The invention relates generally to a device which measures temperature of an object, such as a thermometer. More particularly, the invention relates to a system and method for measuring temperature using an infrared detector, without having contact with the object.
A common technique for measuring body temperature is through the sensing of infrared (IR) energy from one or more locations on the body. This technique, referred to as “non-contact” thermometry, can be used to measure body temperature in locations that are too confined and/or delicate to allow for direct contact between the body part and a temperature probe. A common example is the tympanic membrane in the inner ear.
The typical infrared thermometer has a probe tip with at least one opening or window at the front of the probe tip. The opening collects IR energy from an object of interest and directs the energy to an IR sensor. The IR sensor outputs a signal based on the IR energy emitted from the object of interest. The output signal is governed by the Stefan-Boltzmann law, which relates energy to the fourth power of temperature difference between the object of interest and the sensor. The output signal from the sensor is electronically and statistically conditioned and adjusted with an offset and gain to calculate a temperature reading for the object of interest. The adjusted temperature calculation is then displayed to the user.
The accuracy and performance of clinical thermometers are affected by many variables. Many IR thermometers employ a very narrow speculum or probe tip that permits the thermometer to be placed in confined spaces, such as the ear canal. The IR sensor, which is too large to be placed in the probe tip, is positioned a significant distance back from the probe tip. Therefore, the IR sensor is not situated at the opening where IR radiation enters the probe. IR radiation must be conveyed to the sensor by an optical waveguide. The waveguide propagates the IR radiation by reflection or refraction until the radiation reaches the sensor. This has the undesirable effect of allowing IR energy to be absorbed in the wave guide. The energy losses can lead to an inaccurate temperature measurements. Waveguides that reflect IR radiation are also prone to surface contamination which can diminish reflectivity, leading to additional energy losses.
IR thermometers also include wide viewing apertures to measure IR radiation from a wide field of view. This is not desirable when IR radiation must be measured from a relatively small target area. In the ear, for example, the temperature of the tympanic membrane is believed to be the most accurate reflection of a patient's core body temperature, as compared to other points in the ear. Temperature within the ear canal can vary significantly from point to point, and temperatures at some locations can differ by 4° F. or more. Dramatic differences in temperature may be found between locations near the ear opening and locations at the interior of the ear canal. Therefore, it is desirable to limit temperature measurements to areas on or immediately adjacent to the tympanic membrane. IR thermometers that sense IR radiation from a wide field of view tend to take extraneous measurements from a wide area having significant temperature variations. These extraneous measurements may be associated with temperatures that deviate significantly from the temperature of the tympanic membrane, leading to a skewed temperature reading. As a result, IR thermometers that sense IR radiation from a wide field of view have limited accuracy.
Some devices that collect IR energy from the ear canal over a wide field of view condition the signal and add a statistical offset to compensate for the errors inherent in measuring IR energy over a wide field of view in the ear canal. Statistical offsets have limited effectiveness in correcting errors, however. Each individual's ear canal is unique, and creates its own set of variables that affect the measurement of IR energy. In addition, different operators use different techniques when operating the IR thermometer, creating inconsistencies in temperature measurement. Therefore, developing a statistical offset introduces an inherent margin of error, since user techniques and the patient's physiology can affect the actual amount of error introduced into the calculation. As a result, thermometers presently used to detect IR energy leave much to be desired in terms of accuracy and performance.
A device in accordance with the present invention includes a sensor assembly for measuring temperature at a target location that emits infrared radiation. The sensor assembly includes a sensor adapted to detect infrared radiation and produce an electrical output, and a focusing lens for focusing infrared radiation from the target location onto the sensor while substantially preventing infrared radiation from points outside the target location from being detected by the sensor.
In a first embodiment, a sensor assembly for a focusing thermometer includes a sensor and a focusing lens. The sensor assembly is operable to measure temperature at a target location that emits infrared radiation. The sensor detects infrared radiation and produces an electrical output. The focusing lens focuses infrared radiation from the target location onto the sensor while substantially preventing infrared radiation from points outside of the target location from being detected by the sensor.
In a second embodiment, a focusing thermometer for measuring temperature at a target location includes a sensor assembly and electronic circuitry that receives electrical output from the sensor assembly and processes the output into a temperature reading. The sensor assembly includes a sensor that detects infrared radiation and produces an electrical output, and a focusing lens for focusing the infrared radiation from the target location onto the sensor while substantially preventing infrared radiation from points outside the target location from being detected by the sensor. The electronic circuitry receives the electrical output from the sensor and processes the output into a temperature reading.
The foregoing summary as well as the following detailed description will be better understood when read in conjunction with the drawing figures, in which:
Referring to the drawing figures in general, and to
The focusing thermometer 10 includes a sensor assembly 20 configured to collect infrared radiation and produce an electrical output signal. The sensor assembly 20 is connected with an analog assembly 40 which receives the output signal. One or more components, such as a signal amplifier 42, may be integrated with the analog assembly 40 to condition the output signal from the sensor assembly 20. The analog assembly 40 is connected with a digital assembly 60. The digital assembly 60 includes a converter 62 that receives the output signal and converts it from an analog signal to a digital signal. The digital signal is then processed to generate a temperature calculation.
The digital assembly 60 is connected to a display assembly 80, which receives output from the digital assembly and displays an output value, such as a temperature reading. The IR thermometer 10 also includes a control assembly 90 containing one or more switches operable to control the thermometer's operation. An electric power supply 95 supplies to power the thermometer components.
