WO1994016298A1

WO1994016298A1 - Two color line scanning pyrometer

Info

Publication number: WO1994016298A1
Application number: PCT/US1994/000620
Authority: WO
Inventors: Arthur E. Goldberg; Eugene F. Kalley
Original assignee: Ircon, Inc.
Priority date: 1993-01-13
Filing date: 1994-01-13
Publication date: 1994-07-21
Also published as: AU6163594A

Abstract

A scanning radiation sensor provides a dual spectral infrared measurement scheme that is capable of providing contactless temperature measurements from a plurality of points along a scan line of a target surface area without knowing the emissivity of the target surface. The sensor is capable of correcting for changes in the emissivity of the target due to varying surface conditions. The dual spectral line scanning infrared sensor determines the radiation from each of a plurality of spots along a scan line on a target, and produces an average radiation from the plurality of spots, and converts the average radiation to a representation of temperature of the target.

Description

TWO COLOR LINE SCANNING PYROMETER DESCRIPTION

Technical Field

Applicants' invention relates generally to a scanning infrared thermometer, and more particularly to a two color line scanning pyrometer to provide a non-contact temperature measurement of a target without knowing the target's emissivity.

Related Patent

This application is related to commonly assigned patent to Kalley- et al., Patent No. 5,173,868, entitled "Scanning Radiation Sensor For Multiple Spots And Methods of Averaging Radiation", (Our Docket IR-6), granted on December 22, 1992, the specifications of which are expressly incorporated herein.

Background Art Any object having a temperature greater than absolute zero radiates electromagnetic energy that increases with temperature. A high proportion of the electromagnetic energy is in the infrared frequency spectrum. A non-contact infrared temperature measurement device utilizes an infrared optical system to collect and focus the radiated energy onto an infrared detector. The output of the detector is first a function of the geometry and spectral . esponse of the optical system and secondly, the detector output depends on the target temperature and emissivity, the effective background temperature and the transmission of the intervening path. Emissivity of the target is the ratio of the radiated energy from the target with that of a black body having the same temperature. Emissivity depends on such surface characteristics as oxidation, texture, chemical makeup, etc. of the target. For a monochromatic pyrometer, if there is no allowance for emissivity, the resultant output of the detector is a factor of the brightness rather than of the actual temperature. In order to have a meaningful and accurate representation of temperature, the emissivity of the target must be determined. A passive system requires that the detector collects only the radiated emissions from the target. In the passive system, the emissivity of the target is usually known, either by separate measurement or through the use of generalized specifications or tables for the material of the target. The system would have provisions for inputing the emissivity value.

Some non-contact infrared measurement devices have an active mode where they measure target reflectivity by measuring light reflected off of the target. Reflectivity R for an opaque target is mathematically related to emissivity £ by the relationship £ = 1 - R. Once an active system has measured reflectivity and therefore emissivity, it can then go to a passive mode and measure target temperature. Active systems are difficult to implement in industry because they require elaborate set that must be well maintained. Such a system is detailed in U.S. Patent No. 4,840,496, issued to Elleman et al. on June 20, 1989.

Passive pyrometers can be classified as monochromatic, dual spectral, or multispectral. A monochromatic pyrometer is sensitive to a single wavelength and the target emissivity at the operating wavelength must be known or estimated, and further, must not vary very much over the surface of the target that is being measured. In addition, errors can arise due to the target not filling the field of view, dust or smoke that may contaminate or obstruct the line of sight between the target and dirty optical surfaces.

Dual spectral pyrometers are sensitive to two separate wavelengths and can correct some of the problems associated with the monochromatic devices. Dual spectral pyrometers can be implemented as ratio pyrometers or as a two wavelength pyrometer with other special algorithms.

A ratio pyrometer develops a ratio of the detector outputs in two different wavelength regions. The premise that becomes the basis for a ratio spectral device is that a change that effects the detected radiation at one wavelength will cause an equal effect in the detected radiation at the other wavelength and therefore the ratio of the two outputs will be constant. A ratio pyrometer is of particular benefit for graybody targets because graybodies will produce the same detector output ratio that blackbodies produce and therefore no special adjustments will be required. If the target is not a black or gray body, then the ratio of the detector outputs will not be the same as for a biackbody and the detector output will need to be modified by a factor which is called E slope correction. The E slope correction will generally work as long as the E slope is a constant, meaning that the target material and its surface condition does not change.

