GB2107474A - Displacement transducer - Google Patents

Abstract

A displacement transducer comprises a pot magnet having an annular pole 31 and a central pole 32 to sense the displacement D of a magnetic material target 41, the central pole 32 being secured at its end 32b which lies at the mouth of the magnet and being free at its other end 32a. Preferably a stainless steel closure body 44 of annular cup form is braced both to the annular pole 31 and central pole 32. Mineral insulated cable primary and second coils 33, 34 are sealed 37, 38 in the pot magnet. <IMAGE>

Description

SPECIFICATION Displacement transducer This invention relates to displacement transducers.

The Publication Nucl Energy, 1981,Vol 28, Feb No 1 pp 79-90 discloses (see Fig 2 on page 80) a high temperature displacement transducer, using mineral insulated (MI) cable winding, which is finding developing use for detection of movement in liquid metals, such as sodium, as used in a fast nuclear reactor.

The present invention is concerned with providing an improvement over the above disclosed device.

The displacement transducer of the present invention comprises: (a) a pot magnet having an annular pole and a central pole defining, with the annular pole, a mouth having a closure body of non-magnetic material, the magnet also having primary and secondary coils on the central pole; and (b) a member of magnetic material at the mouth of the magnet having a displacement capability relative to an element supporting the magnet; characterised in that the central pole is rigid with the annular pole at its end which is at the mouth of the magnet and free at the other end.

The invention is illustrated in a comparative manner with reference to the accompanying drawings in which: Figure 1 illustrates a transducer according to the invention; Figure 2 shows a set oftemperature correction curves for the transducer of Figure 1, and Figure 3 shows a set of temperature correction curves for the prior art transducer referred to above.

In Figure 1 there is shown a pot magnet 30 comprising an annular pole 31 and a central pole 32 loose fitting at the right hand end 32a into pole 31 but fixed at the left hand end 32b (magnet mouth). In the annulus between the poles two coils 33,34 of mineral insulated cable are wound, coil 33 being a primary winding and coil 34 a secondary winding.

The coils have respective connecting leads 35, 36 which pass through seals 37,38. A support block 39, to support the leads 35,36 and thereby avoid stressing the leads at seals 37,38, is tack-welded at 39a to pole 31. A stainless steel annular cup-shaped closure body 44 is provided and it is at this body that two brazes 45,46 are made to fix the central pole 32 in the annular pole 31.

A "target" 41 of magnetic material is shown which has a displacement capability relative to an element 47 in which the magnet 30 is secured at a flange 48.

A hole 49 is provided through the flange 48 to avoid pressure build up in the magnet during brazing of body 44 to the magnet. The hole is sealed after brazing is completed.

The transducer is responsive to variation in the dimension D between target 41 and pole 32.

A typical set of calibration curves for the transduc er described with reference to Figure 1 is shown in Figure 2 where variations of the distance D is shown as a variation in the output voltage V in coil 34. A typical working range is represented by D1 to D2.

The voltage V variation is temperature dependent as shown by the curves T1,T2, etc.

For comparison purposes, Figure 3 shows a typical set of calibration curves for the transducer of the prior art referred to above. Two points are observed from these curves when considered over the typical working range D1 to D2. First, the curves are widely spaced apart and this implies that there are large corrections to be made for small temperature changes, the corrections possibly being larger than the quantity V being measured; and second, the gradient of the curves change and hence automatic or calculated compensation becomes more difficult and may accordingly introduce further errors.

The curves of Figure 2 over the working range D1 to D2 and seen to be closely spaced (low temperature coefficient) and of similar gradients. This greatly reduces the problems of temperature compensation and leads to greatly improved accuracy of measurement.

1. A displacement transducer comprising: (a) a pot magnet (30) having an annular pole (31) and a central pole (32) defining, with the annular pole, a mouth having a closure body (44) of non-magnetic material, the magnet also having primary and secondary coils (33, 34) on the central pole - and (b) a member (41) of magnetic material at the mouth of the magnet having a displacement capability relative to an element (47) supporting the magnet; characterised in that the central pole (32) is rigid with the annular pole (31) at its end which is at the mouth of the magnet and free at the other end.

2. A displacement transducer as claimed in claim 1, suitable for use in hot liquid sodium, in which the body (44) closing off the mouth of the magnet is of stainless steel and the central pole (32) is sealed in this body, the coils (33,34) are of mineral insulated cable, and leads (35,36) to the coils (33, 34) are sealed (37, 38) in the pot magnet.

