RADIATION SENSOR

Abstract: A self-calibrating infrared (IR) sensing device having the capability to measure the attenuation effects of surface contamination on the transmission window and to adjust the gain of the sensor accordingly so as to counter the attenuation. The IR sensing device includes an IR sensor mounted in a housing having an IR transparent window that allows IR radiation originating from outside the housing. The unit measures the increase in temperature and generates a proportional electronic signal. An IR radiator is also included. When activated, the radiator emits IR radiation that passes through the window and is lost to the outside if there is no contamination, or is alternatively reflected by an external mirror onto the sensor. If the surface of the window is contamined, the radiation raises the temperature of the contaminants. This increase in temperature results in a return signal.

Description: RADIATION SENSOR The present invention relates in general to radiation sensors, particularly to infrared (IR) sensing devices, and more particularly to a self-calibrating IR sensing device. IR sensors are used to measure temperatures of remote objects by detecting the infrared radiation emitted from the target object. In a typical configuration, IR radiation enters the housing in which the sensor element is located through an IR transparent window and impinges upon the sensor. The temperature is typically measured by detecting the IR radiation and determining its effect on a thermally isolated radiation absorbing area of the sensor. In many typical applications the radiation from the remote object is gathered and focussed onto the sensing element by an external mirror arrangement for increased effectiveness. When the surface of the window or the mirror arrangement becomes contaminated by particles or residues that absorb IR radiation, incoming IR radiation is absorbed such that the amount of IR radiation passing through the window becomes attenuated. The IR transmission capability of the window and the IR reflectance capability of the mirror arrangement is therefore degraded by the presence of IR-absorbing contaminants. Such degradation results in erroneous temperature readings by the sensor. Accordingly, what is needed in the art is the ability to easily counter the attenuation effects of IR-absorbing contaminants deposited on the transmission window and mirror arrangement so as to accurately detect and measure the IR radiation received from a target object. Emodiments of the present invention provide a self-calibrating infrared _(IR) sensing device having the capability to measure the attenuation effects of surface contamination on the transmission window and, in one aspect, a mirror arrangement. The sensing device of the present invention also includes the capability to adjust the gain of the sensor to counter the attenuation caused by any IR-absorbing contaminants on the transmission window or mirror arrangement. According to a first aspect of the invention, an IR sensing device includes an IR sensor mounted in a housing having an IR transparent window that allows IR radiation originating from outside the housing, for example from a target source, to be directed towards the sensor. The radiation detected by the sensor is made up of a combination of the external IR radiation entering the housing through the IR transparent window and the inherent background radiation from the inner surface of the housing. The IR sensor includes a thermally isolated area of material selected for its ability to absorb IR radiation at a specific frequency or at a range of radiation frequencies. The incoming radiation is absorbed, thereby raising the temperature of the IR absorbing material. A temperature measuring unit coupled to the absorbing material measures the increase in temperature and generates a proportional electronic signal indicative of the temperature. The electronic signal is received and processed by a processor. In one embodiment, an IR radiator is also included within the sensing device housing. The IR radiator is preferably shielded from the IR absorbing material by an internal screen. When activated, the radiator emits IR radiation that passes through the window and is lost to the outside if there is no contamination. If, however, the surface of the window is contaminated, radiation will be absorbed by the contaminants, thereby raising their temperature. This increase in temperature results in a return signal (i.e., IR emissions from the contaminants) that is detected by the sensor. For example, if the radiator is pulsed, the resulting return signal will be in the shape of decaying pulses. The magnitude of the return signal indicates the amount of contaminant on the surface of the window. The return signal is detected and measured by the IR sensor, and is used to signal a warning and/or determine the amount of gain necessary to compensate for the loss of true signal caused by the presence c-f-lhe contamination. Additionally, IR radiation that falls on the inside of the housing is reflected back to the sensor. If the inside surface of the housing is uncontaminated, the return signal will be as expected. If, however, the housing is internally corroded or contaminated, perhaps indicative of leakage, the return signal will be higher as the contamination heats up and emits IR radiation. Again, the appropriate gain is determined to compensate for any contamination in the housing. In an alternative embodiment of the invention, the radiator emits IR radiation that passes through the window and is reflected back into the sensing device housing by an external mirror arrangement. If the surface of the window is contaminated, the reflected radiation will be attenuated (e.g., the magnitude will be reduced). In the case where the IR radiator is pulsed, for example, the magnitude of the reflected signal indicates the clarity of the signal path, or inversely, the amount of contaminant on the surface of the window. The attenuated reflected signal is detected and measured by the IR sensor, and is used to signal a warning and/or determine the amount of gain necessary to compensate for the loss of true signal caused by the presence of the contamination. IR radiation that falls on the inside of the housing is preferably shielded from the sensor by the internal shield. In a further embodiment of the invention a curved IR reflective mirror is positioned within the sensing device housing to reflect IR radiation from the external target onto the IR sensor. In this arrangement, the radiation from the IR radiator is passed to the window either directly or by reflection via the internal curved mirror. This arrangement has no return signal from the inside of the housing, and thus the task of determining the return signal from the contamination on the window is simplified. Use of the internal mirror also helps focus more of the IR radiation entering the window from the external target onto the IR