Scanning infrared thermometer with DC offset and emissivity correction

• US 5,094,544 A
• Filed: 10/19/1990
• Issued: 03/10/1992
• Est. Priority Date: 10/19/1990
• Status: Expired due to Fees

• Current Assignee: Fluke Corporation (Fortive Corp.)
• Original Assignee: Square D Company (Schneider Electric SE)
• Inventors: Ignatowicz, Steven A.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): BENNETT, GEORGE B
• Application Number:
  US07/601,164
• Time in Patent Office: 508 Days
• Field of Search: 374/5, 374/121, 374/124, 374/120, 374/126, 374/127, 374/128, 374/130, 374/129, 250/338.1, 250/342, 340/584, 340/600, 356/43 X, 356/45, 356/48, 358/82, 358/113
• US Class Current: 374/126
• CPC Class Codes: G01J 2005/0092 Temperature by averaging, e.g. by scan thermography G01J5/48
• CPC Class Codes: G01J 5/02 Constructional details
• CPC Class Codes: G01J 5/026 Control of working procedures of a pyrometer, other than calibration; Bandwidth calculation; Gain control
• CPC Class Codes: G01J 5/04 Casings
• CPC Class Codes: G01J 5/48 Thermography; Techniques using wholly visual means
• CPC Class Codes: G01J 5/52 using comparison with reference sources, e.g. disappearing-filament pyrometer
• CPC Class Codes: G01J 5/53 Reference sources, e.g. standard lamps; Black bodies
• CPC Class Codes: G01J 5/80 Calibration using comparison with reference sources G01J5/52

Abstract

A scanning infrared sensor (10) in which the scanner (21), detector (32) and temperature converter (35) are all contained in proximity with one another in a single housing assembly (18) enables correction of both emissivity based on emissivity settings (41) for each of a plurality of spot targets (16'"'"') along a scan line (16) and correction for DC offset errors based on reference temperature measurement (45) of hot and cold references (34, 36). Correction is performed before digital conversion by an A/D converter (56) by a nulling circuit (46), a programmable gain circuit (50) and a bias circuit (62) to produce corrected digital temperature signals on a plurality of output ports (26) respectively associated to a plurality of spot targets (16'"'"') along a scan line (16) on a target (12) which are individually connectable with a multiple temperature display (27), a temperature recorder (28) and a process control (30).

Claims

1. In a scanning infrared thermometer having an optical system for collecting light from a target and means including a photoelectrical detector for converting the collected light to an analog radiation temperature signal having a magnitude related to temperature, the improvement being a correction circuit, comprising:

means for altering the analog temperature signal to produce a corrected analog temperature signal in which errors due to emissivity are reduced including

a reference, and

means for correcting for emissivity;

means responsive to the reference for automatically correcting for DC offset fluctuations prior to correction by said emissivity correcting means;

means including an analog to digital converter for converting the corrected analog temperature signal to generate a corresponding corrected digital temperature signal representative of the magnitude of the corrected analog temperature signal; and

means responsive to the corrected digital temperature signal for displaying the temperature of the target.

2. The scanning infrared thermometer of claim 1 in which said emissivity correcting means includes

means for preselecting an emissivity setting according to the emissivity characteristics of a target, and

means responsive to the preselected emissivity setting for altering the analog temperature signal to produce a corrected temperature signal corrected for different emissivity settings.

3. The scanning infrared thermometer of claim 2 including

means for concurrently determining the temperature of a plurality of spots on a target, and in which

said emissivity setting preselecting means includes means for individually preselecting an emissivity setting for each of the spots of the target.

4. The scanning infrared thermometer of claim 1 in which emissivity correcting means includes means for automatically, proportionately altering the magnitude of the analog temperature signal.

5. The scanning infrared thermometer of claim 4 in which said automatically, proportionably altering means includes

a programmable gain circuit, and

means for automatically controlling said programmable gain circuit to correct for circuit instability.

6. The scanning infrared thermometer of claim 4 in which said automatically, proportionately altering means includes

a programmable gain circuit, and

means for automatically controlling said programmable gain circuit to correct for component variations.

7. The scanning infrared thermometer of claim 4 in which said proportional altering means includes

a programmable gain circuit connected between the detector and the analog to digital converter, and

a controller responsive to changes in emissivity for selectively changing the gain of the programmable gain circuit.

