GB2073428A - A switching arrangement for the digital remote transmission of signals - Google Patents

Abstract

A switching arrangement is described by which a digital electrical signal is produced in response to a change in magnetic field occurring at a location (3), and is conveyed to a remotely- situated indication point (4) by way of an electrical conduction loop (1), in which a constant direct voltage (6) or a constant direct current is connected. The magnetic field sensor is a bistable magnetic element (8) which alters its direction of magnetisation abruptly under the influence of the change in magnetic field e.g. due to movement of a magnet (10). The abrupt change in magnetic field thus produced induces an electrical voltage pulse in an electrical winding (7) connected in the base circuit of a transistor (5), the collector and emitter of which is connected in the conduction loop (1) leading to the indication point (4). A pulse occurring in the winding (7) makes the transistor (5) conductive, whereby the latter transmits a pulse signal via the conduction loop to the indication point (4). <IMAGE>

Description

SPECIFICATION A switching arrangement for the digital remote transmission of signals The invention relates to a switching arrangement suitable for the digital determination of a change of state associated with a change of magnetic field, and for the remote transmission of a digital response signal thus obtained.

The practice has previously been proposed of placing two electrical remote-control leads between a point at which a change of state occurs (measurement point) and a point at which the change of state is indicated (indication point), e.g. a switching installation, of connecting these either by a constant current source or by a constant voltage source, and also by electrical switching elements, comprising a transistor or like four-terminal network, to form a closed circuit. The transistor is so wired that, in the normal case, it is cut-off and, only when the electromagnetic converter in the base circuit conveysa predetermined signal to the base of the transistor, does it become conductive.When a constant voltage is implanted in the remote-control circuit, this produces a change in the current strength, but when a constant current is implanted in the remote-control circuit, this produces a change in the voltage conditions in the remote-control circuit.

Both are indicated at the measuring point by known indicator devices.

The practice has been proposed to employ, as electro-magnetic converters in such switching arrangements, semiconductor elements which are sensitive to magnetic fields, generally Hall effect generators. These have the disadvantage that they are sensitive to temperature and are active components which require a supply of current in order to measure the change of state and to deliver a corresponding response signal.

An object of the present invention is, on the other hand, to provide a switching arrangement which is robust and which, as far as possible, does not require any special current supply at the measurement point.

According to the present invention there is provided a switching arrangement for the digital determination of a change of state associated with achange of magnetic field, and for the remote transmission of the digital response signal thus obtained, via an electrical conduction loop, in which a constant voltage or a constant direct current is implanted, and in which is located a transistor or the like with collector and emitter, in the base circuit of which an electromagnetic converter is placed, characterised in that the electromagnetic converter is a bistable magnetic element (hereinafter referred to as BME) which is coupled magnetically with an electrical winding constituting a sensor winding located in the base circuit of the transistor.

As bistable magnetic elements, also referred to as bistable magnetic switch cores (and hereinafter and in the claims referred to as BME's), it is recommended in particular that so-called Wiegand wires be employed, whose structure and manufacture are described in DE-OS 2,143,326. Wiegand wires are homogeneous, ferromagnetic wires (e.g. of an alloy of iron and nickel, preferably 48% iron and 52% nickel; or of an alloy of iron and cobalt or of an alloy of iron with cobalt and nickel; or an alloy of cobalt with iron and vanadium, preferably 52% cobalt, 38% iron and 10% vanadium) which, due to special mechanical and heat treatment, possess a soft magnetic core and a hard magnetic outer surface, i.e. the suface possesses higher coercive force that the core.Typical Wiegand wires have a length of 5mm to 50mm, preferably 20mm to 30mm. If a Wiegand wire, in which the direction of magnetisation of the soft magnetic core coincides with that of the hard magnetic surface, is introduced into an external magnetic field whose direction coincides with that of the axis of the wire, but is opposed to the direction of magnetisation of the Wiegand wire, on exceeding a field strength of approximately 16 A/cm, the direction of magnetisation of the soft core of the Wiegand wire is reversed. This reversal is also referred to as resetting. On further reversing of the direction of the external magnetic field, and on the external magnetic field exceeding a critical field strength, the direction of magnetisation of the core is again reversed, so that the core and the surface are again of parallel magnetisation.This reversal of the direction of magnetisation ocurs very abruptly and is accompanied by a correspondingly notable change in magnetic flux per unit of time (Wiegand effect). In an induction coil, this alteration of magnetic flux may induce a short and very high voltage pulse (according to the number of turns and to the load resistance of the coil, up to approximately 12 v.) known as a Wiegand pulse.

