DE9422203U1 - Device for measuring temperature using infrared techniques - Google Patents

Description

Applicant; 10 August 1998

1614G101 CS-km
Omega Engineering, Inc.
One Omega Place
Stamford, CT 06907
USA

Device for measuring temperature using infrared techniques

The present invention relates generally to an apparatus for more accurately measuring the temperature of a surface using infrared measurement techniques, and more particularly to such an apparatus which uses a circumscribing laser aiming beam or beams to more clearly define the perimeter of the energy zone from which the temperature is to be measured. Generally speaking, this is achieved by allowing the laser beam to rotate around the perimeter of the energy zone; by using two or

multiple stationary laser beams focused on the perimeter of the energy zone; or by using a controlled single laser beam directed at two or more predetermined locations on the perimeter of the energy zone.

Devices for measuring temperature using infrared radiation from a remote location (commonly referred to as infrared pyrometers or radiometers) have been used for many years to measure the temperature of a surface from a remote location. The principle of operation of these devices is well known. All surfaces with a temperature above absolute zero emit heat in the form of radiant energy. This radiant energy is generated by molecular motions which generate electromagnetic waves. Thus, some of the energy in the material is radiated in straight lines away from the surface of the material. Many infrared radiometers use optical reflection and/or refraction principles to capture the radiated energy or radiant energy from a given surface. The infrared radiation is focused on a detector, analyzed and using well-known techniques, the surface energy is collected, processed and the temperature is calculated and displayed on a suitable display.

Examples of such infrared radiometers are shown on pages JI through J-42 of the Omega Engineering Handbook , Volume 2B. See also U.S. Patent No. 4,417,822 issued November 29, 1983 to Alexander Stein et al. for a laser radiometer; U.S. Patent No. 4,527,896 issued July 9, 1985 to Keikhosrow Irani et al. for an infrared transducer/transmitter based on

and U.S. Patent No. 5,169,235 issued on December 8, 1992 to Hitoshi Tominaga et al. for a radiation-type thermometer. See also Baker, Ryder and Baker, Volume II, Temperature Measurement in Engineering , Omega Press, 1975, Chapters 4 and 5.

When such radiometers are used to measure surface temperature, the instrument is aimed at a target or "spot" within the energy zone on the surface where the measurement is to be made. The radiometer receives the emitted radiation through the optical system and focuses it onto an infrared-sensitive detector, which produces a signal that is internally processed and converted into a temperature reading that is displayed.

The precise location of the energy zone on the surface as well as its size are extremely important to ensure the accuracy and reliability of the resulting measurement. It is understood that the field of view (FOV) of the optical systems of such radiometers is such that the diameter of the energy zone increases directly with the distance to the target. The typical energy zone of such radiometers is defined to be the area from which 90% of the energy focused on the detector originates. To date, no means have been known to accurately determine the size of the actual energy zone, except for its approximation by using a "distance to target table" or by actual physical measurement.

The target size and distance are critical to the accuracy of most infrared thermometers. Each infrared measuring device has

There is a field of view, a viewing angle within which the temperatures that the device sees through this field of view are all averaged. The field of view is described either by its angle or by a ratio of distance to size (D:S). If the value of D:S = 20:1 and if the distance to the object divided by the diameter of the object is exactly 20, then the object fills the device's field of view exactly. A D:S ratio of 60:1 corresponds to a field of view of 1 degree.

Since most infrared thermometers have fixed focal length optics, the minimum spot size occurs at the specified focal distance. If a device has fixed focal length optics with a D:S ratio of 120:1 and a focal length of 60" (I" = 25.4 mm), then the minimum spot size (resolution) that the device can achieve is a value of 60 divided by 120, or 0.5" at a distance of 60" from the device. This value is particularly important when the size of the object is close to the minimum spot size that the device can measure.

Most general-purpose infrared thermometers use a focal length in the range 20" to 60" (50 or 150 cm); those with a special close-up focal length use a focal length of 0.5" to 12". See pages Z54 and Z55 of The Omega Engineering Handbook , Volume 28.

To make such devices more accurate, laser beam targeting devices have been used to determine the exact center

the energy zone. See, for example, pages Cl-10 to Cl-12 of The Omega Temperature Handbook , Volume 27. Various targeting devices such as telescopes with crosshairs have also been used to more accurately identify the center of the energy zone to be measured. See, for example, pages C-10 to C-21 of The Omega Temperature Handbook , Volume 27.

However, using a laser to indicate the center of the energy zone does not provide the user with an accurate definition of the actual energy zone from which the measurement is taken. This inability often leads to inaccurate readings. For example, in cases where the area emitting radiation is smaller than the target diameter limit (too far from a target or too small a target), inaccurate readings occur.

