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1. TEST MODE U S Patent Apr 6 1993 Sheet 5 of 7 5 199 436 148 GET SENSOR RAW DATA 150 SUBTRACT SENSOR OFFSET 152 GET AMBIENT CALCULATE TEMPCO 154 ADJUSTMENT MULTIPLY SENSOR SIGNAL 156 BY GAIN amp TEMPCO GET T AMBIENT 4 158 ADD TO SENSOR SIGNAL ISO 46 LOOK UP 4th ROOT 162 SUBTRACT 32 DIVIDE BY 1 8 166 ADD ADJUSTMENT VALUE 168 FIG 4B U S Patent Apr 6 1993 Sheet 6 of 7 5 199 436 UPDATE TIMER He F G 4C COUNTERS 184 SENSOR CONVERSION DO i A D CONVERSION 172 BATTERY VOLTAGE CONVERSION RESET IOOMS FLAG UPDATEN YES DISPLAY UPDATE DISPLAY RETURN 180 U S Patent Apr 6 1993 Sheet 7 of 7 5 199 436 182 TEST BEEPER FIG 4D 184 TEST DISPLAY SEGMENTS TEST DISPLAY DIGITS 186 READ PUSH BUTTON INCREMENT DISPLAY COUNTER DISPLAY ADJUSTMENT DOT VALUE DISPLAY RAW SENSOR DATA DISPLAY AMBIENT DISPLAY RAW AMBIENT DISPLAY BATTERY VOLTS 5 199 436 1 RADIATION DETECTOR HAVING IMPROVED ACCURACY RELATED APPLICATION This application is a division of application Ser No 07 338 968 filed Apr 14 1989 now U S Pat No 5 012 813 which is a continuation in part of application Ser No 07 280 596 filed Dec 6 1988 now U S Pat No 4 993 419 BACKGROUND Radiation detectors which utilize thermopiles to de tect the heat flux from target surfaces have been used in various applications An indication of the temp2. Kapis the analog to digital conversion factor Vs H H KAD GFE Tc deg F Thermistor lookup table Rt Zt Tu Tco Ts 1 Tco Ts 4 1 2 Tco K Tco Tc Ts 1c2 2 Tc Vs J as Hi Tco K Kh H H 1 T He deg co Th Tc 2 Tz Thf deg K4 4th power lookup table Tc Tt deg F Hc Thf i Final lookup table Ter Te Tt Te ke Tt deg C 5 9 Tf deg F 32 optional The following is a list of the information which may be contained in the EEPROM and therefore be pro grammable at the time of calibration Radiation sensor offset Radiation sensor gain Radiation sensor temperature coefficient Thermistor offset Ambient temperature at calibration Thermistor lookup table Final temperature lookup table Adjustment factor F 45 50 55 60 65 12 Sound source functions Beep at button push in lock mode none 20 40 80 milliseconds long Beep at lock none 20 40 80 milliseconds long Beep at power down none 20 40 80 milliseconds long Beep at lowbattery none 20 40 80 milliseconds long interval 1 2 3 sec single double beep Timeout functions Time to power down 0 5 to 128 sec in 0 5 sec increments Delay until lock 0 5 to 128 sec in 0 5 sec increments Other functions Power on button resets lock cycle Power on button resets peak detect Display degrees C degrees F EEPROM Calibrated pattern to indicate that the device has been calibrated EEPROM checksum for a self check by t
3. adjustment values including that from the potentiometer R4 are added Analog to Digital conversion is performed periodi cally during an interrupt to the loop of FIG 4A which occurs every two milliseconds The interrupt routine is illustrated in FIG 4C Timer counters are updated at 170 A to D conversions are made from 172 only every 100 milliseconds when a flag has been set in the prior interrupt cycle During most interrupts an A D con version does not occur Then the 100 millisecond counter is checked at 174 and if the count has expired a flag is set at 176 for the next interrupt The flag is checked at 178 and if found the display is updated at 180 The system then returns to the main loop of FIG 4A Where the 100 millisecond flag is noted at 172 an A to D conversion is to be performed The system first determines at 182 whether a count indicates there should be a conversion of the thermopile output at 184 or a conversion of the the thermistor output at 186 The thermopile sensor conversion is performed nine out of ten cycles through the conversion loop At 188 the system checks to determine whether a conversion is made from the potentiometer R4 or from the battery voltage divider R1 R2 at 192 These conversions are made alternately FIG 4D illustrates the self test sequence which is called by the mode switch 113 only during assembly During the test the beeper sounds at 182 and all display segments are displayed at 184
4. 334 336 373 374 393 395 1988 Sketch of Radiation Detector manufactured by IR ONICS Corp and distributed by Dermathorm Corp Thermometry James Schooley Ph D CRC Press Boca Raton Florida pp 148 151 172 183 User Manual for Surface Temperature Scanner STS 100 F C amp 101 C Omega Medical Corporation Exergen Corporation Product Advertisement for Exergen EHS Infrared Scanner US 5 199 436 C1 1 2 EX PARTE AS A RESULT OF REEXAMINATION IT HAS BEEN REEXAMINATION CERTIFICATE DETERMINED THAT ISSUED UNDER 35 U S C 307 NO AMENDMENTS HAVE BEEN MADE TO THE PATENT The patentability of claims 1 5 is confirmed
5. parent applica tion had a wide field of view of about 120 it has been determined that a significantly narrower field of view of about sixty degrees or less provides a more accurate indication of tympanic temperature With a narrower field of view the thermopile flake when directly view ing the tympanic membrane also views no more than about 1 5 centimeters along the ear canal and preferably less than one centimeter A better view of the tympanic membrane also results from the cylindrical extension 43 beyond the conical portion of the extension 18 With the ear canal straightened by the probe the extension 43 can extend well into the ear canal beyond any hair at the canal opening The tympanic membrane is about 2 5 centimeters from the opening of the ear canal The conical portion of the extension 18 prevents the tip of the extension from extending more than about eight millimeters into the ear canal Beyond that depth the patient suffers noticeable discomfort With a field of view of about sixty degrees the ear canal which is about eight milli meters wide is viewed about eight millimeters from the tip of the extension 18 Thus only the ear canal within about 1 5 centimeters of the tympanic membrane is viewed as the radiation guide is directed toward the membrane The result is a more accurate reading of the tympanic temperature which is closer to core tempera ture With the present instrument the narrow field of view is obtained
