VAN DE LOO, Paul (Lot 26 Moores Road, Norton Summit, South Australia 5136, AU)
KLOMPENHOUWER, Willem (4 Henley Street, Goolwa, South Australia 5214, AU)
VAN DE LOO, Paul (Lot 26 Moores Road, Norton Summit, South Australia 5136, AU)
| CLAIMS: 1 . A contactless temperature sensing system comprising: a member which comprises a magnetic material having a magnetic property which varies in a predetermined manner over at least a target temperature range; a detector configured to sense a current value of the magnetic property of the magnetic material via a contactless electromagnetic coupling, and to generate, at a detector output, a signal corresponding with said current value; and an electronic processor operatively coupled to the detector output to receive said signal, the processor being configured to process the received signal to determine a current temperature parameter of the magnetic material. 2. The system of claim 1 wherein the magnetic property is one or more of: magnetic permeability; magnetic susceptibility; remanence; and coercivity. 3. The system of claim 1 wherein the detector is configured to sense the reluctance of a magnetic circuit which comprises the magnetic material and a magnet. 4. The system of claim 3 wherein the detector further comprises a magnetic field strength sensor. 5. The system of claim 4 wherein the magnetic field strength sensor is a Hall effect sensor. 6. The system of claim 1 wherein the detector comprises a magnet configured to magnetise the magnetic material of the member, and a sensor configured to generate a signal corresponding with a subsequent strength of a magnetic field generated by the magnetised magnetic material. 7. The system of claim 6 wherein the sensor comprises an inductive coil. 8. The system of claim 1 wherein the magnetic material is designed or selected to have a predetermined Curie point. 9. The system of claim 8 wherein the detector is configured to sense a reduction in remanence of the magnetic material when the temperature of the member exceeds the Curie point, and to generate a signal indicative of said reduction in remanence. 10. The system of claim 1 wherein the detector comprises: a magnet which generates a magnetic field; a movable member disposed within the magnetic field whereby the field causes a force to be exerted upon the movable member; and a force sensor arranged to sense a force acting on the movable member. 1 1 . The system of claim 10 wherein the force sensor comprises a spring-loaded switch, configured such that when the temperature of the magnetic material of the member reaches a threshold value, the field force acting on the movable member comprising the switch causes a change in state of associated switch contacts. 12. The system of claim 1 wherein the detector comprises: a light source configured to generate a polarised beam of light; a magnet disposed to form a magnetic circuit with the magnetic material comprising an air gap containing a magnetic field through which the beam passes; and a polarising light sensor that varies with a polarisation state of the beam. 13. The system of claim 1 wherein the detector comprises: a coil disposed to enclose the member, or at least a part thereof, which comprises the magnetic material; and a circuit for measuring an inductance of the coil, having an output at which a signal representing the current inductance is generated. 14. The system of claim 1 wherein the detector comprises a Wiegand wire disposed within a conductive coil such that a voltage pulse will be generated at the terminals of the coil in response to changes in the magnetisation of the Wiegand wire, and wherein the member further comprises: a first permanent magnet configured to apply a relatively strong magnetic field of a first magnetic polarity to the Wiegand wire; a second permanent magnet configured to subsequently apply a relatively weaker magnetic field of an opposing magnetic polarity to the Wiegand wire; and a third permanent magnet disposed adjacent to the magnetic material, wherein the first, second and third permanent magnets are disposed such that, in use, they move past the Wiegand wire sensor in sequence, whereby the first and second permanent magnets sensitise the Wiegand wire, and the response of the Wiegand sensor to passage of the third permanent magnet depends upon the temperature of the magnetic material. 15. The system of claim 14 which comprises a series of magnets and magnetic materials disposed to pass the Wiegand sensor in sequence, each magnetic material in the series having a higher Curie point than the preceding magnetic material whereby, for a temperature lying between respective Curie points of the first magnetic material in the sequence and a last magnetic material in the sequence, a pulse will be generated at a time corresponding with passage of the first magnetic material having a Curie temperature which is higher than the current temperature. 16. The system of claim 15 wherein the electronic processor is configured to measure a time delay between sensitisation of the Wiegand wire, and a subsequent pulse output from the conductive coil. 17. The system of claim 1 wherein the electric processor is configured with calibration data representing a predetermined relationship between values of the signal at the detector output and corresponding temperature values. 18. The system of claim 1 wherein the member comprises a rotating member. 19. The system of claim 18 wherein the rotating member comprises a clutch disc. 20. A contactless temperature sensing method comprising the steps of: providing a member which comprises a magnetic material having a magnetic property which varies in a predetermined manner over at least a target temperature range; sensing a current value of the magnetic property of the magnetic material via a contactless electromagnetic coupling; and determining a current temperature parameter of the magnetic material based upon the sensed value of the magnetic property. |
FIELD OF THE INVENTION
The present invention relates generally to temperature sensing, and more particularly to systems, apparatus and methods for sensing the temperature of components where it is not practical or desirable to connect to an electrical temperature sensor via physical contacts or conductors. The invention is applicable, for example, to sensing the temperature of rotating or other moving, mechanical, components.
