Geosense VWNPC-3000 User manual

V1.4 March 15
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NATM STRESS CELLS
VWNPC-3000

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CONTENTS
Page
1.0 INTRODUCTION
1.1 General Description 3
1.2 How it works 4
1.3 Application 5
2.0 CONFORMITY 6
3.0 MARKINGS 7
4.0 DELIVERY 8
4.1 Packaging 8
4.2 Handling 8
4.3 Inspection 8
4.4 Functionality test & zero readings 9
4.5 Storage 10
5.0 INSTALLATION 11
5.1 Cell installation 11
5.1.2. Tangential cell VWNPC-3000 11
5.1.3 Radial cell VWNPC-3010 13
5.1.4 Initial readings 14
5.2 Re-pressurising the cell 14
5.3 Cable 16
5.3.1 Cable installation 16
5.3.2 Cable marking 16
5.4 Tools 16
6.0 DATA HANDLING 17
6.1 Monitoring the readings 17
6.1.1 Portable readouts 17
6.1.2 Data loggers 17
6.2 Data reduction 18
6.3 Calibration certificate 21
6.4 Pressure calculation 22
6.5 Stress value 22
6.6 Temperature compensation 23
7.0 MAINTENANCE 25
8.0 TROUBLESHOOTING 25
9.0 SPECIFICATION 26
10.0 SPARE PARTS 26
11.0 RETURN OF GOODS 27
12.0 LIMITED WARRANTY 28

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It is VITAL that personnel responsible for the
installation and use of the NATM Cells READ and
UNDERSTAND the manual, prior to working with the
equipment.
1.1 General Description
The primary uses for NATM Cells are :-
The measurement of stress in concrete
Particular features of Geosense® Vibrating wire are:-
Reliable long term performance.
Rugged; suitable for demanding environments.
High accuracy.
Insensitive to long cable lengths.
The Pressure sensor is based upon ‘industry standard’ Vibrating Wire technology.
When electronically excited, the sensor produces an output signal in the form of an
alternating current. The frequency of the alternating current can then be readily
converted to a fluid pressure by applying individual calibration factors.
Frequency signals are particularly suitable for the demanding environment of civil
engineering applications, since the signals are capable of long transmission distances
without degradation. They are also somewhat tolerant of damp wiring conditions and
resistant to interference from external electrical noise.
Geosense® NPC-3000 NATM Cells are supplied in various configurations to suit
varying installation environments and techniques. Each cells is fitted with a length of
connecting cable, an internal temperature sensor and a surge arrestor.
1.0 INTRODUCTION
This manual is intended for all users of Geosense® NPC-3000 NATM Cells and provides
information on their installation, operation and maintenance.

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1.2 How it works
1 - Sensor cable
2 - VW sensor (no elasticity)
3 - Stress cell body - comprises of two stainless steel rectangular plates welded
together around their periphery, leaving a thin space between the plates which is then
filled with an relatively incompressible de-aired fluid. Pressure applied normal to the plate
is balanced by a corresponding build up of internal fluid pressure which is measured by
the sensor.
4 - Mounting lug - provided at each corners of the cell body to fix the cells in place while
the shotcrete is applied.
5 - Pressure (pinch) tube - this is filled with a relatively incompressible de-aired fluid
and is connected at one end to the fluid filled space between the plates and the other
end is capped. The purpose of this tube is to inflate the cell once the concrete is cured.
6 - End cap
1
25
3
4
6

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1.3 Application
The "New Austrian Tunnelling Method", or NATM, calls for the support of a tunnel by
the rapid application of shotcrete to the freshly exposed ground. The theory behind
this method of support, particularly useful in weaker ground, is that if the inherent
strength of the ground can be preserved, it will be almost self-supporting and will
require much less artificial support in the form of concrete or steel. To preserve the
inherent cohesion of the ground it is necessary to prevent it from breaking up in the
first place and, hence, the need for a rapidly applied layer of shotcrete.
The graph below shows the ground reaction curve which is the amount of support
needed versus the amount of inherent support and ground deformation. In order to
prevent any support deformation it requires a support pressure exerted onto the
tunnel wall to be equal to the original in-situ ground stress.
NATM cells are used to monitor and thus calculate the support pressure and in
combination with other monitoring devices such as a tape extensometer allows an
assessment as to how much shotcrete lining is required and can be used to alter the
amount as construction progresses.
This therefore provides the most cost effective lining to be installed.
Stress
Convergence
Critical convergence