3. A displacement transducer as claimed in claim 1 or claim 2 in which the closure body (44) is of annular cup form and is brazed both to the annular pole (31) and the central pole (32).

4. A displacement transducer substantially as hereinbefore described with reference to Figure 1 of the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Displacement transducer This invention relates to displacement transducers. The Publication Nucl Energy, 1981,Vol 28, Feb No 1 pp 79-90 discloses (see Fig 2 on page 80) a high temperature displacement transducer, using mineral insulated (MI) cable winding, which is finding developing use for detection of movement in liquid metals, such as sodium, as used in a fast nuclear reactor. The present invention is concerned with providing an improvement over the above disclosed device. The displacement transducer of the present invention comprises: (a) a pot magnet having an annular pole and a central pole defining, with the annular pole, a mouth having a closure body of non-magnetic material, the magnet also having primary and secondary coils on the central pole; and (b) a member of magnetic material at the mouth of the magnet having a displacement capability relative to an element supporting the magnet; characterised in that the central pole is rigid with the annular pole at its end which is at the mouth of the magnet and free at the other end. The invention is illustrated in a comparative manner with reference to the accompanying drawings in which: Figure 1 illustrates a transducer according to the invention; Figure 2 shows a set oftemperature correction curves for the transducer of Figure 1, and Figure 3 shows a set of temperature correction curves for the prior art transducer referred to above. In Figure 1 there is shown a pot magnet 30 comprising an annular pole 31 and a central pole 32 loose fitting at the right hand end 32a into pole 31 but fixed at the left hand end 32b (magnet mouth). In the annulus between the poles two coils 33,34 of mineral insulated cable are wound, coil 33 being a primary winding and coil 34 a secondary winding. The coils have respective connecting leads 35, 36 which pass through seals 37,38. A support block 39, to support the leads 35,36 and thereby avoid stressing the leads at seals 37,38, is tack-welded at 39a to pole 31. A stainless steel annular cup-shaped closure body 44 is provided and it is at this body that two brazes 45,46 are made to fix the central pole 32 in the annular pole 31. A "target" 41 of magnetic material is shown which has a displacement capability relative to an element 47 in which the magnet 30 is secured at a flange 48. A hole 49 is provided through the flange 48 to avoid pressure build up in the magnet during brazing of body 44 to the magnet. The hole is sealed after brazing is completed. The transducer is responsive to variation in the dimension D between target 41 and pole 32. A typical set of calibration curves for the transduc er described with reference to Figure 1 is shown in Figure 2 where variations of the distance D is shown as a variation in the output voltage V in coil 34. A typical working range is represented by D1 to D2. The voltage V variation is temperature dependent as shown by the curves T1,T2, etc. For comparison purposes, Figure 3 shows a typical set of calibration curves for the transducer of the prior art referred to above. Two points are observed from these curves when considered over the typical working range D1 to D2. First, the curves are widely spaced apart and this implies that there are large corrections to be made for small temperature changes, the corrections possibly being larger than the quantity V being measured; and second, the gradient of the curves change and hence automatic or calculated compensation becomes more difficult and may accordingly introduce further errors. The curves of Figure 2 over the working range D1 to D2 and seen to be closely spaced (low temperature coefficient) and of similar gradients. This greatly reduces the problems of temperature compensation and leads to greatly improved accuracy of measurement. CLAIMS

1. A displacement transducer comprising: (a) a pot magnet (30) having an annular pole (31) and a central pole (32) defining, with the annular pole, a mouth having a closure body (44) of non-magnetic material, the magnet also having primary and secondary coils (33, 34) on the central pole - and (b) a member (41) of magnetic material at the mouth of the magnet having a displacement capability relative to an element (47) supporting the magnet; characterised in that the central pole (32) is rigid with the annular pole (31) at its end which is at the mouth of the magnet and free at the other end.

2. A displacement transducer as claimed in claim 1, suitable for use in hot liquid sodium, in which the body (44) closing off the mouth of the magnet is of stainless steel and the central pole (32) is sealed in this body, the coils (33,34) are of mineral insulated cable, and leads (35,36) to the coils (33, 34) are sealed (37, 38) in the pot magnet.

3. A displacement transducer as claimed in claim 1 or claim 2 in which the closure body (44) is of annular cup form and is brazed both to the annular pole (31) and the central pole (32).

4. A displacement transducer substantially as hereinbefore described with reference to Figure 1 of the drawings.