Influence of thermal shock of piezoelectric pressure sensors on the measurement of explosion pressures

Abstract Piezoelectric pressure sensors are susceptible to changing temperatures, because resulting mechanical deformations of the sensor membrane and housing may exert a positive or negative force on the piezo crystal, thus changing the reading of this sensor. The consideration and compensation of this influence quantity is a frequent topic of many investigations in the field of combustion chambers, of spark-ignition engines and internal combustion engines. However, this is not the case in the field of the type of protection “flameproof enclosures”. Here a peculiarity is the fast temperature rise during a single explosion and the concurrent influence of the temperature gradient, which is often described as thermal shock. The whole event has a typical duration time of the order of seconds and less. Thermal shocks have so far received little attention, as was also a lesson learnt from the evaluation of an interlaboratory comparison between Ex testing laboratories. The laboratories handle thermal shock in a variety of ways, starting from complete ignorance up to various sophisticated coatings. This was a main source of different results within the field of participants. This work evaluates the behavior of different piezoelectric pressure sensor types with respect to thermal shock. Different temperature protection measures are investigated regarding their functionality, practicability and stability. Possible influences on the sensitivity of the sensors due to the used protective measures regarding thermal shock are shown. The transient temperature load of the sensor membrane is estimated by physical calculations as well as numerical analysis based on surface temperature measurements transformed in a surface heat flux density. This work provides guidelines for typical end-users in the field of flameproof enclosures how to handle thermal shock correctly.