sensor, therefore increasing the magnitude of the signal from the sensor and increasing the sensitivity of the sensor. According to a further aspect of the invention, an IR sensing device is provided. The IR sensing device includes an IR sensor for detecting IR radiation, wherein the IR sensor generates electrical signals in response to and indicative of any IR radiation detected by the IR sensor. The sensing device also typically includes an IR opaque enclosure surrounding the IR sensor, the enclosure having an IR transparent window ^ positioned to allow IR radiation from outside the enclosure to fall on the IR sensor, and an IR radiator positioned within the enclosure, wherein the IR radiator emits IR radiation. In -operation, at least a portion of a first IR radiation signal generated by the IR radiator is absorbed by IR-absorbing material on the window. In response, the IR absorbing material emits a return IR radiation signal that is detected by the IR sensor, which generates a first electric signal proportional to the return IR radiation signal. The sensing device also typically includes a processor coupled to the IR sensor for analyzing the electrical signals generated by the IR sensor, wherein the processor receives and analyzes the first electric signal to determine characteristics of the return signal. According to an alternative aspect of the invention, a mirror element, external to the enclosure, is included for reflecting IR radiation. In operation, at least a portion of a first IR radiation signal emitted by the IR radiator is reflected by the mirror element onto the IR sensor, wherein, the reflected IR radiation signal is detected by the IR sensor, and wherein the IR sensor generates a first electric signal proportional to the detected IR radiation signal. The processor determines characteristics of this reflected signal. In another alternative aspect, a first portion of a first IR radiation signal generated by the IR radiator directly impinges on the window, and a second portion of the first IR radiation signal is reflected by an internal mirror element toward the window. At least a portion of each of the first and second portions of the first IR radiation signal is absorbed by IR-absorbing material on the window. In response, the IR-absorbing material emits a return IR radiation signal that is detected by the IR sensor, which generates a first electric signal proportional to the return IR radiation signal. Again, the processor determines characteristics of the return signal. According to another aspect of the invention a method is provided for measuring the temperature of a remote target object with an IR sensing device, wherein the IR sensing device includes an IR sensor mounted in a housing, the housing having a window through which IR radiation from a remote target object enters the device and impinges on the IR sensor. The method typically includes the step of generating a first IR radiation signal with an IR radiator located within the housing, such that if there is any IR- absorbing contamination on the window, the contamination absorbs at least a portion of the first IR radiation signal and emits a return IR radiation signal. The method also typically includes the steps of detecting the return IR radiation signal with the IR sensor, and generating a first electric signal in response to the return IR radiation signal, wherein the first electric signal is proportional to the return signal. The method further typically includes the steps of analyzing the first electric signal with a processor to determine the amount of IR radiation in the return signal, wherein the amount of IR radiation in the return signal is indicative of the amount of IR absorbing contamination on the window. Thereafter a remote IR radiation signal generated by the remote object is detected, wherein the remote IR radiation signal is indicative of the temperature of the remote object, wherein the remote signal is attenuated by a first amount by the IR absorbing contamination before being detected by the IR sensor. The method also typically includes the step of compensating for the first amount of attenuation in the detected remote IR radiation signal so as to accurately determine the temperature of the remote object. According to an alternative aspect of the invention an external mirror arrangement reflects the generated first IR signal back to the IR sensing device, such that if there is any IR-absorbing contamination on the window, the contamination absorbs at least a portion of the reflected IR radiation signal. The IR sensor then detects this reflected signal, generating a first electric signal proportional to the detected signal. Here, the magnitude of the detected signal is indicative of the amount of IR absorbing contamination on the window. In another alternative aspect of the invention a method includes the step of generating a first IR radiation signal with an IR radiator located within the housing, wherein a first portion of the first IR radiation signal directly impinges on the window, and reflecting, with an internal mirror, a second portion of the first IR radiation signal toward the window, wherein if there is any IR-absorbing contamination on the window, the contamination absorbs the first and second portions of the first IR radiation signal and emits a return IR radiation signal. According to yet another aspect of the invention, an Infra Red (IR) sensing device is provided comprising electronic interface means for processing the electrical signal generated by the sensor, wherein the interface means generates a signal representative of the IR radiation detected by the sensor. Here, the IR radiation means is arranged as before to radiate IR energy so as to have a heating effect on any non IR transparent contamination obscuring the IR transparent window, and there is included a first control means for controlling the IR radiation means to radiate IR energy for a known period; a signal processing means for determine the degree of contamination obscuring the IR transparent window by measuring the shape and characteristics of the electrical signal during and after the known period; and a second control means for modifying the characteristics of the electronic interface means to compensate for the degree of contamination. According to one embodiment, the device includes a mirror element, located external to the housing, for reflecting IR radiation emitted by the IR radiating means onto the IR sensing means through the window, wherein the reflected IR radiation is attenuated by IR-absorbing contaminants on the window. Here, the IR sensing means detects this reflected signal. According to another embodiment, the device includes a mirror element located within the enclosure. In operation, the IR radiating means emits a first IR radiation signal, wherein a first portion of the first IR radiation signal directly impinges on the window, and wherein a second portion of the first IR radiation signal is