Transcript Document

Earth testing
Practical
Earth Testing Techniques and
Measurement Instruments
Earth_testing_2006
Eric van Riet
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Practical Earth Testing
Content
• Principles
• Test Methods
• Practical Measurement
• Summary
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Earth / Ground Basics
What is ground?
A conducting connection, whether intentional or
accidental, between an electrical circuit or equipment
and the earth, or to some conducting body that serves in
place of earth*
Ground is a connection to Earth made either
intentionally or accidentally
*NFPA 70-2000 (National Fire Protection Association)
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Earth / Ground Basics
Why ground?
To protect people and equipment
By dissipating stray energy from:
Electrical faults (fuses, breakers etc.)
Lightning strikes
Radio Frequency
Static discharges
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Real Examples
Why test? – Catch the problem before it happens!
Estimate: at least 15% of power quality problems are
related to grounding
Lightning strikes on equipment with poorly maintained
protection systems destroy millions of dollars of equipment
and lost production every year
Using ground testing in a PDM protocol will help prevent
possible dangerous situations and loss of downtime
(= money)
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Earth / Ground Basics
How do you connect to earth?
Cable or tape
Stake or rod
Earth material
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Earth / Ground Basics
Spheres of influence
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Earth / Ground Basics
Attention! Potential gradients!
Umeasure
Potential gradients around
the earth electrode can
reduce the accuracy of
measurements!
Distance a
The probe must always be
placed outside this area!
Typical distance: >20m
Ground Potential
Neutral ground, reference
Umeasure
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Earth / Ground Basics
Types of Grounding Systems
• Many different types available
• Choice depends on local
conditions and required
function
• Simplest form is a single stake
• Mostly used for:
– Lightning protection
– Stand alone structures
– Back-up for utility ground
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Ground rod
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Earth / Ground Basics
Types of Grounding Systems
• ground rod group
• typically for lightning
protection on larger
structures or protection
around potential hotspots
such as substations.
Ground rod group
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Earth / Ground Basics
Types of Grounding Systems
• For areas where there is
rock (or other poor
conducting material) fairly
close to the surface ground
plates are preferred as they
are more effective
Ground plate
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Earth / Ground Basics
Types of Grounding Systems
• A ground mesh consists of
network of bars connected
together, this system is often
used at larger sites such as
electrical substations.
Ground mesh
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Earth / Ground Basics
Types of Grounding Systems
For the purposes of
this presentation the
grounding system
will referred to as
‘ground electrode’.
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Ground Testing Methods
What are the available techniques?
• Resistivity
• Fall of Potential – Three and Four Pole Testing
• Selective Testing
• Stakeless Testing
• Two pole method
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Ground Testing Methods (1)
Resistivity Measurement
The purpose of resistivity measurements is to quantify the
effectiveness of the earth where a grounding system will be
installed.
Differing earth materials will affect the effectiveness of the
grounding system.
The capability of different earth materials to conduct current
can be quantified by the value E (resistivity in W.m).
Resistivity measurements should be made prior to installing a
grounding system, the values measured will have an effect on
the design of the grounding system.
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Ground Testing Methods (1)
Resistivity values for different earth materials
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Ground Testing Methods (1)
Resistivity Measurement ( Wenner method)
Resistivity measurements are performed by using a
four wire method.
Used to determine
which KIND of
earthing should be
used, so BEFORE
placing earth stakes
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Ground Testing Methods (1)
Resistivity Measurement
From the indicated resistance value RE, the soil
resistivity is calculated according to the equation :
 E = 2  . a . RE
E
RE
a
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...... mean value of soil resistivity (W.m)
...... measured resistance (W)
...... probe distance (m)
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Ground Testing Methods (1)
Resistivity Measurement
Curve 1: As E decreases only
deeper down, a deep earth
electrode is advisable
Curve 2: As E decreases only
down to point A, an increase in
the depth deeper than A does
not improve the values.
Curve 3: With increasing depth
E is not decreasing: a strip
conductor electrode is
advisable.
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Ground Testing Methods (2)
Fall of Potential - Testing
•The Fall of Potential method is the most commonly
used method of testing.
•Three or four pole method, this refers to the number of
connections made to the ground tester.
•The forth pole of the connection is made if the wire to
connect to the system under test is particularly long
> 4 meters. The additional wire cancels out an error due
to the extended length of wire used.
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Ground
Earth
Testing
TestingMethods
Methods (2)
(1)
Fall of Potential – 3 / 4 Pole Testing
The E terminal of the
instrument is connected