One method used to determine the distance to the target is to use an infrared distance detector or a Doppler effect distance detector or a cross-sectional image detector similar to those used in photography. However, the exact size of the energy zone must still be known or determined if one wants to have a degree of certainty as to how large the measured area of the surface actually is. This is especially true if the energy zone is too small or the surface surrounding or enclosing the energy zone is of an irregular shape. In the event that the surface does not fill the entire area of the energy zone, the readings will be too low and therefore inaccurate.

Similarly, if the surface is irregularly shaped, the readings will also be erroneous, as part of the object would be missing from the actual measured energy zone. Thus, using a single laser beam on the apparent center of the energy zone does not guarantee accuracy, as the radiometer operator does not have precise knowledge of the boundaries of the measured energy zone.

It is clear that no prior art recognizes this inherent problem, let alone offers a solution to the problems it creates.

Against the above background, it is a primary object of the present invention to provide a device for measuring the temperature of a surface using infrared techniques.

It is a further object of the present invention to provide such a device which provides a more accurate measurement of the surface temperature than is possible using the techniques used to date.

It is a further object of the present invention to provide such a device which allows the user to visually identify the energy zone to be measured on the surface.

It is a further object of the present invention to provide such a device which generates a laser beam or

rays are used to clearly define the extent of the energy zone on the surface.

To achieve the above objects and advantages, the present invention comprises, in brief summary, an apparatus for visually delineating the contour of the energy zone to be measured by means of a radiometer. The method implementable with the apparatus comprises the steps of providing a laser targeting device on the radiometer adapted to emit at least one laser beam against a surface whose surface is to be measured and steering the laser beam around the energy zone to visually delineate the energy zone. The steering of the beam can be carried out in such a way that it is directed to predetermined points on the target zone. This can be achieved mechanically or electrically.

Another embodiment of the invention uses a plurality of laser beams to delineate the outline of the energy zone, either by splitting the laser beam into a number of points through the use of optical fibers or beam splitters or by using a plurality of lasers. One embodiment of the invention includes a laser aiming device adapted to emit at least one laser beam against the surface and means for rotating the laser beam around the energy zone to visibly delineate the energy zone. This rotation may be stepwise or in the manner of a continuous motion.

Another embodiment consists of two or more stationary beams directed to cover the energy zone

The two or more laser beams could be derived from a dedicated laser for each beam or by beam splitters. This can be achieved by mirrors, optics and fiber optics.

Another embodiment consists of a laser beam splitting device that emits a laser beam that is split into a plurality of beams that circumscribe the energy zone.

The above and other objects and advantages of the present invention will become apparent from the detailed explanation of preferred embodiments of the invention in conjunction with the accompanying drawings.

Fig. 1 is a schematic representation of a prior art radiometer using a laser sighting device;

Fig. 2 is a schematic representation of a preferred embodiment of the present invention, wherein the laser beam circumscribes the target zone using a mirror;

Fig. 2A and 2B

show the way in which the laser beam is stepped to identify the energy zone;

Fig. 3 is a schematic representation of an alternative embodiment of the present invention, wherein the laser is pivoted about a pivot point by mechanical movement means;

Fig. 4 is a schematic representation of another alternative embodiment of the present invention, where the laser is guided through a magnetic field to identify the target zone;

Fig. 5 is a schematic representation of another alternative embodiment of the present invention wherein a number of individual laser beams are projected to define the energy zone to be measured;

Fig. 6 is a schematic representation of another alternative embodiment of the present invention, where the laser is mechanically pivoted;

Fig. 7 shows in schematic form the arrangement of a fiber optic to create a pattern of the target zone with the laser beam;

Figure 8 is a detailed sectional view of another alternative embodiment of the present invention, where the laser is mechanically swung around the detector;

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Figures 9A-C illustrate alternative embodiments of the targets or borders that can be projected using the apparatus of the present invention; and

Figure 10 is a schematic representation of another embodiment of the invention wherein the laser is split into a plurality of laser beams defining the energy zone by using optical fibers.

Conventional prior art radiometers have long employed laser aiming devices to assist in appropriate targeting and alignment of the instrument. Figure 1 illustrates the operation of conventional prior art handheld radiometers. One such radiometer, indicated generally by the reference numeral 10, includes a laser aiming telescope 12 which emits a laser beam 14 at a spot or target 18 on the surface 20 whose temperature is to be measured. This spot 18 is located in the center of the energy zone ¹¹ E" to be measured by the radiometer 10. This radiometer 10 comprises a detector 16 connected to conventional internal circuitry and display means (not shown) for converting, calculating and displaying the temperature of the surface 20, which temperature is indirectly calculated from the energy radiated from the surface within the energy zone E. This energy is radiated in straight lines in all directions away from the surface 20 and is captured by the detector 16 on the radiometer 10. Using infrared radiation principles, the radiometer can

capture and measure the infrared radiation in the energy zone E and determine the surface temperature of the energy zone E.