6. the housing A cross sectional view of the extension of the detec tor is illustrated in FIG 2 A base portion 22 is posi tioned within the housing 14 and the housing clamps about a groove 24 As noted the portion 20 extends at about a 15 degree angle from the housing and thus from the base portion 22 The extension 18 is tapered toward its distal end at 26 so that it may be comfortably posi toned in the ear to view the tympanic membrane and or ear canal A preferred disposable element to be used over the extension 18 is presented in parent U S patent applica tion No 07 280 546 and will not be discussed here The edge at the end of the probe is rounded so that when the probe is inserted into the ear it can be rotated somewhat without discomfort to the patient The probe is also curved like an otoscope to avoid interference with the ear By thus rotating the probe the ear canal is scanned and at some orientation of the probe during that scan one can be assured that the maximum temper ature is viewed Since the ear canal cavity leading to the tympanic area is the area of highest temperature the instrument is set in a peak detection mode and the peak detected during the scan is taken as the tympanic tem perature An improved assembly within the extension 18 is illustrated in FIG 2 A thermopile 28 is positioned within a can 30 of high conductivity material such as copper The conductivity should be greater than two watts per cent
7. the thermal capacitance of the thermal mass the thermal resistance through the thermal barrier and the internal thermal resistance Specifically the external thermal resistance can be increased by increased radial dimensions the capacitance of the thermal mass can be increased by increasing its size and the thermal resistance through the longitudinal thermal path through the tube can be decreased by increasing its size On the other hand the size must be limited to permit the extension to be readily positioned and manipulated within the ear Besides the transfer of heat from the environment another significant heat flow path to the conductive thermal mass is through leads to the system To mini mize heat transfer through that path the leads are kept to small diameters Further they are embedded in the plug 36 through bores 70 thus any heat brought into the system through those leads is quickly distributed throughout the thermal mass and only small changes in temperature and small gradients result Because the temperature of the thermal mass is not controlled and the response of the thermopile 28 is a function of its cold junction temperature the cold junc tion temperature must be monitored To that end a thermistor is positioned at the end of a central bore 72 in the plug 36 5 199 436 7 A schematic illustration of the electronics in the hous ing 14 for providing a temperature readout on display 16 in response to the sig
8. up dates the output but locks onto an output after some period of time In the peak process the system output is the highest indication noted during a scan In each of these processes the system may respond to the pro gramming from the EEPROM to perform any number of functions as discussed above In the peak process which is selected for the tympanic temperature mea surement the system locks onto a peak measurement after a preset period of time During assembly the sys tem may be set at a test mode 144 which will be de scribed with respect to FIG 4D In any of the above mentioned modes an output is calculated at 146 Then the system loops back to step 122 The calculation 146 is illustrated in FIG 4B At 148 in FIG 4B the raw sensor data is obtained from memory The sensor offset taken from the EE PROM is subtracted at 150 and the ambient temperature 5 199 436 13 previously obtained from the potentiometer RT1 is accessed at 152 The temperature coefficient adjustment is calculated at 154 At 156 the sensed signal is multi plied by the gain from EEPROM and by the tempera ture coefficient At 158 the fourth power of the ambient temperature is obtained and at 160 it is added to the sensor signal At 162 the fourth root of the sum is ob tained through a lookup table Whether the display is in degrees centigrade or degrees Fahrenheit is determined at 164 If in degrees centrigrade a conversion is per formed at 166 At 168
9. 5 325 863 A 7 1994 Pompei 5 381 796 A 1 1995 Pompei 5 445 158 A 8 1995 Pompei 5 653 238 A 8 1997 Pompei 6 047 205 A 4 2000 Pompei 6 292 685 Bl 9 2001 Pompei 2002 0026119 Al 8 2001 Pompei FOREIGN PATENT DOCUMENTS EP 0 447 455 5 1997 EP 0 763 349 B1 8 2002 JP 55 11597 1 1980 JP 55 011597 1 1980 JP 58 88627 5 1983 WO WO 90 06090 6 1990 WO WO 98 08431 3 1998 WO WO 00 16051 3 2000 OTHER PUBLICATIONS A simple but interesting history of Infrared Thermom eters Version 017 www Zy Temp com Continued Primary Examiner Beverly M Flanagan 57 ABSTRACT Tympanic temperature measurements are obtained from the output of a thermopile mounted in an extension from a housing The housing has a temperature display thereon and supports the electronics for responding to sensed radiation The thermopile is mounted in a highly conductive can which includes a radiation guide and thermal mass The guide provides a narrow field of view due to a fairly high emis sivity Electronics determine the target temperature as a function of the temperature of the hot junction of the thermopile determined from the cold junction temperature and a thermopile coefficient The tympanic temperature is adjusted to provide an indication of core temperature US 5 199 436 C1 Page 2 OTHER PUBLICATIONS Human Body Temperature Its Measurement and Regula tion Y Houdas and E F J Ring Penum Press 1982 Infrared Thermocouples a
10. 55 Twentier Fox et alls uses 73 359 Twentier Michael Fowler et al Junkert et al Pompei et al O Hara et al Poncy Pompei et al 374 128 Christol et al Pompei et al O Hara et al Jarund Junkert et al Berman et al O Hara et al 73 355 4 797 840 1 1989 Fraden 4 831 258 5 1989 et al 4 895 164 1 1990 Wood 5 018 872 5 1991 Suszynski et al 374 133 FOREIGN PATENT DOCUMENTS 0201790 11 1986 1914468 11 1970 0092535 10 1983 y 1226540 12 1967 United Kingdom 1425765 3 1973 United Kingdom OTHER PUBLICATIONS Houdas et al Human Body Temperature Plenum Press NY 83 Det Tronics advertisement InTech Oct 1987 p 48 Dexter Research Center product description for the Model 1M Thermopile Detector Oct 1980 Proceedings of the Eighth Annual Conference of the IEEE Engineering in Medicine and Biology Society Nov 7 10 1986 vol 3 of 3 pp 1606 1608 Fraden Jacob Application of Piezo Pyroelectric Films in Medical Transducer Journal of Clinical Engi neering Mar Apr 1988 pp 133 138 Looney Joseph M Jr and Pompei Francisco Ear Thermometry Reprinted from Medical Electronics Jun 1989 Primary Examiner Kyle L Howell Assistant Examiner John P Lacyk Attorney Agent or Firm Hamilton Brook Smith amp Reynolds 57 ABSTRACT Tympanic temperature measurements are obtained from the o
