Gossen MetraWatt GEOHM 5 User manual

User Manual
GEOHM 5
Earth Tester 3-349-418-03
3/12.20

2
Meanings of Symbols on the Instrument
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without permission in writing from Gossen Metrawatt GmbH.
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Warning regarding dangerous electrical voltage
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„WEEE“.

GEOHM 5 Table of contents
3
1Introduction ...........................................................................................................4
1.1 General description ...........................................................................................4
1.2 Warnings...........................................................................................................4
1.3 General settings (first use) ................................................................................5
1.4 List of parameters measured by the Earth Tester .............................................6
1.5 Standards applied .............................................................................................6
2Instrument description .........................................................................................7
2.1 Instrument Casing .............................................................................................7
2.2 Front panel........................................................................................................7
2.3 Connector panel................................................................................................9
2.4 Base..................................................................................................................9
2.5 Instrument Messages......................................................................................10
2.6 Earth Resistance.............................................................................................11
2.6.1 Standard four-lead test method................................................................11
2.6.2 Standard four-lead test method in combination with sensitive test clamp 14
2.6.3 Earth Resistance measurement with two test clamps..............................16
2.7 Specific Earth Resistance................................................................................19
2.8 Current (True RMS).........................................................................................22
3Memory and other operations............................................................................24
3.1 Memory ...........................................................................................................24
3.1.1 Storing of test results................................................................................25
3.1.2 Recalling of stored results........................................................................26
3.1.3 Erasing stored results...............................................................................28
3.2 RS 232 communication ...................................................................................29
3.3 Reset of the instrument ...................................................................................30
4Maintenance ........................................................................................................31
4.1 Batteries..........................................................................................................31
4.2 Cleaning..........................................................................................................32
4.3 Recalibration ...................................................................................................32
4.4 Service ............................................................................................................33
4.5 Device Return and Environmentally Compatible Disposal...............................33
5Technical specification.......................................................................................34
5.1 Measurement functions...................................................................................34
5.2 General characteristics....................................................................................36
6Standard accessories.........................................................................................37
6.1 Optional accessories.......................................................................................37
7Repair and Replacement Parts Service, Calibration Center and Rental ..........
Instrument Service..............................................................................................38
8Product Support..................................................................................................38

GEOHM 5 Introduction
4
1 Introduction
We are very pleased to offer a high quality, professional grade test instrument, for
carrying out four wire Earth Resistance measurements, as well as specific ground
resistance measurements on which the estimation of earthing quality is based. The
equipment was designed and produced based on many years experience of producing
and dealing with Earth Resistance and Electric installation test equipment.
1.1 General description
The Earth Tester is a professional, hand–held, battery powered test instrument. It is
intended for carrying out Earth Resistance measurements in accordance with
International standard IEC 60364-6-61 (VDE 0100 Teil 610) and European standard
EN 61557 - 5.
The instrument is supplied with all of the basic accessories necessary for carrying out
the tests.
The electronic section of the Earth Tester is produced in SMD technology, which
requires practically no service intervention. A custom designed LC display offers easy to
read main results as well as subresults, parameters and messages. Application is
simple and clear and the operator does not need to attend any special training (except
to read this Instruction Manual) to operate the instrument.
1.2 Warnings
In order to ensure operator safety while carrying out various measurements and tests
using the Earth Tester, as well as to keep the test equipment undamaged, it is
necessary to consider the following general warnings:
If the test equipment is used in a manner not specified in this Instruction
Manual, the protection provided by the equipment may be impaired!
Do not use the instrument and accessories if any damage is noticed!
Service intervention or calibration procedure must only be carried out by a
competent, authorized person!
Never connect the instrument onto high voltage.
Do not charge when alkaline batteries are fitted!
Turn power off and disconnect any measurement accessory connected to
the instrument before opening battery cover.