BACKGROUND OF THE INVENTION
It is often desirable to monitor the temperature of moving mechanical components, such as clutches and couplings in drive trains of machines such as motor vehicles, conveyer belt drives, and all manner of other drive systems.
By way of example, there is a need to provide cost-effective, reliable temperature sensing on clutches of automotive dual-clutch automated manual transmissions (Dual-Clutch Transmissions, or DCTs). These are well-known in the literature and are increasingly available on production road vehicles. The first production DCT was fitted to the 2003 Volkswagen Golf k4 R32.
In a DCT, clutches are actuated in response to commands from a microcontroller which controls the gear selection and change functions. For optimum shift quality, that is gear changes that do not exhibit excessive 'shift shock' imparting jerky fore-aft motion to the passengers, the microcontroller may prolong the period of time over which clutch engagements and disengagements occur. This involves clutch 'slippage' for a time longer than would otherwise be employed, and results in the dissipation of mechanical energy as heat at the clutch lining. In circumstances in which frequent gear changes occur, such as stop-start city driving, or on hilly or winding roads, the temperature of the clutch may rise to level at which the durability and life of the clutch starts to suffer. In this situation it is desirable that the microcontroller change the clutch actuation strategy to one of more rapid engagement and disengagement. This will result in less smooth operation, and may be sensed by the passengers, but serves to prolong clutch life.
There is accordingly a need to sense the temperature of the clutches and communicate to the microcontroller. As DCT systems become more prevalent in production vehicles, there will be increasing cost pressures on the transmission components as the transmissions are fitted to cheaper cars, rather than only to premium models. This exacerbates the requirement for a cost-effective method of measuring clutch temperature.
Known methods of measuring temperature of moving members include techniques such as battery-powered sensors affixed to the members, which use wireless transmission to communicate sensor measurements to a receiver on an adjacent stationery card.
Alternatively, slip rings may be used to transmit power and signals across a rotating interface. However, these techniques are too expensive to be practical in lower-cost vehicles. Alternative methods, such as measuring the temperature of oil or other lubricant in which the clutch is immersed, are not sufficiently responsive to clutch temperature. That is, the delay between the clutch temperature rising and this being detected by a rise in oil temperature is too long, leading to the risk of clutch overheating. Furthermore, these methods are not applicable to newer 'dry-clutch' transmissions.
In addition to measuring the temperature of rotating, or other moving mechanical parts, contactless temperature sensing may be desirable in a variety of other applications. For example, in high temperature and/or highly corrosive environments it may be impractical to provide conductive connections (e.g. wires) to a temperature sensor. Furthermore, prior art contactless sensors, such as those employing electronic devices with wireless communications interfaces, may simply be unable to survive in hostile environments.
There is, therefore, a need for new systems, methods and apparatus for contactless temperature sensing, such as for sensing the temperature of moving members, which mitigate these technical and cost constraints of the prior art. SUMMARY OF THE INVENTION
In one aspect, the invention provides a contactless temperature sensing system comprising:
a member which comprises a magnetic material having a magnetic property which varies in a predetermined manner over at least a target temperature range; a detector configured to sense a current value of the magnetic property of the magnetic material via a contactless electromagnetic coupling, and to generate, at a detector output, a signal corresponding with said current value; and an electronic processor operatively coupled to the detector output to receive said signal, the processor being configured to process the received signal to determine a current temperature parameter of the magnetic material.
Advantageously, a system embodying the invention enables contactless temperature sensing of the member which comprises the magnetic material. The member may be wholly or partially fabricated from the magnetic material, or the magnetic material may comprise a separate component inserted into, or affixed to, and in thermal contact with, the member.
