Patent GB-843525-A (GB)
Title: Improvements in or relating to electromagnetic devices
IPC: G01F1/50
Filed: 1958-04-21
Abstract: 843,525. Electromagnetic transducers. WESTINGHOUSE ELECTRIC CORPORATION. April 21, 1958 [April 30, 1957], No. 12542/58. Class 40 (1). A transducer of the type having a primary winding (A.C. energized) and a pair of secondary windings on opposite sides thereof, has aligned stationary hollow magnetic cores disposed adjacent to each winding and an armature which moves linearly relative to the core members, the spacing and dimensions being so chosen that there is a predetermined non-linear relationship between the movement of the armature and the coupling between the primary and secondary windings. Preferably the armature is displaced in accordance with pressure or fluid flow and the change in coupling is proportional to the square root of armature displacement. In Fig. 1 the rate of flow in a pipe 19 is measured in terms of the pressure difference across bellows 24, which are joined to the -pipe on opposite sides of the constriction 17. This pressure difference is proportional to the square of the rate of flow so that with the above arrangement the electrical output will be linearly related to the flow rate. The pressure difference displaces the armature 16 which is normally symmetrically disposed between the primary winding 10 and the coaxial secondaries 12, 14, so that the electrical outputs from the latter are no longer equal and opposite. The hollowed-out shape of the armature 16 and the positions of the hollow cylindrical cores 38, 40, 42 are so chosen that the electrical output of the two secondaries in series opposition is proportional to the square root of the displacement of the armature. The length of the reduced section of the armature is approximately the same as that of the core 38. The position of zero output may correspond to zero or a predetermined value of flow rate in the pipe. For other applications the square-root relationship may be modified by altering the positions of the cores (Fig. 3, not shown), which may be separated by air or other non- magnetic material. The armature is preferably enclosed in a sealed tube 18 to prevent loss of pressure. In further modifications (Figs. 5 and 7, not shown) the armature is dumb-bell shaped and each secondary winding is provided with two separated fixed cores in addition to the core of the primary winding; the outer pair of secondary cores are of reduced radial thickness. The electrical outputs of the secondaries can be applied in series opposition to an A.C. voltmeter, or preferably (Fig. 8, not shown) via bridge rectifiers to opposite ends of a centretapped load resistor across which is a centrezero D.C. voltmeter to show the magnitude and sense of the armature displacement. If the tap on the resistor is not at the centre, a greater weight will be given to displacement in one direction compared with the other. If the fluid in the pipe is compressible it is necessary to evaluate the square root of the product of pressure P and differential pressure dP (Fig. 9). Here a device 184, 188 as above gives a signal to the amplifier 206 representing #P, which can be indicated at 208 and used as input to a second device 216, 224 where #dP is measured. The output signal at 252 represents #P.dP and can be used via a servo mechanism to correct changes in the flow rate.