Also on returning of the core, a pulse is produced in an induction coil, which is however of much lower amplitude and of a different sign from the case of the reversal from the anti-parallel to the parallel direction of magnetisation.

If, as external magnetic field, an alternating field is selected, which is capable of reversing magnetisation firstly of the core and then also of the surface layer and of bringing these to magnetic saturation, Wiegand pulses occur, due to the reversal of the direction of magnetisation of the soft magnetic core, alternately of positive and negative polarity, which is termed symmetrical excitation of Wiegand wire. For this purpose, field strengths of approximately -(80 to 120 A/cm) to +(80to 120 A/cm) are required. The change of magnetisation of the surface also occurs abruptly and also produces a pulse in the induction coil, which is however much smaller than the pulse induced in the reversal of the core and is generally not evaluated.

If however an external magnetic field is selected which is capable of reversing only the soft core but not the hard surface layer in direction of magnetisation, the high Wiegand pulses occur only with unchanged polarity which is referred to as asymmet rical excitation of the Wiegand wire. For this purpose, a field strength is required in one direction of at least 16 A/cm (for the resetting of Wiegand wire) and in the opposite direction a field strength of approximately 80 to 120 A/cm.

It ischaracteristic of Wiegand effect that the amplitude and width of the pulses it produces are largely independent of the speed of change of the external magnetic field and thatthey possess a high signal-to-noise ratio.

Also suitable for the purpose of the invention are differently constructed bistable magnetic elements which possess two zones of differing magnetic hardness (coercive force) magnetically coupled to each other, and may be employed in the same manner as Wiegand wires for producing pulses by an induced, abrupt reversal of the soft magnetic zone. Thus, a bistable magnetic switch core in the form of a wire has previously been proposed in, for example, DEEPS 22,514,131, which comprises a hard magnetic core (e.g. of nickel-cobalt), an electrically conductive intermediate layer (e.g. of copper) deposited thereon, and a soft magnetic layer (e.g. of nickel-iron) deposited thereon.Another variant addi tionallyemploysa core of a magnetic, nonconductive metal inner conductor (e.g. of berylliumcopper), on to which the hard magnetic layeris deposited, then onthisthe intermediate layer, and on this the soft magnetic layer. This bistable magnetic switch core does, however, produce smaller switch pulses than a Wiegand wire.

Thus, according to the present invention a BME, together with an appropriate sensor winding which is connected galvanically to the base of the transis tor, is employed not only to release an electrical, pulse-shaped signal as response to a certain change in magnetic field atthe position of the BME, but also to convey this pulse by way of remote-control leads to the indication point This pulse produced in the sensor winding is conveyed to the base of the transistor and makes it conductive, so that with implanted constant voltage, the current strength changes in the conduction loop between the measurement point and the indication point (emittercollector circuit of the transistor), whereas, with implanted constant current, it is the voltage that changes.

Here, the BME can operate without external voltagesource; and electrical connection must simply be provided at the measurementpoint between the sensorwinding and the transistor.

An especially advantageous feature of the present invention is that the process of reversal of magnetisation in the BME, which releases the characteristic pulse, is largely independent of temperature over a wide temperature range. Moreover, the pulses produced possess a high signal-to-noise ratio and the pulse form and height are independent of the particular kind and speed of pulse release. Thus, the employment of a BME in the switching arrangement according to the invention has the advantage of very considerable reliability in operation and freedom from malfunctioning.

Due to the high signal yield, a Wiegand wire is preferably employed as BME, and the sensor winding is placed around the BME.

There are numerous possible ways of effecting excitationof the BME in order to release pulses. A prerequisite of any kind of excitation is, of course, that the BME is situated in part of a time-variable magnetic field, in which case the manner in which the magnetic field is created is immaterial. When the alternation of the magnetic field changes so strongly that symmetrical exxcitation is possible (with Wiegand wires, field strengths of approximately +(80 to 1 20A/cm) are required for this purpose), an alternating pulse-train is released in the sensor winding, of which however only the pulses of one polarity are employed for rendering the transistor conductive.With weaker alternating magnetic fields, only asymmetrical excitation of the BME is possible, for which purpose a field strength of approximately 80 to 120A/cm is required with Wiegand wires in one direction, i.e. for the reversal of the soft magnetic zone to the parallel magnetisation direction (relative to the magnetisation direction of the hard magnetic zone), whereas, for resetting of the magnetisation direction of the soft magnetic zone from parallel to anti-parallel orientation, a magnetic field in opposite direction of only approximately -16 A/cm is required. With asymmetrical excitation by a suitable alternating magnetic field, a train of pulses of constant polarity is produced in the sensor winding.

