CA1063210A - Two-core magnetic temperature sensor - Google Patents
Two-core magnetic temperature sensorInfo
- Publication number
- CA1063210A CA1063210A CA240,286A CA240286A CA1063210A CA 1063210 A CA1063210 A CA 1063210A CA 240286 A CA240286 A CA 240286A CA 1063210 A CA1063210 A CA 1063210A
- Authority
- CA
- Canada
- Prior art keywords
- temperature
- cores
- temperature sensor
- coupled
- magnetic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 230000035699 permeability Effects 0.000 claims abstract description 6
- 238000004804 winding Methods 0.000 claims description 12
- 239000000463 material Substances 0.000 claims description 8
- 230000004907 flux Effects 0.000 claims description 4
- 239000011162 core material Substances 0.000 description 43
- 230000007704 transition Effects 0.000 description 10
- 230000008859 change Effects 0.000 description 4
- 230000007423 decrease Effects 0.000 description 3
- 230000001939 inductive effect Effects 0.000 description 2
- 230000008901 benefit Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
- G01K7/36—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using magnetic elements, e.g. magnets, coils
- G01K7/38—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using magnetic elements, e.g. magnets, coils the variations of temperature influencing the magnetic permeability
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measuring Temperature Or Quantity Of Heat (AREA)
- Coils Or Transformers For Communication (AREA)
Abstract
TWO-CORE MAGNETIC TEMPERATURE SENSOR
Abstract of the Disclosure A temperature sensing device which utilizes a pair of inductively wound magnetic cores is disclosed. The cores are constructed so that the permeability of one core changes with temperature at a rate which is different from the rate that the permeability of the other core changes, with respect to temperature. A plot of inductance vs. temperature, thus varies so that the curves for the two cores intersect at the temperature which is to be sensed. The cores are connected together in a four-arm inductance bridge network and a null detector is coupled to the bridge network to provide an electrical output signal.
Abstract of the Disclosure A temperature sensing device which utilizes a pair of inductively wound magnetic cores is disclosed. The cores are constructed so that the permeability of one core changes with temperature at a rate which is different from the rate that the permeability of the other core changes, with respect to temperature. A plot of inductance vs. temperature, thus varies so that the curves for the two cores intersect at the temperature which is to be sensed. The cores are connected together in a four-arm inductance bridge network and a null detector is coupled to the bridge network to provide an electrical output signal.
Description
~ 1063210 TWO-CORE MA(~7NETIC TEMPERATVRE SENSOR
Background of the Invention Magnetic cores, such as toroidal-shaped cores, have been previously used for temperature sensing. The prior art methods of temperature sensing utilized transition characterist-ics of the magnetic core such as the Curie temperature tran-sition and/or first order transitions such as those described in United States Patent No. 3,534,306 issued on October 13, 1970, in the name of Watrous et al.
B~y way of further example of the prior art, the U.S.
Patent to Yetter, No. 3,~39,783, March 8, 1966, relates to a temperature-responsive current controllin~ inductor device which relies on a first order transition to accomplish temp-erature sensing, a first order transition being defined in the Yetter patent as one in which a discontinuity occurs in the first derivative of the Gibbs free energy. A second order transition is one in which the second derivative of the free energy function is discontinuous but the first derivative is continuous. Temperature sensors which rely on the Curie point transition are examples of this type of sensor.
Prior temperature sensing devices of this type relied on the fact that at a certain temperature a drastic change of the magnetic characteristics of the core would occur. Thus, if a wire were wound around the core to form an inductance element, the inductance of the element would change drastically when the predetermined temperature was reached. This required specific core materials that were specially formulated and carefully controlled in order to provide the desired rapid transition at the exact temperature that was desired. A
different specially manufactured magnetic core would then have to be substituted in the sensor in order to sense another temperature.
B -1 ~
`"`-` 1063210 Summary of the Inventio_ The sensing device of the present invention, by contrast to the prior art, does not depend upon any rapid change of inductance state of the magnetic core. The present invention is directed to a temPerature sensor which has two continuously varying magnetic permeability vs. temperature characteristics which intersect at the point at which the temperature is to be sensed, and there is no first or second order transition associated with the cores over the temperature range, that is, the inductance is a 10 continuous, transitionless function of temperature over the temperature range. In the present sensing device, the inductance of the cores varies in a gradual manner until the inductance of both cores is approximately equal at a pre-determined temperature which is then sensed by the sensing circuit. The advantage of this approach over the prior art devices is that by changing the inductance of the core by changing the number of windings on the core, the cross-over point where the two inductances are equal may be changed so that the temperature sensor may be used over wide range temperatures.