The fundamental principle underlying the invention is the recognition that magnetic properties of magnetic material may be sensed, without physical contact, via various forms of electromagnetic coupling, and furthermore that if those properties vary in a predetermined manner with temperature then a contactless sensor may be configured to enable temperature parameters of the magnetic material to be determined. In this context, a 'temperature parameter' may be the actual temperature of the material, to some known degree of precision or accuracy. Alternatively, a temperature parameter may be an indication of whether the temperature of the magnetic material is above or below a predetermined temperature of interest, or lies within a particular temperature range.
Relevant magnetic properties of magnetic materials that may be detected, either directly or indirectly, using appropriate sensor means, include: magnetic permeability; magnetic susceptibility; remanence (i.e. degree of magnetisation); and/or coercivity. As will be understood by those skilled in the relevant art of materials science, these are generally related, however different sensing techniques may measure each one more or less directly.
In some embodiments, in which the most directly measured property is magnetic susceptibility, a detector is configured to sense the reluctance of a magnetic circuit which comprises the magnetic material and a magnet, such as a permanent magnet or an electromagnet. The detector may further comprise a magnetic field strength sensor, such as a Hall effect sensor, which produces an output electrical signal, such as a voltage, which is dependent upon the strength of a surrounding magnetic field.
In such embodiments, the field strength varies in accordance with changes in magnetic reluctance of the magnetic circuit, which in turn depends upon the susceptibility of the materials in the circuit, including the magnetic material. The circuit may be calibrated by recording a relationship between the field strength sensor output signal and temperature of the magnetic material within the target temperature range, and the electronic processor may then be configured by programming it with this calibration data.
In an alternative embodiment the detector comprises a magnet, such as a permanent magnet or an electromagnet, configured to magnetise the magnetic material of the member, and a sensor configured to generate a signal corresponding with a subsequent strength of the magnetic field generated by the magnetised magnetic material. For example, in the case of a rotating part, such as a clutch disc, the magnet and the sensor may be arranged sequentially adjacent to the disc, such that a component of the disc comprising the magnetic material first passes the magnet, and subsequently passes the sensor. The sensor may comprise an inductive coil across which a voltage is generated which depends upon the number of turns in the coil, and the rate of change of magnetic field strength as the magnetised magnetic material transits the sensor. The rate of change of the magnetic field's strength in turn depends upon the speed of relative motion between the sensor and the magnetic material, and the strength of the magnetic field which is proportional to the remanence of the magnetic material.
In such embodiments, the electronic processor is preferably configured to receive a measure of speed of relative motion of the sensor and the magnetic material, such as a measure of the angular velocity of a rotating disc. Alternatively, the electronic processor may be configured, e.g. by programming of a microcontroller, to determine the angular velocity of a rotating part by measuring the periodicity of detection of pulses corresponding with detection of the magnetic material at the sensor. The electronic processor is further configured to determine a current temperature parameter of the magnetic material from the magnitude of signal pulses generated as the magnetic material passes through the sensing region of the sensor.
Embodiments of the invention based upon sensing of magnetic remanence are particularly practical for measuring whether the temperature of the magnetic material, and hence the member, is above or below a predetermined threshold temperature. The magnetic material may be designed or selected to have a predetermined Curie point which, as is well-known to persons skilled in the relevant art of materials science, is a temperature above which a magnetic material, such as a ferromagnetic or ferrimagnetic material, becomes paramagnetic. Accordingly, above the Curie point the remanence of the magnetic material is dramatically reduced, which is readily sensed by detecting an absence of substantial signal pulses generated at the sensor outputs, e.g. an absence of voltage pulses at the terminals of a sensor coil.
In yet another embodiment, the detector comprises a magnet, such as a permanent magnet or an electromagnet, which generates a magnetic field, and a movable member disposed within the magnetic field whereby the field causes a force to be exerted upon the movable member. The detector then further comprises a sensor arranged to sense a force acting on the movable member. The movable member is disposed adjacent to an air gap in the magnetic circuit, and a force exerted upon the movable member will tend to close the gap. The magnitude of the force depends upon the strength of the field, which in turn depends upon the permeability of the magnetic material. For a magnetic material in which the permeability varies in a predetermined manner over a target temperature range, a signal generated by the force sensor will vary in accordance with corresponding variations in temperature of the magnetic material of the member.
