GB2291499A - DC stable infrared detector compensation system - Google Patents
DC stable infrared detector compensation system Download PDFInfo
- Publication number
- GB2291499A GB2291499A GB9517893A GB9517893A GB2291499A GB 2291499 A GB2291499 A GB 2291499A GB 9517893 A GB9517893 A GB 9517893A GB 9517893 A GB9517893 A GB 9517893A GB 2291499 A GB2291499 A GB 2291499A
- Authority
- GB
- United Kingdom
- Prior art keywords
- detector
- compensating
- output
- voltage signal
- thin wires
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 230000005855 radiation Effects 0.000 claims description 10
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 7
- 229910052802 copper Inorganic materials 0.000 claims description 6
- 239000010949 copper Substances 0.000 claims description 6
- 230000008878 coupling Effects 0.000 claims 1
- 238000010168 coupling process Methods 0.000 claims 1
- 238000005859 coupling reaction Methods 0.000 claims 1
- 230000008859 change Effects 0.000 description 11
- 238000000034 method Methods 0.000 description 8
- 238000005259 measurement Methods 0.000 description 7
- 239000000463 material Substances 0.000 description 5
- 229910052782 aluminium Inorganic materials 0.000 description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 4
- 230000000712 assembly Effects 0.000 description 4
- 238000000429 assembly Methods 0.000 description 4
- 230000001143 conditioned effect Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 230000035945 sensitivity Effects 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 229910000833 kovar Inorganic materials 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 229920002799 BoPET Polymers 0.000 description 1
- 239000005041 Mylar™ Substances 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 238000009529 body temperature measurement Methods 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920000098 polyolefin Polymers 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000005476 soldering Methods 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
- G01J5/02—Constructional details
- G01J5/06—Arrangements for eliminating effects of disturbing radiation; Arrangements for compensating changes in sensitivity
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Radiation Pyrometers (AREA)
- Photometry And Measurement Of Optical Pulse Characteristics (AREA)
Description
2291499 1 DC STABLE DETECTOR COMPENSATION SYSTEM
BACKGROUND OF THE INVENTION
1---_Fieldof the Invention
PATENT The present invention relates generally to techniques for remote temperature measurement based on detecting IR radiation emitted from a target and more particularly to techniques for compensating thermal gradients within an instrument to reduce noise and increase accuracy.
is 2. Descrii:)tion of the Relevant Art Typically, remote IR temperature measuring devices utilize an IR focusing system to focus IR radiation emitted by a target on an IR detector element. This detector element includes a black body which increases in temperature when the IR radiation from the target is focused on the detector element and a thermopile for emitting a sense voltage having a magnitude indicating the magnitude of the temperature gradient between a hot junction (the black body heated by the focused IR emitted by the target) and a reference cold junction. The measuring device has circuitry for displaying the temperature of the target based on the magnitude of the sense voltage output by the detector element.
The detector element must be very sensitive since the magnitude of the temperature change due to the focused IR emitted by the target may be less than 16-3o F. and the sense -voltage has a small magnitude. Accordingly,the measuring device must be designed to provide a low noise environment.
one source of noise is caused by thermal gradients between the detector element and other components caused by changes in the ambient temperature. When the ambient temperature changes different parts of the instrument change temperatures at different rates. Accordingly, heat may flow -c the detector element a!--na ther=al gradients and add a is 2 noise component to the sense voltage that will cause the temperature reading to be inaccurate. As is well-known in the art, the rate of heat flow (H) through a material is calculated by the formula:
H = KA(t2-tl) /L where K is the thermal conductivity of the material, A is the cross-sectional area, L is the length, and t, and t2 are the different temperatures at the ends of the material.
One type of stabilization technique for compensating thermal transients utilizes a chopper to periodically interrupt the focused IR radiation and to reference the detector element to the ambient temperature. However, use of a chopper increases the cost of the measurement device.
Another source of noise is change of temperature of the detector element itself which may be compensated by a balancing system utilizing two detector elements with a measuring detector element exposed to the focused IR radiation to provide a sense voltage output and a compensating detector element for providing a compensating voltage output. Both voltage outputs vary by a nearly linear offset in response to a change in ambient temperature so the effect of the change is compensated by subtracting the compensating voltage output from the sense voltage output.
Various techniques such as enclosing the detector elements in materials having a high thermal resistivity have also been utilized to isolate the detector element from thermal transients.
However, current techniques that do not use choppers have limited sensitivity. Accordingly, a technique for stabilizing the detector element that provides for high sensitivity and does not utilize a chopper would be of great utility in the art.