In its broader aspects, the invention comprehends a temperature sensor including first and second separate inductively wound magnetic cores each having an independent, self-contained magnetic flux path provided by a closed loop configuration of magnetically permeable material so that no substantial amount of magnetic flux is externally coupled from either of the cores. The cores have different inherent magnetic permeability vs. temperature characteristics which are controlled so that the inductance vs. temperature characteristics of the two cores intersect at the temperature which is to be sensed within a predetermined temperature range, and so that the inductance is a continuous, transitionless ~063210 function of temperature over the temperature range. An alternating current source of voltage is coupled to the sensor and sensing means are coupled to the sensor which indicates that at least one of the magnetic cores is affected by a temperature of a predetermined magnitude when the output signals derived from the magnetic cores are approximately equal.
Although two magnetic cores have been connected in series to achieve temperature compensation, as is shown in United States Patent No. 3,824,502, issued on July 16, 1974 to Bardash et al, the utilization of two series connected magnetic cores that have different temperature character-istics for sensing temperatures over a relatively large range of tem~eratures without a transition change of the magnetic state of the core has not previously been accomplish-ed.
Description of the Drawings The present invention is illustrated by reference to the following drawings in which:
Fig. 1 is a schematic illustration of a described embodiment of the ~resent invention;
16~632~0 1 Fig. 2 is a graph showing inductance vs. temperature characteristics of the two magnetic cores employed in the circuit of Fig. l; and Fig. 3 is a diagrammatic illustration showing an output voltage signal vs. temperature characteristics for the schematic of Fig. 1.
Technical Description of the Invention The present invention utilizes a pair of magnetic cores which are preferably toroidal-shaped cores and which are wound with an electrical wire to form a pair of inductance elements. The inductance vs. temperature characteristics of the two cores are purposely made to be different, preferably due to the employment of different materials in each of the cores. The cores 10, 12 are preferably constructed of linear material as contrasted to a square-loop material used in the device of the Bardash et al U.S. patent. One of the cores of the present invention may be constructed of a material that is commer-cially sold by the Ferroxcube Corporation under the trademark of Ferroxcube 3E2A and the other material may be (trademark) made of Ferroxcube 3D3 material. The inductance of one of the two cores will be less than the other below a pre-determined sensing temperature and will be greater than the inductance of the other core above the predetermined sensing temperature. At the predetermined desired sensing temper-ature, the inductance of both cores will be equal.
1 The inductively wound cores 10, 12 shown in the schematic of Fig. 1 may be contained in a separate unit 14 which may be positioned at a remote location in order to sense the ambient temperature at that location. The cores 10, 12 are wound with the wires 11, 13 which are connected to the terminals 16, 18, respectively, of a four-arm inductive bridge circuit 20. The other two inductive bridge circuit impedances are formed by the secondary windings 22, 24 of a transformer 26. The primary winding 28 of the transformer 26 is coupled to an alternating source of voltage 30. A
conventional null detector circuit 32 is connected across the terminals 34, 36 of the bridge circuit 20 to sense when the inductance of the two cores 10, 12 are equal so it can provide an electrical output signal which indicates that the desired temperature has been sensed. The null detector 32 may be replaced by any conventional sensing device or circuit for sensing the output of an A.C. bridge circuit;
the design of such devices and circuits being well-known in the art.
An inductance vs. temperature plot for the cores 10, 12 is in Fig. 2 where the solid-line curves 10', 12' correspond respectively to the cores 10, 12 of Fig. 2. It can be seen from this graph the two curves cross at the intersection point 38 which represents the temperature T which is to be sensed. The inductance of the cores 10, 12 can be easily changed by changing the number of windings on the cores; and thus, a new temperature T' may be sensed by changing the windings in a controlled manner due to a shifting of the inductance vs. temperature characteristics 10', 12' 1063Z~0 1 to different locations so that they cross at the point 39, as shown by the dotted-line curves. A temperature sensor having a relatively large sensing range is, therefore, provided by the present invention. The reference temperature that is to be sensed may be controlled by adjustment of the control wiper 25 which is connected to the secondary windings 22, 24 of the transformer 26, or alternately by utilization of saturable transformer windings and at least one movable magnetic control element, such as the magnet 27, that is magnetically coupled to the windings.
