GB2228571A - Electromagnetic measuring probe - Google Patents

Description

roll, 1 TITLE: DEVICE FOR A MEASURING PROBE The invention relates to a

device according to the preamble of the main claim. This preamble is based on the measuring probe T3.3 in prior public use, order no. 801.16.01 of the applicant, which comes closest to the subject of the invention. Probes and parts of probes of the same generic type are described in German Offenlegungsschrift 3,437,253 and in US Patent Specifications 2,933,677, 3,761,804, 4,005,360 and 4,041,378. Such measuring probes are used, for example, to measure the thickness of varnish coatings, the layer thickness of metal layers on base metals etc. The layer thicknesses representatively lie between several hundred micrometers and several tens of nanometers.

These devices are undoubtedly measuring devices which measure in a nondestructive manner.

It has, however, been noticed that inexplicable measuring errors occur during the measuring of very 1 i - 2 i layers and it is known that, when measuring some surfaces which are polished bright, impairments of the gloss occur in spite of the nondestructive measuring.

The application points on the layers to be measured, on which the convex end face was placed, have been inspected and it has been seen that considerable dents occur here. In manual application.. there are both dents and scratch marks, which lead from the place where the convex end face sets down to the actual meas- uring point. Even if these probes, which are in fact intended for manual operation, are applied carefully using a stand, for example to aluminum, there are indentations. If the aluminum is anodized, the outermost, thin layer may collapse, similar to the encrusted surface on old snow when it is trodden on. A representative depth of such impressions is for example around one micrometer. If the liyer is, for example, 120 micrometers thick, this of course makes relatively little difference. The thinner the layer, the greater the error. If the indentation is 1.5 micrometers and the layer to b.e measured is likewise 1.5 micrometers thick, a measuring error of 50% is produced by the indentation alone, to say nothing of measuring in the nanometer r a n 9 e.

The object of the invention is to avoid such indentations to such an extent that the error either does not arise at all or remains negligible.

According to the invention, this object is achieved by the defining part of the main claim.

i 1 i i 1 i 1 i i i 1 i i 3 - It has namely been found that, in the case of the known probes, it is the probe mass together with a contribution of the cable mass, which has its energy destroyed by the indentations. The energy destroyed is after 2 all, E = 112 x m. x f Even if should be careful when applying sneed comnonent increases with a the user is told he it, nevertheless the power of two. However, the mass m can be influenced by the design and this is where the invention comes in.

It should be pointed out that on the outside of the probe T3.3-there is indeed a sliding sleeve which is in effective connection with the probe body by a spiral spring. However, this helical spring does not uncouple at the first instant at which the convex end face is applied. At the beginning of contact, the system can be regarded as a rigid body. In addition, the spring force of the helical spring is approximately 100 ponds, which has an effect on the very small convex end f a c e.

The half-pot core may representatively have an outside diameter of 3 mm and is 13 mm thick in the middle. Tbus it has virtually a mass of zero. The same applies to the coil device.

The spring device may be very soft, for example in the lower decipond range and may also itself be very lightweight, since after all the mass to be held is negligible. The active circuit enables the continuing cable to be thinner and thus lighter and more flexible. Until now, it was therefore approximately 4 mm thick, - 4 because a cable had to b-e chosen of which the cores do not suffer if the cable is wound up or otherwise twisted. On the other hand, the active circuit can already emit a useful signal, for example phase-coded andlor frequency-coded andlor amplitude-coded, and in the frequency coding in particular it then no longer matters how the cores lie in the cable.

The features of claim 2 achieve the effect that the spring device does not have to engage the coil body, that a carrier is provided for the half-pot core and that the length of the tappet element can be used for longitudinal guidance.

The features of claim 3 have the effect that the tappet element is lighter and the extremely thin leads lie protected, not only from a mechanical aspect but also for example against acid vapors, alkaline vapors etc.

The features of claim 4 have the effect that the through-bore can be produced easily, the leads have allround protection and the mass distribution of the tappet element is symmetrical, seen axially.

The features of claim 5 have the effect that the tappet element can be produced easily, its mechanical properties are easily comprehensible and it adapts to the coaxial design of the probe.

The features of claim 6 have the effect that the tappet element is even light-er. It is best if it consists of titanium.

The features of claim 7 have the effect that 1 i i 1 i i i i the tappet element is sufficiently long for the guidance but short enough for weight purposes.

