In the manufacturing operation of pressure sensors, autofrettage denotes the procedure of active ?overload? by subjecting the pressure sensor selectively once or many 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 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 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. This selective effect on the structural conditions by way of autofrettage is an integral part of the 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 ? Suck of your own! However, it should not be figured every sensor will automatically reap the benefits of subjecting it to autofrettage. Autofrettage can only be used for ductile materials, but under no circumstances for brittle ones. Conditioning must be scheduled and completed very selectively sufficient reason for great care through the production stages. Ill-considered ?overpressurising? of pressure sensors by laymen who like experimenting can not only damage the sensor permanently, but additionally bring about dangerous preliminary damage and subsequently possibly in accidents caused by fatigue and bursting of the sensor. In this way, an improvement in instrumentation will only be achieved, if at all, by hit or miss.