While the inductance of the curve 10' preferably in-creases with increasing temperature and the inductance of the curve 12' preferably either decreases or remains relatively constant, this is not a necessary requirement. Unlike the temperature compensating elements of the previously mentioned Bardash et al U.S. Patent, it is not necessary for the permeability of one core to increase while the other core decreases, it being sufficient that the inductances vs.
temperature characteristics of the two cores merely vary differentially so that they intersect at the desired temperature to be sensed.
Fig. 3 illustrates the output signal that is sensed by the null detector 34. It is seen that when the temperature is below the sensing temperature T, the output signal 40 is of a first phase, but that the magnitude of the output signal will decrease as the cross-over point 38 is approached. At the cross-over point 38 no reading is obtained by the null detector indicating that the desired temperature T
has been reached. As the temperature increases 1 beyond the sensed temperature T, the output signal 42 is of a phase which is opposite to the phase of the output signal 40 and increases in magnitude as the temperature increases beyond the intersection point 38.
Although a null detector is the presently preferred output detector because of its simplicity, it is desirous that other types of detectors, including magnitude and phase responsive indicators, may be employed in the present invention.
Background of the Invention Magnetic cores, such as toroidal-shaped cores, have been previously used for temperature sensing. The prior art methods of temperature sensing utilized transition characterist-ics of the magnetic core such as the Curie temperature tran-sition and/or first order transitions such as those described in United States Patent No. 3,534,306 issued on October 13, 1970, in the name of Watrous et al.
B~y way of further example of the prior art, the U.S.
Patent to Yetter, No. 3,~39,783, March 8, 1966, relates to a temperature-responsive current controllin~ inductor device which relies on a first order transition to accomplish temp-erature sensing, a first order transition being defined in the Yetter patent as one in which a discontinuity occurs in the first derivative of the Gibbs free energy. A second order transition is one in which the second derivative of the free energy function is discontinuous but the first derivative is continuous. Temperature sensors which rely on the Curie point transition are examples of this type of sensor.
Prior temperature sensing devices of this type relied on the fact that at a certain temperature a drastic change of the magnetic characteristics of the core would occur. Thus, if a wire were wound around the core to form an inductance element, the inductance of the element would change drastically when the predetermined temperature was reached. This required specific core materials that were specially formulated and carefully controlled in order to provide the desired rapid transition at the exact temperature that was desired. A
different specially manufactured magnetic core would then have to be substituted in the sensor in order to sense another temperature.
B -1 ~
`"`-` 1063210 Summary of the Inventio_ The sensing device of the present invention, by contrast to the prior art, does not depend upon any rapid change of inductance state of the magnetic core. The present invention is directed to a temPerature sensor which has two continuously varying magnetic permeability vs. temperature characteristics which intersect at the point at which the temperature is to be sensed, and there is no first or second order transition associated with the cores over the temperature range, that is, the inductance is a 10 continuous, transitionless function of temperature over the temperature range. In the present sensing device, the inductance of the cores varies in a gradual manner until the inductance of both cores is approximately equal at a pre-determined temperature which is then sensed by the sensing circuit. The advantage of this approach over the prior art devices is that by changing the inductance of the core by changing the number of windings on the core, the cross-over point where the two inductances are equal may be changed so that the temperature sensor may be used over wide range temperatures.
In its broader aspects, the invention comprehends a temperature sensor including first and second separate inductively wound magnetic cores each having an independent, self-contained magnetic flux path provided by a closed loop configuration of magnetically permeable material so that no substantial amount of magnetic flux is externally coupled from either of the cores. The cores have different inherent magnetic permeability vs. temperature characteristics which are controlled so that the inductance vs. temperature characteristics of the two cores intersect at the temperature which is to be sensed within a predetermined temperature range, and so that the inductance is a continuous, transitionless ~063210 function of temperature over the temperature range. An alternating current source of voltage is coupled to the sensor and sensing means are coupled to the sensor which indicates that at least one of the magnetic cores is affected by a temperature of a predetermined magnitude when the output signals derived from the magnetic cores are approximately equal.
