Pressure Cells Types, Working Principle and Applications by Encardio-rite

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Pressure Cells
Types, Working Principle, Applications
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WHAT IS A PRESSURE CELL?
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USES OF PRESSURE CELLS IN GEOTECHNICAL FIELD
TABLE OF CONTENT
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WORKING PRINCIPLE OF A PRESSURE CELL
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TYPES OF PRESSURE CELLS
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WHAT IS A PRESSURE CELL?
Pressure cells are one of those geotechnical
instruments that are designed to moni- tor
stress or pressure on concrete structures,
retaining walls, abutments, embank- ments,
buildings, tunnel linings, etc. A pressure cell
is a transducer that converts pressure or stress
into a readable elec- trical output. They are
specially designed to measure the total stress in
various con- struction fields. Pressure cells
are available in different shapes, sizes, and
types.
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USES OF PRESSURE CELL IN GEOTECHNICAL FIELD
The rock/soil formation is completely dependent
on the rock/soil type, stress history, shear,
and normal stress levels, boundary and drainage
conditions, and several environmental
effects. The precise assessment of stress and
changes that occur in foundation soil/rock
formations is of great importance for safe
engineering design. While constructing the large
civil engineering projects like tall buildings,
dams, un- derground tunnels, etc., measurement
of stress plays a vital role.
The types of stress can be categorized
as Measurement of total stress at a point within
a soil mass/foundation rock/ concrete
structure. Measurement of contact stress against
the face of a structural element.


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USES OF PRESSURE CELL IN GEOTECHNICAL FIELD
The vibrating wire pressure cells are much
reliable and faster than all the other types as
they are capable of taking readings electrically
as the frequency output is almost immune to
external noise. The cable from the pressure
sensor is connected to the readout unit or data
logger and is protected against any possible
damage during construction to give all-around
reliable data.
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USES OF PRESSURE CELL IN GEOTECHNICAL FIELD
The applications of pressure cells (stress cells)
are as below- Pressure cells are designed to
monitor radial and tangential stresses in
shotcrete tunnel linings, underground
excavations, unlined caverns, foundations. Measure
ment of contact stress against the face of a
structural element. They are used to monitor
mine backfill. To measure the orientation and
magnitude of total pressure and stress
distribution within dam embankments and the
interface of soil and concrete. To determine
contact pressure on retaining and diaphragm
walls, piers, and abutments.



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WHAT IS THE WORKING PRINCIPLE OF A PRESSURE CELL?
A pressure sensor converts the stress or applied
pressure into measurable electrical
output. Pressure can be defined as the applied
force per unit area that a fluid exerts on its
surroundings. The pressure is given by
Pressure (P) Force (F)/Area (A)
The pressure transducers consist of a sensor with
a constant area and respond to the force applied
by fluid pressure. The force applied tends to
deflect the diaphragm inside the pressure cell.
The de- flection of the diaphragm is calculated
and converted into readable electrical output
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TYPES OF PRESSURE CELLS
Model EPS-30V-Series Earth and Concrete Pressure
Cells The Encardio-Rite earth and concrete
pressure cell primarily consist of a flexible and
circular flat capsule constructed from two
stainless steel discs. These stainless steel
discs are welded around the periphery and
connected to a spe- cially designed
Encardio-rite pressure transducer incorporating
the latest vibrating wire technology. The
vibrating wire technology allows for remote and
digital readout. The pressure cell has
inherently high sensitivity and, it is not
necessary to produce a large strain on the area
being monitored for the measurement of stress.
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TYPES OF PRESSURE CELLS
Encardio-Rite offers three types of Model
EPS-30V-Series pressure cells

Model EPS-30V-S
Earth Soil Pressure Cell Suffix S for use in
soil, earth or rock fills The Model EPS-30V-S
Earth Soil Pressure Cell is 200 mm F x 7 mm
thick. It consists of two stainless steel
diaphragm plates welded around the
periphery. The pressure pad is connected to the
vibrating wire pressure sensor through a 6 mm dia
x 165 mm long stainless tube. The narrow cavity
inside the pressure pad and the tube is filled
with fluid.
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TYPES OF PRESSURE CELLS