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2.0 CONFORMITY
Geosense Ltd
Nova House
Rougham Industrial Estate
Rougham, Bury St Edmunds
Suffolk , IP30 9ND
United Kingdom
Tel: [phone] Fax: [phone]
Email: [email protected].uk, Web: www.geosense.co.uk
Declaration of Conformity
We Geosense Ltd at above address declare under our sole responsibility that the
Geosense products detailed below to which this declaration relates complies with protection requirements
of the following harmonized EU Directives,
The Electromagnetic Compatibility Directive 2014/30/EU
Restriction on the use of certain Hazardous Substances RoHS2 2017/2102/EU
Waste electrical & electronic equipment WEEE 2012/19/EU
Equipment description Vibrating Wire NATM Stress Cells
Make/Brand Geosense
Model Numbers VWNPC-3000, VWNPC-3010
This equipment has been designed and manufactured with reference to the following standards:
All mechanical drawings used in the production of this equipment are based upon BS 8888
Electrical/electronic drawings are based upon BS 3939.
A technical file for this equipment is retained at the above address
This Declaration of Conformity was prepared according to EN ISO/IEC 17050-1:2004.
Martin Clegg December 2020
Director

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3.0 MARKINGS
Geosense® NPC-3000 NATM Cells are labelled with the following information:-
Manufacturers website & telephone number
Product type
Pressure range
Model
Serial number
Cable length
CE mark
Maximum pressure

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4.3 Inspection
It is important to check all the equipment in the shipment as soon as possible after
taking delivery and well before installation is to be carried out. Check that all the
components detailed on the documents are included in the shipment. Check that the
equipment has not been physically damaged.
ALL Geosense® NPC-3000 NATM Cells carry a unique identification serial number
which is located on the cable close to the pressure sensor body and at the free end of
the cable. All are supplied with individual calibration sheets that include their serial
numbers and these will shipped with the cells.
Calibration Sheets contain VITAL information about the NATM
Cell. They MUST be stored in a safe place. Only copies
should be taken to site.
(Continued on page 9)
4.0 DELIVERY
This section should be read by all users of Geosense® NPC-3000 NATM Cells.
4.2 Handling
Whilst they are a robust devices, Geosense® NPC-3000 NATM Cells are precision
measuring instruments. They and their associated equipment should always be
handled with care during transportation, storage and installation.
Once the shipment has been inspected ( see below ), it is recommended that cells
remain in their original packaging for storage or transportation.
Cable should also be handled with care. Do not allow it to be damaged by sharp
edges, rocks for example, and do not exert force on the cable as this my damage the
internal conductors and could render the installation useless.
4.1 Packaging
Geosense® NPC-3000 NATM Cells are packed for transportation to site. Packaging
is suitably robust to allow normal handling by transportation companies.
Inappropriate handling techniques may cause damage to the packaging and the
enclosed equipment. The packaging should be carefully inspected upon delivery and
any damage MUST be reported to both the transportation company Geosense®.

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4.4 Functionality test & zero readings
CHECK the Cells ‘Zero Readings’ against
the factory ‘Zero Readings’ on arrival to
ensure they have not changed due to
damage during transportation. To do this,
connect a Vibrating Wire readout to the
bare cable ends (Black and Red
conductors). – See readout manual for
connection guidance.
*NB If the readout display is in
‘Period’ units ( eg 0.03612 ) a
calculation must be performed to
convert to Hz2/1000 ( Linear Digits )
units, since the calibration sheet is
presented in Hz2/1000 units. The
Geosense Readout model VW200
displays the readings in ‘Period’. The
RST readout / logger unit Model
Number VW2106 displays the readings
in Linear digits. See Section 6 of this
manual for more information on units
and conversion routines.
Prior to carrying out a ‘Zero Reading’
CHECK, ensure that the NATM Cells have
been stored in a reasonably stable
temperature for at least 30– 60 minutes.
Record the values displayed on the readout ( and units ) against the NATM Cell serial
numbers. If these ‘out of the box’ CHECK readings show significant differences ( +/-
40 digits ) to the zero pressure values on the calibration sheets, contact Geosense for
assistance. ( It should be noted that the ‘CHECK Readings WILL be affected by the
atmospheric pressure & altitude ).
If components are missing or damaged, contact the delivery company, the supplier
and / or Geosense™.
(Continued from page 8)

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4.4 Storage
Whilst Geosense® NPC-3000 NATM Cells are relatively robust they are a precision
instrument and if they need to be stored care should be taken to protect them against
any impact or weight.
Ideally they should be stored in their original packaging but if not do not stack units
on top of each other or any other item that could damage the sensor or connecting
pipework from the cell body.
It is recommended that they be stored in a dry environment to prevent moisture
migrating along the cables and storage areas should be free from rodents as they
have been known to damage connecting cables.