IE873029L

IE873029L - Magnetic field transducer

Info

Publication number: IE873029L
Application number: IE873029A
Authority: IE
Inventors: Thomas Werner
Original assignee: Mannesmann Kienzle Gmbh
Priority date: 1986-11-12
Filing date: 1987-11-11
Publication date: 1988-05-12
Also published as: PT86096A; EP0273129A2; PT86096B; JPH0684892B2; DK585087D0; DE3784665D1; JPS63135816A; EP0273129A3; ES2039404T3; DE3638622C2; EP0273129B1; DE3638622A1; IE62182B1; DK585087A

Abstract

To achieve the largest possible signal/noise ratio in a rod-shaped magnetic field transmitter with a permanent magnet and a Hall generator, it is proposed to use a ring magnet (1) and to arrange the Hall generator (3) in the space (2) of minimum magnetic induction given by field displacement within the ring magnet (1). <IMAGE> [EP0273129A2]

Description

o 0 "MAGNETIC FIELD TRANSDUCER" The invention relates to a magnetic field transducer having a permanent magnet and a Hall generator.

Rod-shaped induction transducers ares as a rules used for monitoring rotations in machines and vehicles* or for recording rotational speed. These cooperate with suitable ferro-magnetic pulse discs or gear "heels., which are connected to the object to be monitored, and with which they are associated by screwing into position in the relevant bearing or transmission housing* The advantages of induction transducers are to be seen especially in that they are suited to a ruling environment with temperature changes between -40° C and +150° C on account of their robustness and that they can also be manufactured relatively economically. It therefore follows that the fact that induction transducers extract energy from the object being monitored may in certain instances be disregarded.

As dynamically operating transducers, induction transducers are, however, usable only to a limited extent or not at all, if relatively low rotational speeds or the movement of shafts in the standstill region require to be recorded. Should the sensitivity of such a transducer be enhanced in order to correspondingly achieve a low limiting frequency,, then there is the danger, in particular in motor vehicles? of exposing transducers to very varied vibrations, so that, for example, even when the object to be monitored is stationary., signals are produced and thereby a state of affairs is simulated which has not in fact taken place.

If the demand for a limiting frequency of zero is to be fulfilled and at the same time the problem described above is to be avoided, then it is obvious to use static transducerss for example make-and-break oscillators or magnetic field transducers which have field plate generators or Hall generators as active elements. In thiss make-or-break oscillators are usable for the foregoing circumstances only to a limited extents since., on the one hands, 5 frequencies of over 500 hz cannot be recorded with the required degree of accuracy and* on the other hand,, considerable disturbances appear in the higher temperature range on account of changes in the coil values.

Deficiencies of this kind may be avoided in known manner with magnetic field transducers; however*, the required d„c. amplification necessitates 10 considerable dependence on, for example,, a signal supplied by a Hall generator of a given noise voltage level and on the age-dependent and temperature-dependent changes of the signals as well as the temperature-dependent drift behaviour of the d«c. amplifier itself. This dependence may be achieved only by substantial expenditure on control technology., The rod-shaped transducer 15 architecture required for use in such circumstances presents*, however, particular problems in this regard. It is required that the Hall generator be positioned at the front of a rod-shaped permanent magnet, thereby unfailingly ensuring that a ground signal or noise signal is given first and then subsequently strengthened. This noise signal is relatively high in contrast 20 to the useful signal achievable, and temperature-dependent because of the circuit arrangement of the Hall generator.

Stemming from the monitoring technology principle that the amplifier connector of the transducer should essentially amplify useful signals onlv9 an object of the present invention is to improve the monitoring technology 25 requirements of a preferably rod-shaped magnetic field transducer and5 in particulars, to create as high a useful signal/noise signal ratio (i.e. signal to noise ratio) as possible.

According to the invention., there is provided a magnetic field transducer having a permanent magnet and a Hall generator., wherein a ring 30 magnet is provided as the permanent magnet and the Hall generator is disposed at the opening of the ring magnet so that the axis of the Hall generator and the axis of the ring magnet substantially coincides, and the Hall generator is, in the case of an open magnetic circuits disposed in a space of minimal magnetic induction defined within the ring magnet by field displacement. 35 A preferred embodiment is characterised in that an extension or tongue introduceable into the opening of the ring magnet is formed on a printed circuit board carrying the electrical components of the transducer, the Hall generator is disposed on the tongue or extension of the printed circuit board - 3 - RQBP iBPaavM which extends into the ring magnet at its front end, and the ring magnet is fixed onto the tongue or extension of the printed circuit board.