A ratio pyrometer will also provide improvements over a monochromatic pyrometer when the target area does not fill the field of view of the pyrometer and the background in the field of view is at a much cooler temperature such as may be the case when measuring the temperature during processing of wire. Under this condition, the ratio of the detector outputs will be essentially unchanged and thereby still provide an accurate temperature reading.

A ratio pyrometer can also provide improvements over a monochromatic pyrometer if the field of view is obstructed by dust or smoke or if the lens is dirty, assuming that the dust, . smoke or dirt effects radiation equally at both wavelengths.

Dual spectral pyrometers can also implement the following equation: ± = _A_ + _B_ + C

T TL1 TL2

where T is the temperature to be determined.

TL1 is the temperature reading using the detector output for L1 wavelength and an emissivity of 1 .

TL2 is the temperature reading using the detector output for L2 wavelength and an emissivity of 1. A, B, C are constants which must be empirically determined for each process. Dual spectral pyrometers that implement the above equation can be effective for targets whose E slope is not constant. However, it may be difficult to determine A, B, or C.

Multispectral pyrometers are similar to dual spectral devices except radiation at more wavelengths is detected. Since more wavelengths are being detected, the range between adjacent wavelengths can be smaller and averaging methods could be employed to increase the accuracy of the device. The multispectral device can also be used as a dual spectral device with the operator selecting the adjacent wavelengths according to the temperature band that is to be monitored so that a wider overall temperature range can be covered by a single device. The increased complexity of the device and other environmental factors common to industrial processes restrict the applications of such a device.

Most dual spectral pyrometers have been limited to spot pyrometers that receive radiation from a single spot on the target. Scanning infrared pyrometers are well known that scan a target for the infrared radiation from a plurality of points along a scan line to produce a temperature output. The sampling of the radiation from the various points along the scan line is at a very high rate. This limits the allowable response time of the radiation detectors and circuitry. Single spot pyrometers can be effective even if their detectors, preamplifiers and other conversion circuits have response times of several milliseconds. Line scanners require detectors and associated circuitry to have response times of a few tens of microseconds or less.

Another problem with providing a dual spectral line scanning pyrometer is how to average different data samples to improve the signal to noise ratio. A dual spectral spot pyrometer can time average data over many milliseconds by using means such as a RC time constant in an analog circuit. A line scanning pyrometer will be scanning one point after another and therefore the time available to time average for each point is small and other means of averaging must be employed. Yet another problem with providing a dual spectral line scanning pyrometer is that the dual spectral radiation signals for each point being scanned must be processed at the same time. A dual spectral spot pyrometer is only receiving data from one spot and therefore there is less need to process these signals at the same exact time. In fact some dual spectral spot pyrometers alternatively process one spectral region and then the other.

Because of the problems associated with the dual spectral devices mentioned above, scanning infrared detectors have been limited to devices using a single spectral region. Estimating or calculating target emissivity becomes a major consideration and factor in the accuracy of the readings from these types of scanning devices. If the estimate is the result of an initial calibration procedure, it may not be valid for later measurements. Errors can also result from dust or smoke between the target and the detector.

The present invention eliminates these and other problems without loss of performance or reliability.

Summary of the Invention

Accordingly, the principal object of the present invention is to provide a dual spectral line scanning infrared pyrometer that is capable of providing contactiess temperature measurements from a plurality of points along a scan line of a target surface area without knowing the emissivity of the target surface.