One of the numerous possible applications of the invention is the contactless rotary speed control of rotors. For this purpose, magnets can be fitted to the rotor which have opposite directions of magnetisation and, as the rotor moves, are conveyed periodically past the BME, whereby they produce at the position of the BME magnetic alternating field which produces in the sensor winding a train of pulses, the frequency of which is directly proportional to the rotary speed of the rotor. Since the pulse width in the case of normal Wiegand wires is 201is, the Wiegand wire may produce pulse frequencies in excess of 10 kHz.

In otherfields of application, it may be sufficient to indicate a change of state at the measurement point by only one pulse, e.g. by the operation of switch keys or terminal switches. For this purpose, a rod in the switch may be provided with a permanent magnet, which, on actuation of the switch, is moved towards the BME and excites this to release a pulse, or a permanent magnet can be placed close to the BME but immovable in relation thereto, which is influenced by a moved ferromagnetic object, whereby its field is changed at the position of the BME and causes the BME to release a pulse.

If the change of state at the measurement point, which has to be indicated, does not immediately show a sign change of a magnetic field, but only a change in field strength without sign change, the BME can still be excited for pulse-release by coupling with it a permanent magnet, the magnetic field of which is opposite to the variable magnetic field and which "pre-tensions" the BME magnetically, i.e.

provides itwith pre-magnetisation. In this case, the static field and the variable field are superimposed at the position of the BME. If, for example, the variable field at the position of the BME is changed by moving a permanent magnet towards the BME, this magnetweakens the field of the other permanent magnet firstly at the location of the BME, until the resulting magnetic field art a certain distance away, reverses its direction, whereupon as the distance decreases, the field of the moved magnet dominated the static field of the unmoved magnet. Thus, with satisfactory field strengths, the BME can be excited not only asymmetrically but also symmetrically.

Instead of pre-tensioning the BME with a permanent magnet, this can also be carried out with a D.C.

winding. Indeed, in the case of the switching arrangement according to the invention, this can be done without further involvement since the sensor winding can provide the winding for premagnetisation of the BME,.whilstthe constant current source delivers the required constant direct current which is already required for implanting the direct current in the remote-control leads. At the same time, the remote-control leads are utilised to supply the direct current to the sensor winding.

In certain cases, the variable magnetic field associated with the state to be monitored, which, as we know releases a pulse in the sensor winding on the occurrence of a pre-determined change of state, does not produce any further pulse with the same change of state, because the field is static or has only fluctuations of a kind which, on the occurrence of the predetermined change of state, do not lead to a time-alternating A.C. field at the position of the BME, which is suitable for exciting the BME asymmetrically. In such cases, it may however be desired to obtain a happening or a change of state, e.g.

exceeding a limit value or operating a key, not only by a brief signal in the form of a single pulse, but in the form of a persistent or periodically occurring signal. Forthis purpose, the single pulse occurring can, of course, be converted in a holding circuit to a persistent signal; in this case, however, a special signal is then required, to indicate for example falling short of the above-mentioned limit value or the release of a key and to cancel the output signal of the holding circuit.

The present invention offers a simpler and neater solution, according to which a periodic, magnetic alternating field is superimposed upon the variable magnetic direct field. The periodic, magnetic alternating field may be produced basically by nonelectrical means, e.g. by a rotating permanent magnet. The production of the field electrically is preferred, however, employing an A.C. winding.The consequence is that the resulting magnetic field at the location of the BME is a pulsating magnetic field which, in the one state (e.g. "Limit value not yet reached"), is a pulsating direct or alternating field which, however, is so weak in one direction that it cannot even provide the field strength required for the magnetic resetting of the BME, which is essential for asymmetrical excitation of the BME; whereas, in the other state (e.g. "Limit value exceeded"), the resulting field, by the changing of its direct field component, has become an alternating field, the amplitude of which is sufficient at least for the asymmetrical excitation of the BME.In this state, therefore, a periodic train of pulses is produced in the sensor winding; indeed, with asymmetrical excitation, within each cycle of the exciter alternating current, one pulse occurs, whilst, with symmetrical excitation, within each cycle of the exciter atlernating current, two pulses occur with opposite sign. This train of pulses persists as long as the particular state is maintained.

Embodiments of the present invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a switching arrangement in which a constant voltage is implanted in a conduction loop between the measurement point and the indication point; Figure 2 shows a switching arrangement with current implanted in the conduction loop; and Figure 3 shows a switching arrangement, as in Figure 2, but with periodic output signal.

