Patent Application
20100289901
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.
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° C. Because of this, the voltages generated by the associated electronics are also subject to fluctuations.
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.
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.
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.
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° C. and 100° C., the measurement error component caused by the electronics drift can be reduced in this manner to fractions of a degree.
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).
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.
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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 005 167.5 | Jan 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/006871 | 8/21/2008 | WO | 00 | 7/19/2010 |
