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Pressure cells

 
FAQ#077 - Which are the maximum cable lengths from instrument to datalogger?

 

The cable lengths depend from many factors, first of all installation and cable protections (screen, earth, etc...). Assuming that instruments are installed in a workmanlike, for the maximum cable lengths should be followed the next suggestions:

DIGITAL INSTRUMENTS: see FAQ#073

ANALOGUE INSTRUMENTS: see both documents:

Cable length guide line with internal multiplexers
Cable length guide line with external multiplexers

 

 

 

 
FAQ#030 - Why do the NATM pressure cells have repressurizing tubes?

NATM pressure cells are normally used to measure tangential and radial stresses in concrete tunnel lining. They are embedded in concrete and after curing the cell shall be repressurized to mantain the intimate contact between the pessure pad and the surrounding material.

NATM Stress Cells
Hydraulic Pressure Cells

 
FAQ#022 - Why NATM pressure cells have repressurizing tubes?

NATM pressure cells are normally used to measure tangential and radial stresses in concrete tunnel lining. They are embedded in concrete and after curing the cell shall be repressurized to mantain the intimate contact between the pessure pad and the surrounding material.

NATM Stress Cells
Hydraulic Pressure Cells

 
FAQ#021 - Is the repressurizing hand pump for NATM pressure cells filled by de-aired oil, ready to use? Which kind of oil is used for this purpose?

Yes it is. The pump is filled at factory under vacuum with de-aired oil. For normal use within concrete the oil inside the pump is enough to repressurize 50 pcs. of NATM pressure cells. The oil we use is Edwards Ultra-grade 19 type for vacuum-pump use.

 

NATM Stress Cells
Hydraulic Pressure Cells

 
FAQ#020 - How to obtain better results from pressure cells installed in earthfill?

The measurement of total pressure in geomechanics, even if is one of the most interesting parameters for the designer, is generally considered not reliable. Case histories report more nonsuccessful examples than for all the other types of measurements. Theoretical studies made by many researches have highlighted the critical parameters in the design and manufacturing of pressure cells. If the instruments are accurately designed and manufactured and the choice of the model has been done properly, the problem becomes how to use the cell.

In the paper presented by Mr. D. Bruzzi and Mr. A. Zattoni (SISGEO) and Mr. G. Pezzetti (ISMES) at 5TH International Simposium FMGM/99 in Singapore, the authors discuss the main issues related both to laboratory calibration and field installation problems, and a practical approach is presented in order to improve the quality of the results.

The conclusion is that pressure cells provide relative measures that can become absolute by using simple and practical rules deriving from a good knowledge of the basic problems related to design, manufacturing and installation of total pressure cells. For a complete view of this paper, click here to download the .pdf file.

Earth Pressure Cells