In a variation upon this embodiment, the force sensor comprises a spring-loaded switch, such that when the temperature of the magnetic material of the member reaches a threshold value, the field force acting on the movable member comprising the switch causes a change in state of associated switch contacts. The change of switch state comprises a signal receivable by the electronic processor, which determines in response to the switch closure that the threshold temperature has been reached or exceeded. The properties of the magnetic material, the design of the magnetic circuit, and the strength of the switch, may all be configured such that the change of switch state is accurately aligned with a desired temperature.
In a still further embodiment the detector comprises a light source configured to generate a polarised beam of light. The light source may be, for example, a semi conductor laser having a substantially polarised output. Alternatively, the light source may be an unpolarised source, such as a lamp or a light-emitting diode, in combination with a polarising filter. The detector may further comprise a magnet, such as a permanent magnet or an electromagnet, disposed to form a magnetic circuit with the magnetic material comprising an air gap containing a magnetic field, the strength of which will vary with the permeability of the magnetic material, and hence with a temperature over the target temperature range. The polarisation of the light beam will rotate as it passes through the magnetic field, by an angle which depends upon the magnetic field strength. The detector then further comprises a polarising light sensor, such as a polarising filter disposed in front of a photo detector, having a signal output comprising, for example, a voltage or current derived from the photo detector. The output signal from the sensor will thereby depend upon the angle of rotation of the optical field, which will vary in accordance with the permeability, and hence temperature, of the magnetic material.
This embodiment of the invention may be calibrated by measuring a relationship between temperature of the magnetic material and magnitude of the sensor output signal, and the electronic processor may then be configured, for example by programming it with a corresponding calibration table.
In yet another embodiment, in which no magnet is required, the detector comprises a coil disposed to enclose the member, or at least a part thereof, which comprises the magnetic material. As is well-known to persons skilled in the art of electrical circuit design, a coil comprises a circuit element having an inductance which depends upon the permeability of materials enclosed within the coil. Accordingly, the inductance of the coil varies with permeability of the magnetic material, and therefore with temperature within the target temperature range. The detector thus further comprises a circuit for measuring inductance of the coil, having an output at which a signal representing the current inductance is generated. The electronic processor may be configured with calibration data comprising measurements of the relationship between the inductance output signal and the temperature of the magnetic material.
In a further embodiment, the detector comprises a Wiegand wire disposed within a conductive coil such that a voltage pulse will be generated at the terminals of the coil in response to changes in the magnetisation of the Wiegand wire. In this embodiment, the member further comprises at least a first permanent magnet configured to apply a relatively strong magnetic field of a first magnetic polarity to the Wiegand wire, a second permanent magnet configured to subsequently apply a relatively weaker magnetic field of an opposing magnetic polarity to the Wiegand wire, and a third permanent magnet disposed adjacent to the magnetic material. The first, second and third permanent magnets are disposed such that, in use, they move past the Wiegand wire sensor in sequence, whereby the first and second permanent magnets sensitise the Wiegand wire, and the response of the Wiegand sensor to passage of the third permanent magnet depends upon the temperature of the magnetic material. More particularly, the third permanent magnet and the magnetic material are arranged such that, below a Curie point of the magnetic material the Wiegand wire passes through a corresponding magnetic field when moving past the third magnet, whereas above the Curie point the magnetic field does not extend substantially to the location of the Wiegand wire. Consequently, a pulse is generated at the terminals of the conductive coil, i.e. the sensor output, only if the temperature of the magnetic material is below the Curie point.
Advantageously, a series of magnets and magnetic materials may be disposed to pass the Wiegand sensor in sequence, each magnetic material in series having a higher Curie point than the preceding magnetic material. For a temperature lying between the Curie point of the first magnetic material in the sequence and a last magnetic material in the sequence, a pulse will be generated at a time corresponding with passage of the first magnetic material having a Curie temperature which is higher than the current temperature. The electronic processor may therefore be configured to measure a time delay between sensitisation of the Wiegand wire, and a subsequent pulse output from the conductive coil. This time delay is thereby associated with a corresponding temperature range.
In another aspect, the invention provides a contactless temperature sensing method comprising the steps of:
providing a member which comprises a magnetic material having a magnetic property which varies in a predetermined manner over at least a target temperature range;
sensing a current value of the magnetic property of the magnetic material via a contactless electromagnetic coupling; and
determining a current temperature parameter of the magnetic material based upon the sensed value of the magnetic property.
