In Rich manufacturing operation of pressure sensors, autofrettage denotes the procedure of active ? Reliable ? by subjecting the pressure sensor selectively once or many times to a pressure above the nominal pressure range. This technique is applied, to experience maximum stability, in particular of the zero point, in later operation. Assuming the right design of the sensor, autofrettage enables a long time of trouble-free operation of the sensors even at high load cycles achieving the specified overload range, without resulting in zero-point shift or similar effects.
In autofrettage, certain local regions of the sensor, in which during the selective overload the yield point of the sensor material is locally exceeded, become plasticised, producing a permanent change of the instrumentation characteristics. This selective influence on the structural conditions through autofrettage can be an integral portion of the development of the sensor and of the associated manufacturing process. Which pressure the sensor is put through and how often, should be determined individually for each sensor design by means of a complicated FEM simulation and extensive test series.
Caution ? no experiments of your! However, it must not be concluded that every sensor will automatically benefit from subjecting it to autofrettage. Autofrettage can only just be utilized for ductile materials, but under no circumstances for brittle ones. Conditioning must be scheduled and carried out very selectively sufficient reason for great care during the production stages. Ill-considered ?overpressurising? of pressure sensors by laymen who like experimenting can not only damage the sensor permanently, but additionally result in dangerous preliminary damage and subsequently possibly in accidents caused by fatigue and bursting of the sensor. In this manner, a noticable difference in instrumentation will only be achieved, if at all, by hit or miss.