V.W. NATM Pressure Cell is designed to measure radial and tangential stress in shotcrete, concrete, and rock in tunnels linings.
It is composed of 2 rectangular stainless steel plates welded together around the periphery with the narrow gap between the plates filled with hydraulic fluid.
Once the stress increases in shotcrete or concrete, the fluid pressure in the cell rises as the plates are squeezed together and it is delivered to the sensor. At this time, tension of vibrating wire is changed and plucking coil senses changes in the frequency.
Once the primary coil generates a frequency signal on the vibrating wire, then the secondary coil sends the frequency to a measuring instrument. Measured frequency can be converted into pressure with a gage factor.