It is a further object of the invention to provide a dual spectral line scanning infrared pyrometer that is capable of correcting for changes in the emissivity of the target due to varying surface conditions. A further objective of the invention is to provide a dual spectral line scanning infrared pyrometer that provides for spots to be identified on the target and for the data for points within these spots to be averaged whether the data is taken within one scan or adjacent scans. In one embodiment of the invention, an optical system including a rotative reflective member collects light, such as infrared light, from one of a plurality of spots along the scan line of the target and splits the collected light into two separate paths. The rotative reflective member allows the optical system to collect light from each of the plurality of points on the target in sequence along the scan line. The first path contains a bandpass optical color filter to allow passage of light from a selected spot at a specific wavelength to a first photoelectric detector for conversion to a first analog signal representative of the detected radiation at the specified wavelength. The second path contains a second bandpass optical color filter which allows passage of light from the same selected spot at a different wavelength to a second photoelectric detector for conversion to a second analog signal representative of the detected radiation at the second wavelength. To have increased speed, the detectors may be photodiodes that are reversed biased and the optical filters will be positioned away from cutoff regions of the detector. The two analog outputs are coupled to a divider circuit to produce a signal that is the ratio of the radiances at the two wavelengths. The ratioed signal is then sent to an analog to digital converter and then to a microprocessor where it is further processed to produce a temperature signal in digital form. The temperature signals from the target points along the scan line are averaged to produce an average temperature signal for the target. In the preferred embodiment of the invention, an optical system includes a rotative reflective member for directing light from one of a plurality of points along the scan line of the target to a second reflective member. The rotative reflective member allows the optical system to collect light from each of the plurality of points on the target in sequence along the scan line. The reflected light from the second reflective member is directed to an achromatic objective lens for focusing the light on an optical fiber splitter that divides and delivers the light to two optical filter/detector combinations that respond to the light at two different specific wavelengths. The outputs of the detector are two separate analog signals representative of the detected radiation at the specified wavelengths. The two analog detector outputs are amplified by log amplifiers whose outputs are coupled to a difference circuit having an analog output signal that is the log of the ratio. The log of the ratio signal is further processed by an analog to digital converter and a microprocessor where it is further processed to produce a temperature signal. The temperature signals from the target points along the scan line can be averaged to produce an average temperature signal for the target or the target points can be grouped into spots and the target points within a spot can be averaged. Other features and advantages of the invention will be apparent from the following specification taken in conjunction with the accompanying drawings in which there is shown a preferred embodiment of the invention. Reference is made to the claims for interpreting the full scope of the invention which is not necessarily represented by such embodiment.

Brief Description of the Drawings

FIG. 1 is an isometric view of a housing for containing a single color scanning infrared thermometer constructed according to the prior art.

FIG. 2 is a sectional side view of the scanning infrared thermometer of Fig. 1 to illustrate the optical path of the detected radiation and various components therein.

FIG. 3 is a functional block diagram of the scanning infrared thermometer of Fig. 1.

FIG. 4 is a functional block diagram of a two color spot infrared thermometer according to the prior art.

FIG. 5 is a sectional side view of a two color scanning infrared thermometer enclosed in the housing of Fig. 1 to illustrate the optical path of the detected radiation and various components therein according to the present invention.

FIG. 6 is a functional block diagram of a two color scanning infrared thermometer according to the present invention.

FIG. 7 is a detailed block diagram of the two color scanning infrared thermometer of Fig. 6 according to the present invention. 8

Detailed Desciption

Although this invention is susceptible to embodiments of many different forms, a preferred embodiment will be described and illustrated in detail herein. The present disclosure exemplifies the principles of the invention and is not to be considered a limit to the broader aspects of the invention to the particular embodiment as described.

FIG. 1 illustrates a scanning radiation thermometer 10 constructed according to the prior art and as detailed in commonly assigned U.S. Patent Application Serial No. 07/600,638 of Paris, filed on October 19, 1990 entitled "Scanning Radiation Sensor With Movable Baffle Assembly and Method Of Sensing". A target 12, such as a section of steel, glass, or plastic is marked by the thermometer 10 with a beam 14 of visible laser light along a scan line 16. The marking line consists of a solid line or if the target is divided into different target spots 16', dashed lines from which radiation is detected and converted to temperature. The target spots can also be specified while using a PC to monitor the temperature profile being scanned. The thermometer 10 is aimed and the scanning line 16 is positioned on the target 12 by physically moving the housing 18 on a vertical swivel assembly connected to a base 19 and mounted on a horizontal swivel assemble 25. An operator can manually select the number, length, and relative location of each of the spot targets 16'.

Referring now to Fig. 2, a sectional side view of the scanning infrared thermometer 10 along section II of Fig. 1 illustrates the optical path of the detected radiation and various components that comprise the device. Radiation from the target 12 passes along the same path 14 as is used for marking the target 12 and passes through an elongated fixed baffle opening 20 to be reflected off of a rotating reflective member 21 , such as a planar scanning mirror, which rotates about a vertical axis and reflects the received radiation from path 14 to a fixed, folding mirror 22 along path 14'. The folding mirror 22 redirects the received radiation along horizontal path 14" to an objective lens 24 which is part of focusing lens assembly 26 having a drive motor for automatic focusing, not a part of this invention. Filter assembly 30 passes the received radiation through lens 26 along path 14"' to impinge upon detector 32 which is usually a photoelectric converter such as a photodiode. Preamp circuits are located on circuit board 29 mounted inside the housing 18. Control and conversion circuits are located on circuit boards mounted inside the housing 18.

