Ferromagnetic element with temperature regulation

• US 4,769,519 A
• Filed: 01/14/1987
• Issued: 09/06/1988
• Est. Priority Date: 06/28/1985
• Status: Expired

• Current Assignee: Delaware Capital Formation Incorporated (Dover Corporation)
• Original Assignee: Metcal Incorporated (Dover Corporation)
• Inventors: Hall, William D.
• Primary Examiner(s): Leung, Philip H.
• Application Number:
  US07/003,288
• Time in Patent Office: 601 Days
• Field of Search: 219/10.77, 219/10.75, 219/10.43, 219/10.41, 219/10.71, 219/499, 219/497, 219/501, 324/57 R, 324/57 PS
• US Class Current: 219/667
• CPC Class Codes: G05D 23/26 the sensing element having a permeability varying with temperature
• CPC Class Codes: H05B 3/0023 for heating by passing the current directly across the material to be heated
• CPC Class Codes: H05B 6/06 Control, e.g. of temperature, of power

Abstract

A ferromagnetic element has current passed through it either by direct electrical connections or by induction. The current through the ferromagnetic element may be far greater than is necessary to heat the element above its effective Curie temperature. As the element is heated and is passing through its effective Curie transition (that is its temperature is rising from below its effective Curie temperature to, or above, its effective Curie temperature) the change in permeability of the element is sensed and the current through the element is cut off. The element then cools. When the temperature falls below the effective Curie temperature, the full current is restored. The heating and cooling process repeats itself indefinitely. The result is that the element is maintained at its effective Curie by a pulsating current fed to the element. The Curie transition may be sensed by directly sensing changes in permeability as by an auto-transformer winding, on the element; or by sensing changes in the power to the element by reason of the change in resistance of the element as it passes through the effective Curie temperature.

Claims

1. In a temperature regulating device,

a ferromagnetic element having a permeability well above one below its effective Curie temperature and a permeability of about one at its effective Curie temperature,

first and second power supplies, said first power supply having a relatively small power output as compared to the power output of said second power supply,

means for supplying the power output of said first power supply to said element,

said first power supply including means for producing an alternating current output having a frequency so high that the skin depth of said alternating current flowing through said element is substantially greater at temperatures below said effective Curie temperature that it is at said effective Curie temperature,

means for selectively supplying the output of said second power supply to said element to heat the same, said second power supply having a sufficient power output to heat said element above its effective Curie, and

means controlled by the change in skin depth of the alternating current flowing in said element for se1ectively controlling the power from said second power supply to said element and thereby regulating the temperature of said element.

2. In a temperature regulating device as defined in claim 1 in which said first power supply has a radio frequency output,

said second power supply having an output for feeding said element with current which flows through said element to heat said element without substantial skin effect.

3. In a temperature regulating device:

a ferromagntic element having a permeability well above unity at temperature well below the effective Curie temperature of said element, and

control means for applying pulses of electric current to said element with each pulse heating said element to tis effective Curie temperature;

said element cooling between pulses,

said control means including means for sensing the permeability of said element during each pulse and for terminating such pulse when such permability declines to a given value and for sensing the permeability of said element after the cessation of each pulse and for producing the next pulse only after said element has cooled so that its permeability is above said given value.

4. In a temperature regulating apparatus as defined in claim 3, said control means comprising means for holding the temperature of said element constant by controlling the duration of said pulses.

5. In a temperature regulating apparatus as defined in claim 4, wherein the time interval between the end of each pulse and the beginning of the next one is at least a predetermined time period.

6. In a temperature regulating device as defined in claim 3,

said means for sensing the permeability of said element including a source which passes radio frequency current through said element and responds to the skin depth of that current to determine the permeability of said element to terminate each pulse when the permeability declines to said given value and to produce the next pulse only after said element has cooled so that its permeability is above said given value.

7. In a temperature regulating device as defined in claim 6:

said pulses of electric current being an alternating current of a frequency much lower than the frequency of said radio frequency current.

