U.S. patent application number 12/863466 was filed with the patent office on 2010-11-18 for thermographic camera.
This patent application is currently assigned to TESTO AG. Invention is credited to Andreas Messerschmid, Karl Schuler, Martin Stratmann.
Application Number | 20100289901 12/863466 |
Document ID | / |
Family ID | 40668439 |
Filed Date | 2010-11-18 |
United States Patent
Application |
20100289901 |
Kind Code |
A1 |
Stratmann; Martin ; et
al. |
November 18, 2010 |
THERMOGRAPHIC CAMERA
Abstract
The invention relates to a thermographic camera comprising at
least one infrared radiation detector and at least one adjusting
device that supplies control and/or supply voltages required for
operating the thermographic camera. In order to design a
thermographic camera in which the temperature-induced drift of the
electronics can be compensated while the cost of parts is reduced,
a storage medium in which at least one temperature-related
characteristic curve is stored is provided on the thermographic
camera, and the thermographic camera automatically compensates a
temperature-induced drift of the at least one adjusting device on
the basis of the characteristic curve. The invention further
relates to a method for operating such a thermographic camera.
Inventors: |
Stratmann; Martin;
(Freiburg, DE) ; Schuler; Karl; (Titisee-Neustadt,
DE) ; Messerschmid; Andreas; (Bonndorf-Gundelwangen,
DE) |
Correspondence
Address: |
HOFFMANN & BARON, LLP
6900 JERICHO TURNPIKE
SYOSSET
NY
11791
US
|
Assignee: |
TESTO AG
Lenzkirch
DE
|
Family ID: |
40668439 |
Appl. No.: |
12/863466 |
Filed: |
August 21, 2008 |
PCT Filed: |
August 21, 2008 |
PCT NO: |
PCT/EP2008/006871 |
371 Date: |
July 19, 2010 |
Current U.S.
Class: |
348/164 ;
348/E5.09 |
Current CPC
Class: |
H04N 5/3651 20130101;
H04N 5/33 20130101 |
Class at
Publication: |
348/164 ;
348/E05.09 |
International
Class: |
H04N 5/33 20060101
H04N005/33 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 19, 2008 |
DE |
10 2008 005 167.5 |
Claims
1. A thermographic camera, with at least one infrared radiation
detector and with at least one adjustment device, which generates
and provides control and/or supply voltages necessary for the
operation of the thermographic camera, characterized in that a
storage means is provided on the thermographic camera in which at
least one temperature-dependent characteristic curve is stored, and
in that, based on the characteristic curve, the thermographic
camera automatically compensates for a temperature-induced drift of
the at least one adjustment device.
2. The thermographic camera according to claim 1, characterized in
that the infrared radiation detector is formed by a bolometer, in
particular a bolometer with a focal plane array (FPA) having a
plurality of individual sensors (pixels).
3. The thermographic camera according to claim 1, characterized in
that the detector amplification can be regulated by an analog
change of the control voltage, the control current or the
integration time of the adjustment device, or digitally by a coding
that can be processed by a processor.
4. The thermographic camera according to claim 1, characterized in
that the storage means holds one or more characteristic curves,
each associated with one or more adjustment devices.
5. The thermographic camera according to claim 1, characterized in
that at least one temperature sensor is provided in the area of the
adjustment devices of the camera in order to determine the ambient
temperature/component temperature of the adjustment devices.
6. A method for operating the thermographic camera, in particular
the thermographic camera according to claim 1, characterized by the
following method steps: a. a one-time performance of the
calibration process comprising the steps: i. placing the
thermographic camera in a temperature-stabilized environment; ii.
determining the control and/or supply voltages provided by the
adjustment device or devices; iii. repetition of step ii at
different temperatures; iv. determination of a characteristic curve
from the voltages determined in the step or steps ii; v. storage of
the characteristic curve in a storage means provided on the
thermographic camera; b. the performance of one or more
measurements using the compensation of the control and or supply
voltages based on the characteristic curve determined in step a.
Description
[0001] The invention relates to a thermographic camera with at
least one infrared radiation detector, such as a thermal detector
or a pyrodetector, and with at least one adjustment device that
provides control and/or supply voltages necessary for the operation
of the thermographic camera. The invention further relates to a
method for operating a thermographic camera.
