Fast combined temperature, pressure, and heat flux sensors for rough environments
Accurate measurement of pressure, temperature, and heat flux at high frequency is often required in harsh environment, such the one due rocket launchers, atmospheric entry or on-ground rocket and conventional engine tests. An Italian company active in the space sector has developed a general, small sensor unit layout that enables to measure pressure, temperature and retrieve heat flux on a surface. The sensor unit is provided with fast commercial sensors flush mounted; the sensor choice c
The Italian donor is proposing small size metallic sensor units (typically 15-30 mm in diameter) provided with high-frequency temperature and/or pressure sensors to be flush mounted on the measurement surface. Pressure is directly measured from the embedded sensors, with possibility of measurement down to 10 Pa levels. Temperature is measured through coaxial thermocouples and heat flux is derived from the postprocessing software. During calibration activities, uncertainty in pressure measurement is below 0.5%, below 2% for convective-conductive heat flux and below 5% for radiative heat flux. The architecture is very robust and was qualified for space including severe launch conditions and atmospheric re-entry (ESA EXPERT mission). In general, the units are suitable for strong vibrating, hot, and/or humid environments. The sensor units are provided along with dedicated postprocessing software that can be used to retrieve the instantaneous heat flux from the measured temperature using each probe individual calibration. Units operating with a single temperature sensor can be provided and calibrated to retrieve heat flux from a single temperature measurement. Dedicated amplification and signal conditioning electronics can be provided with bandwidth up to 20 kHz.
Innovations & Advantages
The technology is more flexible and rugged than straight application of commercial items, that are often not available for the user requested conditions. It is qualified for much harsher than typical sensor environments providing cheap, robust and accurate high-frequency results. The dedicated calibration of each unit allows a high degree of customization with respect to the application requirements in terms of dimensions, sensors, and conditions. The commercial sensors typically used to manufacture the sensor units are Kulite pressure sensors (up to 140 bar compensated up to 232 °C), and MEDTHERM coaxial thermocouples (response time in the microseconds range). The unit is manufactured out of stainless steel or copper; if needed sealing is performed with high temperature glues or potting. All the qualification test levels for the sensors have been accomplished successfully by the proposed sensors.
The sensor unit layout is defined considering two different requirements:
1. The unit has to function as a calorimeter, so its dimensions should be uniform and bigger enough than the central flush mounted thermocouple to allow the correct numerical reconstruction of heat flux during the post-processing.
2. The unit has to allow the placement of different sensors, in particular pressure ones, that could be much bigger, and survive vibrations, shocks etc.
The suggested minimum diameter due to the previous bullet 1 is around 10-15 mm. The minimum height is around 25 mm.
Current and Potential Domains of Application
The sensor are meant to be used in harsh environment including high vibration and shock (up to 1400 g), high temperature (up to 1300 K), humid environments. The typical bandwidth is in the range of several tens of kHz with dedicated signal conditioning electronics with certified bandwidth of 20 kHz. Current domain of application has been hence rocket launchers, atmospheric re-entry or on-ground rocket and conventional engine tests.
Potential further domain of applications can be all those where is needed to have measurement of pressure, temperature and heat flux with bandwidth up to at least 20 kHz in harsh environments.