11. REEXAMINATION CERTIFICATE 5861st United States Patent Pompei et al US 5 199 436 C1 10 Number 54 75 73 RADIATION DETECTOR HAVING IMPROVED ACCURACY Inventors Francesco Pompei Wellesley Hills MA US Philip R Gaudet Jr Concord MA US Assignee PNC Bank National Association Pittsburgh PA US Reexamination Request No 90 007 951 Feb 24 2006 Reexamination Certificate for 60 51 52 58 56 Patent No 5 199 436 Issued Apr 6 1993 Appl No 07 646 855 Filed Jan 28 1991 Related U S Application Data Division of application No 07 338 968 filed on Apr 14 1989 now Pat No 5 012 813 which is a continuation in part of application No 07 280 546 filed on Dec 6 1988 now Pat No 4 993 419 Int CI A61B 6 00 2006 01 A61B 5 00 2006 01 US CL La eat een 600 474 600 549 Field of Classification Search None See application file for complete search history References Cited U S PATENT DOCUMENTS 2 710 559 A 6 1955 Heitmuller et al 2 984 747 A 5 1961 Walker 3 374 354 A 3 1968 Hood 3 781 837 A 12 1973 Anderson et al 4 302 971 A 12 1981 Luk 4 317 998 A 3 1982 Dore 4 854 730 A 8 1989 Fraden 4 895 164 A 1 1990 Wood 45 Certificate Issued Aug 21 2007 4 907 895 A 3 1990 Everest 4 993 419 A 2 1991 Suszynski 5 012 813 A 5 1991 Pompei et al 5 199 436 A 4 1993 Pompei et al 5 293 877 A 3 1994 O Hara et al
12. Then the system steps each character of the display from zero through nine at 186 The system then enters a test loop At 188 the system senses whether the button 108 has been pressed If so a display counter is incremented at 190 The dis play for the unit then depends on the count of the dis play counter With the zero count the adjustment po tentiometer value is displayed at 192 Thereafter if the display counter is incremented by pressing the button 108 the raw sensor data is displayed With the next increment ambient temperature is displayed at 196 and with the next increment the raw output from the ambi ent temperature sensor RT1 is displayed With the next 20 25 30 35 45 50 55 65 14 increment the battery voltage is displayed After the test the assembler sets the mode switch to the proper operating mode While this invention has been particularly shown and described with references to preferred embodiments thereof it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims We claim 1 A temperature detector comprising a housing adapted to be held by hand an extension from the housing adapted to be inserted into an ear a radiation sensor supported within the detector and which receives radiation passing into the extension from a target area in th
13. United States Patent Pompei et al UAC CAC A US005199436A 1 Patent Number 5 199 436 45 Date of Patent Apr 6 1993 54 75 73 21 22 60 51 52 58 56 RADIATION DETECTOR HAVING IMPROVED ACCURACY Inventors Assignee Notice Appl No Filed Francesco Pompei Wellesley Hills Philip R Gaudet Jr Concord both of Mass Exergen Corporation Newton Mass The portion of the term of this patent subsequent to Feb 19 2008 has been disclaimed 646 855 Jan 28 1991 Related U S Application Data Division of Ser No 338 968 Apr 14 1989 Pat No 5 012 813 which is a continuation in part of Ser No 280 546 Dec 6 1988 Pat No 4 993 419 Int Ck5 U S CL m Field of Search 2 658 390 3 273 395 3 282 106 3 491 596 3 581 570 3 777 568 3 878 836 3 933 045 3 949 740 4 005 605 4 062 239 4 456 390 4 566 808 4 602 642 4 614 442 4 626 686 4 634 294 4 636 091 4 662 360 4 684 018 4 722 612 4 784 149 4 790 324 A61B 6 00 MES 128 664 128 736 128 664 736 374 123 374 127 129 132 133 135 References Cited U S PATENT DOCUMENTS 11 1953 9 1966 11 1966 1 1970 6 1971 12 1973 4 1975 1 1976 4 1976 2 1977 12 1977 6 1984 1 1986 7 1986 9 1986 12 1986 1 1987 1 1987 5 1987 8 1987 2 1988 11 1988 12 1988 Machler Schwartz Barnes Dean Wortz Risgin et 73 3
14. a measure of the thermal resis tances between Ten Te and Tg core temperature can be computed as T Ta kc Ter Ta This computation can account for a difference of from one half to one degree between core temperature and sensed ear temperature depending on ambient tempera ture A similar compensation can be made in other applica tions For example in differential cutaneous tempera ture scanning the significance of a given differential reading may be ambient temperature dependent The actual computations performed by the processor are as follows where H is the digital value of radiation signal presented to the processor Ho is the electronic offset Hc is corrected H deg K Tc is ambient and cold junction temperature deg F Taf is 4th power of Tamb deg K Tt is target temperature deg F Tz is ambient temp during cal deg F Td is the displayed temperature Rt is the thermistor signal Kh is a radiation sensor gain cal factor Zt is a thermistor zero cal factor Th is the hot junction temperature 10 15 25 30 35 a is the Seebeck coefficient of the thermopile at a specified temperature J is the number of junctions in the thermopile Tco is a temperature coefficient for the Seebeck coef ficient Ts is the temperature at which a is specified Ter is core temperature kc is a constant for computing core temperature Vs is the sensor output voltage Gre is the gain of the front end amplifier
15. and Ts is that specifica tion temperature Again it can be seen that temperature compensation is based on the average thermopile tem perature rather than just the cold junction temperature By substituting equation 4 into equation 3 and solv ing for Ty the hot junction temperature is found to be 4 TH Teo Ts 1 Teo Ts 1 2 Tco 8 Teo Tc 73 Te2 2 Vs J a 5 3 Tco 5 The actual sensor output Vs can be determined from the digital value available to the processor from the equation Kap 6 Vs H Ho Gu where K Apis the analog to digital conversion factor in volts bit and Grzis the gain of the front end amplifier Reference to the hot junction temperature rather than the cold junction temperature in each term of the rela tionship for determining the target temperature pro vides for much greater accuracy over a wide range of ambient temperatures and or target temperatures To provide a temperature readout the microproces sor makes the following computations First the signal from thermistor is converted to temperature using a linear approximation Temperature is defined by a set of linear equations y M x x0 b where x is an input and xo is an input end point of a straight line approximation The values of M xo and b are stored in the EEPROM after calibration Thus to obtain a temperature reading from the thermistor the microprocessor determines from the values of xo