In Figure 1 two remote-control leads 1 and 2 can be seen which lie between a measurement point 3 and an indication point 4. The two remote-control leads 1 and 2 are connected at the measurement point 4 to the emitter and collector of a n-p-n transistor 5, and at the indication point 4 to a direct voltage source 6 which implants a constant voltage UO in the conduction loop which is thus closed.

Between the base and the emitter of the transistor 5 lies a winding 7 which acts as a sensor winding and encloses a Wiegand wire 8. Adjacent the Wiegand wire 8 and parallel thereto, a bar-type permanent magnet 9 is provided as resetting magnet, which is capable of returning the Wiegand wire 8 magnetically, i.e. which can reverse the poles of its soft magnetic core from the parallel (relative to the magnetisation direction of the hard magnetic surface) to the anti-parallel direction of magnetisation.

If a stronger, oppositely directed magnetic field is superimposed on the field of the resetting magnet 9, for example, by moving a stronger, oppositely orientated bar magnet 10 nearer in the direction of the arrow 11, the field of the magnet 10, within a certain separation distance, will dominate the field of the magnet 9 to such an extent that the soft magnetic core in Wiegand wire 8 is returned to the parallel direction of magnetisation, so that in the sensor winding 7 a Wiegand pulse is induced which makes the transistor 5 conductive. With suitable polearrangement, however, the Wiegand pulse can also block a transistor which was previously conductive.

Due to the implanted constant voltage, in both cases, this produces in the closed conduction loop formed by the remote-control leads 1,2, a change in currentstrength which can be measured at the measurement point 4 from a measurement resistance Rand can be registered.

The embodiment shown in Figure 2 differs essentially from that of Figure 1 in that, instead of a constant voltage, a constant current 1c from a constant current source 12 is implanted in the conduction loop formed by the remote-control leads 1,2. At the measurement point 3, the remote-control leads 1 and 2 are connected to the collector and emitter of a p-n-p transistor 5'. Between the base and the emitter of the transistor 5' lies a winding 7 which acts as sensor winding and encloses a Wiegand wire 8. Between the base and the collector of the transistor 5' lies a pre-resistance Rev which is great relative to the ohmic resistance of the sensor winding 7. This ensures that the transistor is normally blocked if a diode 13 is also placed before the emitter.

If the magnet 10 is moved nearerto the Wiegand wire 8 in the direction of the arrow 11, within a certain distance therefrom, the field of the magnet 10 at the location of the Wiegand wire 8 becomes so strong that a Wiegand pulse is induced in the sensor winding 8. This pulse makes the transistor 5' conductive. Due to the constant current-strength 1o implanted, this is connected to a change in the collector-emitter voltage, which can be measure at the indication point 4 between the terminals 14 and 15 and registered.

When the magnet 10 is removed, the Wiegand wire 8 can be caused to revert magnetically by the magnetic field producing the current lo in the winding 7, and is then ready to release a further pulse when the magnet 10 is again brought into proximity.

Compared with the embodiment of Figure 2, that of Figure 3 is provided in addition with a further exciter winding 16 on the Wiegand wire 8, which winding is connected to an A.C. source 17. By this arrangement on exceeding the prescribed distance threshold, the magnet 10 releases not only one pulse but a periodic train of pulses in the sensor winding 7, as long as it is located on the far side of this distance threshold; this means that, in each cycle of the exciter alternating current, one Wiegand pulse is received with asymmetrical excitation, and with symmetrical excitation, two pulses of differing polarity.

Claims (7)

1. Aswitching arrangement for the digital determination of a change of state associated with a change of magnetic field, and for the remote transmission of the digital response signal thus obtained, via an electrical conduction loop, in which a constant voltage or a constant direct current is implanted, and in which is located a transistor or the like with collector and emitter, in the base circuit of which an electro magnetic converter is placed, in which the electromagnetic converter is a bistable magnetic element (hereinafter referred to as BME), which is coupled magnetically with an electrical winding constituting a sensor winding located in the base circuit of the transistor.

2. A switching arrangement according to claim 1, in which the BME is a Wiegand wire.

3. A switching arrangement according to claim 1 or 2, in which the sensor winding encloses the BME.

4. A switching arrangement according to any one of the foregoing claims in which, associated with the BME, is a magnetwhich produces a static magnetic field at the location of the BME.

5. A switching arrangement according to any one of the foregoing claims, in which, associated with the BME, is a magnet which produces a magnetic alternating field at the location of the BME.

6. A switching arrangement according to claim 5, in which the magnet which producesthe alternating field is a winding which preferably surrounds the BME and which is connected to an alternating current source 17.

7. A switching arrangement substantially as hereinbefore described with reference to any of Figures 1 to 3 of the accompanying drawings.