Apart from the advantages of magnetic field tranducers already described9 which are based on functional principles,, the solution according to 5 the invention offers in addition the advantage that it makes possible the construction of a rod-shaped magnetic field transducer with the lowest possible noise voltage level- The remaining noise voltage level substantially corresponds to the production-technology determined«, so-called ohmic2 zero components of the Hall generator- But this may also be compensated for in the 10 arrangement selected according to the invention in which the Hall generator is magnetically biased. This may be achieved in the solution according to the invention in an especially simple manner,, in that the Hall generator is arranged positioned opposite the zone of minimum magnetic induction. The solution according to the invention thus solves the problem posed in all 15 aspects.

A magnetic field transducer according to the invention has a further advantage in that it may be used not only in cases where up until now induction transducers were not installable, but it is also capable of being installed,, without further adjustment, instead of an Induction transducer, in 20 that the same transducer architecture may be selected and3 indeed, the invention is similarly independent of any rotational position,, i.e. it can-be secured by scrawing-in. It is furthermore advantageous that the adjustment of the transducer may take place both outside the transducer housing as well as by a mechanical movement between the ring magnet and the printed circuit board 25 which is capable of inherently good controls thus rendering the transducer suitable for mass production.

The invention is more particularly described as follows with reference to the accompanying drawings.

Figure 1 shows a representation of the principle of a magnetic field 30 transducer according to the invention having an axialIv magnetized magnet and of the magnetic field prevailing in the case of an open magnetic circuit; Figures 2, 3 and 4 show different field representations in the case of a magnetic circuit according to Figure 1 disturbed by a ferro-magnetic 35 element; Figure 5 is a view of an assembled magnetic field transducer according _ 4 _ to the vnventions ready for installations, with associated ferro-magnetic pulse disc; Figure 6 is a partial view of the magnetic field transducer according to Figure 5; 5 Figure 7 is a block circuit diagram concerning the current supply and the signal processing for the Hall device; Figure 8 is an oscillogram of the signal voltage of a Hall switch., which is in a state-of-the-art magnetic field transducer; Figure 9 is an oscillogram of the signal voltage of a Hall device 10 according to the invention; Figure 10 is an oscillogram of the signal voltage at the output from the differential amplifier after the Hall device according to the invention; and Figure 11 is a representation of a principle of a magnetic field 15 transducer having a radially magnetized magnet.

As Figure 1 illustrates5 there exists, in the case of an axially magnetized ring magnets preferably a hollow cylindrical magnet., a rotational ly symmetrical space 2 of a relatively low magnetic potential or relatively weak magnetic induction. Near the pole of the magnets there is a radial expansion 20 of the space 2 and a zone within which the magnetic induction approaches zero. A Hall generator 3 is now positioned according to the invention with respect to the ring magnet 1 so that it finds itself exactly in the position where the magnetic induction for an undisturbed magnetic circuit is a minimum. If the magnetic circuit according to Figure 1 is disturbed by a 25 ferro-magnetic element 4S then the collecting effect of the ferro-magnetic element 4 gives rise to a distortion of the magnetic field, or a displacement and deformation of the neutral field or free field "space" 2, and causes an increasing saturation of the Hall generator 3 in the case of a movement of - 5 - the ferro-magnetic element 4 in the direction of the arrow to the position illustrated in Figure 3 and, at the same time., it causes an increases in the axial direction of the magnetic inductions in components of the magnetic induction which determine the Hall voltage. For further movement of the magnetic element 4 into the position illustrated in Figure 4, the field of the magnet is "dragged along"; however., the effect of saturation in the Hall generator 3 increasingly diminishes until finally the field springs back again into the output disposition illustrated in Figure 1. The oscillogram of Figure 9 shows the trace of the potential in question at the outputs of the Hall generator 3„ As is shown in Figure 5* which consists of an embodiment of a transducer ready for installations, it can be seen that the Hall generator 3 is disposed on the end face of an extension or tongue formed on a printed circuit board 5, which extends into the cylindrical opening 6 of the ring magnet 1. The printed circuit board 5 also carries, in known manner, the signal-forming and signal-amplifying electrical components of the magnetic field transducers this printed circuit board being held in a sleeve-like transducer housing 7 formed as a screw connector, into which it is moulded so as to be vi brat ion-free. The connection of the ring magnet 1 to the printed circuit board 5 Is naade outside the housing 7, after the positioning of the Hail generator in the "field-free space™ Z of the ring magnet 1 has taken place,., for example by a suitable adhesive 8. On the measuring head side*, the transducer housing 7 is closed off by means of a magnetically non-conducting cap 9. On the opposite side., a plug socket 10 is secured, onto which bayonet-type connecting means 11 are formed,, which, although this is not shown, are provided with a screw cap cooperating with the plug to be connected.

