Infrared electronic thermometer and method for measuring temperature

• US 4,797,840 A
• Filed: 01/20/1987
• Issued: 01/10/1989
• Est. Priority Date: 04/17/1985
• Status: Expired

• Current Assignee: Thermoscan Incorporated (The Procter & Gamble Company)
• Original Assignee: Thermoscan Incorporated (The Procter & Gamble Company)
• Inventors: Fraden, Jacob
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): Cosimano, Edward R.
• Application Number:
  US07/009,181
• Time in Patent Office: 721 Days
• Field of Search: 128/736, 136/213, 136/214, 250/338.3, 250/342, 364/557, 374/2, 374/128, 374/133
• US Class Current: 702/104
• CPC Class Codes: G01J 2005/065 by shielding
• CPC Class Codes: G01J 5/0022 for sensing the radiation of moving bodies
• CPC Class Codes: G01J 5/0025 Living bodies ear thermometers G01J5/0011; detecting, measuring or recording for diagnostic purposes A61B5/00
• CPC Class Codes: G01J 5/02 Constructional details
• CPC Class Codes: G01J 5/025 Interfacing a pyrometer to an external device or network; User interface
• CPC Class Codes: G01J 5/04 Casings
• CPC Class Codes: G01J 5/046 Materials; Selection of thermal materials
• CPC Class Codes: G01J 5/049 Casings for tympanic thermometers
• CPC Class Codes: G01J 5/06 Arrangements for eliminating effects of disturbing radiation; Arrangements for compensating changes in sensitivity for adjusting of solid angle of collected radiation G01J5/07; means for wavelength selection G01J5/0801
• CPC Class Codes: G01J 5/064 Ambient temperature sensor; Housing temperature sensor; Constructional details thereof
• CPC Class Codes: G01J 5/08 Optical arrangements
• CPC Class Codes: G01J 5/0804 Shutters
• CPC Class Codes: G01J 5/0808 Convex mirrors
• CPC Class Codes: G01J 5/0814 Particular reflectors, e.g. faceted or dichroic mirrors
• CPC Class Codes: G01J 5/0818 Waveguides
• CPC Class Codes: G01J 5/34 using capacitors, e.g. pyroelectric capacitors
• CPC Class Codes: G01J 5/532 using a reference heater of the emissive surface type, e.g. for selectively absorbing materials
• CPC Class Codes: G01J 5/80 Calibration using comparison with reference sources G01J5/52

Abstract

An electronic infrared thermometer is disclosed comprising a housing forming an interior chamber, a pyroelectric sensor mounted within the chamber for sensing temperature change and generating an indicative electrical signal, means for directing infrared radiation from the object to be measured to the pyroelectric sensor, a shutter assembly for controlling the passing of infrared radiation to the pyroelectric sensor, an ambient temperature sensor for sensing ambient temperature within the interior chamber and generating an electrical signal indicative thereof, an electrical circuit for processing the electrical signals to calculate the temperature of the object to be measured, and an indicator for indicating the calculated temperature. The process for measuring the temperature of an object is also disclosed comprising shielding the pyroelectric sensor from infrared radiation from exterior to the thermometer housing, selectively exposing the pyroelectric sensor to infrared radiation substantially solely from the object to be measured to generate a first electrical signal related to the absolute temperature of the object to be measured, sensing the ambient temperature of the pyroelectric sensor and generating a second electrical signal proportional thereto, and electrically processing the first and second electrical signals to calculate the temperature of the object to be measured.

Claims

1. A thermometer comprising:

a housing;

a sensor carried by said housing and responsive to infrared radiation for generating an electrical signal which exhibits a transient response upon initial receipt of said radiation;

means, carried by said housing, in optical alignment with said sensor, for directing infrared radiation from an object, the actual temperature of which is to be measured, to impinge upon said sensor;

means, carried by said housing, for enabling response of said sensor to said radiation;

and electrical means carried by said housing and responsive essentially only to said transient response of said signal for processing said signal to develop an indication of the actual temperature of said object.

2. A thermometer as defined in claim 1 in which said directing means is so interconnected to said sensor as to be in thermal equilibrium therewith.

3. A thermometer as defined in claim 1 in which said directing means is in itself of low emissivity to infrared radiation in avoidance of contributing to radiation directed from said object to said sensor.

4. A thermometer as defined in claim 1 in which said directing means exhibits substantial thermal isolation from ambient sources of heat external to said directing means.

5. A thermometer as defined in claim 1 in which said sensor includes a pyroelectric material which generates an electrical charge in response to a change in its temperature produced by its receipt of said radiation.