In other aspects, the invention provides various apparatus for sensing magnetic properties of a magnetic material, wherein the magnetic properties vary in a predetermined manner over at least a target temperature range.
Further preferred features, advantages and applications of the invention will be apparent to those skilled in the art from the following description of preferred embodiments, which should not be considered to be limiting of the scope of the invention as defined in any of the preceding statements, or in the claims appended hereto.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are described with reference to the accompanying drawings, in which:
Figure 1 illustrates schematically a contactless temperature sensing system according to an embodiment of the invention;
Figure 2 illustrates schematically a detector arrangement comprising a Hall effect sensor according to a first embodiment of the invention;
Figure 3 illustrates schematically a detector arrangement comprising a remanence sensor according to a second embodiment of the invention;
Figure 4 illustrates schematically a detector arrangement comprising a moving magnetic switch according to a third embodiment of the invention;
Figure 5 illustrates schematically a detector arrangement comprising an inductance-based sensor according to a fourth embodiment of the invention; Figure 6 illustrates schematically a detector arrangement comprising an optical sensor according to a fifth embodiment of the invention; and
Figure 7 illustrates schematically a detector arrangement comprising a Wiegand effect sensor according to a sixth embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Figure 1 shows schematically a contactless temperature sensing system 100 embodying the invention. A member 102, the temperature of which is to be sensed, comprises a magnetic material, such as magnetic insert 104, which is in thermal contact with the material of the member 102. While the member 1 02 comprises a rotating member, the invention is not limited to sensing the temperature of rotating bodies. In general, embodiments of the invention may be used for contactless sensing in a variety of applications, including, but not limited to, sensing the temperature of moving components more generally.
The magnetic material 104 has at least one magnetic property which varies in a predetermined manner over a target temperature range. The temperature-dependent magnetic property may comprise, for example, magnetic susceptibility, magnetic permeability, magnetic remanence, or any combination of these and other related magnetic properties.
A detector 106 is configured to sense a current value of the temperature-dependent magnetic property of the magnetic material 104. According to various embodiments of the invention, this detection is achieved via electromagnetic coupling across a gap 108 between the member 102 and the detector 106. Accordingly, contactless sensing of the temperature-dependent magnetic property, and accordingly of one or more relevant temperature parameters of the member 102, may be achieved. The detector 106 generally includes a sensor (not shown in Figure 1 ) the configuration of which depends upon the particular magnetic property that is to be detected, and the particular means used for sensing of that property. A number of specific detector arrangements are described below, with reference to Figures 2 to 7.
The detector 106 has a detector output 1 10, at which a signal is generated corresponding with a currently sensed value of the relevant magnetic property. Typically, the output signal will be a current or a voltage, and may be either analog (i.e. a continuously varying value), or digital (i.e. having binary or other discrete states) such as a switch output.
A processor 1 12 comprises a Central Processing Unit (CPU) 1 14 which is operatively associated with a storage memory device 1 16. One or more peripheral interfaces, e.g. 1 18, are also operably associated with the CPU 1 14, and are available for receiving input and/or generating output as required in particular embodiments of the invention. For example, user interface elements, such as keyboards, keypads and display devices, may be provided to enable manual control and monitoring of the system 100. Alternatively, input and output interfaces 1 18 may be associated with other components and devices of a large system comprising the contactless temperature sensing system 100. By way of example, in an automotive application the member 102 may be a rotating clutch plate, the temperature of which is to be monitored within a larger DCT system. Additional interfaces e.g. 1 18, may be associated with other parts of the DCT system, such as the clutch actuators and other control and sensing elements of the overall automotive transmission system. A full description of such a DCT system is beyond the scope of the present disclosure, but will be known to those of ordinary skill in the relevant art of automotive transmission design.
An input interface 120 is configured to receive the signal output from the detector, 106. Where the signal output is an analog signal, the interface 120 may comprise an analog-to-digital converter for producing a digital signal that may be retrieved and processed by the CPU 1 14. An interface 120 comprising an analog-to-digital converter may further comprise a sample-and-hold circuit, enabling the CPU 1 14 to obtain sample values of the output signal from the detector 106 at specified instants in time. Alternatively, an interface 120 comprising an analog-to-digital converter may further comprise a clock, such as an electrical oscillator, for sampling of the analog input at discrete time intervals, for providing the CPU 1 14 with a digitised and sampled version of the analog waveform output from the detector 106.
