GB1082241A - Improvements relating to self-balancing electrical measuring apparatus - Google Patents

Abstract

1,082,241. Electric selective signalling. H. TINSLEY & CO. Ltd. April 10, 1964 [Jan. 16, 1963], No. 1935/63. Heading G4H. A self-balancing electrical measuring apparatus comprises two digital systems of the type described in Specification 918,415, one of the systems determining rapidly the most significant digits and making corresponding adjustments to the other system which then determines the least significant digits. In Fig. 1 a voltage V to be measured is connected by a switch 28 to terminals 19 and 20 and balanced against the voltage across resistance 16, as described in Specification 918,415, by means of decade counters T1-T4 which control respective conductance arrays C1-C4 and corresponding indicators N1-N4 which indicate the four most significant digits. Switch units T1-T4 also control relay units R1-R4 which switch precision conductance arrays C<SP>1</SP>1-C<SP>1</SP>4 into the same condition as C1-C4. Resistance R16 is chosen so that at balance the fourth digit is too high by one digit. At balance, selector TB moves from position 6 to position 7 thereby causing switch 28 to apply the voltage V to the terminals 19<SP>1</SP> and 20<SP>1</SP> of the precision circuit. As the setting is too high the first error pulse from switch 21<SP>1</SP> is positive and passes through switch 102 to lead 103, the zero contact of switch 105 (which is controlled by decade counter T5), and through diode D1 to step stage T4 down one digit. The setting now being too low the next error pulse is negative and passes through D2 and inverter 107 to step stage T5 down from 0 to 9 and cause switch 105 to move to its 1-9 contact. Succeeding positive pulses pass through D3 to step T 5 down to its correct value, and when this is achieved the next negative pulse switches the switch 102 so that its output goes to lead 104 and adjusts the final stage S6 in a similar manner. If the voltage V should fall during the measurement, stages T5 and T6 attempt to secure a balance but if they both fall to zero before balancing a positive pulse passes through D5, inverter 110, and closed switch 105<SP>1</SP> to a relay 73 which causes the whole measurement process to start again. If the voltage V rises, a negative pulse on contacts 1-9 of switch 108 operates relay 73; if contact 0 of switch 108 is engaged the pulse steps the stage T6 to 9 and the next pulse will operate the relay. Switches T2C-T4C are closed only when their respective stages are at zero and allow the preceding stage to be stepped back one digit when a stage is stepped from zero to nine by a pulse from D1. The circuit shown can be turned into a bridge circuit for measuring resistance by connecting the unknown resistance across the moving contacts of switch 28 and connecting suitable fixed resistances between points C and D and between points C<SP>1</SP> and D<SP>1</SP>.