reflected by the mirror element toward the window, wherein at least a portion of each of the first and second portions of the first IR radiation signal is absorbed by IR-absorbing material on the window. According to a further aspect of the invention, an Infra Red (IR) sensing device arrangement is provided. The arrangement typically comprises a first IR sensing device and a second IR sensing device located proximal the first IR sensing device, wherein the sensing devices typically function as in any of the above described embodiments. The arrangement includes first and second mirror elements external to the first and second enclosures, for reflecting IR radiation. The arrangement also typically includes a processor coupled to the first and second IR sensors for analyzing electric signals generated by the first and second IR sensors. In operation, at least a first portion of a first IR radiation signal emitted by the first IR radiator is reflected by the first mirror element onto the first IR sensor, at least a second portion of the first IR radiation signal emitted by the first IR radiator is reflected by the second mirror element onto th second IR sensor, at least a first portion of a second IR radiation signal emitted by the second IR radiator is reflected by the second mirror element onto the second IR sensor, and at least a second portion of the second IR radiation signal emitted by the second IR radiator is reflected by the first mirror element onto the first IR sensor. The first IR sensor generates a first electric signal proportional to the IR radiation signal detected thereby, and the second IR sensor generates a second electric signal proportional to the IR radiation signal detected thereby, wherein the processor receives and analyzes the first and second electric signals to determine characteristics of the detected IR radiation signals. According to an embodiment, there is provided a single mirror element, external to the first and second enclosures. In operation, the portions of the radiation signals from the respective radiators are reflected by this single mirror element. According to another embodiment of the aspects of the invention employing two sensing systems, the first window has a first amount of contamination, the second window has a second amount of contamination, and the processor determines the first and second amounts of contamination using the characteristics determined from the first and second electric signals. According to still another embodiment of the aspects of the invention employing two sensing systems, the first IR sensing device further includes a third mirror element, external to the first enclosure for directing radiation from a target source onto the first IR sensor, and the second IR sensing device further includes a fourth mirror element, external to the second enclosure for directing radiation from the target source onto the second IR sensor. According to still another embodiment of the aspects of the invention employing two sensing systems, the first IR sensing device further includes a second mirror element, external to the first enclosure for directing radiation from a target source onto the first IR sensor, and the second IR sensing device further includes a third mirror element, external to the second enclosure for directing radiation from the target source onto the second IR sensor. Although described above in the context of IR sensors, to which the invention is most preferably applied (for an IR sensor, the detection of contaminants by means of heat absorbed and re-radiated is advantageous) it has been appreciated pursuant to the invention that the principles may be applied to other radiation, particularly optical sensors. Further aspects and preferred features may be found in the claims. Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Figure 1 is a sectional schematic diagram of a typical IR sensor arrangement according to the present invention; Figure 2 is a sectional schematic diagram of an assembled IR sensing device including the IR sensor of Figure 1, according to an embodiment of the present invention; Figure 3 is a schematic diagram showing effects of contamination on the IR transmission of the transmission window; Figure 4 is a schematic diagram showing an arrangement of an IR sensing device including an IR radiator according to an embodiment of the present invention; Figure 5 is a schematic diagram showing an arrangement of an IR sensing device including an IR radiator and an external mirror arrangement according to an embodiment of the present invention; Figure 6 is a schematic diagram showing the effects of IR radiation emitted from the IR radiator; Figure 7 is a schematic diagram showing an arrangement of two IR sensors according to an embodiment of the present invention; Figures 8a and 8b illustrate an example of an IR pulse and associated return signals, respectively, according to an embodiment of the present invention; and Figure 9 is a schematic diagram showing an embodiment of an internal reflector according to the present invention. Figure 1 is a sectional schematic diagram of an IR sensor arrangement 10 according to an embodiment of the present invention. IR sensor 10 includes an area of IR absorbing material 12 mounted on a substrate 11 with a temperature measuring unit 13 positioned as is well known to effectively measure the temperature of IR absorbing material 12. Absorbing material 12 includes material selected for its ability to absorb IR radiation at a specific frequency or at a range of radiation frequencies as required for specific applications. In preferred aspects, temperature measuring unit 13 is any temperature measuring device capable of generating an electrical signal responsive to and indicative of the temperature of the IR absorbing material. In more preferred aspects, temperature measuring unit 13 includes a plurality of thermopiles that generate a voltage on the order of approximately 100 microvolts per degree Celsius temperature rise. Examples of such thermopiles include Polysilicon - Aluminum junctions and Aluminum - Diffusion junctions. One hundred such thermopiles connected in series generate approximately ten milli-volts for a one degree Celsius temperature rise. This signal is amplified using well know means or circuitry arranged to compensate for such inherent errors as offsets, gain variations, unwanted temperature dependencies and drift. The parameters associated with the correction of these inherent errors are stored in a nonvolatile memory to permit calibration of the sensing arrangement after manufacture and installation in a housing as will be described in more detail below. Calibration of the sensor is accomplished, for example, by using a heating element embedded in insulated absorbing area 12. Passing a current through the heating element causes the temperature of the absorbing material 12 to rise by a controlled amount. This effect is measured and the results are used to calibrate the