The fe-atures of claim 8 have the effect of preventing he spring device being overloaded if the tappet element is pushed too far into the probe. In addition, they have the effect of limiting how far galvanic lines of the conductor device can be bent off in the interior of the probe.

The features of claim 9 have the effect of pre- venting an excessive deflection in radial direction, which relieves the spring devices and also makes it possible to provide just a small gap between the halfpot core and the front region of the tappet element.

The features of claim 10 have the effect of avoiding a flexible line between the half-pot core and the conductor wafer. In fact, the conductor wafer could also be provided such that it is fixed to the body. However, then film conductors would be necessary, which although they are mass-produced articles, their fixing presents soldering problems. The capabitity exists of producing conductor wafers together with active circuit with a weight of 0.5 grams, which is quite acceptable.

The features of claim 11 have the effect that 2-5 the spring device is small and short and the spring forces are introduced into the tappet element.

The features of claim 12 have the effect that the spring devices are minimally small and therefore have little mass. With radial arrangement, they can also be fixed well.

The features of claim 13 have the effect of creating defined fixing regions on the spring device, making its behavior become clear and assembly simple.

The features of claim 14 have the effect that the spring device has the same properties on all sides and no preferred or disadvantaged regions occur.

The features of claim 15 have the effect that, in spite of the smallness of the spring devices, they 10 can be made soft.

The features of claim 16 achieve the effect of a rigidity in radial direction, so that the convex end face lies fixed in this direction.

The features of claim 17 have the effect of allowing for the coaxial design of the probe and giving the wafer the same properties in alldirections.

The features of claim 18 have the effect of avoiding internal stresses in the wafer, which occur for example during the punching operation, so that then the wafer follows Hook's law over its entire stroke.

The features of claim 19 have the effect that the spring device can absorb the lateral forces without the occurrence of friction and otherwise required longitudinal guidance mechanisms.

The features of claim 20 have the effect of allowing for the coaxial design of the probe, making the behavior of the spring device clear and the distance from retaining ring to retaining ring t he same everywhere. As a result, the components holding the 1 i i 1 i i 1 1 i 1 i ---- i 7 retaining rings in place can likewise be designed clearly and simply.

The features of claim 21 have the effect that the spring devices also prevent any movement of the half-pot core.

The features of claim 22 have the effect of facilitating the production, storage and assembly and of making the behavioral properties beco.me more c 1 e a r.

The material according to claim 23 is particularly well suited for the purposes concerned.

The features of claim 24 have the effect that the tappet element remains lightweight, clear in design, that few parts are required and that a secure seating of the inner retaining ring on a very large surface is obtained.

The features of claim 25 facilitate assembly and mutual retention.

The features of claim 26 have the effect that the outer retaining ring can be retained over a large area and mechanically clearly as well as simply in terms of assembly. Parameters according to claim 27 have proved very successful in the case of'an actual probe. 25 Features according-to claim 28 are also possible without monolithic, integrated and thus, in view of the numbers, currently scarcely cost-effective semiconductor circuits and do not prevent the object of the invention being achieved.

The features of claim 29 have the effect of avoiding having to clean the probe after each measurement when measuring in corresponding environments. Rather, many points can be measured one after the 5 o t h e r.

A coating according to claim 30 is very abrasion resistant and also easy to machine.

A coating according to claim 31 is not only abrasion resistant and acid and alkaline resistant. In addition, it does not absorb any moisture, so that the coil device is also not influenced by moisture.

The features of claim 32 prevent a lateral ingress of vapors or liquid to the-half-pot core.

Features according to claim 33 are suitable in particular for probes which have to measure on very soft material andlor have to measure in the lower measuring ranges of this measuring technique.

The features of claim 34 have the effect of minimizing the properties of the cable which are damaging with respect to the invention.

Values according to claim 35 have proved successful with even far better measuring properties.

The invention is now described with reference to exemplary embodiments. In'the drawing:

Fig. 1 shows a measuring probe on a scale of 1:1, partially exploded, Fig. 2 shows a radial section through the lower to middle region of the assembled probe according to Fig. 1, shown to scale, i i i i i i 1 i - 9 Fig. 3 shows a section through the assembled probe of Fig. 1, shown to scale, Fig. 4 shows a plan view of a spring platelet, on a scale of 1:5, Fig. 5 shows the plan view of a further spring platelet, on a scale of 1:5, Fig. 6 shows the lower region of Fig. 2 once again, enlarged by a factor of 1.55, for a 2nd exemplary embodiment.