Although two magnetic cores have been connected in series to achieve temperature compensation, as is shown in United States Patent No. 3,824,502, issued on July 16, 1974 to Bardash et al, the utilization of two series connected magnetic cores that have different temperature character-istics for sensing temperatures over a relatively large range of tem~eratures without a transition change of the magnetic state of the core has not previously been accomplish-ed.
Description of the Drawings The present invention is illustrated by reference to the following drawings in which:
Fig. 1 is a schematic illustration of a described embodiment of the ~resent invention;
16~632~0 1 Fig. 2 is a graph showing inductance vs. temperature characteristics of the two magnetic cores employed in the circuit of Fig. l; and Fig. 3 is a diagrammatic illustration showing an output voltage signal vs. temperature characteristics for the schematic of Fig. 1.
Technical Description of the Invention The present invention utilizes a pair of magnetic cores which are preferably toroidal-shaped cores and which are wound with an electrical wire to form a pair of inductance elements. The inductance vs. temperature characteristics of the two cores are purposely made to be different, preferably due to the employment of different materials in each of the cores. The cores 10, 12 are preferably constructed of linear material as contrasted to a square-loop material used in the device of the Bardash et al U.S. patent. One of the cores of the present invention may be constructed of a material that is commer-cially sold by the Ferroxcube Corporation under the trademark of Ferroxcube 3E2A and the other material may be (trademark) made of Ferroxcube 3D3 material. The inductance of one of the two cores will be less than the other below a pre-determined sensing temperature and will be greater than the inductance of the other core above the predetermined sensing temperature. At the predetermined desired sensing temper-ature, the inductance of both cores will be equal.
1 The inductively wound cores 10, 12 shown in the schematic of Fig. 1 may be contained in a separate unit 14 which may be positioned at a remote location in order to sense the ambient temperature at that location. The cores 10, 12 are wound with the wires 11, 13 which are connected to the terminals 16, 18, respectively, of a four-arm inductive bridge circuit 20. The other two inductive bridge circuit impedances are formed by the secondary windings 22, 24 of a transformer 26. The primary winding 28 of the transformer 26 is coupled to an alternating source of voltage 30. A
conventional null detector circuit 32 is connected across the terminals 34, 36 of the bridge circuit 20 to sense when the inductance of the two cores 10, 12 are equal so it can provide an electrical output signal which indicates that the desired temperature has been sensed. The null detector 32 may be replaced by any conventional sensing device or circuit for sensing the output of an A.C. bridge circuit;
the design of such devices and circuits being well-known in the art.
An inductance vs. temperature plot for the cores 10, 12 is in Fig. 2 where the solid-line curves 10', 12' correspond respectively to the cores 10, 12 of Fig. 2. It can be seen from this graph the two curves cross at the intersection point 38 which represents the temperature T which is to be sensed. The inductance of the cores 10, 12 can be easily changed by changing the number of windings on the cores; and thus, a new temperature T' may be sensed by changing the windings in a controlled manner due to a shifting of the inductance vs. temperature characteristics 10', 12' 1063Z~0 1 to different locations so that they cross at the point 39, as shown by the dotted-line curves. A temperature sensor having a relatively large sensing range is, therefore, provided by the present invention. The reference temperature that is to be sensed may be controlled by adjustment of the control wiper 25 which is connected to the secondary windings 22, 24 of the transformer 26, or alternately by utilization of saturable transformer windings and at least one movable magnetic control element, such as the magnet 27, that is magnetically coupled to the windings.
While the inductance of the curve 10' preferably in-creases with increasing temperature and the inductance of the curve 12' preferably either decreases or remains relatively constant, this is not a necessary requirement. Unlike the temperature compensating elements of the previously mentioned Bardash et al U.S. Patent, it is not necessary for the permeability of one core to increase while the other core decreases, it being sufficient that the inductances vs.
temperature characteristics of the two cores merely vary differentially so that they intersect at the desired temperature to be sensed.