8. The scanning infrared thermometer of claim 7 in which said DC fluctuations correcting means is connected between the detector and the proportionally altering means.

9. The scanning infrared thermometer of claim 1 in which said DC offset fluctuations correcting means includes

a nulling circuit connected between the detector and the analog to digital converter, and

a controller responsive to changes in emissivity for selectively changing the DC offset of the nulling circuit.

10. The scanning infrared thermometer of claim 1 in which said digital temperature signal generating means includes a memory encoded with linearizing data for producing a linearized and corrected digital temperature signal.

11. The scanning infrared thermometer of claim 10 in which said linearizing data is in a direct look-up table format.

12. The scanning infrared thermometer of claim 10 in which said memory is a static memory.

13. The scanning infrared thermometer of claim 10 in which said memory is encoded with data for selectively producing linearizing data for display of temperature selectively in Celsius degrees and Fahrenheit degrees.

14. The scanning infrared thermometer of claim 1 including a bias circuit for selectively biasing the analog to digital converter to selectively alter the corrected digital temperature signal in accordance with a relatively cold reference temperature signal.

15. The scanning infrared thermometer of claim 1 in which said corrected temperature signal producing means includes a controller responsive to at least one reference temperature signal circuit for changing at least one of the analog temperature signals in accordance with control signals from said controller.

16. The scanning infrared thermometer of claim 15 in which said controller is responsive to a relatively cold reference temperature signal.

17. The scanning infrared thermometer of claim 16 in which said controller is responsive to a relatively hot reference temperature signal.

18. The scanning infrared thermometer of claim 15 in which said controller is responsive to a relatively hot reference temperature signal.

19. The scanning infrared thermometer of claim 1 including

means for causing said optical system to scan for individual measurement of a plurality of discrete spots on a target, and

said emissivity correcting includes means for correcting for emissivity at least once per complete scan of the scanning means.

20. The scanning infrared thermometer of claim 19 in which the emissivity fluctuation correcting means includes means for correcting for fluctuations in emissivity individually for each spot per scan in accordance with preselected emissivity settings for such spot.

21. The scanning infrared thermometer of claim 1 including

a housing assembly for protectively enclosing in proximity the corrected analog temperature signal producing means and the corrected digital temperature signal generating means, and

an interface including a plurality of output ports connected with said corrected digital signal generating means and mounted to the housing for respectively receiving therefrom corrected digital temperature signals for a plurality of different spots.

22. The scanning infrared thermometer of claim 21 including means mounted within the housing assembly for linearizing the converted digital temperature signals for each spot.

23. The scanning infrared thermometer of claim 21 in which said temperature displaying means is mounted to the housing assembly.

24. The scanning infrared thermometer of claim 21 in which said housing assembly is formed of a single housing within which all of the corrected analog temperature providing means and the corrected digital temperature signal generating means are enclosed.

25. The scanning infrared thermometer of claim 24 in which

said analog temperature signal producing means includes means for concurrently providing corrected analog temperature signals for each of a plurality of samples for each of a plurality of spots on the target, and

said corrected digital temperature signal generating means includes means responsive to each of the corrected analog temperature signals for providing an average corrected digital temperature signal for each of said spots.

26. The scanning infrared thermometer of claim 1 in which

said analog temperature signal producing means includes means for concurrently providing corrected analog temperature signals for each of a plurality of samples for each of a plurality of spots on the target, and

said corrected digital temperature signal generating means includes means responsive to each of the corrected analog temperature signals for providing an average corrected digital temperature signal for each of said spots.

27. In a scanning infrared thermometer having a scanning optical system for collecting light from a target and means including a photoelectrical element for converting the collected light to an analog temperature signal with a magnitude related to temperature, the improvement being a correcting circuit, comprising:

means for automatically altering the analog temperature signal to correct for DC offset errors from the detector to produce a first order corrected analog temperature signal;

means including an analog to digital converter for converting the corrected analog temperature signal to a corresponding corrected digital temperature signal representative of magnitude of the corrected analog temperature signal; and

means responsive to the corrected digital temperature signal for displaying the temperature of the target.

28. The scanning infrared thermometer of claim 27 in which said analog temperature signal altering means alters the analog signal in accordance with a reference signal.

29. The scanning infrared thermometer of claim 28 in which said altering means includes

a nulling circuit, and

means for controlling the nulling circuit to produce a null output when the optical system is sensing a reference target.