A single-pole measuring probe 11 has a body 12 consisting of aluminum, which is substantially tubular and coaxial to a geometrical longitudinal axis 13. The measuring probe 11 is connected via a two-core cable 15 of 2. 5 mm thickness, fixed against tensile stress by a grub screw 16. Protruding into the upper region of a coaxial hollow space 17 are two pins 18, 19, to which two very flexible litz wires 21, 22 are connected. In order that the upper ends of the litz wires 21, 22 are soldered on, a window 23 is provided over the middle of the one-piece body 12. There a conductor wafer 24 can also be seen. This is 5.9 mm wide and 29.3 mm long. Since the representations are to scale, the dimensions of the other parts can be obtained from this. The geometrical longitudinal axis 13 runs centrally through the conductor wafer 24, with respect to its he.ight, its width and also its length. It bears electric components 26 and at least one active component 27, which are only symbolically indicated however. The components 26, 27 have their output in the soLdering points - 10 28, 29 and emit a frequency-modulated voltage corresponding to the measurement result. The litz wires 21, 22 are much longer than in fact corresponds to the greatest distance between the pins 18, 19 and the sol- dering points 28, 29. They are designed as loops and offer virtually no mechanical resistance when the conductor wafer 24 approaches the pins 18, 19. The conductor wafer 24 lies freely in the hollow space 17 and does not touch its inside wall 31. A coaxial and circular-cylindrical fixing flange 3.2 is coaxial to the longitudinal axis 13. Its disk-shaped head 33 is provided, in the plane of the drawing of Fig. 2, with a slit 34, in which the lower edge region of the conductor wafer 34 is fixed by adhesive 36. The fixing flange 32 does not touch the inside wall 31 anywhere and goes downwards into a circular-cylindrical annular neck 37, which likewise lies coaxially. Centrally, the fixing flange 32 has a through-bore 38, provided upwards with a chamfer. The fixing flange 32 consists of plastic and is thus on the one hand better able to adhere with respect to the conductor wafer 24 consisting of plastic and also has a high electric insulation resistance. In the through-bore 38 there is fitted axially immovably, connected to the fixing flange 32, the upper r.egion of a central tube 39 of a tappet el.ement 41, which consists of titanium. The central tube 39 has a throughbore 42, which at the bottom goes into a first cylinder space 43 and even further down into a still larger cylinder space 44. From the conductor i 1 i i 1 i 1 i i i i i i i i i - 11 wafer 24 there leads downwards two very thin lines 46, 47. Immovably seated in the cylinder space 44 is a core housing 48, which in fact takes up the entire cylinder space 44, but is provided with a slit 49, which lies in the plane of the drawing of Fig. 2, so that the lower region of the lines 46, 47 can pass further downwards. In a circular-cylindrical receptacle 51 at the end of the core housing 48, there is seated a half- pot core 52. It is provided downwards with a hemispherical surface 53, on which the end face 54 of its outer wall 56 and the end face 57 of its inner wall 58 also lie. Between the outer wall 56 and the inner wall 58 there ties a coaxial annular winding space 59 for a coil 61. The winding space 59 is cast at the bottom, so that the coil 61 is protected and retains its position.