In the interest of completeness, reference should be made to the fact that a thread 12 formed on the transducer housing 7 serves to secure the magnetic field transducer, for example on the transmission housing of a motor vehicle, a ring-shaped surface 13 being effective as an abutment face, while two six-sided rings 14 and 15 are provided for applying a fitting tool, such as for example a spanner. A ferro-magnetic pulse disc 16 is disposed on the gear box side on the object to be monitored; projections, two of which are indicated by numerals 17 and 18s which cooperate with the magnetic field transducer9 are angled onto the disc.

The block circuit diagram in Figure 7 illustrates that for the operation of the Hall generator 3 in a known manner, a reference voltage transmitter 19 and a constant current source 20 are provided3 and that the two signal signal channels K1 and K2 of the Hall generator 3 are connected to the inputs of a differential amplifier 21. An impulse generator 22 is connected to the output of the differential amplifier 21s which is uncoupled by means of a transistor 23 of a first transmission line connectable at Ql. A further impulse generator 24 is connected in parallel with impulse generator 22 ands for the purpose of signal transmission controls provides an anti-phase signal at a connecting point Q2 for a second transmission line by means of a coupling transistor 25» The juxtaposition of the slightly idealised oscillograms of the signal voltages (Figures 8 and 9) which can be measured., on the one hands at the outputs 1(1 and KZ of a Hall generator in accordance with the state of current technical development ands on the other hand,, at the outputs of a Hall generator in accordance with the invention^ clearly shows the useful voltage/disturbing voltage relationship (i.e. signal/noise ratio) attainable with the arrangement according to the invention- The no-load voltage of the Hall generator is indicated by ULS and SI and S2 indicate the greatly differing disturbance or noise signals. From the point of view of completeness, the voltage trace at the output of the differential amplifier 21 is shown isn Figure 10, by way of contrast.

Figure 11 illustrates a variant of the inventive arrangement of the Hall generator 3 inside a radially magnetized ring magnet 25. - 8 -

Claims

1. Magnetic field transducer, having a permanent magnet and a Hall generator, characterized in that an annular magnet (1) is provided as 5 a permanent magnet, and in that the Hall generator (3), which is disc-shaped per se, is associated with the opening of the annular magnet (1) such that an imaginary centre axis, situated at right angles to the disc plane, of the Hall generator (3) and the geometric axis of the annular magnet (1) substantially coincide and the Hall 10 generator (3) is arranged, with an open magnetic circuit, in a space (2), existing as a result of field displacement within the annular magnet (1), of minimum magnetic induction.

2. Magnetic field transducer according to claim 1, characterized in 15 that an attachment which may be introduced into the opening of the annular magnet (1) is constructed on a conductor plate (5) carrying the electrical components of the transducer, in that the Hall generator (3) is arranged on the end side on the attachment of the conductor plate (5) which penetrates into the annular magnet (1), and 20 in that the annular magnet (1) is fixed to the attachment of the conductor plate (3).

3. Magnetic field transducer according to claim 1, characterized in that the annular magnet (1) is axiallv magnetized, and in that the 25 Hall generator (3) is associated with an end side of the annular magnet (1).

4. Magnetic field transducer according to claim 1, characterized in that the annular magnet (25) is radially magnetized, and in that the 30 Hall generator (3) is positioned in the centre of the annular magnet (26).

5. Magnetic field transducer according to claim 1 and substantially as described herein with reference to the accompanying drawings. 35 TOMKIHS & CO.