SUMMARY OF THE =VENTION
The present invention is a remote temperature measuring instru=ent including a compensation system that provides high stability and sensitivity without requiring the use of a chopper. Ac:zor--4--g zz one aspect -,f t_he invention, 3 separate measuring and compensating detector elements are mounted in a heat sink and connected to a circuit board by very thin wires.
According to another aspect of the invention, the thin wires, and circuit boards are contained in a thermally insulating enclosure to isolate the thin wires from air currents formed in the interior of the measuring device.
According to another aspect of the invention, the thin wires connect each detector element to an analog to digital convertor (ADC) on the circuit board. A microprocessor receives the digitized sense voltage and compensating signals and processes the signals to compensate for changes in ambient temperature and to reduce noise from the compensating detector.
Other features and advantages of the invention will become apparent in view of the following detailed description and the appended drawings.
BRIEF DESCRIPTION. OF THE DRAWINGS
Fig. 1 is a cross-sectional plan view of a preferred embodiment of the invention; Fig. 2 is a graph depicting the error due to a change in ambient temperature as a function of time; Figs. 3A and 3B are detailed perspective views of the interconnection of the detector leads, thin wires, and circuit board contacts of a preferred embodiment; Fig. 4 is a perspective view of the insulating enclosure of a preferred embodiment; and Fig. 5 is a schematic diagram of the temperature compensation circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will now be described with reference to the preferred embodiments. In the drawings, like or corresponding parts will be given the same reference numbers throughout the several views.
Fig. 1 demicts the IR optical system and detector stabil;za t4 on system.
:n Fig. 'I an!R lens jo focuses!R 4 radiation emitted from a target onto a sensing detector assembly 12 mounted in an aluminum block 14. A compensating detector assembly 16 is also mounted in the block 14 and is shielded from the incident IR radiation. The aluminum block 14 is located in the interior of a device housing (not shown).
As is well known in the art, the detector assemblies 12 and 16 include detecting elements which are commercially available thermopiles, such as manufactured by Dexter Research Center of Dexter, Michigan, that are enclosed in a standard hermetically sealed housing with standard detector leads utilized to provide electrical contacts from the exterior of the sealed housing to the detector elements. in Fig. 1 the hermetically sealed housings of the detector assemblies 10 and 16, which enclose the detector elements, are depicted with the is standard detector leads 121 and 161 extending from the housings.
A circuit board 18, having functions described more fully below, is mounted on the metal block 14. The standard detector leads 121 and 161, providing the electrical contacts from the detector elements are connected to terminals on the circuit board 18 by pairs of very thin wires 20 and 22. In Fig. 1, the contacts on the circuit board IS are depicted as posts, which are usually copper, but the contacts can also be pads on the circuit board 18. The thin wires 20 and 22, standard detector leads 121 and 161, and circuit board contacts are contained in an thermally insulating enclosure 24.
The instabilities in a D.C. thermopile based instrument are due to drifts in the circuit, signal instability within the detector, and thermal gradients between the detector and other optical components. The inventors have found that the greatest single inst-ability source is signal instability within the detector and that the signal instability has three sources: (1) the heat load on the positive detector lead; (2) the heat load on the negative -or lead; and (3) the rate of 4 detect.emperature change of the entire detector.
The rate of temperature change is controlled by mounting the detector assemblies 12 and 16 in the aluminum block 14 which functions as a heat sink. Further, the effects of.temperature change are compensated by a balancing system described below with reference to Fig. 3. However, the effects of heat load on the leads are unique to each detector and cannot be compensated by the balancing system.
It has been discovered that the use of very thin wires 20 and 22 in place of the standard positive and negative detector leads 121 and 161 to connect the detector assemblies 12 and 16 to the circuit board IS reduces the heat load to the detector leads. It has also been discovered that the containment of the thin wires 20 and 22 and circuit board contacts in a thermally insulating cover 24 further increases is stability.
Fig. 2 is a graph depicting the measurement error in OF as a function of time for different configurations of the instrument. Each graph represents the error resulting from removing the instrument from an oven at 1206F and operating the instrument at room temperature.
In Fig. 2, the first curve 30 represents the error for an uncompensated detector. After about-10 minutes the measurement.is off by about -120F and then returns to the correct value in about an hour. The second curve 32 represents the error for a balanced system utilizing very thin wires not contained in an insulating enclosure to connect the detector posts to the circuit board contacts. The range of error is about +/-4F with the measurement returning to the correct value in about an hour. The third curve represents the error for a balanced system utilizing very thin wires contained in an insulating enclosure. The range of error has been reduced to about +/-20F with the measurement returning to the correct value in about an hour.
