VW Stress Station Manual
The basic total pressure cell (TPC) is comprised of two stainless steel plates which are laser-welded together around the periphery, leaving a thin space between the plates which is filled with a special de-aired oil (see Fig. 1). For environmental reasons INTERFELS is avoiding the use of mercury as a TPC fluid. This approach is made possible by particular design features of the INTERFELS TPC such as:
- The steel plates are always rounded thus minimizing errors from stiff boundary sections of the TPC to the stress readings.
- The two steel plates which make up the TPC are of unequal thickness. There is a thicker base plate which gives the TPC a solid shape and which also provides the connections for the pressure tube and the pinch tubes; and there is a significantly thinner cover plate which is bent at its periphery to minimize the stiffness of the TPC in its outer section. This thinner side is the most sensitive side of the TPC.
- The height to width ratio of the INTERFELS TPC is very small, actually smaller than any other commercially available TPC. This gives superior TPC performance even in stiff media such as concrete.
The oil-filled space of the TPC is connected via a pressure tube to a membrane switch pressure sensor. Stresses applied nor- mal to the plates of the TPC which shall be monitored are balanced by a corresponding built-up of internal fluid pressure which is then measured by the membrane switch using a manual compensation pump.
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