6. A thermometer as defined in claim 1 in which said sensor is a pyroelectric element sandwiched between a first electrode disposed in use to face said object and a second electrode on the opposed surface of said element, said first electrode exhibiting the characteristic of high emissivity and absorption of said infrared radiation.

7. A thermometer as defined in claim 1 in which said sensor is a pyroelectric element sandwiched between a first electrode disposed in use to face said object and a second electrode on the opposed surface of said element, and in which said second electrode is nontransparent to and highly reflective of said infrared radiation.

8. A thermometer as defined in claim 1 in which said sensor is a pyroelectric element sandwiched between a first electrode disposed in use to face said object and a second electrode on the opposed surface of said element, and in which said first electrode is transparent to far infrared radiation and said second electrode is substantially reflective thereto.

9. A thermometer as defined in claim 1 in which said directing means delivers said infrared radiation from said object spread over an area relatively large laterally to the direction of the impingement of said radiation upon said sensor, and in which said sensor correspondingly responds over an area encompassing said spread.

10. A thermometer as defined in claim 1 in which said electrical means automatically becomes insensitive to further input signals from said sensor after receipt of said transient response.

11. A thermometer as defined in claim 1 in which said electrical means includes means for calculating the absolute temperature of said object by integration of the level of said response over a fixed time frame.

12. A thermometer as defined in claim 1 in which said sensor exhibits said transient in response to a single pulse of said radiation, and in which said electrical means responds only to said single pulse.

13. A thermometer as defined in claim 1 which said sensor is mounted within said housing, and in which said housing includes means to equalize the pressure on both sides of said sensor.

14. A thermometer as defined in claim 1 in which a heating element is carried by said housing in a position to yield heat to said sensor and provide a calibrating stable infrared level imposed upon said sensor;

and in which said electrical means responds to said sensor as heated by said element.

15. A thermometer as defined in claim 1 in which said electrical means includes an electronic memory which contains a predetermined table of correction data in accordance with known possible sources of error and changes in responsive characteristics of said sensor, with said electrical means programmed to adjust the calculated absolute temperature of said object in accordance with said correction data.

16. The thermometer of claim 1 wherein said directing means comprises an elongated guide of predetermined length having an outer end to receive infrared radiation from the object to be measured and an inner end in operative alignment with said sensor, in which said guide is mounted to said housing and interconnected to said sensor so as to be in thermal equilibrium therewith and with said guide having a smooth and shiny interior surface and an outer surface, and means on said outer surface for thermally isolating said outer surface from external ambient heat sources.

17. The thermometer of claim 16 wherein said means for thermally isolating comprises a thermoisolator coating on said outer surface.

18. A thermometer as defined in claim 1 in which said sensor is responsive to a predetermined electrical calibration signal;

in which said electrical means include means for applying to said sensor said electrical calibration signal;

and in which said electrical means responds to the sensor output from said calibration signal by correcting calculation of said actual temperature.

19. A thermometer as defined in claim 18 in which said electrical means at least approximately doubles the sensitivity area to said radiation of said sensor following response to said calibration signal.

20. A thermometer as defined in claim 18 in which said sensor is a pyroelectric element sandwiched between a first electrode disposed to face said object and a second electrode on the opposed surface of said element, and in which one of said electrodes comprises two separate and spaced electrode segments wherein said segments are included in said applying means.

21. A thermometer as defined in claim 20 which further includes means for interconnecting said segments prior to said response of said sensor to said radiation.

22. A thermometer as defined in claim 1 which further includes means carried by said housing and responsive to the ambient temperature of said sensor prior to said initial receipt of said radiation for generating another electrical signal representative of said ambient temperature, and in which said electrical means processes said other electrical signal to calculate actual temperature of said object.

23. A thermometer as defined in claim 22 in which said housing defines an interior chamber, and in which said ambient temperature means also is disposed within said chamber in thermal equilibrium with said sensor.

24. A thermometer as defined in claim 22 in which said ambient temperature means exhibits its electrical signal in slow response as compared with the response of said sensor to said radiation.

25. A thermometer as defined in claim 22 in which said ambient temperature means is mounted within a cavity defined within the interior of said housing.

26. A thermometer of claim 22 wherein the temperature of the object to be measured by said electrical means is calculated using the equation:

space="preserve" listing-type="equation">T.sup.2 =(V.sub.ir /f(T.sub.a)+T.sub.a.sup.4).sup.1/4,

where T_s is the absolute temperature of the object to be measured, V_ir is the first electrical signal generated by said sensor, T_a is the absolute ambient temperature determined by said electrical means from said other electrical signal generated by said ambient temperature means, and f(T_a) is a polynomial in T_a given by equation;

space="preserve" listing-type="equation">f(T.sub.a)=a.sub.0 +a.sub.1 T.sub.a +a.sub.2 T.sub.a.sup.2 +a.sub.3 T.sub.a.sup.3 +. . . ,

where the polynomial coefficients a₀, a₁, a₂, a₃ . . . are determined by exposing said sensor at a known ambient temperature to objects having known temperatures.

