Piston position-sensing system for hydraulic cylinder

摘要

The cylinder serves as a waveguide cavity for electromagnetic waves in a frequency band from e.g. 50 MHz to 1.6 GHz. The position of the piston is determined from the resonant frequency which is related directly to the distance of the piston from the cylinder end. A film of oil (11) is maintained in or on the boundary between relatively moving parts (2,3), one of which incorporates a contact element and seal (4) of high surface conductivity in a groove (5). Contact is enhanced by forces (12,10) acting along and at right angles to the interface (1).