The actual size and shape of the energy zone is determined by the optics of the radiometer and by the distance between the radiometer and the target. Each radiometer has a defined angle of view or "field of view" (FOV), typically stated in the specifications of the instrument. The size of the energy zone E is predetermined if the field of view and the distance to the target are known. It is obvious that the further the radiometer is held from the target (i.e., the greater the distance), the larger the energy zone E is.

This can be expressed as a "distance to spot size ratio". For example, with a "distance to spot size ratio" of 40:1, the energy zone has a diameter of 1" (I" = 25.4 mm) at a distance of 40", or a diameter of 1/2" at a distance of 20". Pyrometer manufacturers usually provide field of view diagrams to determine the energy zone at specific distances.

As can be easily seen, such laser targeting devices are only able to identify the center of the measured energy zone and not the outer perimeter of the energy zone from which the measurement is actually taken. The further the radiometer 10 is positioned from the surface, the larger the energy zone E. The actual energy zone E can therefore, depending on the size and

the configuration of the surface 20, understandably contain irregularly shaped portions of the surface 20 or even extend beyond the edges of the surface. In such cases, the resulting measured temperature would of course be inaccurate. Without knowledge of the outer perimeter of such an energy zone E, the user of the radiometer 10 would have no knowledge of this fact, or the resulting measurements could be inaccurate.

The present invention provides a means for visually defining the energy zone E such that the user of the radiometer 10 can observe the actual measured energy zone to determine where the energy zone lies relative to the surface being measured. In various embodiments of the present invention, a fine laser line or lines are projected against the surface being measured, and these line or lines are positioned to enclose the perimeter of the energy zone E. When a rotating laser beam is used, positioning can be accomplished either by moving the laser itself or by moving the laser beam emitted by the laser. If the perimeter of the energy zone E on the object could be identified by moving the laser beam in a path around the perimeter of the energy zone E, the user would be able to quickly and accurately determine whether the energy zone from which the measurement was taken was entirely on the surface being measured and whether the surface was of a type that would otherwise provide an accurate measurement.

The extent of the energy zone E is identifiable as a function of the so-called "angle of view" of the particular radiometer, such as

·

·

specified in its specification, and the distance between the radiometer and the target. Identification of the size and shape of the energy zone is easily accomplished using conventional mathematical formulas. Once identification is made, the laser beam is then projected around the perimeter of the energy zone E in accordance with the methods and apparatus described below. A simple "target" approach is to project the laser beam at the same angle as the field of view of the radiometer, from the same axis; alternatively, the laser beam angle is mechanically adjusted in accordance with "distance to spot size ratio" calculations. In either case, the perimeter of the energy zone is identified by the laser beam.

Fig. 2 illustrates a first embodiment of the present invention, in which the laser aiming device 12 emits a laser beam 14 which is directed at a mirrored surface 30 disposed in front of the laser beam 14. The mirror 30 is rotated using drive means 32 so that the beam is rotated in a circular manner to define the measured energy zone E on the surface. Alternatively, the mirror 30 may be rotated by vibratory means or by application of a magnetic field (not shown). Rotation of the mirror 30 should be at an angle of refraction corresponding to the 90% energy zone E to thereby rotate the laser beam 14 around the circumference of the energy zone E, making it visible to the user of the radiometer 10.

Alternatively, a prism with predetermined angles may be used instead of the mirror 30 so that the prism is made to act as a reflective mirror surface and thereby direct the laser beam around the perimeter of the energy zone.

Figures 2A and 2B illustrate the manner in which the laser beams can be used to delineate the measured energy zone E on the surface. It is important that the rotation of the beam 14 be carefully controlled so that the rotation occurs at a rate that can be followed visually. This allows full intensity of the beam. As shown in Figures 2A and 2B, the laser beam is rotated around the energy zone E in a series of steps, allowing the laser beam to remain at each step for at least one hundredth of a second before moving to the next position. This is accomplished by creating a plurality of steps E-I, E-2, etc. around the energy zone E. The laser beam 14 would stop at each step for the predetermined period of time to allow the beam to be visually observed before moving on to the next step.

Fig. 3 illustrates another embodiment of the present invention, wherein laser 112 itself is rotated or translated to write a circle defining energy zone E, by mechanically pivoting laser 112 about pivot point 120 using drive means 132. Alternatively, laser 112 may be rotated by vibratory means (not shown) or by applying a magnetic field (not shown). However, rotation of laser 112 should be at an angle of refraction that is 90%

Energy zone E, whereby the laser beam 114 can be rotated around the circumference of the energy zone E in order to make it visible to the user of the radiometer 10.

