Blackbody radiation sensing optical fiber thermometer system

• US 4,750,139 A
• Filed: 08/29/1985
• Issued: 06/07/1988
• Est. Priority Date: 01/24/1985
• Status: Expired due to Term

• Current Assignee: Luxtron Corp. (Advanced Energy Industries, Inc. (China))
• Original Assignee: Accufiber Incorporated
• Inventors: Dils, Ray R.
• Primary Examiner(s): Gruber, Felix D.
• Application Number:
  US06/770,679
• Time in Patent Office: 1,013 Days
• Field of Search: 364/557, 364/571, 250/227, 250/339, 374/130, 374/131, 374/133, 374/141, 374/161, 374/170
• US Class Current: 702/134
• CPC Class Codes: G01J 2001/4406 Plural ranges in circuit, e.g. switchable ranges; Adjusting sensitivity selecting gain values
• CPC Class Codes: G01J 2001/446 Photodiode
• CPC Class Codes: G01J 2005/607 on two separate detectors
• CPC Class Codes: G01J 5/064 Ambient temperature sensor; Housing temperature sensor; Constructional details thereof
• CPC Class Codes: G01J 5/08 Optical arrangements
• CPC Class Codes: G01J 5/0801 Means for wavelength selection or discrimination
• CPC Class Codes: G01J 5/0821 Optical fibres
• CPC Class Codes: G01J 5/52 using comparison with reference sources, e.g. disappearing-filament pyrometer
• CPC Class Codes: G01J 5/602 using selective, monochromatic or bandpass filtering
• CPC Class Codes: G01J 5/80 Calibration using comparison with reference sources G01J5/52

Abstract

An optical fiber thermometer system utilizing the laws of blackbody radiation includes a sensor responsive to the temperature within a region to be tested for transmitting light energy generated as a function of the temperature according to Planck'"'"'s equation along an optical transmission line, and a detector responsive to the light energy for producing an electrical current. The current is amplified by a linear amplifier having provision for automatically controlling the gain of the amplifier, depending upon the magnitude of the input current, to reduce the dynamic range of the input current. The output of the linear amplifier is a voltage which is used by a signal processing network to yield an accurate indication of the temperature within the region to be tested by solving the Planck equation between two predetermined wavelengths representing upper and lower limits of an optical filter which filters light energy entering the detector.

Claims

1. A system for measuring temperature within a region to be tested comprising:

(a) sensor means responsive to the temperature within said region for transmitting light energy generated as a function of said temperature along an optical transmission line;

(b) detector means responsive to said light energy for producing an electrical signal;

(c) linear amplifier means for converting said electrical signal to an output voltage whose magnitude is a linear function of said electrical signal, said linear amplifier means including automatic gain control means for adjusting a selectively controllable gain factor in response to the magnitude of said electrical signal; and

(d) signal processing means for converting said output voltage into a display signal indicating the temperature within said region.

2. The system of claim 1 wherein said sensor means comprises a black body emitter coupled to the tip of a high temperature optical fiber.

3. The system of claim 1 wherein said sensor means comprises a pyrometer having an input lens for collecting light energy and means for coupling light energy from said lens into said optical transmission line.

4. The system of claim 1 wherein said sensor means comprises an optically-transmissive light pipe.

5. The system of claim 2, 3 or 4 wherein said optical transmission line comprises an optically-transmissive fiber.

6. The system of claim 5 further including fiber calibration means for inserting a predetermined amount of light into said optically-transmissive fiber and for measuring losses of light intensity within said optically-transmissive fiber to provide an error correction factor as a function of said light intensity losses.

7. The system of claim 6 wherein said optically-transmissive fiber comprises a high-temperature fiber detachably coupled to a low-temperature fiber, said low-temperature fiber having an input end, and mirror means disposed adjacent said input end for reflecting light transmitted by said calibration means through said low-temperature fiber.

8. The system of claim 3 wherein said pyrometer includes mirror means for reflecting light from said optical transmission line through said coupling means back into said optical transmission line.

9. The system of claim 8 wherein said mirror means comprises a half-silvered mirror deposited on said input lens.

10. The system of claim 1 wherein said automatic gain control means comprises means responsive to said electrical signal from said detector for increasing the gain factor of said linear amplifier means if said signal is below a first predetermined threshold limit, and for decreasiang said gain factor if said signal is above a second predetermined threshold limit.

11. The system of claim 10 wherein said gain factor is removed by said signal processing means in converting said output voltage into said display signal.

12. The system of claim 11 wherein said linear amplifier means includes at least one operational amplifier having a plurality of selectively connectable parallel shunt paths, each of said paths including a resistor whereby said gain is adjusted by selectively connecting differing ones of said shunt paths in parallel with said operational amplifier.

