FR2664045A1 - RACE DETECTOR, WITH A MEASURING COIL WITH BODY A FERROMAGNETIC MATERIAL. - Google Patents

Abstract

a) Stroke detector, with a measuring coil whose body is a ferromagnetic material. b) characterized in that the body (11) consists of a ferromagnetic material and of a material which conducts electricity well, but which is not ferromagnetic, which are arranged along the same axis throughout the extent of the measurement range, and in that that the effects which occur in the two materials are determined with respect to each other, in such a way that the influence of the temperature is practically constant on the measuring signal (U) at least in the vicinity of the entire measuring range . c) The invention relates to travel detectors., with a measuring coil whose body is a ferromagnetic material.

Description

i "Stroke detector, with a measuring coil whose body is a

ferromagnetic material "

  The invention starts from a travel detector with a measuring coil traversed by a current

  This is a method of measuring the motion of the body which is moved in relation to a body and whose damping caused by the depth of the body into the measuring coil is used as a measuring signal. German patent application 31 09 930 0 discloses a running detector, in which the core rod with the measuring coil is immersed in a brass sleeve arranged in a tube. Alternating current passing through the coil is determined such that the eddy currents develop only on the surface of the brass. This principle, said eddy currents applied here, actually has a low dependence on temperature. But at different temperatures, there is a temperature drift which depends on the depth at which the plunger is pushed into the measuring coil. This temperature drift can only with difficulty and costly be compensated in an electrical operating circuit. .25 The stroke detector, according to the invention,

  is characterized in that the body consists of a

  fomagnetic material and a material which conducts electricity well, but not ferromagnetic, which are arranged along the same axis throughout the entire range of

  of measurement, and that the effects

  in both materials are determined

  in relation to each other, in such a way that

  temperature is almost constant on the measurement signal at least in the vicinity of

the measurement domain.

  On the other hand, it has the advantage that the measurement curves supplied at different temperatures are practically parallel over the whole range of measurements. The temperature drift is thus practically constant over the entire measuring range and can be processed. in a simple way

  in an electrical circuit of interpretation The shelter

  of the stroke detector is particularly straightforward, as it requires a plunger

  ferromagnetic, deposit only one layer of

  electrical conductor, but not ferromagnetic. In a simple manner, the detector of

  The race can be calibrated on the measurement reports

  required by the frequency of the alternating current

plicated to the stroke detector.

  Other embodiments and perfecti

  Advantages of the travel detector are possible. According to one characteristic of the invention, the body is made as a tubular-shaped plunger of ferromagnetic material, which is surrounded by

  externally by a material leading well the elec-

  tricity, but not ferromagnetic.

  According to another characteristic of the in-

  vention, a sheath is placed on the body,

  water in a material that conducts electricity well,

but not ferromagnetic.

  According to another characteristic of the in-

  vention, at least one of the two materials is

in the form of a layer.

  Finally, according to another characteristic of the invention, the measuring coil is arranged on a

  coil body in matter poorly conducts electricity

té and non ferromagnetic.

  An exemplary embodiment of the invention is shown in the drawings and will be described in more detail

in the following description.

  FIG. 1 shows a cross-sectional view through

  to a running detector, Figure 2 shows a diagram with

  the schematic curve of the measurement signal U in function

  depth of penetration, when working with

  with a ferromagnetic material or with a

  electricity-carrying but not ferromagnetic

  FIG. 3 represents a diagram with the schematic graph of the measurement signal U in FIG.

  according to the depth of depression S at different

  your temperatures, when working in accordance with

  the invention with the two layers of materials.

  In FIG. 1, a detection is

  stroke member, the plunger 11 of which is guided almost frictionlessly in a bobbin body 12

  a material leading poorly to electricity and not ferro-

  magnetic material, for example a plastic material or austenitic steel The plunger 11 consists of a tube 13 made of a ferromagnetic material, on the outer side of which is attached a jacket 14 in one

  electricity-efficient but non-ferrous

  magnetic, for example aluminum But it is also possible, instead of a shirt, to deposit

  a layer of this material conducts electricity well

  cited, but not ferromagnetic In this case, it is particularly simple to deposit the layer on the outer side of the tube 13, that is to say on the side

  which is turned towards the coil body 12 The depth

  sinker body sink 11 in the body

  of the coil 12 then corresponds to the measuring race

  In FIG. 1, the plunger 11 is shown in its maximum driving position. On the body of the spool 12, that is to say on the side facing away from the plunger 11, a spool measurement

  is wound on the measuring coil 15 is available

  a protective sheath 16 This sheath of

  16 is used to protect the spool 15 from soiling

  vis-à-vis the surrounding environment and the electronic fields

  external magnetic The protective sheath 16

  penetrates into two housing parts 17, 18, whose

  or whose relative variation in spacing

  relative to each other must be determined.

  One of the parts of the casing, the part 17 is fixed so-

  and in solidarity with the panel of pro

  16 by means of flange-shaped extensions.

  The other housing part 18 is movable, but

  fixed integrally on the plunger body 11

  annular race 19 is formed in the housing part 18 and another in the plunger 11; in these grooves is embedded a stop ring 21 The plunger 11 is, in this way, moved according to the sliding of the housing part 18 The detector

  10 may be used on a pneumatic element

  A hydraulic or hydraulic system in which the plunger body, then the piston rod of the piston and the body of the coil are designed as hydraulic cylinders can be thought of its application for example to a clutch disc. In what follows, we will first explain in detail each of the effects of measurement, ie how the measuring effect will be exploited only on a ferromagnetic material or only on a

  material that conducts electricity well, but not

  romagnetic If the coil 15 is traversed by a

  alternating current and if the alternating magnetic field

  If the coil 15 acts on a material that conducts electricity well, but not ferromagnetic, then only the so-called eddy current effect occurs. Due to the eddy currents that form on the surface of the material, which conducts electricity well, no

  ferromagnetic, there is a decrease in

  ductance of the measuring coil 15, so that

  the value of the measuring voltage U decreases

  the material penetrates into the measuring coil 15, the greater is the formation of eddy currents, since more surface is then available. In this way, the measurement curves designated 25, 26 are obtained.