In alternative embodiments, the output signal from the detector 106 may comprise one or more binary digit values, and in such embodiments the interface 120 may comprise corresponding latches for holding values of the output values for retrieval by the CPU 1 14. The storage memory 1 16 generally comprises, in use, a body of program instructions 122. The program instructions 1 22 are executable by the CPU 1 14 in order to implement the necessary processing of received signal values from the detector 106 to determine one or more current temperature parameters of the magnetic material 104, and thus the member 102. The memory 1 16 will also generally include permanent and/or transitory data used by the CPU 1 14 in processing the input signals.
The processor 1 12 may comprise discrete electronic components, such as a microprocessor 1 14, one or more memory ICs 1 16, one or more peripheral interface ICs 1 18, and one or more input interface ICs 120. Alternatively, all of these elements may be integrated onto a single chip, such as a microcontroller chip. The use of a microcontroller is particularly advantageous in embedded systems, such as a DCT system, due to the small size, high level of integration, and relative robustness of such devices.
Various other implementations of the processor 1 1 2, as will be apparent to persons skilled in the art of analog and digital electronic design, are also possible within the scope of the present invention. It is not, for example, necessary that the processor 1 12 comprise a CPU 1 14. In alternative embodiments, the processor 1 12 may comprise discrete or integrated digital and/or analog components other than a software programmable component such as the CPU 1 14. However, the microprocessor or microcontroller-based processor 1 1 2 is highly flexible, by virtue of its programmability, and may be employed with all of the specific embodiments of the detector 106 that are described hereafter, with reference to Figures 2 to 7.
The magnetic material 104 may be any suitable material, such as a ferromagnetic or ferrimagnetic material, having magnetic properties which vary in a known manner over at least a temperature range within which the temperature of the member 102 is to be monitored. Various metallic materials, crystalline materials, and mixtures or alloys thereof, are known to have specific temperature-dependent properties. A specific property of ferromagnetic and ferrimagnetic materials is the Curie point, or Curie temperature, which is the temperature at which the spontaneous alignment of magnetic dipoles within domains of the material breaks down, and above which the material substantially ceases to exhibit spontaneous magnetisation and instead becomes paramagnetic. This transition at the Curie temperature can generally be detected by a suitable sensing arrangement, and accordingly may be used as a magnetic property for monitoring whether or not the temperature of the magnetic material 104 is below or above the Curie point.
By way of example, Table 1 lists the Curie temperature of a number of representative magnetic crystalline materials. The table illustrates the possibility to select magnetic materials 104 for the purpose of detecting temperatures over a wide range.
Table 1: Curie Temperatures of selected ferromagnetic and ferrimagnetic materials
More generally, magnetic materials 104 having any desired Curie point within the range of available materials may be created by forming alloys or other combinations of two or more suitable materials. By way of example, US Patent No. 5,665,819, in the name of Rudolf K Tenzer, which was issued on 9 September 1997, discloses methods for forming ferrite compositions having Curie temperatures within the range of at least 1 15°C to 393°C. More generally, magnetic materials 104 will have magnetic properties, such as permeability, susceptibility, remanence and so forth, that vary continuously with temperature. Accordingly, in any given detector arrangement it is possible, in principle, to implement a contactless temperature sensor by calibrating detected signal values, e.g. at output 1 10, against independently measured or controlled temperatures of the member 102. Such calibration data can then be stored within the memory 1 16, to enable temperature sensing across the corresponding range of calibrated temperature values. The generality of this technique will be apparent to persons skilled in the art, and can be applied to a number of the embodiments described hereafter with reference to Figures 2 to 7.
Turning now to Figure 2, there is shown a detector arrangement 200 which includes a rotating disc 202 fixed to a shaft 204. The disc 202, which is a member whose temperature is to be monitored, comprises an insert of magnetic material 104. A magnetic circuit 206 comprises a magnetic member 208, which is made of a suitable high permeability material such as iron. A permanent magnet 21 0 provides the magnetomotive force (MMF) inducing a magnetic field in the circuit 206. A Hall effect sensor 21 2 detects the field strength in the circuit 206, which varies as the insert 104 passes the magnet 210.
At those points in time, such as illustrated in Figure 2, when the magnetic material 104 is within the magnetic circuit 206, the field strength detected by the Hall effect sensor 212 depends upon the susceptibility of the insert 104, which in turn depends upon its temperature. In this embodiment, the magnetic member 208, the magnet 210, and the Hall effect sensor 212 comprise the detector 106, and the detector output 1 10 is the output of the Hall effect sensor.