sensor. Substrate 11 is preferably as thin as possible so that temperature measurement unit 13 is as close as possible to IR absorbing material 12. In addition, substrate 11 is preferably arranged such that the thin section of substrate 11 between absorbing material 12 and temperature measuring unit 13 is thermally isolated from the bulk of the arrangement. This helps ensure that heat loss from (the thin area of) substrate 11 does not degrade the accuracy of the signal generated by temperature measurement unit 13. Figure 2 is a sectional schematic diagram of an assembled IR sensing device 100 including IR sensor 10, according to an embodiment of the present invention. IR sensor 10 is mounted in a housing 130 having a window 140 through which IR radiation 150 can pass substantially unhindered. The IR radiation falling on IR sensor 10 is absorbed by IR absorbing material 12, which causes an increase in the temperature of absorbing material 12 and a corresponding signal change from temperature measurement unit 13. Figure 3 is a schematic diagram showing effects of contaminants 210 on the IR transmission properties of transmission window 140. When present on window 140, contaminants 210 typically absorb a portion of incoming IR radiation 150 so that less IR radiation is passed through to sensor 10. The dotted lines of attenuated IR radiation 220 indicate that the amount of IR radiation passed through window 140 is less than the amount of incoming IR radiation 150. In general, the greater the amount of contaminants 210 deposited on window 140, the greater the absorption of incoming IR radiation 150, and therefore, the greater the attenuation resulting in IR radiation 220. Figure 4 is a schematic diagram showing an arrangement of an IR sensing device 200 including an IR radiator 310 according to an embodiment of the present invention. There is mounted within the enclosure 130 an IR radiating device 310 which is electrically controlled to emit IR radiation 320. Preferably, IR radiating device 310 is thermally isolated from IR sensor 10 so as to avoid heat transfer from IR radiating device 310 by either conduction or direct radiation. Figure 5 is a schematic diagram showing the effects of IR radiation emitted from IR radiator 310 in IR sensing device 200. When an electrical signal is applied to IR radiating device 310, IR radiation 320 is emitted. Some of the radiated energy 320 falls on IR window 140. If window 140 is free of contaminants 210, IR radiation 320 passes through window 140 and is dissipated into the surrounding environment. When window 140 is obscured wholly or partially by an IR-opaque contaminant 210, some of radiated energy 320 is absorbed by contaminant 210. The temperature of contaminant 210 increases as a direct result of the absorption of radiated energy 320, thereby causing a corresponding increase in the level of IR radiation 410 emitted from contaminant 210. This increase in IR radiation 410 is detected by IR sensor 10. It will be appreciated that some of the IR radiation 340 radiated by IR radiator 310 does not fall on window 140, but rather falls on the inside of enclosure 130. This causes a temperature rise in enclosure 130. This temperature rise results in a corresponding increase in IR radiation 420 emitted by enclosure 130 which is also detected by IR sensor 10. Figure 6 is a schematic diagram showing an arrangement of an IR sensing device 200 including an IR radiator 310 and a mirror arrangement according to an embodiment of the present invention. As shown, there is mounted within the enclosure 130 an IR radiating device 310 which is electrically controlled to emit IR radiation 320. Preferably, IR radiating device 310 is thermally screened from IR sensor 10 by a screen 160 so as to avoid heat transfer from IR radiating device 310 by either conduction or direct radiation. When an electrical signal is applied to IR radiating device 310, IR radiation 320 is emitted. Some of the radiated energy 320 falls on IR window 140. If window 140 is free of contaminant(s) 210, IR radiation 320 passes through window 140 and is reflected back from mirror 250 such as to pass through window 140 and fall onto IR sensor 10. It will be appreciated that the magnitude of the radiation reflected back from mirror 250 is dependent upon the power emitted by IR radiator 310 and the amount of contamination 210 on window 140 and on mirror 250. Mirror 250 is made of material selected for its ability to reflect IR radiation at a specific frequency or at a range of radiation frequencies as required for specific applications. Figure 7 is a schematic diagram showing an arrangement of two IR sensors according to an embodiment of the present invention. Figures 8a and 8b are schematic diagrams showing an example of an IR pulse emitted by radiator 310 and associated return signals (IR radiation emitted by contaminants 210), respectively, according to the present invention. When an electrical pulse 510 is applied to IR radiator 310 for a time 520, the signal generated by temperature measuring unit 13 of IR sensor 10 rises and falls in response to the IR radiation emitted by the enclosure and contaminants 210 as shown in Figure 6b. If there are no contaminants then the return signal 550 will have a shorter decay time. If contaminants are present, the return signal 540 from the contaminants will have a longer decay time. The decay time will vary depending on the specific contaminant(s). When radiator 310 is pulsed, for example for 50 milliseconds, sensor 10 sees a return signal dependent upon the heating effect of the outgoing pulse of IR radiation. This return signal will have a number of components each with their own characteristics (e.g., window contaminant component). Each component is separately measured as desired. The return signal is a good indication of the reduction of the effective area of window 140 since only the signal falling on IR-opaque contaminants 210 has a heating effect which therefore causes a temperature rise and a return signal. The greater the surface area of window 140 rendered opaque the greater the return signal. Manual application of contaminants of differing composition allows for accurate re-calibration curves to be established and for a correct re-calibration constant to be programmed into the sensor device. Further, the rate at which the return signal decays is indicative of the thermal bonding between sensor 10 and the structure which may be indicative of corrosion in or around the sensor mounting. Given that the thermal conductivity of the contamination is different from the thermal conductivity of the enclosure then by design, selection of materials or application of specific contaminants on window 140, the decay time of the temperatures of enclosure 130 and contaminants 210 will also be different. At the end of the radiated IR pulse the returned IR signals from contaminants 210 and enclosure 130 will show this difference. If there are no contaminants 210 then the return