A cold reference source 34, such as a piece of blackened copper allows for an independent radiation measurement for use in calibration and making conversion corrections in the processing of the received radiation. A motor 36 rotates the reflective member 21 and correspondingly, an encoder 38 which indicates the angular position of the reflective member 21 for control purposes. The rotation of the reflective member 21 thus allows the thermometer 10 to alternately detect radiation from the target 12 and the reference source 34. An alignment laser 40 provides the means for marking the target 12 with the scan line as outlined above. A cylindrical, cup shaped baffle 42 encloses the reflective member 21 and rotates in synchronization with it. A window opening 44 in a vertical cylindrical side wall of the baffle 42 is radially aligned with an aperture 45 and the reflective member 21 to enable the received radiation along path 14 to enter the interior of the baffle 42 and impinge on the reflective member 21 along path 47. Reflected radiation from the reflective member 21 exits the baffle 42 along path 14' through an axial opening 46. The walls of the baffle 42 serve to block radiation or light from sources other than from the target 12 or the reference source 34 from impinging on the reflective member 21 . Further details are contained in the above referenced Paris U. S. Patent application.

Also within housing 18 is a control circuit 41 as shown in Fig. 3 which serves to operate the scanner or reflective member 21 through control line 33 and the alignment laser 40 through control line 31 to mark the target 12 with the spot targets 16' from which radiation is detected and converted to temperature. Output 37 of the detector 32 is fed to converter 35 which produces a representation of temperature for each of the scanned spot targets 16' with corrections added by emissivity setting circuit 39 which could be electronically or manually determined. Converter 35 will average the temperature readings for each of the target spots 16' to produce an average temperature for the target 12 along scan line 16 as detailed in the above referenced Kalley et al. U.S. Patent Application.

Fig. 4 provides details of a dual spectral infrared spot thermometer according to the prior art. Radiation 51 from target 50 is collected by an achromatic or color corrected objective lens 52 which focuses the received radiation 51 along line 53 to dichromatic mirror 54. Lens 52 causes the different wavelengths of the collected radiation to focus at the same point. The dichromatic mirror 54 is tilted at a 45 degree angle and will allow light greater than a predetermined wavelength to penetrate straight through along line 55 to an optical color filter 57 and detector 58 and will reflect light less than the predetermined wave length along line 56 to another optical color filter 59 and detector 60. The spectral radiance emitted at a given wavelength λ, from a biackbody surface is given as:

Eq. 1 = [C,/ λ>] x [1/[exp(C₂/λT) - 1]] where spectral radiance W cm-² sr¹ λ = wavelength in μ c, = 1 1 ,905 Watts cm² μ⁴

C. = 14,388 μ degrees K

when λT « C₂, Equation 1 reduces to Wien's approximation: Eq. 2 N_λ = [C,/ λ⁵] x [exp(-Ca/λT)J

For a real body with emissivity £,

N_λ = £ [C,/ λ*] [exp (-C₂/λT)] The ratio of the radiances at two wavelengths, λ_s, λ_L. is

N_λs £_λs [λjs exp(-C₂/λ_sT)

Eq. 3 — - = — - x x

N_λs ε_λL [ s]⁵ . exp(-C₂/λ_LT)

For a gray body, Eχ_s = Bχ_L

Reducing Equation 3 and converting to Log_1o:

N_λs λ_L C₂ [λ_L -λ_s] 1 og₁₀ — - = 5 Log₁₀ x x --

N_λs λ_s 2.3026 [λ_L λ_s] T

Solving for T yields:

[λ_L -λ_s]

6249 x

[λ_L xλ_s]

Eq. 4 T 5 Log₁₀ [λ_L /λ_s] - Log₁₀ [N_λS/N_λL] where: T = Temperature in degrees K λ_L, λ_s = Wavelengths in μ

