Patent GB-760542-A (GB)
Title: Improvements in or relating to electrical bridge networks
Inventor: DION WARREN EMIL
IPC: G05B1/02
Filed: 1954-09-04
Abstract: 760,542. Electric indicating systems. BRISTOL CO. Sept. 4, 1954, No. 25708/54. Class 40 (1). [Also in Groups XXXV and XXXVI] An electric measuring bridge network comprises a single ratio arm branch automatically or manually adjustable for balance, and plural measuring branches, each comprising a fixed and a variable impedance in series connected in parallel across an alternating voltage source with an unbalance responsive circuit connecting the junction of the ratio arms and the junctions of the impedances of the measuring branches; there being provided plural relays respectively. energized by a direct current traversing each variable measuring impedance which release in response to any open circuit therein to operate contacts disconnecting the appropriate measuring branch from the network. In Fig. 2, plural measuring resistances 10, 11, 12, 13 variable, e.g. in response to temperature or mechanical strain are connected in series at points 18, 19, 20, 21 with corresponding fixed resistances 14, 15, 16, 17 and normally closed contacts 61, 71, 81, 91 of relays 60, 70, 80, 90 across the secondary of an A.C. energized transformer 25, together with a common fixed resistance 33 and a. resistance potentiometer 30. The respective junctions 18, 19, 20, 21 are connected through normally closed relay contacts 62, 72, 82, 92 and series resistances 36, 37, 38, 39 to the input of an A.C: responsive servo system 40 returned to the slider of potentiometer 30, which is operative to adjust the slider for bridge balance and indicate on scale 32 a measure of the average value of the quantity to which the resistances 10, 11, 12, 13 are responsive. The relay coils (or high impedance to A.C.) are connected respectively between the junctions 18, 19, 20, 21 and a D.C. source 44 returned to the common connection of resistances 10, 11, 12, 13 so that on open circuiting of any of the latter resistances the associated relay is released and its contacts open to disconnect the faulty branch from the bridge, which is then readjusted to indicate the average value appropriate to the remaining operative measuring resistances. Lamps 64, 74, 84, 94 in series with the associated relay coils indicate the absence of faults in the measuring branches. In modifications resistance 14 is placed on the opposite side of the relay contacts (Fig. 3, not shown), and indicator lamps are provided to show operation and non-operation respectively of the contacts of each relay (Fig. 4, not shown). An audible signalling device may replace or supplement each lamp indicator. The measuring resistances may all respond to a variable condition at a single point or to plural variable conditions at different locations. The apparatus is applicable to automatic temperature control (Fig. 5); the slider potentiometer 30 being manually adjustable to present the temperature of an enclosure heated by burner 47 whose fuel supply is controlled by unbalance responsive servo system 40 controlling fuel valve 46. The temperature is measured by resistances 10, 11, &c. connected as shown in Fig. 2, and any bridge unbalance due to temperature deviation from the preset value causes the servo system to readjust the fuel supply so as to restore the temperature. In the systems described, the rebalancing adjustment may be manual. Specification 252,060, [Class 40 (i)], is referred to.