signal 550 will have a shorter decay time. If contaminants 210 are present, the return signal 540 from contaminants 210 will have a longer decay time. Figures 8a also illustrates the example of an IR pulse emitted by radiator 310 which results in an associated reflected signal (IR radiation reflected by mirror 250) according an embodiment of the present invention. When an electrical pulse 510 is applied to IR radiator 310 for a time 520, the signal generated by temperature measuring unit 13 of IR sensor 10 rises and falls in response to the IR radiation reflected by mirror 250. If IR-opaque contaminants 210 are present on window 140, or on mirror 250, the reflected IR signal will have a reduced amplitude. The reduction in amplitude in the reflected signal relative to IR signal 320 will vary depending on the specific contaminant(s). When window 140 is obscured wholly or partially by IR-opaque contaminant 210, some of reflected radiation is absorbed by contaminant 210. The temperature of contaminant 210 increases as a direct result of the absorption of this radiation, thereby causing a corresponding increase in the level of IR radiation 410 emitted by contaminant 210. This increase in IR radiation 410 is detected by IR sensor 10. Figure 8b also illustrates an example of a return signal 530 (radiation emitted by contaminants on window 140) associated with the IR pulse of Figure 6a. When a small amount of contaminant(s) is present, the return signal 530 will have a shorter decay time 550. When a larger amount of contaminant(s) is present, the return signal 530 will have a longer decay time 540. The return signal 530 is dependent upon the specific contaminant(s) and upon the heating effect of the contaminant(s) by the reflected IR radiation signal. An electronic signal processor, coupled to sensor 10 and to IR radiator 310, is provided to control IR radiator 310 and to receive and analyze the electrical signals from temperature measurement unit 13. The processor determines the characteristics of contaminant(s) 210 and determines the gain necessary to compensate for the difference in window transmissibility or mirror reflectance. In a preferred embodiment, the processor includes a digital microprocessor and an analog-to-digital converter (ADC). In this embodiment, signals received from temperature measuring unit 13 are applied to the ADC, and the resulting digital signals are then processed by the microprocessor. The compensation and calibration constants are stored in a memory such as a digital nonvolatile memory coupled to the processor. It will be appreciated that additional signals can be generated by the signal processor to indicate the amount of contaminants 210 on window 140 or to signal that the magnitude of such contamination has exceeded a predetermined threshold and that the accuracy of the compensated signal may now be outside predetermined limits. It will be further appreciated that all or some of the components of the signal processor can be integrated into the same substrate 11 with IR sensor 10. In addition to the detection of the degree of contamination on window 140 by IR- opaque material, the invention can also detect changes in the IR reflection characteristics of enclosure 130. This addition capability permits the generation by the signal processor of additional warning signals indicating deterioration of enclosure 130 due to contamination or leakage. A change in the rate of decay of the signal reflected from enclosure 130 is indicative of changes in the conditions of the mounting of the sensor 10 and/or enclosure 130 due perhaps to contamination, material deterioration such as corrosion or mechanical wear or creepage. Extraction of an indication of such changes from the return signals by the signal processor permits the generation of warning signals. Figure 9 is a schematic diagram of an IR sensing device including an internal reflector arrangement according to an embodiment of the present invention. Reflector 170 focuses incoming IR radiation and focuses it onto IR sensor 10. As shown, reflector 170 preferably has a parabolic-shaped cross-section, however, it may have a linear cross- section, or any other curved cross-section. Reflector 170 is made out of material selected for its ability to reflect IR radiation at a specific frequency or at a range of radiation frequencies as required for specific applications. The internal mirror arrangement as shown in Figure 9 increases the effective size of IR sensor 10 since it increases the percentage of the incoming IR radiation that falls on IR sensor 10. Additionally, this internal mirror arrangement eliminates the effects of return signals from the inside of housing 130 due to the background radiation of the housing and internal contamination. Rather, the mirror arrangement reflects more of the IR radiation 320 from IR radiator 310 through window 140, so as to increase the heating effects of the IR radiation 320 on contaminants 210, thereby increasing the magnitude of the return signal generated by the contaminants 210. This helps ensure that the task of detecting the return signal from contaminants 210 in the midst of receiving IR radiation from a target source is not made more complex or expensive. The addition of IR radiator 310 together with a means to control it allows the transmission efficiency of the window, and where relevant the reflectance efficiency of the mirror arrangement, to be determined and also to gain an indication of potential risks to the ongoing performance of the sensor installation. All such contraindications can be signaled to a controller (e.g., ECU or CPU) by means specific to the application. In many typical applications, the temperature of a target source is measured by focussing, or directing, radiation from the target source onto the sensing element using one or more mirrors. An embodiment of such a mirror arrangement is also shown schematically in figure 4. It will be appreciated that the mirror 260 has similar characteristics to mirror 250 and can easily be constructed from the same materials and formed at the same time. Alternately, mirror 260 can be a separate component. The shape of mirror 250 is designed to reflect the radiation 320 from IR radiator 310 back onto IR sensing element 10. It will be appreciated that in a situation where more than one sensing device is installed in close and fixed proximity, the design of the mirror 250 can be more complex such as to reflect a first part of the IR radiation 320 back onto the sensing element 10 within housing 130 and a second part of the IR radiation 320 onto the sensing element 10' in a second housing 130', as shown in Figure 5, for example. The IR radiation reflected onto IR sensor 10 in housing 130 will cause sensor 10 to generate a first electrical signal, and the IR radiation reflected onto the IR sensor 10' in the second housing 130' will cause sensor 10' to generate a second electrical signal. In a like manner, the IR radiator 310' and mirror 