GB844170A - Improvements in automatic differential balances - Google Patents

Abstract

844,170. Differential weighing-apparatus. COMMONWEALTH SCIENTIFIC & INDUSTRIAL RESEARCH ORGANIZATION. June 25, 1957 [June 29, 1956], No. 20061/57. Class 40 (1). A specimen is suspended from a differential balance system and an electromotive force proportional to the displacement of the balance from its null position is derived and integrated by a servomotor or a coulometer and maintains the balance substantially in its null position. The electromotive force necessary to do this is measured and gives the rate of change of weight of the specimen. In one embodiment (Fig. 2) the specimen 4 is suspended from an arm of a beam 2 attached to a torsion wire 1 fixed at 8 and attached via a torsion head to a motor through a high gear ratio at 14. A small A.C. signal is also applied to the motor in order to increase the linearity of its response. A lightsensitive cell at 10 is used to detect the displacement of the beam and the output of this device is fed through a magnetic amplifier and rectifier mixed with a bias from biasing means 17 and fed to the motor. This mixed output is also fed to a voltage divider 20 from where it is passed to a recording device 21. A slide wire 24 attached to the torsion head is fed with a small D.C. potential and its output is indicative of the cumulative weight change and is added to a small correcting voltage derived from voltage divider 20 for correcting the error due to the retarded position of the torsion head and is also fed to recorder 20. The specimen being weighed is contained in an electrical furnace and the temperature of this furnace is caused to vary linearly with respect to time and is also recorded on recorder 21. An alternative means of converting the deflection of the beam into an electromotive force using a phototransistor and an associated circuit is described. A further embodiment of the invention is described wherein the specimen is suspended from one arm of a balance and the silver anode of a coulometer is suspended from the other. The deflection as before is sensed by a light-sensitive device and the resultant signal is amplified and causes a current to flow through the coulometer to change the weight of the suspended electrode.