  27 in Figure 2, curves that present a negative slope

  The three measurement curves 25, 26, 27 represent

  feel the function at each of the different temperatures

  rents, the curve 26 corresponding for example to a temperature Tl = 20, the curve 25 at a higher temperature T 2 = 1100 and the curve 27 at a lower temperature T 3 = 40 'The values of the temperatures are

  relate to the prevailing ambient temperature in the

  stroke detector 10 From the repre-

  schematic diagram of Figure 2, it can be seen that the influence of temperature is

  variable throughout the range of measurement.

  The more the plunger 11 is pushed into the measuring coil 15, the larger the deviations of the signal of

  measure with respect to curve 26 which must be

  identied as the calibration curve on the diagram

  shown in Figure 2 This measurement error which in-

  tervient under the action of temperature differences is not directly proportional to the depth

  S and can hardly be

  thought in an operating circuit.

  If, on the contrary, the measuring coil 15 is traversed by an alternating current, and if only

  a magnetic material makes him vis-à-vis, then the former

  operation of the measurement signal is based on the so-called

  ferromagnetic or inductive The magnetic field

  ternative of the coils traversed by the alternating current

  native acts on the surface of the ferromagnetic material

  Because of the ferromagnetic properties, during the ferromagnetic effect, the depth of insertion of the plunger 11 into the measuring coil 15 into

  becoming larger, produces an increase in

  This means that the measuring curves 28, 29 and 30 of the diagram according to FIG. 2 have a positive slope. The three measurement curves for the ferromagnetic effect are taken at the same temperatures T 1, T 2 , T 3 that during the eddy current effect But it is necessary, in this respect, to point out that with a ferromagnetic material

  both the ferromagnetic effect and the

  during, as indicated below,

  above, the eddy current effect, there is a decrease in the inductance of the measuring coil and the ferromagnetic effect causes an increase in the inductance of the coil Which of the two effects prevails, depends in the first place of the frequency of the alternating current, which runs through the coil 19 Plus the

  frequency is high, the greater the importance of

  tion of the eddy current effect.

  presented in Figure 2 are drawn up for

  identical queries, for example 5000 Hz.

  inductance of the coil as a function of the effect

  The ferromagnetic effect is again dependent on the depth of depression. In addition, there is no further linear influence of the temperature on the measurement signal U. From this diagram it can be seen that

  for greater depth of penetration, the erosion

  temperature caused by temperature, at the same time

  temperature T 2 and at the temperature Tl, changes in

  depending on the depth of penetration.

  As already mentioned above, for a ferromagnetic material there is no

  frequency zone, in which only

  the ferromagnetic effect or exclusively the ef-

  eddy current fuse If we determine the parameters

  meters, that is to say the properties of the material of the plunger, for example the layer thickness of the two materials used and the value of the frequency of the alternating current, which goes through the coil 15, one can obtain a trace almost parallel of the curves of

  measured at different temperatures This parallel plot

  In practice, it is possible in almost the whole extent of the measuring range. Only in the two extreme zones do drifts occur.

  zero point, which can be offset against

  easily in an electrical circuit of

  In addition, in the embodiment of the travel detector 10, the coil 15, viewed in the direction

  axial, is performed longer than the range of de-

  In this way, it is possible to ignore, for the production of the measurement signal, inhomogeneous magnetic fields that occur in the marginal area of the coil.

measuring 15.

  For measuring curves 31, 32, not

  shown in FIG. 3, while a plunger 11 is grasped by a measuring coil 15, it is also

  the eddy current effect that the ferro-

  As the two effects present

  different slopes and variations depending on

  In this way, it is also possible to work with several coils instead of the single measuring coil shown in FIG. he is

  It is also possible to arrange one over the other

  measuring coils, which are then connected

  electrically with each other in a cor-

  In an exemplary embodiment, a ferromagnetic material, for example unalloyed steel with a layer thickness of 2.5 mm, was used as the material.

  driving electricity, but not ferromagnetism

  that, aluminum with a layer thickness of

  lmm at an alternating current frequency of 5000 Hz.

Claims (5)

  1. Stroke detector (10) with a measuring coil (15) carrying alternating current, which moves relative to a body (11) and whose damping is caused by the depth   of driving (s) of the body (11) into the coil of   sure (15) is used as the measurement signal (U)   characterized in that the body (11) consists of a material   ferromagnetic material and a material that conducts   electricity, but not ferromagnetic, which are   placed along the same axis throughout the whole area of   measure, and in that the effects that occur   in the two materials are determined relative to each other, so that the influence of the temperature is substantially constant on the measuring signal (U) at least in the vicinity of all the measurement domain.   2. Stroke detector according to the claim   1, characterized in that the body is made   as a plunger body (11) of tubular shape   ferromagnetism, which is externally surrounded by a material that conducts electricity well, but non-ferromagnetic.   3. Race detector according to any one   that claims 1 and / or 2, characterized in that   a sheath (14) is arranged on the body (11), sheath made of a material that conducts electricity well, but not ferromagnetic.   4. Race detector according to any one   than claims 1 to 3, characterized in that   at least one of the two materials is placed under me of diaper.   5. Race detector according to any one   claims 1 to 4, characterized in that   the measuring coil (15) is arranged on a coil body (12) made of a material that causes poor electricity and non-ferromagnetic.