27. The thermometer of claim 26 wherein the the signal V_ir is approximated by using the formula:

space="preserve" listing-type="equation">V.sub.ir =f(T.sub.a) (T.sub.s.sup.4 -T.sub.a.sup.4).

28. A thermometer as defined in claim 1 in which said enabling means further includes:

a shutter carried by said housing and movable between a first position blocking transmission of said radiation from said directing means to said sensor and a second position which enables passage of said radiation to said sensor;

means for moving said shutter between said first and second positions;

and means for controlling movement of said shutter to enable response of said sensor to said radiation to exhibit said transient response upon receipt of said radiation.

29. A thermometer as defined in claim 28 in which said controlling means enables movement of said shutter to said first position substantially upon termination of said transient response.

30. A thermometer as defined in claim 28 in which said controlling means includes means for suppressing and absorbing noise and shock developed upon the movement of said shutter between said first and second positions.

31. A thermometer as defined in claim 28 in which said housing includes an interior chamber in which said sensor is contained, and in which said shutter is mounted as to be in thermal equilibrium with said sensor.

32. A thermometer as defined in claim 28 which includes means for supplying said electrical means with input signals indicative of the ambient temperature of the said sensor, and in which the actuation of said shutter enables the calculation of the temperature differential between said sensor and said object.

33. A thermometer as defined in claim 28 in which said electrical means includes means for responding to actuation of said shutter in order to provide an indication signal that causes said transient response to be measured.

34. A thermometer as defined in claim 28 in which said shutter exhibits a low thermal conductivity between a first surface which faces said directing means and a second surface which faces said sensor.

35. A thermometer as defined in claim 28 in which both of said surfaces of said shutter are reflective to the said radiation.

37. The method of claim 1 wherein the temperature of the object to be measured is calculated using the equation:

space="preserve" listing-type="equation">T.sub.s =(V.sub.ir /f(T.sub.a)+T.sub.a.sup.4).sup.1/4,

where T_s is the absolute temperature of the object to be measured, V_ir is the first electrical signal generated by said pyroelectric sensor, T_a is the absolute ambient temperature determined from said second electrical signal, and f(T_a) is a polynomial in T_a given by the equation;

space="preserve" listing-type="equation">f(T.sub.a)=a.sub.0 +a.sub.1 T.sub.a +a.sub.2 T.sub.a.sup.2 +a.sub.3 T.sub.a.sup.3 +. . . ,

where the polynomial coefficients a₀, a₁, a₂, a₃ . . . are determined by exposing said pyroelectric sensor at a known ambient temperature to objects having known temperatures.

38. The device method of claim 37 wherein the signal V_ir is approximated by using the formula:

space="preserve" listing-type="equation">V.sub.ir =f(T.sub.a) (T.sub.s.sup.4 -T.sub.a.sup.4).

36. A method for measuring the temperature of an object with a thermometer having a housing providing an interior chamber and an ambient temperature sensor and a pyroelectric infrared sensor mounted within the chamber comprising the steps of:

shielding said pyroelectric sensor from infrared radiation from exterior to the said thermometer housing;

selectively exposing said pyroelectric sensor to infrared radiation substantially solely from the object to be measured to generate a first electrical signal which is a function of the temperature of the object to be measured and the ambient temperature of said pyroelectric sensor immediately prior to said selective exposing;

sensing the ambient temperature of said pyroelectric sensor and generating a second electrical signal proportional thereto;

and electrically processing said first and second electrical signals to calculate the temperature of the object to be measured.

39. The method of claim 36 which comprises calibrating the sensitivity of said pyroelectric sensor prior to selectively exposing said pyroelectric sensor to infrared radiation from the object to be measured.

40. The method of claim 39 wherein the said pyroelectric sensor is adapted to exhibit piezoelectric properties and calibrating the sensitivity of said pyroelectric sensor comprises:

applying a predetermined calibration signal to said pyroelectric sensor so as to cause said pyroelectric sensor to generate a responsive electrical calibration signal;

and correcting said first electrical signal generated by said pyroelectric sensor based upon said responsive electrical calibration signal and a predetermined standard value.

41. The method of claim 40 wherein calibrating the sensitivity of said pyroelectric sensor comprises:

applying a predetermined level of infrared radiation to said pyroelectric sensor so as to cause said pyroelectric sensor to generate a responsive electrical calibration signal;

and correcting said first electrical signal generated by said pyroelectric sensor based upon said responsive electrical calibration signal and a predetermined standard value.