to the electrode under
test
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Ground
Earth
Testing
TestingMethods
Methods (2)
(1)
Fall of Potential – 3 / 4 Pole Testing
If the length of this wire
is greater than 4 meter
it is recommended that
an extra wire is
connected between the
electrode under test
and the ES terminal to
eliminate any error
introduced due to the
length of the lead, this
is then known as the 4
pole test
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Ground
Earth
Testing
TestingMethods
Methods (2)
(1)
Fall of Potential – 3 / 4 Pole Testing
The test spike C2 is
placed in the ground
some distance from
electrode under test
(typically 50 meter)
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Ground
Earth
Testing
TestingMethods
Methods (2)
(1)
Fall of Potential – 3 / 4 Pole Testing
During
the test
theP2 is
The voltage
spike
instrument
drives
a
placed in the
ground
current
through
the
test
some the
distance
from
From
current
and
spike,
through
electrode
underthe
test
voltage
measurements
surrounding
earth
(typically
feet) .and
made
it is80
possible
to
returns
through
Once the
are
calculate
astakes
valuethe
of in
electrode
under
test,
place the
test
can
ground
resistance.
the
potential caused by
proceed.
this current is
measured using the P2
spike.
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Ground
Earth
Testing
TestingMethods
Methods (2)
(1)
Fall of Potential – 3 / 4 Pole Testing
A number of readings
should be taken with
the the P2 spike at
different distances, say
from 20 to 35 meters at
3 meter intervals.
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Ground
Earth
Testing
TestingMethods
Methods (2)
(1)
Fall of Potential – 3 / 4 Pole Testing
The distance of the P2 spike is varied to ensure that it is
positioned outside of the sphere influence of the electrode
under test.
When the P2 spike is close to the electrode under test the
measured value appears to be lower and as it becomes
influenced by the C2 spike the measured value rises.
The optimal point of measurement is outside of the
influence of the electrode and the C2 spike.
Taking a series of measurements and plotting these
against distance produces the curve shown.
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Ground
Earth
Testing
TestingMethods
Methods (2)
(1)
Fall of Potential – Creating the ‘S’ Curve
The optimum value is that indicated on the flat part of
the curve
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Ground
Earth
Testing
TestingMethods
Methods (2)
(1)
The 62% Rule
The 62% rule is a guide to how far away the P2 and C2
stakes should be placed from the electrode under test.
The distances are nominally based on the depth of the
electrode.
Depth of Electrode Distance from E to Distance from E to
under Test (E)
Potential Stake (P2) Current Stake (C2)
6
50
82
8
62
100
20
81
131
30
100
161
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Ground
Earth
Testing
TestingMethods
Methods (2)
(1)
Distances for Electrode Arrays
The 62% rule is a guide to how far away the P2 and C2
stakes should be placed from the electrode under test.
The distances are nominally based on the depth of the
electrode.
Widest Dimension
Distance from E to
(Diagonal, diameter or
Potential Stake (P2)
Straight-line) of Electrode
Array under Test (E)
65
100
80
165
100
230
165
330
230
430
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Distance from E to
Current Stake (C2)
165
265
330
560
655
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Ground Testing Methods (3)
Selective Measurement Method
selective
A• The
current
clampmethod
is used
is isolate
based on
to
thethe
testfall of
potential
test in to
current
injected
• But:
without the
need
the
electrodes
under
to disconnect the
test.
ground electrode under
test.
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Ground Testing Methods (3)
Selective Measurement Method
This application
example shows the
benefit of the selective
test in a typical
installation
Firstly the ground
spikes are positioned
according to the
requirements of the
system under test.
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Ground Testing Methods (3)
Selective Measurement Method
Then individual
elements of the system
can be measured by
placing the currentclamp
around the different
connections to ground
without the need of any
disconnection.
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Ground Testing Methods (3)
Selective Measurement Method - Advantages
• Ground electrodes can be tested without powering down
the system they are protecting – saving time and money
• Testing can be carried out without disconnecting – saves
time, money and improves safety
• Multiple electrodes can be tested quickly simply by
moving the current clamp to individual electrodes
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Ground Testing Methods (4)
• The stakeless method eliminates the need for temporary
ground stakes. This is useful in a wide range of situations.
Examples include:
•
•
•
•
Inside buildings
Airports
Urban locations
Chemical and industrial plants
• The stakeless method is not available on all ground testers.
However, it comes standard on the Fluke 1623 and 1625 earth
ground testers.
• The temporary ground stakes are replaced by two current clamps.
The first clamp generates a voltage on the ground condutor, the
second clamp measures the current flowing due to the generated
voltage.
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Ground Testing Methods (4)
• The Fluke 1623 and 1625
testers are able to measure
earth ground loop
resistances for multi
grounded systems using only
current clamps.
• With this test method, two
clamps are placed around
the earth ground rod or
connecting cable and each
connected to the tester.
Earth ground stakes aren‘t
used at all.
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Ground Testing Methods (4)
The clamps are placed around the
ground conductor
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Ground Testing Methods (4)