16. by two changes to the prior radiation guide The reflectivity within the guide is reduced Radiation entering the tube at greater angles must be reflected a greater number of times from the radiation guide before reaching the thermopile flake With the higher emissiv ity such radiation is less likely to reach the flake to be detected The field of view is further decreased by ex tending the enlarged rear volume between the flake and the radiation guide Radiation which enters the radia tion guide at greater angles yet travels through the radiation guide leaves the guide at greater angles and is thus unlikely to be viewed by the flake The length of the radiation guide is another parameter which affects the field of view By using a planoconvex lens as the window 35 the field of view can be further limited Both of the above approaches to decreasing the field of view increase the amount of heat which is absorbed by the can in which the thermopile is mounted The added heat load adds to the importance that the can including the radiation guide have a large thermal mass and high thermal conductivity as discussed below As distinguished from the structure presented in the parent application the volume 31 surrounding the ther mopile and the radiation guide are formed of a single piece of high conductivity copper This unitary con 5 199 436 5 struction eliminates any thermal barriers between the foremost end of the radiation guide and t
17. comprises a thermopile and a can enclosing the thermopile The can structure in cludes an elongated radiation guide of a first internal diameter The radiation guide extends from a viewing window to a rear volume of larger internal diameter in which the thermopile is mounted The guide may be gold plated In accordance with one feature of the present inven tion the portions of the can forming the radiation guide and rear volume are formed in a unitary structure of high thermal conductivity material The can structure has an outer surface with an outer diameter at its end adjacent to the window which is less than an outer diameter about the rear volume The outer surface is tapered about the radiation guide such that a unitary thermal mass of increasing outer diameter is provided about the end of the radiation guide adajacent to the rear volume The unitary can structure maximizes con ductance and thermal mass within a limited diameter To avoid changes in fixtures used in mounting the ther mopile within the can the unitary can of limited diame ter may be supplemented with an additional thermal mass which surrounds the rear volume and a portion of 10 15 25 35 40 45 50 55 60 65 2 the unitary thermal mass and which is in close thermal contact with the can structure It has been found that a narrow field of view radiation detector provides a more accurate reading of tympanic temperature In the detector of the p
18. d in that Kh is temperature compensated relative to the average temperature of the thermopile rather than the cold junction or ambient temperature Further the hot junction temperature rather than the cold junction temperature is referenced in the relation ship The gain calibration factor Kh is temperature com pensated by the relationship Tz where is an empirically determined gain in the sys tem Tco is the temperature coefficient of the Seebeck coefficient of the thermopile and Tz is the temperature at which the instrument was calibrated The use of the average temperature of the thermopile rather than the cold junction temperature provides for a much more accurate response where a target temperature is signifi cantly different from the ambient temperature As noted the relationship by which the target tem perature is determined includes the hot junction temper ature as the second term rather than the cold junction temperature Hot junction temperature is computed from the relationship Q Tg T m o 1 rf a Vs J a TH TO where Jy is the number of junctions in the thermopile and cay is the Seebeck coefficient at the average tem 20 25 30 35 40 45 65 10 perature of the thermopile The Seebeck coefficient can be determined from the relationship Ty om Ga 1 rJ where asis the specified Seebeck coefficient at a partic ular specification temperature
19. e ear a temperature display on the housing for displaying temperature and a battery powered electronics in the housing for con verting radiation sensed by the sensor to tempera ture displayed by the display the electronics in cluding a processor for providing an inner body temperature displayed on the housing as a function of the received radiation indicating target temper ature compensated by an indication of ambient temperature to provide an inner body temperature approximation 2 A temperature detector as claimed in claim 1 wherein the inner body temperature is core tempera ture 3 A radiation detector comprising a radiation sensor mounted to view a target of biolog ical surface tissue a temperature sensor for sensing ambient tempera ture an electronic circuit coupled to the radiation sensor and temperature sensor and responsive to a signal from the radiation sensor and the temperature sensed by the temperature sensor to provide an indication of an internal temperature adjusted for the ambient temperature to which the surface tissue is exposed and an output for providing an indication of the internal temperature 4 A radiation detector as claimed in claim 3 wherein the output is a display 5 A radiation detector as claimed in claim 3 wherein the biological surface tissue includes a tympanic mem brane and the display provides an indication of core temperature k e US005199436C1 a EX PARTE
20. ectrically pro grammable once programmed the EEPROM serves as a virtually nonvolatile memory Prior to shipment the EEPROM may be pro grammed through the microprocessor to store calibra tion data for calibrating the thermistor and thermopile Further characterization data which defines the per sonality of the infrared detector may be stored For example the same electronics hardware including the microprocessor 73 and its internal program may be used for a tympanic temperature detector in which the output is accurate in the target temperature range of about 60 F to a 110 F or it may be used as an indus trial detector in which the target temperature range would be from about 0 F to 100 F Further different modes of operation may be programmed into the sys tem For example several different uses of the sound source 90 are available Proper calibration of the detector is readily deter mined and the EEPROM is readily programmed by means of an optical communication link which includes a transistor T2 associated with the display A communi cation boot may be placed over the end of the detector during a calibration characterization procedure A photodiode in the boot generates a digitally encoded optical signal which is filtered and applied to the detec tor T2 to provide an input to the microprocessor 73 In a reverse direction the microprocessor may communi cate optically to a detector in the boot by flashing spe cif