GEOHM 5 Introduction
5
1.3 General settings (first use)
There is usually voltage or current noise present on the earthing system under test,
caused by mains voltage somewhere in the near or far vicinity. Mains voltage frequency
is different in different countries (50 Hz in European countries etc., 60 Hz in the United
States etc.). In order to get stable test results, regardless of noise levels, it is advisable
to insert the nominal frequency of the mains system.
The instrument’s measuring system assures excellent noise immunity. In extremely
noisy conditions, the stability of results can be further improved by means of averaging.
The frequency and algorithm, once set, will stay set, even after replacing batteries.
Insert the frequency of mains voltage (50/60 Hz)
Setting the unit of Specific Earth Resistance parameter (m/ft)
Setting the measuring algorithm
Switch OFF the instrument.
Keep ON key pressed while switching on the instrument until Fr
followed by 50 or 60 value (last selected) starts to flash.
Hz
Press UP/DOWN key to select appropriate frequency of mains
voltage.
Press START key to confirm “Frequency”. Unit mor ft (last
selected), used in Earth Resistivity measurement, starts to flash.
m
Select appropriate unit (mor ft).
Press START key to confirm “Unit selection”. Measuring algorithm
type starts to flash.
Normal algorithm
Improved noise rejection
algorithm (by means of averaging
tehniques)

GEOHM 5 Introduction
6
Press START key to confirm measuring algorithm. The instrument is
ready for regular measurements.
Note:
In general it is recommended to use the ‘Normal’ measuring algorithm because of the
instrument’s high intrinsic noise immunity.
If the results are still unstable further improvements can be achieved by averaging eg.
selecting the ‘Improved measuring algorithm’. However, this prolongs the measuring
time significantly (up to 20 seconds).
New selection is also offered after each resetting of the instrument (see the procedure
in chapter 3.3. (Reset of the instrument!)).
1.4 List of parameters measured by the Earth Tester
Parameter
Function switch
position
Used accessories
Earth Resistance RE
(classic four-lead method)
REARTH
Four test terminals
Two test rods
Selective Earth Resistance Rs
(classic four-lead method
plus test sensitive clamp)
Rs(clamp)
Four test terminals
Two test rods
One sensitive test clamp
Selective Earth Resistance RE
(two test clamps)
RE(2 clamps)
Two test clamps
Earth Resistivity 
EARTH
Four test terminals
Four test rods
Current (True RMS)
ICLAMP
One sensitive test clamp
1.5 Standards applied
Earth Tester is designed in accordance with European safety standard
EN 61010 –1
EMC (noise and immunity) in accordance with European standards
EN 61326-1: 2006
Measurements in accordance with European standard EN 61557-5, Part 5: Earth
resistance (EN 61557-5 Earth resistance)

GEOHM 5 Instrument description
7
2 Instrument description
2.1 Instrument Casing
The instrument is housed in a plastic casing, which maintains the protection class
defined in the general specifications. The casing consists of a main section, which
includes the operator's panel and connectors and of a moveable cover.
The cover is permanently fixed to the base section and cannot be detached.
2.2 Front panel
The front panel consists of a custom LCD, a rotary switch, and a keyboard, see the
figure below.
mA
M
Vkm
ft
Hz
MEM
1
Figure 1. Front panel
1

GEOHM 5 Instrument description
8
Legend:
1 Custom designed LCD.
2 CURSOR up key to:
Increment storage MEM code.
View previous result
Set the instrument to general settings
Earth resistivity function: Increment the distance »a« between test rods
3 START key to:
Start any measurement.
Leave the recall function
Cancel save or clear procedure
Select/set function parameters in General settings:
Earth resistivity unit (m or ft)
Frequency (50 or 60) Hz.
4 DISP key to display the subresults of the selected function. (Check current and
potential probe resistances (Rc and Rp) in EARTH, R EARTH and functions.)
5 MEM key to store and recall results.
6 CLR key to erase memorized results and/or reset the instrument
7 CURSOR down key to:
Decrease storage MEM code.
View the next result
Earth resistivity function: Decrease the distance »a« between test rods
8 Rotary switch to:
Select the measurement function or OFF position. (Auto OFF will occur
automatically, 10 minutes after the last strike to any key or function switch
rotation.)
Cancel, save or clear procedure
Exit recall procedure

GEOHM 5 Instrument description
9
2.3 Connector panel
Figure 2. Connector panel
Legend:
1 Test terminals:
Blue –test terminal H
Black –test terminal E
Red - test terminal S
Green - test terminal ES
2 Clamp test terminals C1 and C2
3 RS 232 connector (to connect Earth Tester to PC)
4 Battery charger connector
The test connector is intended for connection of the test cable and is accessible only
when the instrument cover is lifted up. RS 232 and battery charger connectors are
accessible only when the cover of the instrument is closed. For safety reasons both
connector fields cannot be accessible at the same time, the cover of the instrument
selects the accessible one.
2.4 Base
Figure 3. Base
E-Clip 2
blue
black
E-Clip 1
red
black

