GB1093760A - Improvements in or relating to electric measuring devices - Google Patents

Abstract

1,093,760. Electric selective signalling. SIEMENS A.G. Nov. 11, 1965, No. 47845/65. Heading G4H. [Also in Division G1] In an electrical measuring device four transducers e.g. strain gauges, are connected to form a bridge 9, Fig. 1, having the output diagonal connected in opposition with that of a second compensator bridge 10 through an amplifier 15 controlling a servomotor 14 which moves a sliding-contact 13 of a potential divider or potentiometer 12 until the two bridge outputs balance when the position of contact 13 indicates the output voltage of bridge 9. The input diagonals of bridges 9, 10 are fed by current transformers 5, 6 whose primary windings 3, 4 are connected in series with a low-resistance A.C. source, whereby the excitation currents of the two bridges have a constant magnitude ratio. Alternatively, the device comprises a single current transformer, Fig. 6 (not shown), whose secondary winding energizes the transducer bridge, whereas the primary winding energizes the second bridge or vice versa. Rectifiers may be included in the secondary circuits of the current transformers and a plurality of bridges formed by transducers may have their outputs connected in series each bridge being fed by a separate current transformer, Figs. 2, 3, 4 (not shown). A smoothing circuit may be included in the input circuit of the amplifier, Fig. 4 (not shown). The compensator bridge may be replaced by transformers 67, Fig. 5, having parallel-connected primary windings fed by a current transformer 61, the secondary windings being series-connected and tapped to provide decade steps. The output of the transducer bridge 63 is connected across the secondary windings of transformers 67 through an amplifier 64 whose output supplies a device 65 for comparing the output voltages of bridge 63 and transformers 67 and controlling a device 66 which effects appropriate connections to the tappings on transformers 67 so as to reduce the output of the amplifier to zero.