GB620166A - Improvements relating to electrical vibrometers - Google Patents

Abstract

620,166. Vibrometers. SMITH, R. B., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Aug. 19, 1946, No. 24657. [Class 106 (iv)] [Also in Group XXXVIII] A vibration detector comprises a mass seismically supported from a base and a magnetic circuit formed in two parts, one mounted on the mass and separated by two air-gaps from the other which is mounted on the base, the arrangement being such that vibration causes equal and opposite variations in the length of the air gaps so that the resultant current in the coil when closed through an external circuit is a measure of the amplitude of vibration. A seismic block 1 is supported above a base 2 by plate springs 3, preferably, all of non-magnetic material, the springs conveniently of beryllium-copper. Each limb of a magnetizable laminated U-shaped iron core 4, clamped in a channel in the base 2 and retained by pins 5, is wound with a coil 6 of about 10,000 turns rigidly secured thereto. A permanent magnet core 7 is bolted to the base 2 to form a third limb and can be magnetized after assembly through a coil 8. A core 9 of magnetizable material preferably laminated is rigidly secured to the seismic block 1 and completes a magnetic circuit across main air gaps 10, 11 and a subsidiary air gap 12. A pillar extending from the base 2 into a recess in the block 1 may be provided to limit the permissible relative movement, buffer pads may be provided to avoid shock. The assembly may be enclosed and sealed and an inspection window provided.