Patent GB-683903-A (GB)
Title: Improvements in or relating to an apparatus or a method of comparing electric quantities of different magnitudes
IPC: G01R31/36
Filed: 1950-02-07
Abstract: 683,903. Electric analogue calculating systems; measuring bridges; voltage and current measuring ; battery testing equipment. McCOLPIN - CHRISTIE CORPORATION. Feb. 7, 1950, No. 3115/50. Class 37. Relates to battery testing and discloses apparatus wherein an indicator produces a direct measurement of the prevailing difference between the maximum and minimum cell voltages. In the A.C. bridge circuit, Fig. 1, one arm associated with the three-cell battery 10 under test comprises three parallel connected identical transductors 15, 16, 17. It is demonstrated in the Specification that any bridge unbalance affecting voltmeter 41 is solely a function of the difference between the highest and lowest cell voltages. If, for example, the voltages of the cells are all different and the cells 11 and 12 designated E 1 , E 2  are the highest and lowest respectively, then in the transductor 15 the flux generated by the control winding 19 connected to cell 11 is greater than the flux generated by the oppositely wound control winding 18 connected to cell 12 and the nett flux proportional to the voltage difference produces a decrease in the inductance of transductor 15. Under these conditions the voltage of the cell 13 designated E 3  is at an intermediate value and the algebraic sum of (E 1 -E 2 ) (E 1 -E 3 ) and (E 3 -E 2 ) produces cancellation of E 3  and since the transductors are in parallel the current increase in the lower branch of the bridge 34 and the deflection on voltmeter 41 are both proportional to E 1 - E 2 . As shown, the other arm making up the lower branch of the bridge consists of another transductor 35 and this is pre-saturated and operated near the reversal point on its reactance-current curve so that for normal cell voltage differences its inductance increases with increase in current to produce a high standard of bridge sensitivity and for abnormal cell voltage differences producing excessive saturation in the transductors 15, 16, 17, the inductance decreases with increase in current whereby bridge sensitivity is low and damage to the voltmeter obviated. Fig. 1 is modified, Fig. 4 (not shown), by making each of the transductors 15, 16, 17 an arm in a separate bridge circuit and providing each bridge with a separate co-operating transductor 35 so that in totality there are three bridges in series, with the voltmeter 41 connected between the two end bridges. In other arrangements two transductors are associated with a threecell battery through a resistor connected across the battery. In one such arrangement, Fig. 2 (not shown), the two transductors form one arm of a bridge; in another, Fig. 5 (not shown), both transductors are in one bridge but in separate arms, and still another, Fig. 3 (not shown), similar to the latter incorporates a duotriode to provide an amplified out-of-balance voltage operating the voltmeter. Preferably the battery 10 is tested when the specific gravity of the electrolyte in the battery is at a value such that its resistivity is a minimum.