Coaxially to the geometrical longitudinal axis 13, the half-pot core 52 has a blind hole 62, which is open at the bottom and in which a sapphire 63 is seated, the convex end face 64 of which lies in the hemispherical 20 surface 32. In order that the lines 46, 47 can pass through the slit 49 into the winding space 59, the halfpot core 52 likewise has a slit 66 as a continuation of the stit 49. The slit 49 and 66 is cast with resin. The tappet element 41 has in its lower region 67, according to Fig. 2, an. outwardly projecting, coaxial, radial collar 68. It lies approximately on a level with the cylinder space 43, above the cylinder space 44. Its upwardly directed coaxial, radial annular surface 69 forms the one side of a stop, the other side of which is formed by a complementary annual sur face 71, which is part of a C-shaped o.r G-shaped receptacle 72, which is arranged so as to be fixed to the body. After a distance of 0.8 mm, the annular sur face 69 strikes the annular surface 71. A downwardly directed coaxial, radial annular surface 73 also forms a stop half together with a smaller, radial and coaxial annular surface 74 of the receptacle 72. After a move ment of 0.8 mm outwards, the annular surface 73 strikes the annular surface 74. The collar 68 has an axially directed, coaxial, downwardly pointing, narrow member 76, which partially protrudes into the lower inlet 77 of the receptacle 72 and there partially overlaps axially an inwardly directed member 78. The clearance between the one member 78, representing a circular ring, and the other similarly formed member 76 is 0.3 mm on both sides in each case and the lower region 67 can, for example, be deflected to the right or left by this amount before an overload protection occurs. The receptacle 72 is of two parts and consists of an inner L-ring 79, the cross-member 81 of which bears the down wardly directed annular surface 71 and in normal operation does not touch the collar 68 anywhere. At the top, the cross-member 81 has a downwardly directed chamfer 82, in order that a spring-element, still to be discussed, can bend unhindered. On the outside, the L ring 79 is held by the inner wall 31, which has a greater diameter there, due to an outwardly directed step 83, than for example in the region of the i i i i j i i i i i 1 - 13 conductor wafer 24. A lug 84 of the longitudinal member 86 is bent outwards into an axially and radially extending slit 87 of the body 12, which lies in the plane of the drawing of Fig. 2. Therefore, the L-ring 5 79 and the parts adjoining it can no longer turn. The L-ring 79 is thus at the same time also a locking washer. The second part of the receptacle 72 consists of a C-ring 88. It has an external thread 89, with which it is screwed into an internal thread 91, which begins at the bottom on an annular surface 92 of the body 12. The outer wall 93 of this C-ring 88 extends up to the level of the cylinder space 43. Its radial, coaxial and circular-cylindrical cross-member 94 is relatively thick for mechanical protection and lies with its outer surface 96 above the annular surface 92. From the cross-member 94, the upwardly directed member 78 goes off. Between the member 78, the cross- member 94 on the one hand and the holding wall 97 of the tappet element 41, bounding the cylinder space 44 on the outside, there is a small gap 98, which hinders or excludes the ingress of foreign bodies. As can be seen, the gap 98 is the beginning of an also sealing labyrinth, which is directed outwards after the gap 98, then again directed downwards, then again directed outwards, then directed upwards and, underneath the annular surface 71, is again directed inwards. once the gap 98 has narrowed to zero, it also serves at the same time as radial stop against overloading and excessive deflection of the tappet element 41 and of the - 14 parts connected to it, in radial direction.

Two identical spring platelets 99, 101 position the tappet element 41, and the parts connected to it, relative to the body 12, the half-pot core 52 in par- ticular being retained extremely accurately coaxially to the geometrical longitudinal axis 13. The spring platelet 99 is 0.05 mm thick and consists of Cu-Be2. Its outside diameter is 9.6 mm and the inside diameter is 2.8 mm. It lies concentrically to the geometrical longitudinal axis 13 and has an outer retaining ring 102 and an inner retaining ring 103. These are continuously annular. Three spring arms 104 are provided angularly offset by 1200 in each case, which run over the majority of their length on radii about the geometrical longitudinal axis 13 and are joined in their end regions by roots 106, 107, on the one hand to the inner retaining ring 103 and on the other hand to the outer retaining ring 102. Since the roots 106, 107 have extremely rounded transitions, the extended S-shaped slits 108 are produced. According to Fig. 6, spring platelets 109, which likewise have an outer retaining ring 111 and an inner retaining ring 112, may also be used. Here slits 112, 113, 114 and 116 are provided, the slits being somewhat less than 1200 long in each case. As a result, 0.4 mm wide webs 117 remain between them, to be precise three webs 117 in each case, due to the 1200 arrangement. However, the group of slits denoted by 113 are offset by 600 with respect to the group of slits denoted by 112. -The slits denoted by 1 i i i i i i 114 have the same offset with respect to the slits denoted by 113, etc. The pattern shown in Fig. 6 is thus produced. The spring platelet 109 is 0.2 mm t h i c k.

