Patent GB-759264-A (GB)
Title: Improvements relating to digital voltage measuring apparatus
Inventor: WOOD LESLIE
IPC: G01R1/28
Filed: 1953-04-13
Abstract: 759,264. Voltage measurement. METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. April 6, 1954 [April 13, 1953], No. 10052/53. Class 37. Digital measuring apparatus for voltages comprises a cascaded multi-stage potentiometer having plural graduated stages each of which consists of equal resistance elements in series separated by tapping points, and in which each higher stage is engaged by a pair of movable contacts separated by the space between alternate tapping points which energize the next succeeding lower stage; the unknown voltage being compared with the potentiometer voltage to develop an error voltage which operates control apparatus to automatically adjust each potentiometer in succession from the highest to the lowest to reduce the error voltage by successively finer adjustments, and there being provided means for numerically indicating the potentiometer settings at which the error voltage is zeroized and means whereby no potentiometer may be adjusted until the preceding potentiometer has been adjusted with the exception of the highest potentiometer which is initially adjusted. In Fig. 1 a voltage-measuring potentiometer comprises four interconnected tapered decade stages P1, P2, P3, P4 representing respectively 1000's, 100's, 10's. and units of which P1, P2, P3. comprise each 11 tapped sections and P4 comprises 10 such sections; P1 being traversed by a pair of movable contacts 1, 1<SP>1</SP> spaced 2 sections apart energizing P2, P2 being traversed by similarly spaced contacts 2, 21 energizing P3, which is traversed by similarly spaced contacts 3, 3<SP>1</SP> energizing P4; and P4 being traversed by a single contact 4 energizing an unbalance detector 12. Stage P1 is energized by a direct energization voltage at terminals 5 in series with resistances R3, R2, R1 such that the voltage drop across them is equal to that across one step of the potentiometer stage P1, the drop across R1, R2 is equal to that across one stage of P2, and that across R1 is equal to that across one stage of P3. A direct unknown voltage 6 is applied to point X at the lower end of stage P1 over switch 10 and normal relay contacts 7, 8, 9 to reduce the potential thereat and thus apply an error signal to the detector 12, which actuates a stage selector 13 operating relay contacts 7. The unknown voltage is now applied to the point X in series with the opposed voltage drop across R1, R2, R3 whereby the error voltage is reduced proportionately to one step of the 1st potentiometer stage. If the sign of the error voltage is unchanged the stage selector initiates stepping of contacts 1, 1<SP>1</SP> until the sign changes to arrest stepping and release relay contacts 7. A second similar cycle is initiated in which relay contacts 8 are operated applying the unknown voltage over resistances R1, R2 and stepping contacts 2, 2<SP>1</SP> until the error voltage again changes sign, after which a third similar cycle is initiated in which relay contacts 9 are operated so that the unknown voltage is applied over resistance R1 and contacts 3, 3<SP>1</SP> are stepped until the error voltage changes sign. Finally, contact 4 is stepped with the unknown voltage applied direct to point X with relay contacts 7, 8, 9 in their normal position to zeroize the error voltage, at which the unknown voltage is determined by the position of the successive decade potentiometer stages P1, P2, P3, P4, which may comprise uniselector switches having additional contact banks operating indicating or printing means for displaying the result. Each step of P1 may be e.g. 1000 ohms, of P2 200 ohms, of P3 40 ohms and of P4 8 ohms, while the reference voltage must be not less than the maximum voltage to be determined. Fig. 3 shows means for ensuring that succeeding potentiometer stage contacts are not stepped until the preceding contacts have completed their stepping, in which registration of a negative error voltage by detector 12 closes relay contacts Z1 to energize relays D3, X1 over the first position of uniselector S1 to operate contacts 7 (Fig. 1) and contacts X1 to start a multivibrator after a predetermined time delay covering the response of relay D3, and any subsequent change of sign of the error voltage. Oscillation of the multivibrator pulses relay Y1 over the 1st position of uniselector S2 to impulse the stepping uniselector of the potentiometer stage P1 until the error signal sign changes, and contacts Z1 open to de-energize relays D3 and X1. The resultant pulse at P steps uniselectors S1, S2 to their second positions and the cycle is repeated for the stepping uniselectors of potentiometer stages P2, P3 and P4 in succession until the error voltage is finally zeroized. The apparatus is also applicable to the measurement and recording of quantities expressible in terms of voltage.