sensors

VW Pressure Cell

Total pressure cell for measuring stress distribution within soil embankments, dams, and at concrete interfaces.

Range
0.5, 1, 2, 5, 10 MPa
Accuracy
±0.1% F.S.
Resolution
0.025% F.S.

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Overview

Total pressure cell for measuring stress distribution within soil embankments, dams, and at concrete interfaces.

The Geolook Vibrating Wire Pressure Cell (Total Earth Pressure Cell) is designed to measure total pressure in earth fills and embankments, or contact pressure at the interface between the structure and the soil. The cell consists of two circular stainless steel plates welded together around their periphery, with a narrow cavity between them filled with de-aired hydraulic fluid. A high-pressure stainless steel tube connects this cavity to a vibrating wire pressure transducer. As external soil pressure squeezes the plates, the internal fluid pressure rises, which is instantly registered by the sensor.

Read Detailed Description

Benefits & Features

  • Robust stainless steel construction
  • Hermetically sealed Vibrating Wire transducer
  • Long-term stability and reliability
  • Fluid-filled pad ensures uniform pressure distribution
  • Available in 'Earth' and 'Concrete' interface versions
  • Regroutable options available for tunnel linings
  • Integral thermistor for temperature correction

Detailed Description

Operating Principle

The fundamental principle is hydraulic pressure transfer. The active face of the cell is sensitive to the total pressure (soil + pore water pressure) acting against it.

When the soil compresses the cell plates, the incompressible hydraulic fluid inside transmits this force directly to the diaphragm of the vibrating wire sensor. The sensor outputs a frequency signal that is converted into pressure units (kPa or MPa) using a polynomial calibration factor.

Earth Cells vs. Concrete Cells

Selecting the right cell stiffness is crucial to prevent 'arching' (where the sensor takes more or less load than the surrounding material).

  • Earth Pressure Cells: Have flexible plates and a lower aspect ratio to match the modulus of soil.
  • Concrete Interface Cells: Feature a thicker, stiffer plate on one side to be mounted against the rigid structure, with the sensitive face pressing against the soil.

Installation Best Practices

Proper installation is critical for accurate data. The cell must be bedded in fine sand or stone-free material to ensure uniform contact. Point loading from a single rock can puncture the diaphragm or give a falsely high reading.

For embankment installations, cells are typically placed in arrays at different elevations to map the vertical stress distribution profile as the dam height increases.

NATM Tunnel Monitoring

In New Austrian Tunneling Method (NATM) projects, pressure cells are installed in the shotcrete lining to measure radial and tangential stress. This data confirms whether the rock mass is self-supporting or if the lining is taking excessive load.

We offer specialized 're-groutable' cells for this purpose, which ensure intimate contact with the rock face even if the shotcrete shrinks during curing.

Why Vibrating Wire?

Buried pressure cells are often located hundreds of meters from the nearest readout station. Voltage-based sensors (like strain gauge bridges) suffer from signal drop over these distances.

The Geolook VW cell outputs a frequency signal that remains stable over cable lengths exceeding 2 kilometers, ensuring that the pressure reading you see in the control room is exactly what is happening deep inside the dam.

Available Models

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Specifications

Range
0.5, 1, 2, 5, 10 MPa
Accuracy
±0.1% F.S.
Resolution
0.025% F.S.
Cell Diameter
200mm (Standard)
Material
Stainless Steel 304/316
Over-range
150% F.S.
Frequency Range
2000 - 3500 Hz