21. erature of a target surface may be provided as a function of the measured heat flux One such application is the testing of electrical equipment Another application has been in the scanning of cutaneous tissue to locate injured subcu taneous regions An injury results in increased blood flow which in turn results in a higher surface tempera ture Yet another application is that of tympanic tem perature measurement A tympanic device relies on a measurement of the temperature of the tympanic mem brane area in the ear of an animal or human by detection of infrared radiation as an alternative to traditional sub linqual thermometers SUMMARY OF THE INVENTION An improved tympanic temperature measurement device is presented in parent U S patent application No 07 280 546 That device provides for accuracy within one tenth of a degree over limited ranges of ambient temperature and accuracy to within one degree over a wide range of ambient temperatures An object of the present invention is to provide a tympanic temperature measurement device which would provide accuracy to within one tenth degree over a wide range of ambient temperatures In obtaining that accuracy an object of the invention was to continue to avoid any requirement for a reference target or for control of the temperature of the thermopile as such requirements had resulted in complexity and difficulties in prior tympanic tempera ture measurement devices A radiation detector
22. es the outer diameter at the distal end and minimizes interference when rotating the extension in the ear to view the tympanic membrane area The tapered region is spaced six millimeters from the end of the extension to allow penetration of the extension into the ear canal by no more than about eight millimeters One of the design goals of the device was that it always be in proper calibration without requiring a warm up time This precluded the use a heated target in a chopper unit or heating of the cold junction of the thermopile as was suggested in the O Hara et al U S Pat No 4 602 642 To accomplish this design goal it is necessary that the system be able to operate with the thermopile at any of a wide range of ambient tempera tures and that the thermopile output have very low sensitivity to any thermal perturbations The output of the thermopile is a function of the difference in temperature between its warm junction heated by radiation and its cold junction which is in close thermal contact with the can 30 In order that the hot junction respond only to radiation viewed through the window 35 it is important that the radiation guide 32 be throughout a measurement at the same tempera ture as the cold junction To that end changes in tem perature in the guide 32 must be held to a minimum and any such changes should be distributed rapidly to the cold junction to avoid any thermal gradients To mini mize temperature changes the t
23. he portion of the can surrounding the thermopile which serves as the cold junction of the thermopile Further at least a por tion of added thermal mass which surrounds the radia tion guide is unitary with the can as well Specifically a taper 39 results in an enlarged region 41 which serves as a thermal mass in accordance with the principals of the parent application The taper 39 continues along a con ductive thermal mass 34 which surrounds the can and a conductive plug 36 Both the mass 34 and plug 36 are of copper and are in close thermal contact with the can 30 The outer sleeve 38 of the extension 18 and the inter mediate extension 20 are of plastic material of low ther mal conductivity The sleeve 38 is separated from the can 30 and thermal mass 34 by an insulating air space 40 The taper of the can 30 and thermal mass 34 permits the insulating space to the end of the extension while mini mizing the thermal resistance from the end of the tube 32 to the thermopile a parameter discussed in detail below The inner surface of the plastic sleeve 38 may be coated with a good thermal conductor to distribute across the entire sleeve any heat received from contact with the ear Twenty mils of copper coating would be suitable In contrast with the prior design the portion of the sleeve 38 at the foremost end of extension 18 has a re gion 43 of constant outer diameter before a tapered region 45 The region of constant outer diameter re duc
24. he pro cessor FIGS 4A 4D provide a flowchart of the firmware stored in the microprocessor 73 From reset when the instrument is turned on the system is initialized at 110 and the contents of the EEPROM are read into memory in the microprocessor at 112 At 114 the processor reads the state of power and mode switches in the system At 116 the system determines whether a mode switch 113 has placed the system in a self test mode If not all eights are displayed on the four digit display 82 for a brief time At 120 the system performs all A to D conversions to obtain digital representations of the thermopile output and the potentiometer settings through multiplexor 76 The system then enters a loop in which outputs dic tated by the mode switch are maintained First the tim ers are updated at 122 and the switches are again read at 124 When the power is switched off from 126 the system enters a power down loop at 128 until the system is fully down At 130 the mode switch is checked and if changed the system is reset Although not in the tym panic temperature detector some detectors have a mode switch available to the user so that the mode of operation can be changed within a loop At 132 136 and 140 the system determines its mode of operation and enters the appropriate scan process 134 lock process 138 or peak process 142 In a scan process the system updates the output to the current reading in each loop In a lock process the system
