Infrared electronic thermometer and method for measuring temperature

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.

What is claimed is: 
     
       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.Iadd., said directing means including 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 inter-connected 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.Iaddend.;   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 to 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.]. .Iadd.includes .Iaddend.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 includes 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.   
     
     
          . 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:   .[.T.sup.2 .]. .Iadd.T.sub.s .Iaddend.=(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:     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 a 0 , a 1 , a 2 , a 3  . . . are determined by exposing said sensor at a known ambient temperature to   
     
     
        objects having known temperatures. 27. The thermometer of claim 26 wherein the signal V ir  is approximated by using the formula: 
     
     
       V ir  =f(T a )(T s   4  -T a   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. 
     
     
         0. 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. 
     
     
        1. 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 34 in which both of said surfaces of said 
     
     
        shutter are reflective to the said radiation. 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;   .Iadd.generating an indicator signal upon said exposing of pyroelectric sensor; .Iaddend.   and .Iadd.in response to said indicator signal .Iaddend.electrically processing said first and second electrical signals to calculate the   
     
     
        temperature of the object to be measured. 37. The method of claim 36 wherein the temperature of the object to be measured is calculated using the 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:     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 a 0 , a 1 , a 2 , a 3  . . . are determined by exposing said pyroelectric sensor at a known ambient   
     
     
        temperature to objects having known temperatures. 38. The method of claim 37 wherein the signal V ir  is approximated by using the formula: 
     
     
       V ir  =f(T a )(T s   4  -T a   4 ). 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.