents its capacitance as a multiple of that of Cq. The moving coil movement may be shunted during discharge by a further relay contact and series resistance (Fig. 8, not shown). The phases of operation of the transistors and relay, and the successive reductions of the movement deflection are illustrated (Fig. 4, not shown). The pointer 12 of the moving coil movement is restorable (Fig. 5) to a zero position by an iron armature 30 co-operating with an electromagnet 31 in the required zero position, energizable to retain the pointer when it approaches zero and de-energized when its pointer deviates from zero; by obturation of the illumination of a photo-cell 15, this may be utilized in conjunction with the circuit of Fig. 3 to zeroize the pointer, to free it for deflection on discharge of Cx, to initiate successive charges of Cq to step the pointer towards zero, and to again zeroize the pointer and reset the relay controlling R1 to R3 in readiness for the next measurement. The pointer may carry an electrode interposable between two other electrodes at the zero position, which are connected to a voltage source, whereby zero restoration is achieved electrostatically (Fig. 9, not shown). The apparatus is applicable to the measurement of the number of subscribers connected at a given time to a radio or TV relay system. Specification 1,002,298 is referred to. The Provisional Specification (Figs. 1, 2, not shown) describes digital read-out of the deflection of the pointer utilizing a photo-electrically controlled servo-system deflecting a binary coded disc obturating illumination of a photocell, or a binary coded sector obturating light reflected to a photo-cell by a mirror carried by the movement.