Fast air temperature sensors

PT-100 air temperature sensor with enhanced dynamic properties

To enhance the accuracy and dynamic of air temperature measurement especially for applications in interferometry and machine calibration a new high dynamic temperature sensor has been developed. Most of the demands  for this development came from the area of machine tool calibration and other application areas of laser interferometry where the need for accuracy becomes always higher. The limiting factor for laser interferometry accuracy in air is the exact knowledge of the air refractive index which strongly depends on the air temperature. Another factor is the upcoming wish to mount temperature sensors on moving parts, for example on measurement reflectors on moving stages. To follow temperature changes with moving sensors especially in non climatized rooms is a very challenging task for the sensor dynamic.

Fast air temperature sensor
Fast air temperature sensor

The new developed sensor is based on Pt-wire on ceramic substrate. Due to it’s symmetrical construction there is no directionality in the dynamical properties. The surface is passivated so the sensor can be calibrated in a wet media.

Because the small mass and the very thin cylindrical ceramic carrier substrate the sensor is mechanical sensitive. To prevent an accidental damage a protection cover is available. The sensor can be used with and without the protection cover, whereupon the protection cover makes the sensor larger but has very less influence on the dynamical properties.

Wired and wireless connection of multiple temperature sensors to a device

Performance of the new sensor in comparison to a conventional sensor
Performance of the new sensor (blue) in comparison to a conventional sensor (green)

To enhance the accuracy the sensor is usually equipped with an integrated measurement electronics (wired and wireless) which allows the calibration of the whole measurement chain at once. A climate station to use up to 15 wired and 15 additional wireless sensors is also available.
The following performance has been reached: T63=6.3s, measurement interval: >0.9s, resolution 0.1mK (wired) or 10mK (wireless), accuracy: +-50mK (depending on calibration).
The following graph shows the performance of the new sensor (blue) in comparison to a conventional type with a flat measuring resistor in a slotted protection cap (green). To provoke a realistic temperature change a stage with the sensors was moved over a thermal source and after some time again away. It is clear visible that the new developed sensor is significantly faster. It also allows the detection of the turbulence air flow where the conventional sensor only deliver a smooth value.

Besides the interferometry the new developed high dynamic temperature sensor has many fields of application, for instance the evaluation of the quality of climatized rooms and the surveillance of measurement chambers or climate chambers.

The new temperature sensors were the result of a joint research project between the TU Ilmenau, Institute for Process Measurement and Sensor Technology, and SIOS Meßtechnik GmbH. The project was funded by the German Federal Ministry for Economic Affairs and Energy.