According to Fig. 2, the outer retaining ring 102 of the spring platelet 99 is clamped between the radial, upwardly directed end face 118 of the cross member 81 and the downwardly directed end face 119 of a sleeve 121. The sleeve 121 is circular-cylindrical and coaxial and does not touch the tappet element 41 any where. The sleeve 121 can be pushed in from below with backlash towards the inner wall 31 and has an inwardly directed bulge 122. At the top, the sleeve 121 has an upwardly directed end face 123, between which and the step 83 the outer retaining ring 102 of the spring platelet 101 is clamped in place. A further effect of this design can thus be seen: If the C-ring 88 is screwed upwards, it presses the L-ring 79 upwards, without being able to twist it due to the lug 84. The latter presses the sleeve 121 upwards and consequently the outer retaining rings 102 of the spring platelets 99, 101 are also held exactly, level and sharp-edged, both by non-positive connection and also by positive connection. At the level of the end face 119, the cen tral tube 39 has a radial,-coaxial, upwardly directed end face 125, on which the inner retaining ring 103 of the spring platelet 99 rests. On this upper side, again there lies a radial, coaxial, downwardly directed end face 124 of a spacer sleeve 126, which fits with i i its inside diameter onto the central tube 39. At the level of the end face 123, the spacer sleeve 126 has an upwardly directed end face 127, which is coaxial, radial and level and on which the underside ofthe inner retaining ring 103 of the spring platelet 101 rests. on the upper side of the inner ring 103 lies a downwardly directed end face 128 of the annular neck 37, which is radial, coaxial and level. If the fixing flange 32 is pressed downwards with collar 86 held in place, and the fixing flange 32 is fixed by adhesive on the central tube 29, the inner retaining rings 103 of the spring platelets 99, 101 are held non-positively and positively in place.

The body 12 has in the region of the grub screw 16 right at the top an external thread 129. Its outer surface 131 is circular-cylindrical up to an outer ring 132. This has a radial, coaxial, upwardly directed, annular end face 133 and a downwardly directly, radial, coaxial and annular, but further inwardly jutting end face 134, which faces downwards. In the outer ring 132 there is a through-hole 136, through which one of the passive components 26 on the conductor wafer 24 can be adjusted with a screwdriver. Underneath the end face 134, the body 122 goes over into a coaxial, circular- cylindrical outer surface 137,.. the outside diameter of which according to Fig. 3 is smaller than the outside diameter of the outer surface 131. Underneath the end face 134, the outer surface 137 extends 6.8 mm wide. Knocked perpendicularly into a corresponding i i 1 i i 1 i i i i bore, so as to be immovable, is a radial stop pin 138. To the extent that the stop pin 138 protrudes from the outer surface 137 with its head, the head 141 is seated in a tangential slit 139, which runs in circumferential direction of a circular-cylindrical sliding sleeve 142, as Fig. 1 shows particularly clearly. Axially, the tangential slit 139 is wide enough that the upwardly directed, coaxial and annular end face 143 c.an strike against the end face 134. The stop pin 138 allows a downwardly directed movement of the sliding sleeve 142 only until the head 141 strikes against the upper wall 144 of the tangential slit 139. Downwards relative to the body 12, the sliding sleeve 142 is... (sic) by a helical spring 146, which is seated in a circular- cylindrical, coaxial hollow space 147, which is formed on the outside by the inner wall 148 of the sliding sleeve 142 and on the inside by an outer wall 149 of the body 12, which is produced by a coaxial downward facing shoulder 151 on the outer surface 137. The wall 149 runs level up to the annular surface 92. At the bottom, the helical spring 146 is supported on an upwardly directed, coaxial, annular end face 152, which is produced by the fact that the sliding sleeve 142 has approximately from the upper region of the collar 68 a diameter reduction 153. There the sliding sleeve 142 guides itself with slight backlash by its coaxial, circular-cylindrical inner wall 154 against the outer wall 149 of the body 12. At the top. the guidance between the outer surface 137 and the inner wall 148 - 18 takes place with slight backlash. The expansive stress of the helical spring 146 makes the head 141 bear against the wall 144. Its force is about 60 ponds and is thus substantially less than the spring force of the probe T3.3. The sliding sleeve 142 has at the bottom a relatively large, polished, coaxial, radial and annular end face 156, which in the view of Fig. 2 aligns in height with the south pole of the hemispherical surface 53 and thus lies lower than the annular surface 92.