In Fig. 4, the laser 212 is rotated about a pivot point 220 by the application of a magnetic field 225 so that the emission of the laser beam 214 occurs around the circumference of the 90% energy zone E to make the beam visible to the user of the radiometer 10. In this embodiment, means (not shown) are provided for modifying the magnetic field 225 to correspond to the 90% energy zone E so that the laser can be rotated accordingly.

In Fig. 5, the laser 312 has at least two components 312A and 312B that produce at least two individual laser beams 314A and 314B around the detector 316. These at least two individual beams 314A and 314B are directed at the surface 320 being measured, at the perimeter of the energy zone E, rather than at the center thereof. By using a number of such laser beams, the energy zone E can be more clearly identified, rather than just the center of the energy zone E. If desired, individual lasers can be used, or laser splitter devices can be used to split a single laser beam.

Fig. 6 illustrates another embodiment of the present invention in which the laser 412 is mechanically pivoted in a circular manner around the detector 416 to emit a laser beam 414 in a circular path onto the surface (not shown) to thereby define the energy zone E

to define. The laser 412 is pivotally mounted on a pivot bearing 420 provided on a connecting arm 421. The arm 421 is mounted on a pivot bearing 424 which is rotated by a motor 422. In this way, the laser beam 414 emitted by the laser 412 rotates around the energy zone E on the surface whose temperature is to be measured and circumscribes the energy zone E.

The rotation of the laser can also be effected using fiber optic techniques as shown in Figure 7, where the laser beam is projected by fiber optic means 501. In this way, the beam from the laser source is fanned out and encircles and thereby defines the energy zone E. By using a sufficient number of fiber optics, the perimeter of the target area E can be circumscribed with a ring of light. This can be achieved by only two fibers 501 arranged 180° apart, since the scanning pattern would be or could be circular.

Fig. 8 illustrates further means for causing rotation of the laser beam 614 emitted by a laser 612. Here, the laser beam 614 is directed to a rotating flat surface mirror 630 where it is reflected against a conical mirror 631 made of plated plastic material. The reflected beam is then projected onto the surface and defines the perimeter of the energy zone E. The flat mirror 630 is driven by a motor 622. In this way, the laser beam 614 rotates around the perimeter of the energy zone E on the surface to be measured. The mirrors

are arranged at such an angle that the laser projection is carried out at the same angle as the recording or scanning angle of the infrared detector.

It is to be understood, of course, that the energy zones E may take on other configurations or shapes than the circular shape shown in Figures 1 to 8. Figures 9A-C show alternatively a square (Figure 9A), a rectangular (Figure 9B) and a triangular (Figure 9C) configuration of the light patterns that may be achieved using the means of the present invention.

Figure 10 illustrates a method of defining the energy zone where a circular shape can be achieved without rotation of the laser beam using a plurality of fixed optical fibers arranged to project a number of points. In this figure, a fixed laser 712 projects a beam 713 which is split into a plurality of beams 714 by a bundle of optical fibers 715 to project onto the surface a pattern 716 defining the energy zone E. Additional configurations may also be used if desired.

Having thus described the invention with particular reference to preferred embodiments, it will be understood that various changes and modifications may be made without departing from the scope of the present invention as defined by the appended claims.

Claims (7)

Divisional application to the German utility model application G 94 22 197.9 New protection claims 1. Device for use in conjunction with a radiometer for temperature measurement, with a detector (16) for capturing infrared radiation emanating from an energy zone (E) on a surface (20) whose temperature is to be measured; an optical system defining a field of view for collecting the infrared radiation to be captured by the detector (16) from the energy zone (E); and a sighting device for identifying the size and shape of the energy zone (E) on the surface (20) by means of visible light, characterized in that the sighting device directs more than two laser beams against the surface to produce a light pattern having a configuration with at least two non-parallel light spot lines to identify the energy zone (E). 2. Device according to claim 1, characterized in that the at least two non-parallel light point lines are connected to one another. 3. Device according to claim 1 or 2, characterized in that the sighting device has a beam splitter for splitting a single laser beam into more than two laser beams. 4. Device according to claim 3, characterized in that the beam splitter comprises a mirror. 5. Device according to claim 3, characterized in that the beam splitter has an optic. 6. Device according to claim 3, characterized in that the beam splitter comprises a fiber optic. 7. Device according to one of claims 1 to 6, characterized in that the more than two laser beams have a beam which is directed towards the center of the energy zone (E).