Non-contacting temperature sensing device

Details Non-contacting temperature sensing device Non-contacting temperature sensing device

1999-07-01

2001-04-24

Wu, Daniel J. (Department: 2632)

Communications: electrical

Condition responsive indicating system

Specific condition

C340S580000, C340S581000, C340S962000, C250S339040, C250S341800

Reexamination Certificate

active

06222454

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a device for the non-contacting temperature measurement of a surface, for example, the surface of a roadway, from a moving vehicle, using an emissivity independent infrared radiation detection method and infrared detectors, although the invention is not limited in scope to automotive applications.
DESCRIPTION OF THE PRIOR ART
One important aspect of automobile related inventions is to improve the safety features. It has been found desirable to be able to remotely measure the road surface temperature from a moving vehicle in an accurate way, either for predicting the likelihood of icing formation or for warning of overheated surface. Earlier road condition monitoring systems used ordinary thermistors to measure the ambient temperature close to road surface as an approximation for the actual surface temperature. Essentially, these systems include a temperature sensing means for measuring the temperature and means for providing a warning if the measured temperature falls within a range indicative of ice-forming conditions.
Infrared sensors have long been used for remote measurement of temperature of a surface based on the fact that when the infrared radiation associated with the temperature of the object impinges on and heats an infrared sensor, it induces a change in the sensor output proportional to the infrared radiation the sensor receives. However, most of such applications are for relatively high temperature measurements (>100° C.). In the case of surfaces with temperatures near or below room temperature, for example, the road surface temperature in winter, the infrared radiation therefrom impinging on the infrared sensor is very weak. Therefore, not all types of infrared sensors are suitable for such applications.
U.S. Pat. No. 5,416,476 by Rendon proposes using infrared detectors as the temperature sensing means in order to detect potentially icy conditions on roads. This patent describes a system and method for detecting potentially icy conditions on roads with an infrared detector mounted externally of a vehicle and aimed at a road surface. The detector is arranged to read only the infrared temperature wavelength emissions associated with concrete and asphalt to eliminate erroneous readings inadvertently received through infrared emissions of other objects located in the vicinity of the detector. The detector is connected to a processing unit which translates the electrical signals from the detector into a temperature readout display. However, this patent does not state or suggest which type of infrared detectors are suitable candidates.
U.S. Pat. No. 5,796,344 by Mann, et al. further elaborated the signal processing aspect of such systems with consideration for compensation of window contamination from road dust and spray, since the infrared detectors are usually housed in a casing provided with a window. Due to various factors, the window tends to become contaminated with dust, water, spray, etc., while the vehicle is in motion.
These two patents have considered neither the impact of the emissivity variation on the accuracy of the temperature measurement, nor the compensation for the detector substrate and background temperature drift due to the normal operation of a vehicle.
The infrared detector types mentioned by Mann et al. are thermopile or pyroelectric type infrared sensors. Thermopile detectors are known to have long thermal time constant, thus can not respond to fast changes in temperature. Pyroelectric type detectors are intrinsically sensitive to mechanical vibration and shocks, thus are not suitable in a vibrating environment such as on-board a moving vehicle. Pyroelectric type detectors also need a chopper to modulate the incident radiation, complicating the system.
The amount of infrared radiation received by the detector depends on the temperature and the emissivity of the radiating surface. Earlier road temperature measuring devices using infrared detection, represented by Rendon and Mann, et al., detect the infrared radiation within one wavelength band and calculate the temperature based on the assumption that the emissivity of the road surface is a constant value. However, this is a very rough approximation. Different road construction materials can have different emissivity. Under different weather conditions, the same material can also have a different emissivity. Therefore, the temperature interpretation based on constant emissivity assumption is not always valid.
Micro-bolometric detectors have been developed only recently thanks to advanced micro-machining technology. A micro-bolometer is a suspended structure, either as a raised platform over a substrate through surface micro-machining technique, or a flat platform over a cavity in the substrate through bulk micro-machining technique.
FIG. 1
, identified as prior art, shows the structure of a typical micro-bolometer
40
, consisting of a suspended infrared sensing platform
43
supported by thin, long beams
42
, formed on a semiconductor substrate
41
. The platform
43
is formed with infrared sensitive materials, for example VO, Amorphous Silicon, Ti nitride, etc. sandwiched between insulating dielectric layers. The resistance of the infrared sensitive material decreases as the temperature of the sensor increases due to the infrared radiation. The thin, long supporting beams greatly reduce the thermal diffusion into the substrate, and thus improve the thermal isolation. Therefore, the thermal sensitivity of a micro-bolometer is high compared with other uncooled thermal infrared detectors. Since micro-bolometers can be integrated with on-chip electronic circuits, the infrared sensing module can be made on a single chip at a low cost. Micro-bolometers are not as susceptible to vibration or shocks as the pyroelectric detectors are.
In the field of systems for detecting potentially icy conditions on roads, reference may be made to the following United States patents:
U.S. patent
Issue Date
Inventor(s)
3,596,264
Jul. 27, 1971
Ciemochowski
3,891,979
Jun. 24, 1975
Braun
4,222,044
Sep. 9, 1980
Boschung
4,492,952
Jan. 8, 1985
Miller
5,416,476
May 16, 1995
Rendon
5,796,344
Aug. 18, 1998
Mann, et al
SUMMARY OF THE INVENTION
It is an object of the invention to provide a non-contacting temperature sensing device where fast response and accuracy are needed, such as for automotive applications, which reduces the impact of emissivity dependence on the resulting device and which incorporates micro-bolometric detectors as the temperature sensing means.
In accordance with the invention, this object is achieved with a non-contacting temperature sensing device for automotive applications comprising:
a first infrared sensing means for detecting infrared radiation within a first wavelength band and for producing a first signal corresponding to the detected infrared radiation of said first wavelength band;
a second infrared sensing means for detecting infrared radiation within a second wavelength band and for producing a second signal corresponding to the detected infrared radiation of said first wavelength band;
signal processing means for obtaining the ratio of the first and second signals in order to provide a third signal, the third signal being emissivity independent and related to temperature.
Preferably, the device according to the invention, provides a non-contacting temperature sensing device incorporating micro-bolometric detectors as the suitable infrared sensing means in detecting road conditions for automotive applications. Further, the first and second infrared sensing means each include an active infrared sensing element and a temperature drift compensating element. A current bias is applied to the active infrared sensing element as well as to the temperature drift compensating element, which is identical in structure with the active infrared sensing element, and the voltage outputs of these two elements pass through a differential amplifier. The fluctuation in the substrate temperature or the ambient temperature affects the active sensing e

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