In the 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 resulting in zero-point shift or similar effects.
In autofrettage, certain local areas of the sensor, in which 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. Preposterous on the structural conditions through autofrettage can be an integral section of the development of the sensor and of the associated manufacturing process. Which pressure the sensor is subjected to and how often, must 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 used for ductile materials, but under no circumstances for brittle ones. Conditioning should 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, a noticable difference in instrumentation will only be achieved, if, by hit or miss.