A gripping sleeve 157 consists of an upper part 158 and a lower part 159. While the sliding sleeve 142 is of aluminum, the gripping sleeve 156 is of plastic and thus only about 5 grams heavy. The upper part has an internal thread 161, which can be is screwed onto the external thread 129. In the screwed- in state, its coaxial and downwardly directed end face 162 presses onto the complementary, upwardly directed end face 163 of the lower part 159. The lower part 159 is in this case pressed by a downwardly directed shoul der 164, provided close to the end face 163, against the end face 133, as a result of which the gripping sleeve 157 is fixed in all directions. For better holding with the hand, the lower part 159 has gripping rings 166. The lowermost, downwardly directed end face 16 leaves the sli.ding sleeve 142 free at the bottom up to about the level of the cylinder space 44 and tapers before this. The gripping sleeve 157 has a small dis tance from the circular-cylindrical outer surface 168 of the sliding sleeve 142. It also serves to cover the 1 1 i i i i 1 i i i i i 1 i - 19 grub screw 16, the window 23, the through-hole 136 and the tangential slit 139 together with head 141. In th finished assembled state, the gripping sleeve 157 cannot be twisted with respect to the body 12, while the sliding sleeve 142 can turn by approximately 300, according to the length of the tangential slit 139, until it stops against the stop pin 138.

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Claims (36)

CLAIMS:

1. A device for a single-pole, electromagnetic, active measuring probe (11) for the measurement of thin layers, with a coaxial half-pot core (52), with a coaxial central core (58), with a coaxial winding space (59) around the central core (58), with an outer wall (56) around the winding space (59), with a coaxial, convex end face (64) of a body (63) of abrasion-resistant material, with (58), with a galvanic conductor device (18, 19, 21, 22, 26, 27, 46, 47) between the coil device (61) and the end of measuring probe (11), which conductor device (18, a coaxial coil device (61) on the central core the 19, 21, 22, 26, 27, 46, 47)is provided in a coaxial hollow space (17) of a probe body (12), with a cable (15) which leads off from one end of the p measuring probe (11), with a coaxial annular surface (156), which is arranged at a considerable radial distance from the convex end i i i i i 0 1 1k f ace, with a spring device in the flux of force between the end face (53) and the annular surface (92), the end face lyi.ng axially in front of the annular surface in the state of rest, and with a straight-guiding device between the end face nd the annular surface, efined by the following features:

a) The haLf-pot core (52) is axially movable in the probe body (12).

b) In the flux of force between the haLf-pot core (52) and the inside (31) of the probe body (12) is the spring device.

c) The conductor device comprises a very Lightweight conductor framework (24), which bears a very Light weight active circuit (26, 27).

2. The device as claimed in claim 1, wherein a very Lightweight tappet element (41), which is substan tialLy Longer than the half-pot core (52) but substantially shorter than the probe body (12), is pro vided coaxialLy in the front region of the probe body (12), wherein the pot core (52) is rigidly connected to the front region (67) of the tappet element (41) and wherein the spring device (99, 101) is provided between tappet element (41) and probe body (12).

3. The device as claimed in claim 2, wherein the tappet element (41) has a through-bore (42), in which the thin Leads (46, 47) of the coil, device (61) Lie.

4. The device as claimed in claim 3, wherein the through-bore (42) lies coaxially.

5. The device as claimed in claim 2, wherein the tappet element (41) is substantially rotationally symmetrical.

6. The device as claimed in claim 2, wherein the tappet element (41) is of lightweight metal.

7. The device as claimed in claim 1, wherein the tappet element (41) has a length in the centimeter range.

8. The device as claimed in claim 1, wherein the tappet element (41) has in its front region (67) an outwardly projecting collar (68), which protrudes into a receptacle (72) fixed to the body, collar (68) and receptacle (72) forming at least a first stop (69, 71), which prevents an excessive inward movement of the tappet element (41).

9. The device as claimed in claim 8P wherein the collar (68) is L-shaped and the receptacle (72) is com plementarily L-shaped, wherein the free members (76) of the L (81, 76; 940 78) overlap and form a safeguard against excessive radial deflection of the tappet element (41).

10. The device as claimed in claim 2. wherein the tappet element (41) merges at its inner end region with a fixing flan.ge (32), on which a conductor wafer (24) which bears the active circuit (26, 27) is fixed.

11. The device as claimed in claim 1. wherein the spring device (99. 101) lies between the tappet element and the inside of the probe body.

i i i i i i i i i i i A 1 ll,

12. The device as claimed in claim 11, wherein the spring device (99, 101) is arranged at least substantially radially.

13. The device as claimed in claim 12, wherein the spring device (99, 101) has an outer retaining ring (102), with which it is fixed on the inside (31) of the probe body (12), and has an inner retaining ring (103), with which it is fixed on the outside of the.tappet element (41).