N_λS N_λ = Ratio of radiances at the two wavelengths

Detectors 58 and 60 will convert the detected radiation to a current proportional to the radiation which is amplified and converted to a voltage output by preamplifiers 61 , 62 respectively. Divider 63 will provide the ratioed output Nλ_s/Nλ_L which is coupled to converter 65 for conversion to a temperature representation by solving Equation 4. The ratio techniαue is quite general and provides a simple solution for temperature when Wien's approximation is valid for both spectral regions and the spectral regions are narrow, eliminating the need to integrate over the whole spectral regions. FIG. 5 illustrates a dual spectral scanning infrared thermometer 70 according to a preferred embodiment of the present invention in the housing 18 of Fig. 1. A sectional side view illustrates the optical path of the detected radiation and various components that comprise the scanner 70. The scanner 7 includes many of the elements disclosed in Figs. 1 and 2. Radiation from the target 12 passes along path 14 and through the elongated fixed baffle opening 20 to be reflected off of the rotating reflective member 71 , which rotates about a vertical axis and reflects the received radiation from path 14 to a fixed, folding mirror 22 along path 14'. The folding mirror 22 redirects the received radiation along horizontal path 14" to an achromatic or color corrected objective lens 72. The received radiation is then focused onto a randomized fiber bundle 73 that splits the received radiation and delivers half of the received radiation to a first optical filter 74 and first detector 75 and delivers the remaining half of the received radiation to a second, optical filter 76 and second detector 77. This means of splitting the radiation signal provides the means for having both detectors receive radiation from the same spot at the same time. Log amplifier circuits are located on circuit boards 29 mounted inside the housing 18. Control and conversion circuits are located inside the housing 18.

A baffle assembly 42 encloses the reflective member 71 and rotates in synchronization with it. The baffle 42 blocks radiation or light from sources other than from the target 12 or the reference source 34 from impinging on the reflective member 71. This is an improvement that overcomes radiation reflections from other sources from contaminating the detected radiation that previously prevented scanning techniques to be used for two color infrared thermometers. A window opening 44 in a vertical cylindrical side wall of the baffle 42 enables the received radiation along path 14 to enter the interior of the baffle 42 and impinge on the reflective member 71. A cold reference source 34 may be used for lower temperature ranges and it allows for an independent radiation measurement for use in calibration and making some corrections for DC offsets and emissivity. A hot reference source may be used to allow for an independent radiation measurement for use in a gain calibration. Reflected radiation from the reflective member 71 exits the baffle 42 along path 14' through an axial opening 46. An alignment laser 40 provides the means for marking the target 12 with the scan line 16 as outlined above.

Referring to Fig. 6 a control circuit 41 as previously shown in Fig. 3, operates the scanning reflective member 71 through control line 33 and the alignment laser 40 through control line 31 to mark the target 12 with the spot targets 16' from which radiation is detected and converted to temperature. First optical filter 74 will pass radiation at one wavelength to first detector 75 and the optical filter 76 will pass radiation at a shorter wavelength to second detector 77. Some detectors, such as photodiodes, have slow response to radiation whose wavelength is in the detector cutoff transition region. The optical filters for these detectors will -have upper wavelength cutoffs below the detector cutoff regions in order to have increased speed. The ' outputs of detectors 75 and 77, will be currents representative of the radiation at the two different wavelengths. To eliminate long conversion times in the temperature conversion circuits 91 , log amplifiers 78 and 79 eliminate the need for division to compute the ratio of the detected radiations by changing the signals to equivalent logarithmic values and performing a subtraction instead with differential amplifier 80. In some applications, the target 12 is non-gray and there may be variations ir emissivity at the two different wavelengths. As a means to correct for this condition, an E-slope calibration 82 provides an adjustable constant factor for modifying the ratio as calculated by differential amplifier 80. This constant can be set by measuring the target 12 by a thermocouple or other means and adjusting the E-slope control 81 until the device 70 reads the same. Once this adjustment is made, smoke, dust, vapor or other contaminants that effect both wavelengths the same will have no further effects on the accuracy of the temperature readings. Other corrections are added to the output of calibrator 82. A correction factor based on temperature is required to correct for a proportionality of the KT/q factor of the logarithmic amplifiers. A zero scale adjustment 84 allows for having zero scale voltage output at a low end of a particular temperature range. The gain adjustment 85 allows for having full scale voltage at the high end of a particular temperature range. Buffer amplifier 86 utilizes these adjustments to produce a voltage output 90 that is proportion to the ratio of dual spectral radiation from the selected target spot 16'. Converter 91 will calculate the temperature by solving Equation 4. It will determine the average temperature for each of the target spots 16' if multiple samples- are taken for each spot and will compute the average temperature of the complete scan line. The outputs of the converter 91 could be sent to personal computer 92 for display, or sent to an I/O box 93 which generates a 4-20 ma current loop or a 0-10 volt temperature proportional signal, or controls relays operating at various set points for use in process control. As a practical matter, there is a limit as to the lowest radiation level that can be detected by the detectors 75 and 77 in order to maintain an acceptable ratio of the two wavelengths. Low signal detector 96 can be adjusted to trigger an alarm or other protective features if the signal from one of the detectors is below the adjustment. FIG. 7 is a more detailed diagram of the conversion portion of Fig. 6 according to the present invention. Radiation from target 12 is converted to currents II by photodiode detectors 75, 77 respectively, which are reversed biased to improve their speed. Identical logarithmic amplifiers 78, 79 produce an output 101 , 102 respectively, that equals to [-KT/q]ln(ls/les), [-KT/q]ln(ll/les) respectively. Details of the operation of a log amp are well known and are the object of the present invention. The component values of the design are chosen to allow for input currents that may vary over a wide range, from approximately 5nA to 500 uA. To compensate for differences in emitter saturation current of transistors T1 and T2 which can double for every 10 degrees C, these transistors are preferably super matched and the error will appear as a common mode signal that will be rejected by the differential amplifier 80. The output 106 of differential amplifier 80 will then be proportional to [KT/q]ln(ls/ll). Amplifier 108 will compensate for temperature changes in the KT/q factor by adding a positive temperature, coefficient resistor R10 to the summing junction of amplifier 108 which will cause the output voltage 110 to decrease proportionally as the temperature increases. The E slope adjustment 81 previously discussed is multiplied with output 110 to produce an output 112 that is corrected for emissivity for non-gray bodies. Zero adjust resistor R14 provides a means to have zero scale voltage out from buffer amp 86 at zero scale temperature at the selected range. R14 is essentially an offset adjustment and R17 provides a gain adjustment. These adjustments provide for variations in detectors and component tolerances from device to device and from different temperature ranges. The final buffer stage 86 also has the offset adjustment 85 coupled to a summing junction 114 for calibrating the scanner 70 to biackbody standards.