13. The system of claim 12 wherein said shunt paths are selectively connectable by means of signals produced by said automatic gain control means.

14. The system of claim 1 wherein said linear amplifier means includes frequency response adjustment means comprising at least one operational amplifier having a plurality of selectively connectable shunt paths connectable in parallel with said operational amplifier, each of said paths including a capacitor whereby the frequency response of said amplifier is controlled by selectively connecting selected ones of said paths in parallel with said operational amplifier.

15. The system of claim 1 further including a band width control amplification stage connected to the output of said linear amplifier means for selectively controlling the frequency response of said system to said light energy.

16. The system of claim 15 wherein said bandwidth control amplification stage includes an operational amplifier having a switching means for selectively shunting said amplifier by at least one of a plurality of capacitors.

17. The system of claim 2, 3 or 4 wherein said detector means comprises at least one photodiode responsive to said light energy for producing an electrical photodiode current whose magnitude varies as a linear function of the flux density of said light energy of predetermined wavelengths impinging upon said photodiode.

18. The system of claim 17 wherein said detector means further comprises narrowband optical filter means for adjusting the response of said photodiode to respond to selected wavelengths of light energy at which relatively small changes in temperature within said region cause relatively large changes in the output current of said photodiode.

19. The system of claim 18 wherein said detector means further comprises at least two detectors for differing temperature ranges to be measured, each said detector having a different narrowband optical filter means.

20. The system of claim 19 comprising differential temperature measurement means for measuring the difference between the instantaneous temperature within said region and the average temperature within said region.

21. The system of claim 17, including shutter means for blocking the optical input to said photodiodes and memory means for storing in memory a factor representing the dark current output of said photodiodes.

22. The system of claim 2, 3, or 4, further including thermistor means for measuring the temperature of said detector means and for providing said temperature to said signal processing means.

23. The system of claim 2, 3 or 4 further including switching means for grounding the input to said linear amplifier means, whereby the quiescent electrical current within the remainder of said system is provided to said signal processing means.

24. A system for measuring temperature within a region to be tested comprising:

(a) sensor means responsive to the temperature within said region for transmitting light energy generated as a function of said temperature along an optically transmissive path;

(b) detector and amplifier means responsive to said light energy for producing an output signal representative of the intensity of said light energy; and

(c) signal processing means for electronically providing from said output signal a display signal representative of the temperature within said region, said signal processing means including computer means for calculating the temperature (T) within said region as a function of the radiance of light energy (L) according to the function ##EQU12## where f(λ

,T) is Planck'"'"'s function, where λ

is the wavelength of said light energy and λ

₁ and λ

₂ are upper and lower limits respectively, of an optical filter disposed between said sensor means and said detector means.

25. The system of claim 24 wherein said sensor means comprises a blackbody cavity disposed on the end of an optically transmissive fiber.

26. The system of claim 24 wherein said sensor means comprises an optical light pipe.

27. The system of claim 24 wherein said sensor means comprises a pyrometer.

28. The system of claim 25, 26 or 27 comprising calibration means for determining the degree of attenuation of said light energy within said optically-transmissive path.

29. The system of claim 28 wherein said calibration means comprises means for inserting light from a source of light of a predetermined intensity into said optically-transmissive path, and mirror means disposed in said optically-transmissive path for reflecting said light onto said detector means.

30. A system for measuring temperature within a region to be tested comprising:

(a) sensor means responsive to the temperature within said region for transmitting light energy generated as a function of said temperature along an optically-transmissive path;

(b) detector and amplifier means responsive to said light energy for producing and output signal;

(c) signal processing means responsive to said output signal for calculating a display signal representing a temperature value corresponding to the intensity of said light energy utilizing a formula containing a constant representing losses of said light energy along said optically-transmissive path; and

(d) optical path calibration means for measuring losses of said light energy along said optically transmissive path and for correspondingly altering said constant.

31. The system of claim 30 wherein said optical path calibration means comprises mirror means disposed in said optical path, for reflecting said light energy along said path towards said detector and amplifier means, and light insertion means for injecting light energy of known intensity into said path.

32. The system of claim 31 wherein said path includes optical coupling means for detachably connecting said mirror means to said path.

33. The system of claim 32 wherein said path includes a high-temperature portion having an output end and a low-temperature portion having an input end, said input end being detachably coupled to said output end.

34. The system of claim 33 wherein said optical coupling means comprises a housing including an internally disposed mirror, said housing being adapted for connection to said input end of said low-temperature portion.