As stated earlier, the focusing thermometer of the present invention may be used for taking temperature measurements from a variety of locations, such as the ear, mouth and rectum. The specific configuration of the thermometer is not germane to the present invention, and may be designed for a specific application. For purposes of this description, the focusing thermometer of the present invention will be described and illustrated as an IR ear thermometer. It will be appreciated that the present invention is not limited to ear thermometers, since the principles of operation apply equally well to other parts of the body. Moreover, the terminology used in connection with the present invention is used for merely description, not limitation.
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The IR thermometer 100 performs a number of functions and operates in different modes that can be selected and controlled by the user. A control assembly 200 extends along the exterior of the housing and is operable to change the function or mode of operation of the thermometer 100. In
The control assembly 200 contains one or more switches operable to control a different function or mode of operation. In
The focusing thermometer 100 is connected with a source of power to operate the sensor assembly 120, display assembly 160 and other components. The source of power may be a power cord or adapter attachable to a wall socket. Alternatively, the thermometer 100 may be powered by a battery pack. Referring now to
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The focusing lens 122 has an outer face 124 that faces outwardly toward the aperture 108, and an inner face 126 that faces inwardly toward the IR sensor 130. The outer face 124 of the focusing lens may contain one or more coatings to modify or enhance properties of the lens. The lens does not require coatings, however. In
The IR sensor 130 is positioned a specified distance behind the lens 122 to directly receive refracted IR rays from the target location. The distance between the back of the focusing lens 122 and the front of the IR sensor 130 is based on the principle of maximizing the amount of IR energy impinging on the IR sensor from a target location. The distance between the lens 122 and the sensor 130 is very small, typically a few millimeters. In this arrangement, the IR rays from the target location are focused through the lens and refracted directly onto the IR sensor without being bounced multiple times through a waveguide. Since the IR rays are not bounced through a waveguide, the IR energy is projected directly onto the IR sensor without substantial energy loss. A number of thermal detectors and transducers may be used for the IR sensor 130. For example, a mini-thermopile manufactured by H. L. Planar Technology GmbH or other manufacturer may be used as the sensor 130. The mini-thermopile is a relatively small component, less than 10 mm in diameter, and allows for placement of the IR sensor 130 at or near the distal end 106 of the sensor assembly 120. In this configuration, the focusing lens 122 and IR sensor 130 are positioned at the outermost end of the probe, so that bends in the ear canal do not obstruct the optical path between the sensor and the point of measurement.
The focusing lens 122 and IR sensor 130 are interconnected by a bridge component that stabilizes the position of the lens relative to the sensor. In
The collar 132 has a cylindrical portion 133 that surrounds the IR sensor 130, and a tapered frusto-conical portion 134 that surrounds the focusing lens 122. The focusing lens 122 and IR sensor 130 may be connected with the collar 132 by press-fitting the components into the collar, or by using epoxy or other suitable attachment means. The IR sensor is connected to the analog board 142 by soldering or other suitable connection means.
The ear canal has multiple curvatures, providing a twisting path from the ear opening to the tympanic membrane. The thermometer 100 may include a curved probe tip that conforms to the natural curvatures in the ear canal.
The IR thermometer of the present invention may incorporate a number of guards and covers to protect the sensor assembly from damage and contamination. Referring to
The housing 102 includes a biasing element that normally biases the outer cover 114 toward the extended position. In
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IR rays emitted from membrane M, which are represented by the lines labeled “E”, are passed through the focusing lens 122 and projected directly onto the IR sensor 130. The IR sensor 130 is positioned behind the lens at the proper distance relative to the focal length of the lens to only receive IR rays from membrane M. That is, the focusing lens 122 and IR sensor 130 are arranged to only measure IR radiation from the target area onto membrane M. IR rays emitted from points “X” and “Y” in
With the handle portion 110 grasped and held steady in one hand, the first switch 202 is activated on the control pad 201 to take a temperature reading from the tympanic membrane M. If desired, separate switches may be provided for selecting the temperature measurement mode and initiating the actual temperature measurement. The IR thermometer may be operated in a scan mode, which takes multiple readings from the target area, or a “single view” mode, which takes a single temperature measurement. The IR sensor produces an output signal based on the IR radiation emitted from membrane M. Once the output signal is produced by the IR sensor 130, the signal is amplified by the analog assembly 140 and sent to the digital assembly 160. The signal is converted from an analog signal to a digital signal that can be processed.
During digital processing, the digital signal received from the converter is compared with a reformulation of ratio of energy in the IR band with the total radiation, using the Planck distribution formula and Stefan-Boltzmann law, to generate the perceived temperature of the object of interest. Since the IR sensor is focused on membrane M, as opposed to a wide field of view within the ear canal, the energy on the sensor assembly is directly related to the spot temperature of the membrane M. As a result, there is no need to introduce a statistical offset or error correction to account for the large variations of temperature within the ear. The digital assembly sends the processed signal to the display assembly, where the temperature of membrane M is conveyed to the thermometer user.
The terms and expressions which have been employed are used as terms of description and not of limitation. There is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof. It is recognized, therefore, that various modifications are possible within the scope and spirit of the invention. For example, the IR thermometer may include components that utilize optical grating and/or amplification to refine energy measurements. Accordingly, the invention incorporates variations that fall within the scope of the following claims.
Pursuant to 35 U.S.C. § 119, this application claims the benefit of U.S. Provisional Application No. 60/539,228, filed Jan. 26, 2004, the entire disclosure of which is incorporated herein by reference.
Number | Date | Country | |
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60539228 | Jan 2004 | US |