250' associated with the second sensing device can be arranged to reflect part of the IR radiation from the IR radiator 310' in the second housing 130' onto the IR sensor 10' in the second housing 130' and part onto the IR sensor 10 in housing 130. Mirrors 250 and 250' are preferably separate, but can be formed as one integral mirror as desired. If the timings of the electrical pulses applied to the IR radiators 310 and 310' in the two housings are non-overlapping, then by comparison of the electrical signals generated by the IR sensors 10 and 10', the effects of contamination on that part of the window 140 used for transmission and that part used for reception of the main radiation 410 can be determined. Additionally, gain control values based on the attenuation of the main signal 410 can be computed. The following features may be provided independently or in combination with any other features. A signal processing means which generates signals indicating the level of IR opaque contamination on the IR transparent window. An inner surface of the enclosure which reflects IR radiation, wherein the signal processing means generates signals indicating deterioration of the inner surface of the enclosure determined by a change in IR reflectivity of the inner surface. A mounting means for mounting the IR sensing means to the enclosure, wherein the signal processing means generates signals indicating deterioration of the mounting means. A sensor means integrated in a substrate. An interface means and signal processing means integrated into the same substrate as a sensing means. An IR radiating means integrated into the same substrate as a sensing means. A signal processing means including a microcontroller. A mirror element with a parabolic cross- section. Determination of the deterioration_of the mounting means by changes in the time constants of the decay of the temperature of the enclosure. A screen located within the enclosure between the IR radiating means and the IR sensing means. A memory coupled to the signal processing means, wherein the calibration and configuration for the signal processing means is stored in the memory. An IR sensing means including a sensing element for absorbing IR radiation, the device further comprising a heating means for raising the temperature of the sensing element by a controlled amount to assist in calibrating the sensing element. While the invention has been described by way of example and in terms of the specific embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. For example, although pulsed IR radiation signals are discussed, one skilled in the art will realize that sinusoidal varying IR radiation signals can be used. Furthermore, it should be understood that the invention is not restricted to the use of infra red radiation, as optical and other varieties of radiation may be employed in similar fashion. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

Claims: CLAIMS: 1. A radiation sensing device comprising: a radiation sensor (10) mounted within a housing (130) having a window (140) through which external radiation can pass to the sensor; characterised by: a radiation source (310) within the housing (130) arranged to radiate energy to the sensor (10) via the window (140) so that at least a portion of the energy radiated to the sensor is affected by contamination (210), if present, on the window (140); means for analysing the radiation incident on the sensor (10) arranged to compensate for or determine a measure of the effect of contamination (210) on a measure of external radiation based on the effect of contamination (210) on radiation emitted by the source (310). 2. The device of Claim 1, wherein at least a portion of the radiation emitted by the radiator is transmitted to the sensor through the window by a mirror external to the enclosure. 3. The device of Claim 1, wherein at least a portion of the radiation emitted by the radiator is transmitted to the sensor by a mirror internal to the enclosure. 4. The device of any preceding claim arranged for sensing infra-red radiation, wherein the measure of the effect of contamination is based on heat absorbed by or radiated by the contamination. 5. The device of any preceding claim including means for controlling the radiation source to produce time-varying radiation, preferably pulses. 6. The device of any preceding claim arranged as an infra-red temperature sensor, wherein the radiation source is a infra-red generating element, the apparatus being arranged to determine a measure of heat absorption by the contamination, if present. 7. The device of any preceding claim arranged to determine a measure of contamination of the window or housing or deterioration of the housing based on a time characteristic of the measured radiation signal, preferably including a measure of the decay time of a signal from the sensor following radiation by the source. 8. An Infra Red (IR) sensing device comprising: an IR sensor for detecting IR radiation, wherein the IR sensor generates electrical signals in response to and indicative of any IR radiation detected by the IR sensor; an IR opaque enclosure surrounding the IR sensor, the enclosure having an IR transparent window positioned to allow IR radiation from outside the enclosure to fall on the IR sensor; an IR radiator positioned within the enclosure, wherein the IR radiator emits IR radiation, wherein at least a portion of a first IR radiation signal generated by the IR radiator is absorbed by IR-absorbing material on the window, wherein the IR absorbing material emits a return IR radiation signal that is detected by the IR sensor, and wherein the IR sensor generates a first electric signal proportional to the return IR radiation signal; and a processor coupled to the IR sensor for analyzing the electrical signals generated by the IR sensor, wherein the processor receives and analyzes the first electric signal to determine characteristics of the return signal. 9. The device of Claim 8, further comprising a mirror element, external to the enclosure, for reflecting IR radiation, wherein at least a portion of the first IR radiation signal is reflected by the mirror element onto the IR sensor, wherein the reflected IR radiation signal is detected by the IR sensor, and wherein the IR sensor generates a first electric signal proportional to the detected IR radiation signal; and wherein the processor receives and analyzes the first electric signal to determine characteristics of the detected IR radiation signal. 10. The device of Claim 8 or 9, further comprising a mirror element located within the enclosure, wherein the mirror element is capable of reflecting IR radiation, and wherein a first portion of a first IR radiation signal generated by the IR radiator directly impinges on the window, wherein a second portion of the first IR radiation signal is reflected by the mirror element toward the window, wherein at least a portion of each of the first and second portions of the first IR radiation signal is absorbed by IR-absorbing material on the window. 