If output 102 of log amplifier 79 is below a preset level, usually representative of a detector current of 5 nA, low signal detector circuit 96 will swamp the summing junction 114, causing the output 116 to go negative and cause the temperature conversion circuit 77 to provide a warning or invalid reading indication. The output 116 is coupled to the temperature conversion circuit 77 where it will be sampled, averaged, and converted to a temperature reading representative of the detected radiation. Details of the averaging procedure are contained in the above referenced Kalley et al. U.S. Patent No. 5,173,868, entitled "Scanning Radiation Sensor For Multiple Spots And Methods of Averaging Radiation", the specifications of which are expressly incorporated herein.

While the specific embodiments have been illustrated and described, numerous modifications are possible without departing from the scope or spirit of .the invention. Instead of the optical fiber splitter 73 and separate detectors 75 and 77, the scanning reflective member 71 can reflect the radiation to a fixed mirror and then to an achromatic lens that will focus the infrared radiation onto a dual detector or stacked detector which will then transfer the radiation to two separate channels for converting the detected radiation at the two different wavelengths. Such a dual detector or photoelectric converter is detaifed in U.S. Patent 5,149,956. Likewise, the scanning reflective member 71 may hav multiple facets for splitting the detected radiation and reflecting it directly to the achromatic lens without the need for a fixed mirror. Further, the fixed mirror, if used, could also be a dichromatic mirror that is tilted at a 45 degree angle and will allow light greater than a predetermined wavelength to penetrate straight through along to one optical color filter and detector and will reflect light less than the predetermined wave length to another optical color filter and detector to provide the two separate channels for conversion.

As another alternative, instead of discrete components bein used for calibration and compensation of the output signal from the differential amplifier 80, a microprocessor can easily perfor these same functions using well known techniques. If a microprocessor is used, and alternative embodiment is possible whereby the output of the detectors 75, 77 could be inputted to preamplifiers and sent directly to the microprocessor which solves the algorithm previously detailed in Background Art.