GEOHM 5 Instrument description
10
Legend:
1 Plastic housing.
2 Screw (4 pieces) to fix the battery cover.
3 Battery compartment cover.
4 Battery cover warnings.
5 Trade mark label.
6 Plastic holder for carrying strap
2.5 Instrument Messages
Messages are generated on the LCD using special symbols and numeric segment
combinations. The following figure shows all of the possible display segments and the
table beneath describes the messages.
Result value
Unit of displayed result
Operation with memory
Low battery
Higher than
Warning !
Cursors
mA
M
Vkm
ft
Hz
MEM
Figure 4. Display segments
Description of possible display messages:
>1999
Result out of range.
and > 20 V
External voltage is higher than approx. 20 Veff.
and on RC
Current spike resistance is too high
and on RP
Potential spike resistance is too high
and on LowIC
Current tested by clamp is lower than 0,5 mA
and on
Current noise is higher than approx. 2,1 A or / and
noise voltage is higher than approx. 5 V
MEM
Operating with storage (store or recall).
no MEM
No stored result to be recalled.
RCL
Recall function entered.
Clr MEM
Confirm or abort clearing of last stored result?
Clr/ALLalternating
Confirm or abort clearing of all stored results?
FUL
All storage locations occupied.
toP
Last stored result on this location –no more results
bot
First stored result on this location –no more results
SEr
Active serial communication.

GEOHM 5 Instrument description
11
Fr
General settings –selection of frequency
LEn m
Generalsettings–selectionofunitinEarthResistivitymeasurement
t ┌┐, t ┌─┐
Generalsettings –selectionofmeasuringalgorithm
Batteries are too weak –replace the batteries.
rES
*Reset of the instrument (erased memories).
Table 1. Messages
* This indication appears after the insertion of batteries, i.e. when batteries were
removed from the battery compartment for a specific period of time (a few hours), or
if the microprocessor detects an irregularity in its memory or if reset of the instrument
has been performed. Measurement instructions
Measurements
2.6 Earth Resistance
The Earth Tester is able to carry out Earth Resistance measurement using three
different methods. The appropriate one is selected by the operator depending on the
particular earthing system to be tested.
Selective Earth Resistances can be measured using test clamp (without mechanical
disconnection of tested earthing electrode).
Probeless measurement can be done using two test clamps.
2.6.1 Standard four-lead test method
The four-lead connection gives much better results than the three-lead connection, as
there are no problems concerning contact resistance between the test clips and the
(usually rusty) surface of the electrode under test.
The distance from the earthing electrode under test to the current measurement probe H
is at least 5 time the depth of earthing electrode rod or the length of the band electrode
(see Figure 5).
If measuring the total Earth Resistance of a complex earthing system, the required
distance depends on the longest (diagonal) distance (d) between the individual earthing
electrodes (see Figure 6).

GEOHM 5 Instrument description
12
Step 1
Connect the test leads to the instrument and to the object under test in accordance
with the figures below.
Figure 5. Connection of standard 20 m long test leads
Figure 6. Connection of optional 50 m long test leads
REarthtot = RE1 // RE2 // RE3 // RE4
R E1..E4 separate earthing resistance
R.Ppotential spike resistance (P= Potenzial)
R Ccurrent spike resistance (C= Current)
R Earthtot total earth resistance of tested earthing system
d...............probe distance, d 20 m tolerance depending on potential gradient

GEOHM 5 Instrument description
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Step 2
Set the function switch to REARTH position, the following menu will be displayed:

Figure 7. Earth Resistance initial menu
Step 3
Press START key and view the test result. (If you want to perform
more than one measurement press the START key and keep it
pressed until the result has stabilized, then release the key. The last
result will stay displayed.)
Press the DISP key to check the resistances of both the potential
(Rp), and the current (Rc)test probes. After a short period the main
result will automatically be displayed again.
Store the displayed result for documentation purposes, see instructions on how to
use memory in chapter 3.1.1. Storing of test results.
Notes!
When an external voltage higher than 20 Vac/dc. is present between H and E or
ES and S test terminals, the Earth Resistance measurement will not be carried out
after pressing START key, but the message > 20 V will be displayed, marked with
!
symbol!
If a noise voltage higher than approx. 5 V is present between the H and E or ES and
S test terminals, a cursor mark pointing to the “” (noise) symbol will be
displayed, indicating that the test result may not be correct!
If the resistance of the current or potential rod is too high (>(4 k + 100 RE) or
>50 k, whichever is lower), then the test result will be marked with symbol and
the cursor will appear on Rc and / or Rp.
If the test result is out of measurement range (open test leads), >19,99 k
message will be displayed!