11. The device according to claim 8, claim 9 or claim 10, wherein the return signal is proportional to the amount of attenuation caused by the IR-absorbing material, wherein the IR sensor also detects a remote IR radiation signal generated by a remote target object, wherein the remote signal is attenuated by the IR-absorbing material on the window by a first amount, wherein the IR sensor generates a second signal proportional to the attenuated remote signal, and wherein the processor determines the gain needed to compensate for the first amount of attenuation caused by the IR absorbing material when analyzing the second electric signal. 12. The device according to claim 8, claim 9 or claim 10, wherein the reflected signal is reduced in amplitude proportional to an amount of IR-absorbing material on the window, wherein the IR sensor also detects a remote IR radiation signal generated by a remote target object, wherein the remote signal is attenuated by the IR-absorbing material on the window by a first amount, wherein the IR sensor generates a second signal proportional to the attenuated remote signal, and wherein the processor determines the gain needed to compensate for the first amount of attenuation caused by the IR absorbing material when analyzing the second electric signal. 13. The device according to claim 8, claim 9 or claim 10, wherein the IR sensor includes an IR absorbing portion coupled to a temperature measuring unit, wherein when the IR absorbing portion absorbs IR radiation its temperature increases by a proportional amount, and wherein the temperature measuring unit measures the temperature of the IR absorbing portion and generates the electrical signals, wherein the electrical signals are indicative of the temperature of the IR absorbing portion. 14. The device of claim 13, wherein the IR sensor further includes a heating element coupled to the IR absorbing portion, wherein the heating element is configured to raise the temperature of the IR absorbing portion by a controlled amount so as to assist in calibrating the IR sensor. 15. The device according to claim 8, claim 9 or claim 10, wherein the processor includes a means to control the IR radiator to emit the first IR radiation signal. 16. The device of claim 15, wherein the control means controls the IR radiator to emit the first IR radiation signal in the form of one or more pulses, wherein the return signal includes one or more decaying pulses, and wherein the processor analyzes the first electric signal to determine the decay time of the decaying pulses. 17. The device of claim 15, wherein the control means controls the IR radiator to emit the first IR radiation signal in the form of one or more pulses, wherein the reflected signal includes one or more reflected pulses, and wherein the processor analyzes the first electric signal to determine the magnitude of the reflected pulses. 18. The device of claim 15, wherein the processor includes a means for determining the degree of contamination obscuring the window by analyzing characteristics of the first electric signal. 19. The device of claim 18, wherein the processor further includes a means for modifying the characteristics of the electrical signals generated by the IR sensor in response to any IR radiation detected from a remote target object so as to compensate for the degree of contamination obscuring the window. 20. The device according to claim 9 or claim 10, wherein the mirror element has a parabolic cross-section. 21. The device according to claim 8, claim 9 or claim 10, wherein the housing has an inner surface that reflects IR radiation, wherein if the inner surface of the housing is deteriorated it absorbs a second portion of the first IR radiation signal generated by the IR radiator, wherein the inner surface emits a second return IR radiation signal that is detected by the IR sensor, and wherein the IR sensor generates a second electric signal proportional to the second return signal. 22. The device of claim 18, wherein the processor further includes a means for modifying the characteristics of the electrical signals generated by the IR sensor in response to any IR radiation detected from a remote target object so as to compensate for the amount of contamination obscuring the window. 23. The device according to claim 8, claim 9 or claim 10, wherein the processor includes a means for determining an amount of IR-absorbing material on the window using the characteristics of the return signal. 24. The device of claim 23, wherein the processor includes a means for determining an amount of deterioration of the inner surface of the housing from the second electric signal. 25. The device according to claim 8, claim 9 or claim 10, further comprising a screen located within the enclosure between the IR radiator and the IR sensor. 26. The device according to claim 8, claim 9 or claim 10, wherein the characteristics include the amplitude of the detected IR radiation signal. 27. The device according to claim 8, claim 9 or claim 10, further comprising a memory unit coupled to the processor, wherein the processor determines at least one calibration constant from the characteristics of the return signal, and wherein the processor stores the at least one calibration constant to the memory unit. 28. The device of claim 27, wherein the processor includes a means for determining an amount of IR-absorbing material on the window using the amplitude of the reflected signal detected by the sensor. 29. The device according to claim 8, claim 9 or claim 10, further comprising a memory unit coupled to the processor, wherein the processor determines at least one calibration constant from the characteristics of the reflected signal detected by the sensor, and wherein the processor stores the at least one calibration constant to the memory unit. 30. The device of claim 10, further including a second mirror element, external the enclosure, for directing IR radiation emitted by a remote target object onto the IR sensor. 31. A method for calibration of a radiation sensing device, comprising the steps of: emitting radiation from a calibration source (310) to a radiation sensor (10) within a housing (130) having a window (140) for receiving external radiation so that at least a portion of the radiation passes via the window and is affected by contamination (210), if present, on the window; analysing the radiation received at the sensor (10) to determine a measure of or to compensate for the effect of contamination on a measure of external radiation, based on the effect of contamination on radiation emitted by the calibration source (310). 32. A method according to claim 31, wherein at least a portion of the radiation emitted by the radiator is transmitted to the sensor by a mirror external to the enclosure. 33. A method according to claim 31, wherein at least a potion of the radiation emitted by the radiator is transmitted to the sensor by a mirror internal to the enclosure. 