Traceable calibration in a wide temperature range
Numerous vibration tests are carried out under the influence of temperature, whereby reference sensors are mounted on the vibration exciter and/or the device under test. These are thus exposed to temperatures which can be far above or below room temperature, which is where the sensors are usually calibrated.
However, calibration of the sensors in the temperature range of the application is vital in order to be able to correct the influence of the temperature on sensor sensitivity, which can significantly change under the effect of temperature. That is why the calibration should cover the entire frequency range of the application to ensure that the frequency response does not change as a function of the frequency. Also traceability to a national standard must be ensured.
SPEKTRA has developed a calibration method which, in addition to the temperature range from -55°C to 120°C, can also cover the wide frequency range from 10 Hz to 10 kHz. The method is based on a comparison calibration against a reference acceleration sensor according to ISO 16063-21, where the vibration exciter with reference sensor is integrated into a temperature chamber. Thus, it is possible to calibrate not only at room temperature (about 23 ° C.) but in the entire temperature range mentioned above.
For this purpose, a method had to be developed by which the reference sensor can be calibrated by means of a skilful combination of highly accurate primary calibration at room temperature and additional primary and comparison calibrations under the influence of temperature. Special care has been taken to ensure a complete traceability of the measuring chain to the national standard of the PTB. In particular, consideration is also given to the difficult mechanical conditions which arise as a result of the necessary thermal barrier between the table of the vibration exciter and the reference sensor, and which thus so far have restricted the frequency range to a few kHz.
In the future, we will modify our calibration system to be able to do a direct primary calibration of the reference sensors in the climatic chamber by means of a laser vibrometer according to ISO 16063-11. This should significantly improve the measurement uncertainty of the calibration.
We kindly invite you to our presentation of this paper at the IMEKO which will take place from May 30th to June 1st in Helsinki. Of course, you can also contact us directly and we will send you the complete paper in the end of May.
Or you visit us at the intec in Leipzig at our exhibition booth H39 in hall 3 to discuss your individual questions and test applications.