Figure 3 illustrates a detector arrangement 300 which again comprises a rotating disc 302 fixed to a shaft 304. A magnet 306 is disposed to magnetise an insert of magnetic material 1 04 each time the insert passes on the rotating disc 302. A sensor 308 comprises an insulated wire coil, which is preferably wound around a suitable high-permeability material such as iron. As the magnetised insert 104 passes the coil 308, it will first induce a voltage of a first polarity as the field strength at the coil 308 increases, and then a reverse voltage as the field strength reduces. The result is a periodic output pulse 310. Magnetisation of the insert 104 by the magnet 306, and the subsequent magnitude of the pulse 31 0, depends upon the remanence of the material 104, which varies with temperature. In particular, the remanence declines with rising temperature, and drops to a negligible value at the Curie temperature of the material 104.
As is well-known in the art, the magnitude of the pulse 310 depends upon the rate of change of the magnetic field passing the coil 308, and is therefore dependent upon the speed of rotation of the disc 302 and the magnetic field generated by the insert 104. The rotational speed of the disc 302 may be separately monitored and the information provided to the processor 1 1 2, or the processor 1 12 may monitor the rate of rotation according to the frequency of generation of the pulse 310. The magnitude of the pulse 31 0 may then be processed by the processor 1 12 to determine a temperature measurement of the disc 302, for example using previously recorded calibration data.
In addition, where a continuous temperature measurement is not required, the arrangement 300 can be used to monitor whether the temperature of the disc 302 is below or above the Curie point of the material 104. Below the Curie point, pulses 310 will be generated. Above the Curie point the material 104 is no longer magnetisable, and the pulses will substantially disappear.
Figure 4 illustrates a further detector arrangement 400 comprising a disc
402 made entirely of a selected magnetic material, which rotates on a shaft 404. A magnet 406 is disposed adjacent to the disc 402, such that the magnet is attracted to, and tends to move towards, the disc 402. Motion of the magnet 406 is restrained by a coiled spring 408, which provides a restoring force in the event that the magnetic attraction is reduced or disappears. A first metallic contact 410 is affixed to the magnet 406, adjacent to a second metallic contact 412.
By appropriate selection of the strength of the magnet 406 and of the spring 408, the arrangement 400 may be configured such that when the disc 402 is below the Curie point of the magnetic material the conductive contacts 410, 41 2 are brought into contact with another, thereby closing a circuit that may be monitored by an interface 1 20 of the processor 1 12. When the temperature of the disc 402 reaches its Curie point, the magnetic attraction will be dramatically reduced, and the contacts 410, 412 will part, opening the electrical circuit. Figure 5 shows a further detector arrangement 500 in which a rotating disc 502 again is comprised entirely of a magnetic material. The disc rotates on shaft 504. A magnetic member 506, preferably made of a suitable high-permeability material such as iron, is disposed adjacent to the disc 502, such that the magnetic member 506 and the disc 502 comprise a magnetic circuit. An insulated conductive coil 508 is wound around the magnetic member 506.
As is well-known in the electrical arts a conductive coil, such as coil 508, exhibits an electrical inductance that is dependent upon the permeability of the elements in the magnetic circuit comprising the member 506 and the disc 502. In the arrangement 500 a controller 51 0 operates an AC-voltage source 512, and monitors an AC ammeter 514. The ratio between the applied voltage 512 and the measured current 514 is a measure of the inductance of the coil 508, which varies with permeability of the disc 512, which in turn varies with temperature. There will, accordingly, be a relationship between measured inductance and temperature, which can be determined and stored via a calibration process.
The controller 510 may be implemented as additional software instructions executed by the CPU 1 14 of the processor 1 12. In this case, an output interface 1 1 8 may be used for control of the voltage source 512, and the input interface 120 is coupled to the ammeter 514.
Figure 6 illustrates a further detector arrangement 600 in which a rotating disc 602 is coupled to a shaft 604, and comprises an insert of magnetic material 104. A magnet 606 is disposed on one side of the rotating disc 602. On the opposing side there is located a source of polarised light 608, such as a laser. Light from the source 608 passes through a beam splitter 610, and the transmitted portion is reflected from a reflective surface 612 disposed on the disc 602. Light is therefore reflected back to the beam splitter 610, and a reflected portion passes through a polarising filter 614 to a detector 61 6.
