In Meditative manufacturing operation of pressure sensors, autofrettage denotes the procedure of active ?overload? by subjecting the pressure sensor selectively once or several times to a pressure above the nominal pressure range. This technique is applied, in order to achieve maximum stability, in particular of the zero point, in later operation. Assuming a suitable design of the sensor, autofrettage enables many years of trouble-free operation of the sensors even at high load cycles achieving the specified overload range, without leading to zero-point shift or similar effects.
In autofrettage, certain local areas of the sensor, in which during the selective overload the yield point of the sensor material is locally exceeded, become plasticised, resulting in a permanent change of the instrumentation characteristics. This selective influence on the structural conditions by way of autofrettage is 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 an elaborate 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 just be utilized for ductile materials, but for no reason for brittle ones. Faith must be scheduled and completed very selectively and with 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 additionally result in dangerous preliminary damage and subsequently possibly in accidents caused by fatigue and bursting of the sensor. In this manner, an improvement in instrumentation will only be achieved, if at all, by hit or miss.