14. The device as claimed in claim 13, wherein at least one of the retaining rings (102, 103) is continuous.

15. The device as claimed in claim 13, wherein the two retaining rings (102, 103) are interconnected by webs (104), which are separated from each other by slits (108).

16. The device as claimed in claim 12, wherein it comprises a wafer (99, 101).

17. The device as claimed in claim 16, wherein the wafer (99, 101) is arranged coaxially.

18. The device as claimed in claim 16, wherein the configuration of the wafer (99, 101) is formed by an etching process.

19. The device as claimed in claim 1, wherein the spring device (99, 101) is stiff in axial direction with respect to such forces as occur-during measuring.

20. The device as claimed in claim 13, wherein the two retaining rings (102, 103) are concentric and are concentric at the outer circumference or at the inner circumference.

21. The device as claimed in claim 11, wherein two spring devices (99, 101) are arranged at an axial distance from each other.

22. The device as claimed in claim 21, wherein the two spring devices (99, 101) are of the same design.

23. The device as claimed in claim 22, wherein they are of copper-beryllium.

24. The device as claimed in claim 2, wherein the tappet element (41) has an inner tube (39), which is offset with a step (123) from the front region (67) of the tappet element (41), wherein there is seated on the inner tube (39) a first sleeve (126) and a second sleeve (37) and the inner retaining rings (103) of the two spring devices (99, 101) are rigidly grasped one time between the step (123) and the first sleeve (126) and the other time between the first sleeve (126) and the second sleeve (37).

25. The device as claimed in claims 10 and 24, wherein the fixing flange (33) and the second sleeve (37) are of one piece.

26. The device as claimed in claim 24, wherein the first sleeve (126) has exactly opposite it a third sleeve (121), which is rigidly connected to the probe body (12) and the two end faces (119, 123) of which, together with further opposing end faces (83) fixed to the probe body, hold the outer retaining rings (102) of the two spring devices (99, 101).

27. The device as claimed in claim 1, wherein, when i i i i i i i i i i i - 255- a stroke takes place"in the lower to mid tenth of a millimeter range, the spring force of the spring device (99, 101) lies in the lower to mid decapond range.

28. The device as claimed in claim 1, wherein the weight of the conductor framework (24) plus circuit (26, 27) lies in the tenth of a gram range.

29. The device as claimed in claim 1, wherein the half-pot core (52) is covered on its outside fluid tightly by an acid and base resistant, abrasion resistant coating (172).

30. The device as claimed in claim 29. wherein the coating (172) is a PTFE.

31. The device as claimed in claim 29. wherein the coating (172) is a polyimide.

32. The device as claimed in claim 29, wherein.the coating (181) also covers, at least indirectly, the circumference of the half-pot core (52).

33. The device as claimed in claim 1. wherein at least the front region of the probe body (12) is sur rounded coaxially by a sliding sleeve (142), the front end face (156) of which can be pushed back' further than the coaxial annular surface (92) of the probe body (12), wherein, in the state of rest of the sliding sleeve (142), its front end face (156) lies in front of end face (64), wherein.the radial backlash between sliding sleeve (142) and probe body (12) is very small, wherein a helical spring (146), which urges the sliding sleeve (142) into its forward position, lies between sliding sleeve (142) and probe body (12), and wherein a coaxial gripping sleeve (157) is provided around the sliding sleeve (142), is firmly connected to i the probe body (12) and is separated in its region overlapping the sliding sleeve (142) from the latter by a gap.

34. The device as claimed in claim 1, wherein the cable ( 15) is thin.

i i i 1 i 1

35. The device as claimed in claim 35 wherein the cable (15) is 3 mm and less in diameter.

36. A device for a single-pole electromaanetic i i i i j i 1 active measuring probe substantially as described with reference to Figures 1 to 3, Figure 4, Figure 5 or Figure 6 of the accompanying drawings.

i i j i 1 i i i i i i i Published 1990 at The Patent Office, State House. 6671 High Holborn. London WC1R4TP.Ft=ther copies maybe obtained from The Patent CtriceSales Branch, St Mary Cray. Orpington, Kent BRS 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1 87 i i i