Stakeless Measurement Equivalent Circuit
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Ground Testing Methods (4)
• If there is only one path to ground, like at some
residential applications, the stakeless method will not
provide an acceptable value and the Fall of Potential
test method must be used.
• An abnormally high reading or an open circuit indication
on the instrument points to a poor connection between
two or more of the aforementioned critical components.
• An abnormally low reading could indicate the instrument
is measuring a loop of bonding conductors.
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Ground Testing Methods (5)
Two Pole Method
Used where other methods
are not available.
Uses nearby metal
structures as a temporary
spike.
Metal water pipes are
typically used
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Ground Testing Methods (5)
Two Pole Method
Drawbacks:
The resistance of the metal
pipe should be significantly
less than the electrode
under test.
Metal pipes are being
replaced with plastic.
Some metal pipes use
plastic couplings.
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Selecting a test method
Summary of Ground Electrode Test Methods
Advantages
Drawbacks
Fall-ofPotential
• Widely accepted
• When you see the characteristic
curve you know you’ve got a
good measurement.
• You have to disconnect ground
• The stakes may not be to drive
• There may not be space around the
ground electrode to drive the stakes
Selective
Method
• Don’t have to disconnect
electrode
• Widely accepted
• When you see the characteristic
curve you know you’ve got a
good measurement.
• The stakes may not be easy to drive
• There may not be space around the
ground
Stakeless
Method
• Convenience
• Assumes a low-impedance parallel
path
• Possible to get very low readings by
mistakenly measuring on a hardwired loop
Two-pole
Method
• Convenience
• Impossible to judge the integrity of
the “auxiliary electrode.”
• Can’t be sure you are outside the
area of influence
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Ground Testing Applications
When and why ground test?
Prior to designing an grounding system:
the ground material should be evaluated by resistivity
measurement before designing a ground system
Initial test on new ground systems:
the real effectiveness of new ground systems should be
measured before connection – fall of potential test
Periodic tests on ground systems:
ground systems should be checked periodically to ensure
they are not affected by changes in the ground or
corrosion – selective or stakeless test
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Ground Testing Applications
When and why ground test?
Testing prior to addition of major loads:
prior to installation of sensitive equipment such as servers,
CT scanners, control systems, etc. – fall of potential,
selective or stakeless
Safety tests on major equipment and plant
e.g. ground tests on machines, elevators, conveyor belts,
transformers, substations, boards, motors –
stakeless and selective testing especially useful
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Ground Testing Applications
When and why ground test?
All other tests for relevant ground connections e.g. lightning
protection, pipelines, tanks, gas stations, antenna systems,
telecommunication lines, “faraday” cages – fall of potential,
selective or stakeless
PQ troubleshooting, quantify the effectiveness of grounding
by measurement – fall of potential, selective or stakeless
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Choosing the right instrument
Introducing the Fluke 1623 and 1625 Ground Testers
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Fluke 1623
• Feature Summary
• Conventional 3 - and 4 - pole earth/ground
testing
• Selective method
• Stakeless method
• Two pole AC resistance measurement
• One button measurement – press once to
measure with simple GO/NOGO indicators
• Large easy to read display
• Rugged housing rated to IP56
• 2-Year Warranty
• Customer
• Electrical Consultants, Industrial
• Application
• Verification of earth resistance of electrical
& communication systems.
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Fluke 1625 - the expert instrument
Feature summary
• 3- and 4-pole measurement of earth
resistance
• Selective and Stakeless method
• Monitoring and display of probe and auxiliary
earth resistance
• Automatic display of external voltage and
frequency
• Selection of optimal measuring frequency
(AFC)
• measurements down to deep ground layers
possible (high testsignal power: >250mA,
48V)
• Earth impedance R* of high tension towers
- for calculation of genuine short circuit
current
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Fluke 1625 - the expert instrument
Additional features of Fluke 1625
• 2 pole AC resistance measurement
- Resolution: 0.001 Ohm
- Measuring signal: 20V / 250mA
• 2 pole, 4 pole DC resistance measurement
- Range: 3 kOhm, resolution: 0.001 Ohm
- automatic polarity reversal, adaptation of test
period
- short circuit current >200mA as per IEC/EN
61557-5 , UM >4V
• User defined limit settings
- adjustable limits for any individual applications
• Interface and software available as option
- data transfer to PC or printer
- comfortable data evaluation with WinGEO
software
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Fluke 1625 - the expert instrument
Unique: R* - Earth impedance
Measurement of complex
earth-impedance at
55Hz which determines
the real short circuit
current
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Fluke 1625 - the expert instrument
Unique: R* - Earth impedance
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Measurement of
complex earthimpedance at 55Hz
which determines
the real short circuit
current
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Chosing the right instrument
Introducing the Fluke 1623 and 1625 Ground Testers
Feature
3-pole earth measurement
1623
1625