GEOHM 5 Instrument description
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2.6.2 Standard four-lead test method in combination with sensitive
test clamp
Measuring selective earth resistance (test clamp E-Clip 1)
If several earthing electrodes are connected in parallel (see figure 8), then it is very
important to know the quality of each individual electrode. This is especially important
when the earthing system is intended for protection against atmospheric discharging,
because any inductance within the earthing system presents a potential danger (due to
increased resistance to high frequency pulses during the atmospheric discharge).
In order to test each electrode separately, they should be mechanically separated, but
the mechanical connections are usually very difficult to disconnect because of corroded
connection components (screws, nuts, spacers, etc.).
The main advantage of the selective measurement method with clamp is that there is no
need to mechanically disconnect the electrode under test.
Step 1
Connect test leads and sensitive test clamp (E-Clip 1) to the instrument and to the
object under test in accordance with the figure below.
Figure 8. Connection of standard 20 m long test leads and sensitive test clamp
(E-Clip 1)
!
...Ensure that the test sensitive test clamp (E-Clip 1) is connected under the E test
terminal, otherwise the parallel resistance of all other electrodes (RE1 up to RE4) will be
measured!
R E4 selective earthing resistance of electrode E4
U test voltage
I clamp the current measured by sensitive test clamp
R Sselective earth resistance
d...............probe distance, d 20 m tolerance depending on potential gradient
4E
clamp
SR
IU
R

GEOHM 5 Instrument description
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Step 2
Set function switch to ”“ position, the following menu will be displayed.

Figure 9 Earth Resistance initial menu
Step 3
Press START key and view the test result. (If you want to perform
more than one measurement press the START key and keep it
pressed until the result has stabilized, than release the key. The last
result will stay displayed.)
Press the DISP key to check the resistances of both the potential
(Rp), and the current (Rc)test probes. After a short period the main
result will automatically be displayed again.
Store the displayed result for documentation purposes, see instructions how to use
memory in chapter 3.1.1. Storing of test results.
Notes!
When an external voltage higher than 20 Vac/dc. is present between the H and E
or ES and S test terminals, the Earth Resistance measurement will not be carried
out after pressing START key, but the message > 20 V will be displayed, marked
with
!
symbol!
If a noise voltage higher than approx. 5 V is present between the H and E or ES and
S test terminals, a cursor mark pointing to the “” (noise) symbol will be
displayed, indicating that the test result may not be correct!
If the resistance of the current or the potential rod is too high (>(4 k + 100 RE) or
>50 k, whichever is lower), the test result will be marked with symbol and the
cursor will appear on Rc and / or Rp.
If the test result is out of the measurement range (open test leads), >19,99 k
message will be displayed!
If the current measured with the sensitive test clamp is lower than 0,5mA, the
cursor will appear on Low IC(low current), indicating that the test result may not be
correct!
This can happen if measuring a large lightning system or in cases of high current
rod resistance.

GEOHM 5 Instrument description
16
If noise current higher than approx. 2,1 A is present in the clamp loop, a cursor
mark pointing to the “” (noise) symbol will be displayed, indicating that the test
result may not be correct! The value of noise current may be also measured in the
CURRENT function, see chapter 2.8.
2.6.3 Earth Resistance measurement with two test clamps
The two clamp principle enables you to perform rodless measurements. Examples of
use are in built up areas where it may be difficult or impossible to drive test probes into
the ground and measurements of complex earthing systems (see figure 8). The
advantage of this principle is that there is no need to drive measurement probes in or to
separate the measured electrodes.
Equivalent electrical circuit diagram of Figure 10 is presented on the figure below.
Figure 10 Equivalent electrical circuit diagram
If the total Earth Resistance of the parallel connected electrodes RE1, RE2, and RE3 is
much lower than the resistance of the tested electrode RE4, then the following result can
be recorded.
Rresult = RE4 + (RE1 // RE2 // RE3) ≈ RE4
This is a good approximation of selective resistance RE4.
Other specific resistances can be measured by moving the test clamps to other electrodes

GEOHM 5 Instrument description
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Step 1
Connect test clamps to the instrument and to the object under test in accordance
with the figure below (test clamps must be at least 30 cm apart).
Figure 11.. Connection of two test clamps
Step 2
Set function switch to “ ” position, the following menu will be displayed:

Figure 12. Earth Resistance initial menu
Step 3
The measurement commences (constant measurement), results are
continuously displayed.
Last result will stay displayed.
Store the displayed result for documentation purpose, see instructions how to use
memory in chapter 3.1.1. Storing of test results.