[0002] Thermographic cameras are known for determining temperature
profiles of objects and are frequently used in environments with
varying temperatures. The adjustment devices of the thermographic
camera, which must provide various supply and/or control voltages,
are also subject to corresponding temperature fluctuations, which
can certainly amount to as much as 70.degree. C. Because of this,
the voltages generated by the associated electronics are also
subject to fluctuations.
[0003] In addition to an offset displacement and a possible
influence on the detector itself, these voltage fluctuations lead
in particular to a change in the slope of the so-called detector
characteristic and thus bring about an undesired deviation of the
measurement value versus the ambient temperature. Whereas an offset
displacement can be compensated for by the so-called shutter
process, in which the IR radiation detector is calibrated by a
briefly closed diaphragm, it has so far only been possible to keep
the change in the slope of the detector characteristic to a low
level by using correspondingly expensive temperature-stabilized
components.
[0004] It is therefore the problem of the present invention to
provide a thermographic camera in which the temperature-induced
drift of electronics can be compensated for with simultaneously
reduced component costs.
[0005] This problem is solved by a thermographic camera of the type
mentioned above on which a storage means is provided, in which at
least one temperature-dependent characteristic is stored, and in
which the thermographic camera automatically compensates for a
temperature-induced drift of the at least one adjustment device
based on the characteristic curve.
[0006] There are various possibilities for re-regulating the
detector gain by analog or digital means in the thermographic
camera. These adjustment possibilities permit a compensation for
the drift in the electronics. For the calibration, the slopes of
the detector characteristic, as well as the temperature of the at
least one adjustment device, are determined for various ambient
temperatures in a calibration step, and are then described by a
mathematical model. From the latter, at least one characteristic
curve is obtained which, once stored in the camera, can compensate
for the temperature-induced drift of the system and is used in the
measurement. In a temperature measurement range between 0.degree.
C. and 100.degree. C., the measurement error component caused by
the electronics drift can be reduced in this manner to fractions of
a degree.
[0007] Particularly precise and high-resolution images are obtained
with a thermographic camera in which the infrared radiation
detector is formed by a bolometer, in particular a bolometer with a
focal plane array (FPA) having a plurality of individual sensors
(pixels).
[0008] The compensation of measurement values based on a
characteristic stored in memory can be realized especially
expediently in a thermographic camera in which the detector
amplification is accomplished by analog variation of the control
voltage, the control current or the integration time of the
adjustment device, or digitally by a coding processable by a
processor.
[0009] A more precise compensation of the electronics drift that
also takes the temperature over smaller intervals into account can
be achieved by the use of several characteristic curves associated
with individual components or groups thereof, so that in an
advantageous configuration of the thermographic camera, the storage
means can hold one or more characteristic curves, each associated
with one or more adjustment devices.
[0010] It can be additionally expedient to determine the ambient
temperature of the adjustment devices at the time of measurement
separately, for which reason, in an expedient refinement of the
thermographic camera, at least one temperature sensor is provided
to determine the ambient temperature of the adjustment devices, in
particular one temperature sensor for each adjustment device.
[0011] The above problem is also solved by a method for operating a
thermographic camera, for example the thermographic camera as
described above. For this purpose, the camera is first subjected to
a calibration to be performed one time, in which the following
steps are carried out. The camera is housed inside a
temperature-stabilized environment, such as a thermal testing
cabinet, after which the control and/or supply voltages provided by
the electronic components at different temperatures are determined.
Based on a mathematical model, a characteristic curve is derived
from these voltages that are subsequently stored in a storage means
of the thermographic camera for compensation of the electronics
drift. During a measurement process with the thermographic camera,
for example at different temperatures, the drift of the electronics
is compensated for by specifying the correct control voltage based
on the characteristic curve, so that the slope of the detector
characteristic does not change. The above-mentioned compensation
can also be accomplished in a different manner than via the control
voltage, namely by an analog change of the control current or the
integration time, or digitally by an appropriate coding to be
processed by a processor and which is implemented in a chip.
[0012] By means of the above-described invention, therefore, a
thermographic camera is provided in which the temperature-induced
drift of electronic components of the camera can be minimized or
compensated for with reduced component expense.
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