25. ic segments of the digital display 82 Through that communication link an outside computer 106 can moni tor the outputs from the thermistor and thermopile and perform a calibration of the devices A unit to be cali brated is pointed at each of two black body radiation sources while the microprocessor 73 converts the sig nals and sends the values to the external computer The computer is provided with the actual black body tem peratures and ambient temperature in the controlled environment of the detector computes calibration vari ables and returns those variable to be stored in the de tector EEPROM Similarly data which characterizes a particular radiation detector may be communicated to the microprocessor for storage in the EEPROM A switch 108 is positioned behind a hole 110 FIG 1 in the radiation detector so that it may be actuated by a rigid metal wire or pin Through that switch the user may control some specific mode of operation such as converting the detector from degrees Fahrenheit to degrees centigrade That mode of operation may be stored by the microprocessor 73 in the EEPROM so 5 199 436 9 that the detector continues to operate in a specific mode until a change is indicated by closing the switch 108 A switch 106 may be provided either internally or through the housing to the user to set a mode of opera tion of the detector By positioning the switch at either the lock position the scan position or a neutral posi
26. imeter per degree Kelvin The can is filled with a gas of low thermal conductivity such as Xenon The thermopile 28 is positioned within a rear volume 31 It is mounted to an assembly which includes a flange 33 The volume is sealed by cold welding of the flange 33 to a flange 41 extending from the can Cold welding is the preferred approach to making the seal and to utilize past welding fixtures the outer diameter of the can is limited The thermopile views the tympanic membrane area through a radiation guide 32 The radiation guide 32 is gold plated to minimize oxidation It is closed at its forward end by a germanium window 35 To minimize 10 25 35 40 45 50 55 60 65 4 expense the window is square with each side slightly longer than the diameter of the radiation guide 32 The window is cemented with epoxy within a counterbore in a flange 37 at the end of the radiation guide The epoxy serves as a gas seal and mechanical support for the somewhat brittle germanium window The flange serves to protect the germanium window should the detector be dropped The diagonal of the window is less than the diameter of the counterbore and its thickness is less than the depth of the counterbore Therefore if the detector is dropped any force which presses the plastic housing toward the window is absorbed by the flange The germanium need only withstand the forces due to its own inertia Whereas the detector disclosed in the
27. nal from the thermopile is presented in FIG 3 The system is based on a micro processor 73 which processes software routines in cluded in read only memory within the processor chip The processor may be a 6805 processor sold by Motor ola The voltage generated across the thermopile 28 due to a temperature differential between the hot and cold junctions is amplified in an operational amplifier 74 The analog output from the amplifier 74 is applied as one input to a multiplexer 76 Another input to the multi plexer 76 is a voltage taken from a voltage divider R1 R2 which is indicative of the potential V from the power supply 78 A third input to the multiplexer 76 is the potential across a thermistor RT1 mounted in the bore 72 of block 36 The thermistor RT1 is coupled in a voltage divider circuit with R3 across a reference po tential VRef The final input to the multiplexer is a potential taken from a potentiometer R4 which may be adjusted by a user The system may be programmed to respond to that input in any of a number of ways In particular the potentiometer may be used as a gain control or as a DC offset control At any time during the software routine of the micro processor 73 one of the four inputs may be selected by the select lines 78 The selected analog signal is applied to a multiple slope analog system 80 used by the micro processor in an integrating analog to digital conversion 80 The subsystem 80 may be a TSC500A sold b
28. nstant of the thermal barrier any external thermal disturbances such as when the extension contacts skin only reach the conductive thermal mass at extremely low levels during a measure ment period of a few seconds due to the large thermal mass of the material in contact with the cold junction any such heat transfer only causes small changes in temperature and due to the good thermal conductance throughout the thermal mass any changes in tempera ture are distributed quickly and are reflected in the cold junction temperature quickly so that they do not affect temperature readings The thermal RC time constant for thermal conduc tion through the thermal barrier to the thermal mass and tube should be at least two orders of magnitude greater than the thermal RC time constant for the temperature response of the cold junction to heat transferred to the tube and thermal mass The RC time constant for con duction through the thermal barrier is made large by the large thermal resistance through the thermal barrier and by the large thermal capacitance of the thermal mass The RC time constant for response of the cold junction is made low by the low resistance path to the cold junc tion through the highly conductive copper can and thermal mass and the low thermal capacitance of the stack of beryllium oxide rings and pin conductors to the thermopile Although the cold junction capacitance is naturally low there are size constraints in optimizing
29. o the capacitor C1 to recharge the capacitor and thus keep the transis tor T1 on If the microprocessor should fail to continue its programmed routine it fails to charge the capacitor C1 within a predetermined time during which the charge on C1 leaks to a level at which transistor T1 turns off Thus the microprocessor must continue in its programmed routine or the system shuts down This prevents spurious readings when the processor is not operating properly 20 25 30 35 45 55 60 65 8 With transistor T1 on the switch 22 can be used as an input through diode D2 to the microprocessor to initi ate any programmed action of the processor In addition to the display the system has a sound output 90 which is driven through the driver 84 by the microprocessor In order to provide an analog output from the detec tor a digital to analog convertor 92 is provided When selected by line 94 the convertor converts serial data on line 96 to an analog output made available to a user Both calibration and characterization data required for processing by the microprocessor may be stored in an electrically erasable programmable read only mem ory EEPROM 100 The EEPROM may for example be a 93c46 sold by International CMOS Technologies Inc The data may be stored in the EEPROM by the microprocessor when the EEPROM is selected by line 102 Once stored in the EEPROM the data is retained even after power down Thus though el