GEOHM 5 Instrument description
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Notes!
If the test result is out of the measurement range (e.g. open test leads), >99,9 
message will be displayed!
If the current, measured with the sensitive test clamp, is lower than 0,5 mA, the
cursor will appear on Low IC(low current), indicating that the test result may not be
correct!
If the ratio of Noise current / Measurement current 100 or Inoise > 2,1 A, a
cursor mark pointing to the “ ” (noise) symbol will be displayed, indicating that the
test result may not be correct! The value of noise current may be also measured in
the CURRENT function.
Connect the sensitive test clamps (E-CLIP 1) to the C1/C2 test terminals, and the
standard test clamps (E-CLIP 2) to E/H test terminals.
If using a generator clamp other than a recommended, it is necessary to
compensate its impact on the measured results. In this instance use the following
procedure.
To improve measurement results when using third party clamps, it is possible to
reduce the test current. However the accuracy in this instance is not guaranteed.
Procedure for adjusting non original clamp (if used as generator
clamp).
Using a clamp other than that a recommended could seriously impact on the measured
results (due to different coil inductivities).
It is possible to compensate for this effect when using 1/1000 current clamps from
another supplier.
Compensation procedure for non-original clamp:
1. The clamp must have same electrical specification as E-CLIP 2:
current ratio: (1000 A / 1 A)
input current range: 1000 A
1. Perform reset of the instrument (see instructions in chapter 3.3 Reset of the
instrument).
2. The compensation must be performed on a 10 Ω resistive loop.
3. Consider the minimum distance between both clamps.
4. Perform a measurement.
5 After getting the result (it must stay between 3 Ω and 30 Ω) hold the UP key for 10
seconds. If the compensation is successfully performed 'CAL' is displayed.
6. Press now the MEM key to confirm the compensation or any other key to cancel
the procedure.
Note:
Be aware that the published technical specifications are not guaranteed in this case.
The instrument reverts to its factory settings after performing a reset.

GEOHM 5 Instrument description
19
2.7 Specific Earth Resistance
To ensure accurate calculations, it is advisable to measure the Earth Resistivity, when
defining the parameters of the earthing system (required length and surface of earth
electrodes, most appropriate depth for installing the earthing system etc.).
The four test probes are driven in at equal distances “a” to a depth of 5 % of “a”.
The specific Earth Resistance ρ is calculated by the following formula
ρ = 2 π a R
a distance between two probes
R ground resistance between the middle two probes
Different units are used for Earth Resistivity parameter namely:
m (European countries)
ft (The United States)
This is why the Earth Tester offers both units, as well as allowing the use of both units
for the selected distance “a” (m / ft) between the test rods. See the procedure on how to
select appropriate unit in chapter 3.4 General settings.
Step 1
 Connect test leads to the instrument and to test rods, in accordance with the figure below.
Figure 13. Connection of standard 20 m long test leads
The following table shows typical soil resistivity for several types of soil.
Type of Soil
Soil Resistivity E[m]
Wet bog soil
8 ... 60
Arable fields, loam and clay, moist gravel
20 ... 300
Moist, sandy soil
200 ... 600
Dry sandy soil, dry gravel
200 ... 2000
Rocky ground
300 ... 8000
Bedrock
104... 1010
Table 2. Soil Resistivity Efor Various Types of Soil

GEOHM 5 Instrument description
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Step 2
Set function switch to EARTH position, the following menu will be displayed:
m
Figure 14. Earth Resistivity initial menu
Step 3
Set the distance “a” between the test rods. The distance must be the same as the
one used in the practical measurement, otherwise the test result will not be
correct.
Enter “Distance Value adjustment mode”, the following menu will be
displayed:
m
Figure 15. Distance value adjustment menu
Set appropriate Distance “a”. Single press, will increase/decrease the
value for one step, while continuous pressure will increase /
decrease it continuously.
Return to “Earth Resistivity initial menu”.
Step 4
View the test result. (If you want to perform more than one
measurement press the START key and keep it pressed until the
result has stabilized, then release the key. The last result will stay
displayed.)
Check resistances of current (Rc)and potential (Rp) test probe. After
a short period the main results will automatically be displayed again.
Last set distance »a« is flashing.
Available
distances
Step
(m / ft)
(m)
(ft)
1 30
1 90
1