8. In a temperature regulating device as defined in claim 7:

said pulses of electric current comprising pulses of current the frequency of which is 60 Hz.

9. In a temperature regulating device as defined in claim 6, said pulses of electric current comprising pulses of direct current.

10. In a temperature regulating device as defined in claim 6, said electric current falling to zero between pulses.

11. In a temperature regulating device as defined in claim 6, said electric current having a substantial amplitude between pulses.

12. Temperature regulating apparatus, for holding the temperature of a heating element substantially constant while such element is subject to varying cooling loads, comprising:

a heating element of the type that when in use is subject to a varying cooling load,

said heating element including;

a ferromagnetic element having a permeability substantially greater than one when its temperature is below its effective Curie temperature and a permeability on the order of one when its temperature is above its effective Curie temperature,

power delivery means feeding an electric current, through said element, of sufficient amplitude which if maintained continuously and indefinitely, would heat said element far above its effective Curie temperature, so that said element has a Curie transition characterized by a change in permeability of said element, and

control means including means for supplying power to said element in the form of a series of pulses of current with each pulse rising to said amplitude, said control means comprising means for sensing said permeability during each pulse and at least reducing said electric current to said element to terminate the pulse in response to such pemreability falling to a give value during an increase in temperature in said element,

said control means restoring said electric current to said element to start the next pulse only when said permeability is above said given value due to cooling of said element;

whereby a series of pulse is produced, each of which pulses reaches said amplitude, and each of which pulses is of greater duration for larger cooling loads than for smaller cooling loads;

said pulses holding said element at said substantially constant temperature.

13. Temperature regulating apparatus as defined in claim 12 in which said power delivery means is directly connected by an ohmic connection to said element to thereby pass said current through said element,

said element having a current carrying portion,

said current being an alternating current varying at a rate relative to the size of said element so that the current is concentrated along at least one surface of said element below the effective Curie temperature and spreads deeper into the element as the effective Curie temperature is approached so that if one part of the current carrying portion of said element is cooled more than another part of said element the said one part will receive increased heat due to the decreased skin depth of the current in such one part.

14. Temperature regulating apparatus as defined in claim 12 in which said power delivery means comprises means for inducing said current in said element,

said elemenet having a current carrying portion,

said current being an alternating current varying at a rate relative to the size of said element so that the current is concentrated along at least one surface of said element below the effective Curie temperature and spreads deeper into the element as the effective Curie temperature is approached so that if one part of the current carrying portion of said element is cooled more than another part of said element the said one part will receive increased heat due to the decreased skin depth of the current in such one part.

15. Temperature regulating apparatus as defined in claim 12 in which said sensing means comprises inducing magnetization B to said element and detecting the magnetic field H produced thereby.

16. Temperature regulating apparatus as defined in claim 12 in which said sensing means comprises means for detecting a change in the power of said current as the temperature of said element increases and said element undergoes at least part of a Curie transition.

17. Temperature regulating apparatus as defined in claim 16 in which said sensing means comprises means that responds to a change in voltage to detect said change in power.

18. Temperature regulating apparatus as defined in claim 16 in which said sensing means comprises means that responds to a change in current to detect said change in power.

19. Temperature regulating apparatus as defined in claim 12 in which said sensing means includes means for restoring said current to said element after at least a predetermined time interval following the time that said current was at least reduced by said sensing means.

20. The method of temperature regulation, of a heating element subject to a variable cooling load, comprising:

providing said element with ferromagnetic material having a permeability considerably greater than one below its effective Curie temperature and a permeability on the order of one above its effective Curie temperature,

subjecting said element to at least two cooling loads one of which is larger than another one,

passing an electric current, of sufficient amplitude which if fed through said element for a prolonged period will heat said element well above its effective Curie temperature, through said element to heat said element at least to a temperature high enough so that at least a part of the Curie transition takes place,

sensing at least part of said Curie transition and reducing the flow of said current through said element when at least part of said Curie transition is sensed, and

restoring said current through said element to said amplitude,

said sensing and restoring steps recurring alternately to thus provide a pulsating current that holds said element at about its effective Curie temperature and at all times prevents a rise in the temperature of said element substantially above its effective Curie temperature,

said pulsating current comprising pulses of greater time duration for the larger cooling load than for the said another one.