30. on temperature is the tempera ture of the hot junction The hot junction temperature Tg is determined from the sensed thermopile voltage and cold junction temperature and a thermopile coeffi cient The thermopile coefficient is specified at a prede termined temperature and is temperature compensated by the electronic circuit as a function of a temperature between the hot and cold junctions specifically the average temperature Further the electronic circuit determines the gain factor K as a function of the differ ence between a calibration temperature and a tempera ture between the hot and cold junction temperatures When used to measure a biological temperature the radiation detector is further improved by providing an indication of an internal temperature within biological tissue The electronic circuit determines the internal temperature by adjusting a measured temperature of surface tissue for ambient temperature In particular the biological surface tissue may be tympanic membrane or the ear canal adjacent to the membrane and the display may provide an indication of core temperature BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects features and advan tages of the invention will be apparent from the follow ing more particular description of preferred embodi ments of the invention as illustrated in the accompany ing dr wings in which like reference characters refer to the same parts throughout the different
31. resent invention that field of view is obtained by controlling the reflec tance of the surface of the radiation guide the length of the guide and the position of the thermopile behind the guide A field of view of less than about sixty degrees allows for viewing of only a portion of the ear canal within about 1 5 centimeters of the tympanic mem brane Accuracy of the detector may be improved electroni cally as well Accordingly an electronic circuit is cou pled to a thermopile having a cold junction and a hot junction mounted to view a target and to a temperature sensor for sensing the temperature of the cold junction The electronic circuit is responsive to the voltage across the thermopile and a temperature sensed by the temperature sensor to determine the temperature of the target The electronic circuit determines the tempera ture of the target as a function of the temperature of the hot junction of the thermopile determined from the cold junction temperature and a known thermopile coeffici ent A display provides an indication of the target tem perature determined by the electronic circuit As in prior systems the electronic circuit determines target temperature from the relationship T 7 KH 4 T where Tris the target temperature is a gain factor H is a sensed voltage from the thermo pile and T is a junction temperature of the thermopile In accordance with the present invention in a preferred embodiment the juncti
32. rticle appearing at www om ega com website Noncontact Temperature Sensing with Thin Film Thermo pile Detectors by Condrad Hamel Sensors pp 29 31 Jan 1989 Standard Specification for Infrared Thermometers for Inter mittent Determination of Patient Temperature American Society for Testing and Materials Designation E 1965 98 pp 1 16 1998 The Encyclopedia of Electronics Second Printing edited by Charles Susskind Reinhold Publishing Corporation New York pp 260 856 857 864 1967 The Equine Infrared Thermographic Scanner Assuring Performance of the Equine Athlete at the Speed of Light Equine Infrared by Marybeth Ryan Thermal Sensors Based on the Seebeck Effect A W Herwaarden and P M Sarro Sensors and Actuators 10 1986 pp 321 346 Thermography as an Indicator of Blood Perfusion by Tom J Love Annals NY Academy of Sciences pp 429 437 1980 Det Tronics advertisement Intech p 48 Oct 1987 Exergen Product Specification for MicroScanner E Autozero FirstTemp Intelligent Medical Systems Manual Model 2000A pp 1 7 Undated Operation Omega Medical Product Specification for Surface Term perature Scanner STS 100 F C amp 101 C by Omega Medi cal Product Corporation Principles and Methods of Termperature Measurement Tho mas D McGee John Wiley amp Sons Inc Publishers pp 237 239 251 252 257 258 265 266 296 298 302
33. the line segment in which the temperature falls and then performs the computation for y based on the variables M and b stored in the EEPROM The hot junction temperature is computed A fourth power representation of the hot junction temperature is then obtained by a lookup table in the processor ROM The sensed radiation may be corrected using the gain calibration factor Kh the sensor gain temperature coef ficient Tco the average of the hot and cold junction temperatures and a calibration temperature Tz stored in the EEPROM The corrected radiation signal and the fourth power of the hot junction temperature are summed and the fourth root is taken The fourth root calculation is also based on a linear approximation which is selected according to the temperature range of interest for a particular unit Again the break points and coefficients for each linear approximation are stored in the EEPROM and are selected as required An additional factor based on ambient temperature may also be included as an adjustment The temperature of the ear T which is sensed by the thermopile is not actually the core temperature Ter There is thermal resistance between T and T Further there is thermal 5 199 436 11 resistance between the sensed ear temperature and the ambient temperature The result is a sense temperature Te which is a function of the core temperature of inter est and the ambient temperature Based on an assumed constant Kc which is
