GB899179A - Improvements relating to automatic weighing scales - Google Patents

Abstract

899,179. Measuring electrically. MEOPTA PRAHA NARODNI PODNIK. March 19, 1959, No. 9508/59. Class 40 (1). In a weighing-machine, Fig. 3, in which deflection of a pivoted beam by a load to be weighed displaces from a null position the core 8 of a differential transformer 2, suspended from one arm of the beam, the output of the transformer being amplified, rectified, and fed back to a solenoid 5 associated with a core of permanently-magnetized, preferably hard ferrite, material suspended from the other arm of the beam in order to exert a restoring force on the beam, the overall gain of the feedback loop and, therefore, the sensitivity of the device are variable. In Fig. 7, the differential transformer 2 comprises two primary windings 9, 10, connected in aiding series, two secondary windings 12, 13 connected in series opposition, and an earthed screen 11 between the primary and secondary windings. The differential output of the transformer 2 is amplified by a triode 22 having in its anode circuit the primary winding of a transformer 23 whose two secondary windings 24, 25 are supplied with voltages of equal magnitude and opposite phase from secondary windings 26, 27 of a main transformer. The appearance of a voltage on the primary of transformer 23 varies in opposite senses the outputs from secondaries 24, 25 which are rectified by bridges 28, 29 and fed to two identical coils 5a, 5b, comprising the solenoid 5 to produce oppositely polarized fields the resultant of which exerts the restoring force on the beam, and to produce a resultant current representative of the weight of the load, which is measured on a meter 6. The gain of the feedback loop is varied by changing the voltage input to the differential transformer 2 by actuation of a switch 34, or by altering the value of a rheostat 32 in the solenoid circuit; alternatively, a variable gain amplifier may be used. In a modification, Fig. 6, the secondary voltages of the differential transformer are amplified separately by a double triode 21 before being rectified and fed to the coils 5a, 5b of the solenoid; again the input voltage to the differential transformer may be varied, in this case by a potentiometer 17, or a rheostat 18 in the solenoid circuit may be varied. In another modification, Fig. 5 (not shown), the secondary outputs of the differential transformer are not amplified but are separately rectified by rectifier bridges and fed to the coils 5a, 5b. Differential transformer. Fig. 4.-This comprises a frame 7 having two coil chambers in each of which is wound a primary winding 9 or 10, and a secondary winding 12 or 13, separated by the screen 11. The magnetic core 8 is suspended within the central axial bore of the frame 7.