ELECTRO-PNEUMATIC TRANSDUCERS.

This invention relates to transducers arranged to convert an electrical signal to a pneumatic signal.

Hitherto, in such a transducer, air from a 5. regulated supply is exhausted as a jet through a nozzle outlet to impinge upon a plane surface perpendicular to the axis of the jet. The distance between the nozzle outlet and the plane surface is varied by movement of the plane surface in a

10. direction parallel to the axis of the jet according to the strength of an electrical analogue signal and thereby produces a variation in the pressure of the air flow upstream of the nozzle outlet. The variation in pressure is utilised to produce a

15. pneumatic, actuating, signal.

Such an arrangement produces a non-linear relationship between the electrical signal strength and the pneumatic, actuating, signal. This gives rise to a non-linear relationship between input and 20. positioning output.

According to the present invention, a transducer arranged to convert an electrical signal to a pneumatic signal has a nozzle outlet through which air is exhausted from a regulated supply to

impinge upon a moveable plate, and is characterised by mounting the moveable plate on an electrical coil rotatably suspended in a magnetic field in a manner such that upon rotation of the coil against 5. a spring bias by passing the electrical ^' signal through the coil, the distance between the nozzle outlet and the plate is varied to produce a variation in back pressure in the air flow upstream of the nozzle outlet in direct proportion to the 10. electrical signal strength.

The invention will now be described , by way of example, with reference to the accompanying, partly diagrammatic drawings, in which:-

^" Figure 1 is a side elevation of one 15. arrangement of a transducer and a moving coil assembly; and

Figure 2 is a plan view of an alternative arrangement of a transducer utilising a similar moving coil assembly as that shown in Figure 1.

20. In one embodiment of the invention, an electrical coil 2 is mounted on stub spindles 4, 6 carried in end bearings 8, 10 positioned on a frame 12 secured to a permanent magnet assembly 14 of cylindrical form. The magnet assembly 14

25. includes an outer ring 16 and, spaced therefrom to

form a cylindrical gap 18, an inner solid cylinder 20 with the electrical coil 2 moveable through a restricted arc in the cylindrical gap 18. A hair spring 22 extends between one of the stub 5. spindles 4 and the frame 12 to provide a resilient bias against rotation of the electrical coil 2. Electrical connections 24, 26 to the electrical coil 2 are made through the stub spindles 4, 6.

A nozzle 32 is positioned to have an axis of 10. discharge substantially normal to the curved surface of the plate and a nozzle outlet 34 closely spaced from the curved surface plate 30. Rotation of the curved surface plate about the stub spindle axis varies the spacing between the nozzle 15. outlet 34 and the curved surface plate 30. The nozzle is connected to a regulated air supply source with a pressure tapping (not shown) in the connecting line. The magnet assembly and associated attachments are positioned within a 20. gas-tight enclosure (not shown) from which air is exhausted at constant velocity.

In operation, with air being exhausted from the enclosure at constant velocity, and the electrical coil un-excited or subject to a biassing

25. current a reference pressure is established at the pressure tapping in the line connecting the nozzle outlet to the regulated air supply source. Upon applying an electrical analogue signal to the electrical coil 2 a rotation of the electrical coil

30. will occur against the restraining bias of the hair

spring 22. Rotation of the electrical coil 2 is accompanied by rotation of the curved surface plate 30 thereby varying the spacing between the plate and the nozzle outlet 34 and hence the 5. pressure in the air flow upstream of the nozzle outlet to produce a variation in the pressure obtaining at the tapping and thereby produce a pneumatic output signal which will be directly dependent upon the electrical analogue signal 10. applied to the electrical coil.

In the arrangement shown in Figure 1; the curved surface plate and web of Figure 2 are replaced by a disc 36 mounted on the upper stub spindle with the plane of the disc at a slight

15. inclination to the radial plane. A nozzle 38 is positioned to discharge through a nozzle outlet 40 on an axis parallel to, but displaced from, the stub spindle axis closely superjacent an edge portion of the disc 36. Rotation of the electrical

20. coil 2 is accompanied by rotation of the disc 36 and produces a variation in the spacing between the nozzle outlet 40 and the plane surface of the disc. As in the arrangement described with particular reference t ^' o Figure -2, variation in the

25. spacing between the nozzle outlet 40 and the plane surface of the disc 36 produces a variation in the pressure obtaining at the tapping in the line connecting the nozzle outlet to a regulated air supply source dependent upon the strength of the

30. electrical analogue signal producing the rotation of the electrical coil 2.

It will be appreciated that, in both arrangements, care needs to be taken that the flow of air from the nozzle outlet 34 or 40 impinging on the adjacent plate 30 or 36 does not itself produce 5. rotation of the plate and hence introduce an inaccuracy in the relationship between the electrical analogue signal strength and the pressure obtaining at the pressure tapping.