4-pole earth measurement


Specific earth resistance (soil-resistivity according to Wenner)


2-pole resistance measurement DC

4-pole resistance measurement DC

2-pole resistance measurement AC


Selective earth measurement (1 clamp)


Stakeless earth measurement (2 clamps)


Earth impedance of high voltage pylons (55 Hz)

Measuring voltage 20/48 V

Measuring voltage <= 48 V

Automatic frequency control (AFC) (94 ... 128 Hz)
Measuring frequency 128 Hz


Programmable limits, settings

One button measurement concept


Protective rubber holster


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Clamp-On Earth Loop Tester GEO 30
Feature Summary
• Ground loop resistance clamp measurement
• Low level measurement of ground leakage current
• Wide AC current measurement range up to 30A with
one instrument
• Rapid evaluation of continuity loop resistance by
audible HI/LO alarm
• Easy to use, convenient, Display-HOLD function
• Time saving memory function for saving measured
values and automatic recording
• Automatic self calibration ensures correct
measurement every time
Customer
• Residential, Commercial, Industrial Electricians
Application
• Earth loop resistance testing for houses, commercial
and industrial buildings
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Clamp-On Earth Loop Tester GEO 30
LEM GEO 30 - Ground Tester / Current Meter
Stakeless Ground Resistance Measurement
I
I
Current amplifier
U
Rn
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Voltage generator
Rx
The voltage U developed by the clamp is injected into
the circuit. This causes a current I which flows in this
measuring circuit. The second clamp measures this
current I and the earth clamp displays the ground loop
resistance Rx+Rn.
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Clamp-On Earth Loop Tester GEO 30
High quality,
rugged
carrying case
High Quality
measuring
instrument
Includes five language
operators manual
E/D/F/ES/IT
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Calibration loop for
instrument check
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Fluke 1653
• Target Customer – Professional Electrician / Testing Specialist
• Top Line Model with Unmatched performance
• Features
– Volts & Frequency to 500V
– Insulation Resistance
– Continuity Measurement
– Loop /PSC Measurement
– RCD Testing
– Earth resistance Tests
– Phase Sequence Indication
– On-Board Memory
– Interface for Downloading data
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Summary
• Resistivity measurement provides important data
regarding the earth material prior to system design
• Fall of Potential Test is the most widely accepted
• Four pole measurement compensates for voltage
drop in measuring cable
• The 62% rule provides some guidance to the
required distance for the temporary test spikes
• Selective testing allows testing without
disconnection
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Summary
• Selective test is based on fall of potential test that
speeds measurement and provides additional safety
• Stakeless Testing is a fast method for multiple
electrode systems
• Two pole ground testing provides minimal information
and should be used very cautiously
• The Fluke 1623 provides the majority of the required
functions for industrial users
• The Fluke 1625 is the advanced ground tester for
utilities
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Why should I invest on Earth Ground?
• The WW market for Earth Ground is estimated to be $25 Million
• With only two major US competitors (AEMC, Megger), with inferior
product lines, there is no reason why Fluke shouldn’t have 40%
market share in 3 years.
• Fluke 1623 and 1625 are the most complete Earth Ground testers
available anywhere
• In the US, Megger & AEMC do not have the best products, they
only have inroads into Utilities. Perfect value selling opportunity.
• Your customers have been asking for it
• It is core to our strategy (along with PQ, Insulation and
Thermography)
• Another opportunity to educate our customers about a product
category. Take the high road, educate, convert to the best products.
Repeat what you’ve done again and again.
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Who to target?
Earth Ground Market Segment
Elect Contractor Res & Comm
Handy GEO
GEO 30
Saturn GEO Plus
Saturn GEO X
Handy GEO
GEO 30
Fluke 1623
Fluke 1625
Field Service
Industrial Maint
Technician
Utilities - Power &
Telecom
X
X
X
X
X
X
X
X
Earth Ground Testing Methods
Fall of Potential
3-Pole
Handy GEO
GEO 30
Saturn GEO Plus
Saturn GEO X