Claims

CLAIMSWe claim:

1 . In a scanning radiation sensor for providing a non- contact temperature measurement of a target without knowing the emissivity of the target, along a marked scan line containing a plurality of marked spots, said scanning radiation sensor comprising: a) a scanning system for producing a plurality of samples of radiation from each of the plurality of marked spots on said target; b) a first radiation detection means to provide a • first radiation measurement responsive to a first optical wavelength region from each of the plurality of marked spots on said target; c) a second radiation detection means to provide a second radiation measurement responsive to a second optical wavelength region from each of the plurality of marked spots on said target; d) combining means to combine said first radiation measurement and said second radiation measurement to produce a ratio of said first radiation measurement and said second radiation measurement, said ratio a representation of the radiation of each of the plurality of marked spots on said target; e) averaging means for producing an average of said representation of the radiation of each of the plurality of marked spots on said target; and f ) conversion means to convert said average of said representation of the radiation of each of the plurality of marked spots on said target to a representation of average temperature of said plurality of marked spots on said target.

2. The scanning radiation sensor of Claim 1 in which said scanning system for producing a plurality of samples of radiation from each of the plurality of marked spots on said target includes a movable baffle member for

5 protecting said first radiation detection means and said second radiation detection ^'means against reflected radiation from other sources.

3. The scanning radiation sensor of Claim 1 in which said 1 0 combining means of said first radiation measurement and said second radiation measurement includes means for converting said first radiation measurement to a first logarithmic value and means for converting said second radiation measurement to a second logarithmic

1 5 value and means for subtracting said second logarithmic value from said first logarithmic value, said subtracting means to produce a logarithm of said ratio of said first radiation measurement and said second radiation measurement.

20

4. The scanning radiation sensor of Claim 1 further including means for modifying said ratio of said first radiation measurement and said second radiation measurement for changes in emissivity slope of said

25 target.

5. The scanning radiation sensor of Claim 1 further including means for calibrating said ratio of said first radiation measurement and said second radiation

30 measurement for zero offset errors when said scanning radiation sensor is calibrated against a black body.

6. The scanning radiation sensor of Claim 1 further including means for compensating said ratio of said first radiation measurement and said second radiation measurement for changes in ambient temperature.

5

7. The scanning radiation sensor o^'f Claim 1 further including means of generating an alarm signal when said first radiation detection means generates a radiation measurement that is below a predetermined

1 0 level that could produce an invalid temperature measurement.

8. The scanning radiation sensor of Claim 1 in which said first radiation detection means and said second

1 5 radiation detection means includes a fiber optic splitter to provide a first optic path having a first optic filter and a first detector to produce a first radiation measurement responsive to a first optical wavelength and a second optic filter and second

20 detector to produce a second radiation measurement responsive to a second optical wavelength from each of the plurality of marked spots on said target.

9. The scanning radiation sensor of Claim 1 in which said 25 first radiation detection means and said second radiation detection means includes a dual detector having a first optic detector to produce a first radiation measurement responsive to a first optical wavelength and a second stacked optic detector to 30 produce a second radiation measurement responsive to a second optical wavelength from each of the plurality of marked spots on said target.

1 0. In a scanning radiation sensor for providing a non- contact temperature measurement of a target without knowing the emissivity of the target, along a marked scan line containing a plurality of marked spots, said 5 scanning radiation sensor comprising: a) a scanning system for producing a plurality of samples of radiation from each of the plurality of marked spots on said target; b) a first radiation detection means to provide a 1 0 first radiation measurement responsive to a first optical wavelength from each of the plurality of marked spots on said target; c) a second radiation detection means to provide a second radiation measurement responsive to a

1 5 second optical wavelength from each of the plurality of marked spots on said target; d) first conversion means to convert said first radiation measurement and said second radiation measurement into a first and second digital

20 representation of radiation; e) second conversion means to convert said first and second digital representation of radiation to produce a representation of temperature of each of the plurality of marked spots on said target;

25 and f ) averaging means for producing an average of said representation of the temperature of each of the plurality of marked spots on said target.

1 1 . The scanning radiation sensor of Claim 10 in which said second conversion means includes a microprocessor for solving an algorithm described by the equation

5 1 = .A_+ _B + C

T TL1 TL2

where T is the temperature to be determined.

TL1 is the temperature reading using the 1 0 detector output for L1 wavelength and an emissivity of 1. TL2 is the temperature reading using the detector output for L2 wavelength and an emissivity of 1. 1 5 A,B,C are constants which must be empirically determined for each process.

12. The scanning radiation sensor of Claim 10 in which said scanning system for producing a plurality of

20 samples of radiation from each of the plurality of marked spots on said target includes a movable baffle member for protecting said first radiation detection means and said second radiation detection means against reflected radiation from other sources.

25