30. The scanning infrared thermometer of claim 29 in which said altering means includes means for introducing an offset to the input of the analog to digital converter.

31. The scanning infrared thermometer of claim 27 in which said altering means includes means for introducing an offset to the input of the analog to digital converter.

32. The scanning infrared thermometer of claim 27 including means for proportionately altering the magnitude corrected analog signal to further correct it for emissivity.

33. The scanning infrared thermometer of claim 27 in which said analog temperature altering means includes means for altering the DC offset in accordance with a relatively hot temperature reference signal.

34. The scanning infrared thermometer of claim 27 in which said digital temperature signal generating means includes a memory encoded with linearizing data for producing a linearized and corrected digital temperature signal.

35. The scanning infrared thermometer of claim 34 in which said linearizing data is in a direct look-up table format.

36. The scanning infrared thermometer of claim 34 in which said memory is a static memory.

37. The scanning infrared thermometer of claim 34 in which said memory is encoded with data for selectively producing linearizing data for display of temperature selectively in Celsius degrees and Fahrenheit degrees.

38. The scanning infrared thermometer of claim 27 in which said corrected temperature signal producing means includes a controller responsive to at least one reference temperature signal circuit for changing at least one of the analog temperature signals in accordance with control signals from said controller.

39. The scanning infrared thermometer of claim 38 in which said controller is responsive to a relatively cold reference temperature signal.

40. The scanning infrared thermometer of claim 39 in which said controller is responsive to a relatively hot reference temperature signal.

41. The scanning infrared thermometer of claim 38 in which said controller is responsive to a relatively hot reference temperature signal.

42. The scanning infrared thermometer of claim 27 including

means for causing said optical system to scan for simultaneous measurement of a plurality of discrete spots on a target, and

said corrected analog temperature signal producing means includes means for correcting for fluctuations in DC offset at least once per complete scan of the scanning means.

43. The scanning infrared thermometer of claim 27 including

a housing assembly for protectively enclosing in proximity the corrected analog temperature signal providing means and the corrected temperature digital temperatures signal generating means, and

an interface having a plurality of output ports connected with said corrected digital signal generating means and mounted to the housing for respectively receiving therefrom corrected digital temperature signals for the plurality of spots.

44. The scanning infrared thermometer of claim 43 including means for linearizing the converted digital temperature signals for each spot mounted within the housing.

45. The scanning infrared thermometer of claim 44 in which said temperature displaying means is mounted to the housing.

46. In a scanning infrared thermometer having a scanning optical system for collecting light from a target and means including a photoptical detector for converting the collected light to an analog temperature signal with a magnitude related to the temperature of the target, the improvement, comprising:

a correcting circuit responsive to the analog temperature signal circuitry for producing a corrected analog temperature signal corrected for errors due to at least one of (a) variations in DC offset of the light converting means and (b) errors due to target emissivity, at least once per complete scan of the scanning optical system;

a linearizing circuit responsive to the corrected analog temperature signal for producing a linearized corrected digital temperature signal;

a controller responsive to the linearized, corrected temperature signal for controlling the correcting circuit;

a housing assembly for protectively enclosing together in proximity the correcting circuit linearizing circuit and the controller; and

an output interface including

an output terminal mounted to and accessibly from the outside of the housing, and

means for producing a representation of the linearized, corrected temperature signal at said output terminal in digital form.

47. The scanning infrared thermometer of claim 46 in which said correcting circuit corrects for both emissivity errors and DC offset errors.

48. The scanning infrared thermometer of claim 46 in which said correcting circuitry includes a nulling circuit responsive to a relatively cold reference signal to correct for zero offset errors.

49. The scanning infrared thermometer of claim 46 in which said correcting circuitry includes a programmable gain circuit responsive to different emissivity settings for different locations on the target to proportionally alter the magnitude of the analog temperature signal for each said different location.

50. The scanning infrared thermometer of claim 46 including

means for producing a corrected, linearized digital temperature signals for a plurality of different spots on the target, and in which

said output interface has a plurality of input-output parts for receiving the corrected, linearized digital temperature signals for said plurality of spots, respectively.

51. The scanning infrared thermometer of claim 46 in which said controller includes means for selecting different emissivity settings for different ones of said spots on the target where temperature is being measured.