Fig. 3 illustrates the output signal that is sensed by the null detector 34. It is seen that when the temperature is below the sensing temperature T, the output signal 40 is of a first phase, but that the magnitude of the output signal will decrease as the cross-over point 38 is approached. At the cross-over point 38 no reading is obtained by the null detector indicating that the desired temperature T
has been reached. As the temperature increases 1 beyond the sensed temperature T, the output signal 42 is of a phase which is opposite to the phase of the output signal 40 and increases in magnitude as the temperature increases beyond the intersection point 38.
Although a null detector is the presently preferred output detector because of its simplicity, it is desirous that other types of detectors, including magnitude and phase responsive indicators, may be employed in the present invention.
Claims (8)
1. A temperature sensor comprising first and second separate inductively wound magnetic cores each having an independent, self-contained magnetic flux path provided by a closed loop configuration of magnetically permeable material so that no substantial amount of magnetic flux is externally coupled from either of said cores, said cores having different inherent magnetic permeability vs. temperature characteristics which are controlled so that the inductance vs. temperature characteristics of the two cores intersect at the temperature which is to be sensed within a predetermined temperature range, and so that the inductance is a continuous, transitionless function of temperature over the temperature range, an alternating current source of voltage coupled to said sensor and sensing means coupled to said sensor which indicates that at least one of said magnetic cores is affected by a temperature of a predetermined magnitude when the output signals derived from said magnetic cores are approximately equal.
2. A temperature sensor as claimed in Claim 1 and further comprising a transformer having a primary winding and two secondary windings, said primary winding being coupled to said voltage source and said secondary windings comprising first and second impedance arms of a four-arm bridge circuit while said inductively wound magnetic cores comprise third and fourth impedance arms of said four-arm bridge circuit.
3. A temperature sensor as claimed in Claim 2 and further comprising an adjustable means associated with said transformer for adjusting the temperature at which said sensing means will respond.
4. A temperature sensor as claimed in Claim 1, wherein said sensing means comprises a null detector which is coupled across two terminals of said bridge circuit which senses when the impedances of said inductively wound cores are approximately equal.
5. A temperature sensor as claimed in Claim 1, wherein said magnetic cores form a voltage dividing network with said alternating current source of voltage coupled across said network and said sensing means coupled to said network.
6. A temperature sensor as claimed in Claim 5 wherein said magnetic cores are inductively wound so as to form a three-terminal device with said alternating current source of voltage coupled across two terminals of said device and said sensing means coupled to a third terminal of said device.
7. A temperature sensor as claimed in Claim 1, 2 or 3 wherein said magnetic cores are closed loop toroidal-shaped cores.
8. A temperature sensor as claimed in Claim 4, 5 or 6, wherein said magnetic cores are closed loop toroidal-shaped cores.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US53336474A | 1974-12-16 | 1974-12-16 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1063210A true CA1063210A (en) | 1979-09-25 |
Family
ID=24125644
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA240,286A Expired CA1063210A (en) | 1974-12-16 | 1975-11-24 | Two-core magnetic temperature sensor |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5194985A (en) |
| AU (1) | AU8717275A (en) |
| BR (1) | BR7508228A (en) |
| CA (1) | CA1063210A (en) |
| DE (1) | DE2555318A1 (en) |
| FR (1) | FR2295408A1 (en) |
| NL (1) | NL7514324A (en) |
| ZA (1) | ZA757446B (en) |
-
1975
- 1975-11-24 CA CA240,286A patent/CA1063210A/en not_active Expired
- 1975-11-26 ZA ZA757446A patent/ZA757446B/en unknown
- 1975-12-02 AU AU87172/75A patent/AU8717275A/en not_active Expired
- 1975-12-09 DE DE19752555318 patent/DE2555318A1/en active Pending
- 1975-12-09 NL NL7514324A patent/NL7514324A/en unknown
- 1975-12-12 BR BR7508228*A patent/BR7508228A/en unknown
- 1975-12-15 FR FR7538330A patent/FR2295408A1/en not_active Withdrawn
- 1975-12-16 JP JP50149213A patent/JPS5194985A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| FR2295408A1 (en) | 1976-07-16 |
| DE2555318A1 (en) | 1976-06-24 |
| AU8717275A (en) | 1977-06-09 |
| ZA757446B (en) | 1977-07-27 |
| BR7508228A (en) | 1976-08-24 |
| NL7514324A (en) | 1976-06-18 |
| JPS5194985A (en) | 1976-08-20 |
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