Model EPS-30V-C
Concrete Pressure Cell Suffix C for use in
concrete The Model EPS-30V-C Concrete pressure
capsule is similar to EPS-30V-S. For
applications in which the concrete pressure cell
is embedded in concrete, a 600 mm long pinch
tube is welded to the transducer.
Once the concrete is cured, due to cooling the
shrinkage of capsule is created which creates a
gap between the concrete and cell which prevents
the transmission of pressure on the cell. Thus
to fill the gap, a pinch tube is squeezed to push
the fluid to inflate the cell and develop a
positive pressure on it.
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TYPES OF PRESSURE CELLS

Model EPS-30V-I
Soil and Rock-Concrete Interface Pressure Cell
Suffix I for use at concrete and soil
interface
The Model EPS-30V-I Soil and Rock-Concrete
Interface Pressure Cell is similar to the above
except that it is 200 mm F x 10 mm thick and the
diaphragm on one of the side is rigid.
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TYPES OF PRESSURE CELLS
Model EPS-30V-J Jack Out Pressure Cell The total
stress measurement in the soil can be categorized
as follows

Measurement within a soil mass. Measurement at
the face of a structural element.
Encardio-Rite Jack-Out Pressure Cell falls in the
latter category. The name of the cell is derived
from the use of a hydraulic jack during
installation by activating it to keep the cell
in position while the concrete is poured in.
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TYPES OF PRESSURE CELLS
Encardio-Rite Model EPS-30V-J-? Jack-Out Pressure
Cell is used for monitoring changes in stress
base slabs and diaphragm/slurry walls etc. It is
extensively used

Where concrete is cast directly against soil,
i.e. cast in place structures. As a safety
measure to monitor the earth pressure in excess
of designed limits. For verification of design
assumptions and to provide data and information
for safer and more economical future designs.
The Model EPS-30V-J Jack-Out Pressure Cell is
designed to measure the total stress i.e. the
effective stress due to the soil together with
the pore water pressure in the voids between
soil grains. It is suitable for measuring static
or slowly varying stresses only.
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TYPES OF PRESSURE CELLS
Construction of Model EPS-30V-J Jack Out Pressure
Cell The Jackout Pressure cell is 14 mm thick
and has a diameter of either 200 mm or 125 mm.
It is constructed from two stainless steel plates
welded together around the periphery so as to
leave a narrow space between them.
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TYPES OF PRESSURE CELLS
This space is completely filled with de-aired
fluid and connected hydraulically to a pressure
sensor. The sensor has an all welded
construction such that space confining the
hydraulic fluid is entirely metal, not requiring
O rings that tend to trap air and reduce cell
stiffness. The hydraulic fluid is de-aired which
materially improves fluid stiffness and
performance of cell. The pressure transducer is
made of stainless steel construction with size 42
mm ? x 176 mm long. It incorporates the latest
vibrating wire technology and has an inherently
high sensitivity.
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TYPES OF PRESSURE CELLS
The transducer converts the fluid pressure into
an electrical signal in the form of fre- quency,
which can be accurately measured by model EDI-51V
vibrating wire readout unit or any other
conventional vibrating wire readout unit. The
signal can also be transmitted over long
distances to a remote automatic data acquisition
system like Encardio-Rite Model EDAS-10.
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TYPES OF PRESSURE CELLS
Model ESC-30V Shotcrete-Concrete Stress Cell The
Model ESC-30V is used to monitor the radial and
tangential stresses in the shot- crete of
tunnels, particularly where the New Austrian
Tunnelling Method and under- ground works are
being implemented. Measurement of radial and
tangential stresses within shotcrete lining is a
vital fea- ture of this type of stress cell.
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TYPES OF PRESSURE CELLS
The stress cell has a rectangular pressure pad
which is constructed with two stain- less steel
plates, welded around the periphery. The
pressure pad and the electron beam welded
vibrating wire pressure sensor are connected
together by a 6 mm F x 165 mm long stainless
steel tube. The cavity inside the pressure
sensor and the pressure pad is filled with
de-aired fluid.
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TYPES OF PRESSURE CELLS
Construction of Model ESC-30V Shotcrete-Concrete
Stress Cell Increase in stress in the concrete
causes a vibrating wire pressure cell and is con-
verted to an electrical signal which is
transmitted as a frequency signal to read out
the unit. The pressure cell consists of a
magnetic, high tensile strength stretched wire,
one end of which is anchored and the other end
fixed to a diaphragm which deflects in some
proportion to the applied pressure. Any
deflection of the diaphragm changes the tension
in the wire, thus affecting the resonant
frequency of the vibrating wire. The resonant
frequency with which the wire vibrates can be
accurately measured by the vibrating wire readout
unit.
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