The use of the very thin wires and insulating enclosure to improve stability has greatly increased the performance of the DC detector system. The improved detector system can be utilized to make measurements at lower t lUt4on. =, emperatures or higher reso r example, the 6 resolution of a measurement system has been improved from 40:1 (ability to resolve 1 foot target at 40 feet) to 120:1 (ability to resolve-a I foot target at 120 feet).
The standard detector leads 121 and 161, which provide contact with the detector elements within the housing, are typically fabricated of Kovar, of the Stupakoff Ceramic & Mfg. Co., which is an alloy of 29% nickel, 17% cobalt, 0.3% manganese, and the balance of iron, and having the property of forming a hermetic seal with glass. The leads have a thickness of 0.53 mm, and typically pass through a glass sealing member.
In a preferred embodiment, the thin wires 20 and 22 are copper wires having a diameter of 0.08 mm. and a length of about 1.5 cm. The detector leads are trimmed to about 3 mm and the thin wires are attached by the leads by knotting the wires to hold them in place and then soldering the wires to the detector leads.
In a currently preferred embodiment the enclosure 24 is formed by a shrink-wrap process. In preferred embodiment, heat shrink tubing available from the 3-M Corporation of Minneapolis, Minnesota, having a diameter of about 1.511 and fabricated of polyolefin is utilized as the thermally insulating enclosure. However, utilizing mylar or other thin plastic materials is also contemplated.
The interconnection of the standard detector leads 121 and 161, thin wires 20 and 22, and circuit board contacts are depicted in Figs. 3A and 3B. Fig. 3A depicts the wire side of the circuit board 18 with the thin wires 22 connecting the standard detector leads 161 of the compensating detector assembly 16 to pads on the board. Fig. 3B.depicts the component side of the circuit board 18 with the thin wires 20 connecting the standard detector leads 121 of the sensing detector assembly 12 to copper posts on the board.' The shrink-wrapped insulating enclosure 24 is A depicted _4n detail in Fig. t. The Limits of the views of Figs. 3A and B are defined by the circle 29 and those figures - the interconnec- -he 4 depic ions before Lnsulating enclosure is added.
7 Based on the composition of Kovar, the inventors have estimated that the thermal conductivity of the 0.53 mn detector leads is about 0. 8 (Watts cm-1 OK-1) and that a lead having a length of 1 c= would have a thermal conductance of about 1.8 milliWatt/OK. On the other hand, the thin copper wires of diameter 0.08 mm. and length 1.5 cm have a thermal conductance of about 0.13 milliWatt/ OK.
It has been discovered that significant noise reduction will be achieved by thin wires having a thermal conductance of up to about 0.3 milliWatt/OK and a having a thickness of up to about 0.1 mm. Thus, the principles of the invention are realized for thin wires having a thermal conductance from about 0.1 to about 0.3 milliWatt/OK and for copper wires having a diameter from about 0.08 mm. to about 0.1 is mm. The lower limit of the range of thicknesses for the copper wire is due to the difficulty of handling the wire.
It has been discovered that the improved performance exhibited when the insulating enclosure 24 is utilized may due to shielding the thin wires from air currents created in the interior of the device housing when the ambient temperature changes and reducing the temperature differential between the ends of the thin wires.
The above-described compensation system facilitates the use of standard detectors which is important for ease of manufacturing and reducing cost. Further, the use of very thin wires isolates the detector housing from thermal gradients to further increase stability.
Fig. 5 is a circuit diagram of the balancing system utilized in the preferred embodiment to compensate for temperature change in the detector itself:
In Fig. 5 the pair of very thin wires 20 transmitting the sense voltage are coupled to the input of a preamp 40 which has its output coupled the analog input of an ADC 42. The digital output of the ADC 42 is coupled to the.
data input of a microcontroller (MCU) 44 by a data bus 46. The pair of very thin wires 22 transmitting the compensating voltage are similarly coupled to the MCU 44 via a preamp 48 and an ADC 50.
1 a The preamps allow the sense and compensating voltage signals to be conditioned prior to digitizing and the MCU can be programmed to implement well known noise-reduction algprithms including subtraction of the conditioned compensation voltage from the conditioned sense voltage to cancel the linear offset due to change of temperature of the sensing detector 12.
The invention has now been described with reference to the preferred embodiments. Alternatives and substitutions will now be apparent to persons of skill in the art. For example, the use of an aluminum block as a heat sink is not critical nor is the orientation of the block and circuit board. Accordingly, it is not intended to limit the invention except as provided by the appended claims.