As is well-known in the art of electro-magnetics and optics, the presence of a magnetic field causes a rotation in the polarisation state of polarised light. Accordingly, the strength of the signal received by the detector 616 via the polarising filter 614 will vary with the strength of the magnetic field through which the light beam passes between the beam splitter 610 and the reflective surface 61 2. In general, below its Curie point the permeability of the magnetic insert 104 is greater than that of the surrounding disc 602. Accordingly, as the insert 104 passes between the magnet 606 and the polarised light source 608, the magnetic field between the beam splitter 610 and the disc 602 will increase, by an amount that depends upon the permeability of the magnetic material 104, and thus generally upon its temperature. The polarisation vector of the polarised light will rotate in proportion to this magnetic field strength, resulting in a variation in the detected intensity at the detector 616. For example, a maximum detected intensity will occur when the polarisation of the incident light is aligned with that of the polarising filter 614. Any rotation away from this alignment will result in a reduction of detected intensity. The arrangement 600 may therefore be calibrated in order to determine temperature as a function of detected intensity.
Figure 7 illustrates schematically a detector arrangement according to a further embodiment of the invention. The figure shows the actual (rotational) physical layout 700 of the arrangement, along with a linear schematic layout 702, which is an 'unwound' version of the rotational layout 700.
The detector arrangement comprises a plurality of magnetic inserts, arranged in sequence around the disc 702, from a first insert 704 to a final insert 706. A pickup 708 comprising a Wiegand effect sensor is disposed to enable detection of the passage of the magnetic inserts 704 to 706. At the start of each rotation, the Wiegand sensor 708 is sensitised by a sensitising insert 710 comprising two permanent magnets 710a, 710b of opposing polarity. The Wiegand sensor 708 comprises a Wiegand wire 712, around which is wound an insulated wire coil 714. The output of the sensor is a voltage that is developed, in appropriate circumstances, at the terminals of the wire coil 714.
Each of the magnetic inserts 704 to 706 comprises a permanent magnet
71 6 and a magnetic material element 718, such as a suitable ferrite, having a predetermined Curie temperature. Each of the sequential magnetic inserts 704 to 706 has a higher Curie point than the preceding insert.
The detector arrangement 700 works as follows. The first start position magnet 710a has a field of sufficient strength to align the magnetic orientation of both the shell and the core of the Wiegand wire 712 in one direction. The second start position magnet 710b has only sufficient strength to reverse the magnetisation of the Wiegand wire core, producing a small negative pulse 720 at the terminals of the coil 714, as it does so. At the commencement of each rotation, therefore, the Wiegand wire core and shell have opposing magnetisation. The magnetic inserts 704 to 706 on the rotating disc 702 are in close thermal contact with the disc, and have a substantially identical temperature. When the temperature of one of the inserts is below its Curie point, the magnetic material 718 is magnetised by the magnet 716, and the resulting field is relatively strong at the Wiegand sensor pickup 708, as illustrated schematically by the field 722. However, when the magnetic material 718 is above its Curie point, it becomes paramagnetic and the field strength, 724, at the pickup 708, is reduced.
By way of example, assuming that the temperature of the disc 702 is between the Curie point of the first insert 704 and that of the last insert 706, there will be one or more inserts for which the temperature of the magnetic material 718 is above its Curie point, however an insert 726 will eventually be reached for which the temperature is below the corresponding Curie point. At this point, the larger magnetic field 722 passing the Wiegand wire 71 2 will reverse the magnetic orientation of the core of the Wiegand wire 712, producing a large positive pulse 728 at the terminals of the coil 714. The time delay between the initial negative pulse 720 and the positive pulse 728 may be used to identify the insert 726, and accordingly the temperature of the disc 702 to within the resolution provided by the differences in Curie points of successive inserts.
In this embodiment, the voltage pulses at the terminals of the coil 714 may be input to the processor 1 12 via an interface 120 that initiates a timer upon receipt of the negative pulse 720, and stops the timer upon receipt of the positive pulse 728. The elapsed time may be read and processed by the CPU 1 14 in order to generate an indication of the temperature of the disc 702.
While the foregoing description has disclosed a number of embodiments of the invention, it will be understood that this is not intended to be exhaustive of all possible means by which the invention may be put into effect. Other embodiments and variations are also possible, and the overall scope of the invention is as defined in the claims appended hereto.
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