52. In a scanning infrared thermometer having a scanning optical system for collecting light from a target and a detector circuit including a photoelectrical device for converting the collected light to an analog temperature signal having a magnitude related to temperature, the improvement being a correcting circuit, comprising:

means for altering the analog temperature signal to correct for DC offset errors from the detector circuit to produce a corrected analog temperature signal;

means for altering the magnitude of the analog temperature signal to correct for magnitude errors caused by at least two of emissivity effects, circuit stability and component variations;

means including an analog to digital converter for converting the corrected analog temperature signal to a corresponding corrected digital temperature signal representative of the magnitude of the corrected analog temperature signal; and

means responsive to the corrected digital temperature signal for outputting the signal in digital format to at least one of a display, a recorder and a process controller.

53. The scanning infrared thermometer of claim 52 in which said offset correcting means alters the analog signal in accordance with the reference signal.

54. The scanning infrared thermometer of claim 52 in which said offset correcting means includes

a nulling circuit, and

means for controlling the nulling circuit to produce a null output prior to an input to the analog to digital converter when the optical system is sensing a relatively cold reference target, and

means to introduce an offset signal at an input of the analog to digital converter which is generated in response to an independent temperature signal from the cold reference target.

55. The scanning infrared thermometer of claim 54 in which the analog termination signal magnitude adjusting means includes a programmable gain amplifier responsive to the controlling means responsive to an emissivity reference.

56. The scanning infrared thermometer of claim 55 in which the controlling means is also responsive to a relatively hot temperature reference target.

57. The scanning infrared thermometer of claim 55 in which said digital temperature generating means includes a memory encoded with linearizing data for producing a linearized and corrected digital temperature signal.

58. The scanning infrared thermometer of claim 57 in which said linearizing data is in a direct look-up table format.

59. The scanning infrared thermometer of claim 58 in which said memory is encoded to produce temperature readings selectively in standard temperature scales of degrees Celsius and degrees Fahrenheit.

60. The scanning infrared thermometer of claim 59 in which said memory includes address lines which are connected directly to digital converter data output lines.

61. The scanning infrared thermometer of claim 60 in which the controlling means is also responsive to a relatively hot temperature reference target when in view of the optical system.

62. The scanning infrared thermometer of claim 61 in which the controlling means is also responsive to an independent temperature signal from the hot reference target.

63. The scanning infrared thermometer of claim 60 where the controlling means integrates the cold reference readings over successive scan cycles to reduce system noise while controlling the nulling circuit.

64. The scanning infrared thermometer of claim 63 in which the controller and programmable gain amplifier are responsive to a plurality of emissivity settings along the scan line.

65. The scanning infrared thermometer of claim 64 in which the controlling means is also responsive to a relatively hot temperature reference.

66. The scanning infrared thermometer of claim 65 where the controlling means integrates the hot reference readings over successive scan cycles to reduce a system noise while controlling the programmable gain circuit.

67. The scanning infrared thermometer of claim 65 in which the controlling means is also responsive to an independent temperature signal from the hot reference target.

68. The scanning infrared thermometer of claim 67 the improvement being means to select discrete measurement spots from a thermal image including a controller to select samples during successive scans into at least one composite measurement, and

means to output the composite measurements.

69. The scanning infrared thermometer of claim 68 in which the optical system, correcting means, and output means are contained in a single protective housing assembly.

70. The scanning thermometer of claim 69 including means to output the composite measurement as an analog signal.

71. The scanning thermometer of claim 70 including means to output a discrete binary signal respectively representing the composite measurement being above and below a reference setpoint.

72. The scanning infrared thermometer of claim 65 in which the controlling means is responsive to an independent hot temperature reference signal.

73. The scanning infrared thermometer of claim 64 including means to pick out discrete measurement spots from a thermal image including

computing means to select samples along successive scan lines to determine one or more composite measurements, and

means to output the composite measurements.

74. The scanning infrared thermometer of claim 73 in which the optical system, correcting means, and output means are contained in a single protective housing assembly.

75. The scanning thermometer of claim 73 including means to output the composite measurements as an analog signal.

76. The scanning infrared thermometer of claim 75 including means to output a discrete binary signal respectively representing the composite measurement being above and below a reference setpoint.

77. The scanning infrared thermometer of claim 54 in which the controller and programmable gain amplifier are responsive to a plurality of emissivity settings along the scan line.