9
Claims (4)
1 2 3 4 6 7 8 9 11 12 13 14 15 16 17 is 19 1 2 3 4 5 6 7 8 9 1. An improved IR remote temperature measuring device comprising: a measuring detector for providing a sense voltage signal having a magnitude indicating the intensity of an incident beam IR radiation; an IR focusing system for focusing IR radiation emitted from a target onto said measuring detector; a compensating detector, shielded from IR radiation, for providing a compensating voltage signal; a circuit board including compensation circuitry for processing said sense voltage signal and said compensating voltage signal to cancel an offset voltage generated when the temperature of the detectors are changing; and thin wires, having a thermal conductance in the range of from about 0.13 to about 0.2 milliWatt/OK, for electrically coupling said measuring and compensating detectors to said circuit board to transmit said sense voltage and compensating voltage signals to said compensation circuitry.
2. The device of claim 1 further comprising: a thermally insulating enclosure surrounding said 3 thin wires.
3. The device of claim 2 wherein said compensating circuitry comprises: a first preamplifier having an input coupled to receive said sense voltage signal and an output; a first analog to digital convertor having an analog input coupled to the output of said first preamplifier and having a digital output; a second preamplifier having an input coupled t receive said compensating voltage signal and an output; z a second analog to digital convertor having an analog input coupled to the output of said second preamplifier andhaving a digital output; and a processor coupled to the digital outputs of said first and second analog to digital convertor for processing said sense and compensating voltage signals to compensate for an offset voltage caused by changing temperature of the detectors.
1 2 3 4
4. The device of claim 2 wherein said thin wires are fabricated of copper and have a thickness in the range of from of about 0.08 mm, to about 0.1 mm, and a length of about 1. 5 cm.
1
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US27792494A | 1994-07-20 | 1994-07-20 |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9517893D0 GB9517893D0 (en) | 1995-11-01 |
| GB2291499A true GB2291499A (en) | 1996-01-24 |
| GB2291499B GB2291499B (en) | 1998-07-22 |
Family
ID=23062964
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9517893A Expired - Fee Related GB2291499B (en) | 1994-07-20 | 1995-07-20 | DC stable detector compensation system |
Country Status (2)
| Country | Link |
|---|---|
| DE (1) | DE19526557A1 (en) |
| GB (1) | GB2291499B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU712708B2 (en) * | 1997-10-28 | 1999-11-11 | Matsushita Electric Works Ltd. | Infrared sensor |
| WO2003064985A1 (en) * | 2002-02-01 | 2003-08-07 | Calex Electronics Limited | Infrared apparatus |
| EP1886652A1 (en) * | 2006-08-11 | 2008-02-13 | Damm, Hans | Device for use in cryotherapy |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1127944A (en) * | 1966-03-15 | 1968-09-18 | Ass Portland Cement | Improvements relating to pyrometer |
| US4456390A (en) * | 1981-10-26 | 1984-06-26 | Wahl Instruments, Inc. | Noncontact temperature measuring device |
| US4527896A (en) * | 1982-03-04 | 1985-07-09 | Mikron Instrument Company, Inc. | Infrared transducer-transmitter for non-contact temperature measurement |
| USRE34507E (en) * | 1988-04-12 | 1994-01-11 | Citizen Watch Co., Ltd. | Radiation clinical thermometer |
| DE4331574C2 (en) * | 1993-09-16 | 1997-07-10 | Heimann Optoelectronics Gmbh | Infrared sensor module |
-
1995
- 1995-07-20 DE DE1995126557 patent/DE19526557A1/en not_active Withdrawn
- 1995-07-20 GB GB9517893A patent/GB2291499B/en not_active Expired - Fee Related
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU712708B2 (en) * | 1997-10-28 | 1999-11-11 | Matsushita Electric Works Ltd. | Infrared sensor |
| WO2003064985A1 (en) * | 2002-02-01 | 2003-08-07 | Calex Electronics Limited | Infrared apparatus |
| GB2405695A (en) * | 2002-02-01 | 2005-03-09 | Calex Electronics Ltd | Infrared apparatus |
| GB2405695B (en) * | 2002-02-01 | 2006-06-21 | Calex Electronics Ltd | Infrared apparatus |
| US7276697B2 (en) | 2002-02-01 | 2007-10-02 | Calex Electronics Limited | Infrared apparatus |
| EP1886652A1 (en) * | 2006-08-11 | 2008-02-13 | Damm, Hans | Device for use in cryotherapy |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2291499B (en) | 1998-07-22 |
| DE19526557A1 (en) | 1996-01-25 |
| GB9517893D0 (en) | 1995-11-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20020720 |