34. A method of measuring the temperature of a remote target object with an IR sensing device, wherein the IR sensing device includes an IR sensor mounted in a housing, the housing having a window through which IR radiation from a remote target object enters the device and impinges on the IR sensor, the method comprising the steps of: generating a first IR radiation signal with an IR radiator located within the housing, such that if there is any IR-absorbing contamination on the window, the contamination absorbs at least a portion of the first IR radiation signal and emits a return IR radiation signal; detecting the return IR radiation signal with the IR sensor; generating a first electric signal in response to the return IR radiation signal, wherein the first electric signal is proportional to the return signal; analyzing the first electric signal with a processor to determine the amount of IR radiation in the return signal, wherein the amount of IR radiation in the return signal is indicative of the amount of IR absorbing contamination on the window; and thereafter detecting a remote IR radiation signal generated by the remote object, wherein the remote IR radiation signal is indicative of the temperature of the remote object, wherein the remote signal is attenuated by a first amount by the IR absorbing contamination before being detected by the IR sensor; and compensating for the first amount of attenuation in the detected remote IR radiation signal so as to accurately determine the temperature of the remote object. 35. A method of measuring the temperature of a remote target object with an IR sensing device, wherein the IR sensing device includes an IR sensor mounted in a housing, the housing having a window through which IR radiation from a remote target object enters the device and impinges on the IR sensor, the method comprising the steps of: generating a first IR radiation signal with an IR radiator located within the housing; reflecting, with a mirror positioned external the housing, at least a portion of the first IR radiation signal, wherein if there is any IR-absorbing contamination on the window, the contamination absorbs at least a first portion of the reflected first IR radiation signal detecting the reflected IR radiation signal with the IR sensor; generating a first electric signal proportional to the detected signal; analyzing the first electric signal with a processor to determine the magnitude of the detected signal, wherein the magnitude of the detected signal is indicative of the amount of IR absorbing contamination on the window. 36. A method of measuring the temperature of a remote target object with an IR sensing device, wherein the IR sensing device includes an IR sensor mounted in a housing, the housing having a window through which IR radiation from a remote target object enters the device and impinges on the IR sensor, the method comprising the steps of: generating a first IR radiation signal with an IR radiator located within the housing, wherein a first portion of the first IR radiation signal directly impinges on the window; reflecting, with an internal mirror, a second portion of the first IR radiation signal, wherein if there is any IR-absorbing contamination on the window, the contamination absorbs the first and second portions of the first IR radiation signal and emits a return IR radiation signal; detecting the return IR radiation signal with the IR sensor; generating a first electric signal in response to the return IR radiation signal, wherein the first electric signal is proportional to the return signal; and analyzing the first electric signal with a processor to determine the amount of IR radiation in the return signal, wherein the amount of IR radiation in the return signal is indicative of the amount of IR absorbing contamination on the window. 37. A method according to claim 34, claim 35 or claim 36, further comprising the steps of: detecting a remote IR radiation signal generated by the remote object, wherein the remote IR radiation signal is indicative of the temperature of the remote object, wherein the remote signal is attenuated by a first amount by the IR absorbing contamination on the window before being detected by the IR sensor; and compensating for the first amount of attenuation in the detected remote IR radiation signal so as to accurately determine the temperature of the remote object. 38. A method according to claim 34, claim 35 or claim 36, further comprising the steps of: determining a calibration constant with the processor, wherein the calibration constant is a function of the amount of IR absorbing contamination on the window; and storing the calibration constant to a memory unit. 39. The method of claim 38, wherein the step of compensating includes applying the calibration constant to the detected remote IR radiation signal. 40. A method according to claim 34, claim 35 or claim 36, wherein the first IR radiation signal is generated in the form of one or more pulses, wherein the return signal includes one or more decaying pulses, and wherein the step of analyzing includes analyzing the first electric signal to determine the decay time of the decaying pulses. 41. A method according to claim 34, claim 35 or claim 36, wherein the housing has an inner surface that reflects IR radiation, wherein if the inner surface of the housing is deteriorated it absorbs a second portion of the first IR radiation signal generated by the IR radiator, the method further including the steps of: emitting a second return IR radiation signal by the inner surface of the housing; detecting the second return IR radiation signal with the IR sensor; and generating a second electric signal proportional to the second return signal. 42. The method of claim 41, further including the step of determining an amount of deterioration of the inner surface of the housing from the second electric signal. 43. A method according to claim 34, claim 35 or claim 36, wherein the first IR radiation signal is generated in the form of one or more pulses, wherein the reflected signal includes one or more pulses, wherein the detected signal includes one or more pulses having a reduced amplitude relative to the first IR radiation signal, and wherein the step of analyzing includes analyzing the first electric signal to determine the amplitude of the detected pulses. 44. Use of a radiation transmitter integrated within the housing of a radiation sensor to determine a measure of or to compensate for contamination on a window of the housing through which radiation is received by the sensor.

Inventors: BETTS WILLIAM ROBERT, CHARLIER OLIVIER, DIELS ROGER, BETTS, WILLIAM, ROBERT, CHARLIER, OLIVIER, DIELS, ROGER
Applicants: BETTS WILLIAM ROBERT, CHARLIER OLIVIER, DIELS ROGER, MELEXIS NV, BETTS, WILLIAM, ROBERT, CHARLIER, OLIVIER, DIELS, ROGER, MELEXIS, NV
Application year: 2000
Main classification: G01J5
IPC codes: G01J5