In the manufacturing operation of pressure sensors, autofrettage denotes the process of active ?overload? by subjecting the pressure sensor selectively once or several times to a pressure above the nominal pressure range. This process is applied, to experience maximum stability, in particular of the zero point, in later operation. Assuming a suitable design of the sensor, autofrettage enables a long time of trouble-free operation of the sensors even at high load cycles reaching the specified overload range, without leading to zero-point shift or similar effects.
In autofrettage, certain local regions of the sensor, where through the selective overload the yield point of the sensor material is locally exceeded, become plasticised, resulting in a permanent change of the instrumentation characteristics. Blushing on the structural conditions through autofrettage is an integral the main development of the sensor and of the associated manufacturing process. Which pressure the sensor is put through and how often, must be determined individually for every sensor design through a complicated FEM simulation and extensive test series.
Caution ? no experiments of your! However, it must not be concluded that every sensor will automatically reap the benefits of subjecting it to autofrettage. Autofrettage can only be used for ductile materials, but for no reason for brittle ones. Conditioning should be scheduled and carried out very selectively sufficient reason for great care through the production stages. Ill-considered ?overpressurising? of pressure sensors by laymen who like experimenting will not only damage the sensor permanently, but also result in dangerous preliminary damage and subsequently possibly in accidents due to fatigue and bursting of the sensor. In this manner, an improvement in instrumentation is only going to be achieved, if, by hit or miss.