21. The method of temperature regulation of claim 20, comprising:

said current being an alternating current,

the frequency of said alternating current being so related to the size and permeability of said element that the skin depth of the alternating current flow increases when the temperature increases into the Curie transition to thus lower the effective resistance of said element to said alternating current, whereby the power fed to said element changes during the Curies transition,

said sensing step comprising sensing changes in the power of the alternating current fed to said element, to thereby sense at least part of the Curie transition during an increase in the temperature of said element and thereupon reduce the power fed to said element thereby limiting further heating of said element.

22. The method of claim 21 in which said power fed to said element includes the parameters of voltage and current one of which has less percentage variation than the other at temperatures of said element below and during the Curie transition,

said sensing step including the sensing of changes in the other of said parameters to thus ascertain at least a part of the Curie transition and thereupon reduce the power fed to said element and limit the rise in temperature of said element.

23. The method of claim 22 in which the current has the smaller percentage variation, and the change in voltage is sensed to ascertain at least part of the Curie transition.

24. The method of claim 22 in which the voltage has the smaller percentage variation, and the change in current is sensed to ascertain at least part of the Curie transition.

25. The method of claim 20 in which said sensing step comprises applying magnetic induction to said element and sensing the resulting magnetic field in the element to thus determine when the element passes through at least part of the Curie transition.

26. The method of claim 20 in which said sensing step comprises detecting the change in power fed to said element due to at least part of the Curie transition,

providing a power source for supplying said current, and

feeding said current to said element by an ohmic connection.

27. The method of claim 20 in which said current is restored in at least a predetermined time period after it is stopped.

28. The method of claim 20 in which an increase in the permeability of said element is sensed and said current is restored when such increase in permeability is sensed.

29. Temperature regulating apparatus, for holding the temperature of a heating element substantially constant while such element is subject to varying cooling loads, comprising:

a heating element of the type that when in use is subject to a varying cooling load,

said heating element including;

a ferromagnetic element having a permeability substantially greater than one when its temperature is below its effective Curie temperature and a permeability on the order of one when its temperature is above its effective Curie temperature,

a radio frequency power supply feeding current, through said element, of sufficient amplitude, that if maintained continuously and indefinitely, would heat said element far above its effective Curie temperature, so that said element has a Curie transition,

said power supply having an output and also having the parameters of both current and voltage at said output,

feedback means for holding one of said parameters, when the current is on, substantially constant at said output, and

control means for sensing changes in the other of said parameters for turning said radio frequency power supply off and on to produce a series of pulses, said control means turning said power supply off when the permeability of said element falls to a given value due to the heating of said element.

30. Temperature regulating apparatus as defined in claim 29, in which said control means includes a timer for holding said power supply off for at least a predetermined time after it has been turned off by said control means.

31. Temperature regulating apparatus as defined in claim 30 in which said current at said output is held constant.

32. Temperature regulating apparatus as defined in claimed 29 in which said voltage is held constant.

33. The method of temperature regulation, comprising,

providing a ferromagnetic element having a permeability well above unity at temperatures well below the effective Curie temperature of said element,

applying pulses of electric current to said element with each pulse heating said element to its effective Curie temperature,

allowing said element to cool between pulses,

sensing the permeability of said element during each pulse and terminating such pulse when such permeability declines to a give value, and

sensing the permeability of said element after the cessation of each pulse and producing the next pulse only after said element has cooled so that its permeability is above said given value.

34. The method of temperature regulation as defined in claim 33 in which each of said sensing steps comprise passing a radio frequency current through said element and responding to the skin depth at which said current flows in order to determine the permeability of said element.

35. The method of temperature regulation as defined in claim 33 in which the current through said element is turned off between pulses.

36. The method of temperature regulation as defined in claim 33 in which there is a substantial current through said element between pulses.