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Handy GEO
GEO 30
Fluke 1623
Fluke 1625
4-Pole / Soil
Selective
Stakeless
1 Clamp
2 Clamp
X
X
X
X
X
X
X
X
X
X
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Which product for which user?
Function
Can you test if the service is still
connected?
GEO 30
Fluke
Handy
1653
GEO
Yes
Do you want to perform 3-Pole
or 4-Pole Fall of Potential tests
using stakes?
Are you performing tests inside a
building?
Are any test points inside the
building larger than 0.9"
diameter?
Are you interested in soil
resistivity?
Are there high power systems
close by that could influence
measurements?
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Yes
Yes
Fluke
1623
Fluke
1625
Comment
Yes
Yes
Handy GEO only performs the 3-Pole measurement which requires
the service to be disconnected. Fluke 1623, Fluke 1625, and GEO
30 can perform measurements whether the service is connected
(preferred by end users - safer) or disconnected.
Yes
Yes
GEO 30 only performs a stakeless test. All other testers can
perform these tests using stakes (Fall of Potential).
Yes
Yes
Handy GEO cannot perform tests with clamps, necessary for
measurements inside a building, lacking access to soil.
Yes
Yes
The GEO 30 clamp has an inside diameter of 0.9". Fluke 1623 and
1625 have two sized clamps, 2" inside diameter (with kits) and 5"
inside diameter clamp for busbar applications (accessory). For
pylons, another accessory is the 12" inside diameter Split Core
Transformer, affectionately called Big Norma.
Yes
Yes
Necessary for new installations (buildings, substations)
Yes
Utilities and other high end Industrial sites require the Fluke 1625,
because of the Automatic Frequency Control (AFC). If there are
influencing signals, the Fluke 1625 selects a different frequency to
measure.
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1625 worth the money?
Why would anyone pay € 650,- more for the Fluke 1625?
• Utility customers will pay because they see value in the following
advanced features:
– Automatic Frequency Control (AFC) – identifies existing
interference and chooses a measurement frequency to
minimize its effect, providing more accurate earth ground
values
– R* Measurement – calculates earth ground impedance with 55
Hz to more accurately reflect the earth ground resistance that a
fault-to-earth ground would see. Impedance is a frequency
dependent measurement.
– Adjustable Limits – for quicker testing.
• Power utility technicians are interested in two things:
– The ground resistance in case of lightning strike
– The impedance of the entire system in case of a short circuit
on a specific point in the line.
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Product line-up
• Delivery content
• Fluke-1623: Basic GEO Earth Ground Tester
– Contains: Fluke-1623 tester, test leads, batteries, manual (GB,
FR, IT, DE, ES, PT)
•
• Fluke-1625: Advanced GEO Earth Ground Tester
– Contains: Fluke-1625 tester, test leads, batteries, manual (GB,
FR, IT, DE, ES, PT)
• Fluke-1623/1625 Kit: Advanced GEO Earth Ground Tester Kit
– Contains: (1) Fluke-1623 or 1625 tester, (4) stakes, (2) 25m
cable reels, (1) 50m cable reel,
(1) Sensing clamp, (1) Inducing clamp, all necessary
connectors, test leads, batteries, manual,
rugged carrying case
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Accessories
• EI-1623: Selective/Stakeless Clamp Set for Fluke-1623.
– Contains both the Inducing and Sensing clamp all necessary adapters
– Already in the Fluke-1623 Kit.
• EI-1625: Selective/Stakeless Clamp Set for Fluke-1625.
– Contains both the Inducing and Sensing clamp all necessary adapters
– Already in the Fluke-1625 Kit.
• ES-162P3: 3-Pole Stake Kit. (used for both the Fluke-1623 and Fluke-1625)
– Contains: (3) Stakes, (1) 50m cable reel of wire, (1) 25m cable reel of wire
– Already in the Fluke-1623 Kit/Fluke-1625 Kit.
• ES-162P4: 4-Pole Stake Kit. (used for both the Fluke-1623 and Fluke-1625)
– Contains: (4) Stakes, (1) 50m cable reel of wire, (2) 25m cable reel of wire
– Already in the Fluke-1623 Kit/Fluke-1625 Kit.
• EI-162BN: 320mm Diameter Split Core Transformer
– Used as a Selective clamp for ground loop resistance measurement around power
pylons
– Contains the split core transformer and all necessary adapters/connections
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Marcom material
• Distributor product announcement
• Sales PPT
• Value selling tool
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Questions
and answers
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