34. tion any of three modes may be selected The first mode is the normal scan mode where the display is updated continuously A second mode is a lock mode where the display locks after a selectable delay and then remains frozen until power is cycled or optionally the power on button is pushed The sound source may be caused to sound at the time of lock The third mode is the peak mode where the display reads the maximum value found since power on until power is cycled or option ally the power on button is pushed The processor determines when the voltage from the divider R1 R2 drops below each of two thresholds Below the higher threshold the processor periodically enables the sound source to indicate that the battery is low and should be replaced but allows continued read out from the display Below the lower threshold the processor determines that any output would be unreli able and no longer displays temperature readings The unit would then shut down upon release of the power button In the present system the target temperature is com puted from the relationship Tr Kh H Ho T where Tris the target temperature Kh is a gain calibra tion factor H is the radiation sensor signal which is offset by Ho such that H H 0 when the target is at the cold junction temperature of the device to counter any electronic offsets in the system and Ty is the hot junction temperature This relationship differs from that previously use
35. ube 32 and the can 30 are of course well insulated by means of the volume of air 40 Further a high conductance thermal path is provided to the cold junction This conductance is en hanced by the unitary construction Further the can 30 is in close thermal communication with the thermal masses 34 and 36 and the high conductivity and thick ness of the thermal masses increase the thermal conduc tance A high thermal conductivity epoxy solder or the like joins the can and thermal masses The solder or epoxy provides a significant reduction in thermal resis tance Where solder is used to avoid damage to the 20 25 30 35 40 45 50 55 60 65 6 thermopile which is rated to temperatures of 125 C a low temperature solder of indium tin alloy which flows at 100 C is allowed to flow into the annular mass 34 to provide good thermal coupling between all elements The thermal resistance from the outer surface of the plastic sleeve 38 to the conductive thermal mass is high to minimize thermal perturbations to the inner thermal mass To minimize changes in temperature of the guide 32 with any heat transfer to the can which does occur the thermal mass of the can 30 annular mass 34 and plug 36 should be large To minimize thermal gradients where there is some temperature change in the tube during measurement the thermal resistance between any two points of the thermal mass should be low Thus due to the large time co
36. utput of a thermopile mounted in an exten sion from a housing The housing has a temperature display thereon and supports the electronics for re sponding to sensed radiation The thermopile is mounted in a highly conductive can which includes a radiation guide and thermal mass The guide provides a narrow field of view due to a fairly high emissivity Electronics determine the target temperature as a func tion of the temperature of the hot junction of the ther mopile determined from the cold junction temperature and a thermopile coefficient The tympanic temperature is adjusted to provide an indication of core temperature 128 736 European Pat Off Fed Rep of Germany Sweden 5 Claims 7 Drawing Sheets U S Patent Apr 6 1993 Sheet 2 of 7 5 199 436 39 4 i8 x av F3 BW 7747 ARP AUI AR T I A S a SSW 03 U S Patent Apr 6 1993 Sheet 3 of 7 5 199 436 es y N NIE a a DRIVE RIVER 100 102 uj h C R E gt o o B Lo lt o o O gt N N e e O t TET ET UN m c v S TE N LL ul a s i o gt a REF U S Patent Apr 6 1993 Sheet 4 of 7 5 199 436 e FIG 4A 120 UPDATE TIMERS READ SWITCHES 122 124 128 POWER DOWNLOOP 134 SCAN PROCESS LOCK PROCESS 146 CALCULATE OUTPUT
37. views The drawings are not necessarily to scale emphasis instead being placed upon illustrating the principles of the in vention FIG 1 illustrates a radiation detector for tympanic temperature measurements in accordance with the pres ent invention 5 199 436 3 FIG 2 is a cross sectional view of the extension of the detector of FIG 1 in which the thermopile radiation sensor is positioned FIG 3 is a block diagram of the electronic circuit of the detector of FIG 1 FIGS 4A 4D are flow charts of the system firm ware DESCRIPTION OF A PREFERRED EMBODIMENT The radiation detector 12 of FIG 1 includes a flat housing 14 with a digital display 16 for displaying a tympanic temperature measurement Although the dis play may be located anywhere on the housing it is preferred that it be positioned on the end so the user is not inclined to watch it during a measurement The instrument makes an accurate measurement when ro tated to scan the ear canal and the user should concen trate on only the scanning motion Then the display can be read A thermopile radiation sensor is supported within a probe 18 at the opposite end of the housing 14 The extension 18 extends orthogonally from an interme diate extension 20 which extends at an angle of about 15 degrees from the housing 14 As such the head of the detector including the extension 18 and 20 has the ap pearance of a conventional otoscope An on off switch 22 is positioned on
38. y Tele dyne It utilizes the reference voltage VRef from a reference source 82 The microprocessor 73 responds to the output from the convertor 80 to generate a count indicative of the analog input to the convertor The microprocessor drives four 7 segment LED dis plays 82 in a multiplexed fashion Individual displays are selected sequentially through a column driver 84 and within each selected display the seven segments are controlled through segment drivers 86 When the switch 22 on the housing is pressed it closes the circuit from the battery 78 through resistors R5 and R6 and diode D1 to ground The capacitor C1 is quickly charged and field effect transistor T1 is turned on Through transistor T1 the V potential from the storage cell 78 is applied to a voltage regulator 86 The regulator 86 provides the regulated 4 5 volts to the system It also provides a reset signal to the micro processor The reset signal is low until the 5 volt reference is available and thus holds the microprocessor in a reset state When the 5 volts is available the reset signal goes high and the microprocessor begins its pro grammed routine When the switch 22 is released it opens its circuit but a charge is maintained on capacitor C1 to keep transis tor T1 on Thus the system continues to operate How ever the capacitor C1 and transistor T1 provide a very simple watchdog circuit Periodically the microproces sor applies a signal through driver 84 t
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