GB502500A - Improved electromagnetic measuring device - Google Patents

Abstract

502,500. Magnetic and inductance tests. TAIT, W. H. Oct. 12, 1937, No. 27675. [Class 37] A device for measuring pressures or very small movements comprises a U-shaped transformer core a carrying input and output coils b, d on its respective limbs and a magnetic diaphragm h to which the pressure or movement is applied to vary the air gap k, the required measurement being obtained from the changes in the output current of the transformer. For measuring heavy pressures, e.g. that between a screw and bearing block in a rolling mill, the member h, Fig. 1, comprises a circular steel diaphragm spaced from the poles by a washer i, while.for measuring small movements the air gap is provided by two diaphragms h<SP>1</SP>, 1, h2, Fig. 3, the space between which is filled with sponge rubber for damping out any vibrations that may occur, the movements to be measured being imparted through a needle o. Preferably, a balancing transformer is also used, the primaries of both transformers being supplied in series through a barretter from an A.C. supply, the secondaries of the transformers being connected through rectifiers in opposition, so that the measuring instrument, connected to indicate the difference current, normally reads zero and is deflected only on movement of the armature h or h<SP>1</SP>, h<SP>2</SP>. The apparatus may be used for measuring small changes in atmospheric pressure by disposing the armature at the centre of a flexible diaphragm separating two compartments, one of which houses the transformer and is subjected to the pressure variations to be measured, while the other compartment is maintained at constant pressure or evacuated. To reduce errors due to different temperature-coefficients of expansion of the core a and diaphragm h, the poles of the transformer core may be fixed to a disc separated from the diaphragm by a washer.