Sonel MRU-20 Operating Manual

OPERATING MANUAL

EARTH RESISTANCE METER

MRU-20

SONEL SA

ul. Wokulskiego 11

58-100 Świdnica

Version 3.1 24/02/2017

OPERATING MANUAL MRU-20 version 3.1

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The MRU-20 meter is a modern, easy and safe measuring device. Please acquaint yourself with the
present manual in order to avoid measuring errors and prevent possible problems related to operation
of the meter.

OPERATING MANUAL MRU-20 version 3.1

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CONTENTS

1 SAFETY ...................................................................................................... 5

2 MEASUREMENTS .................................................................................... 6

2.1 MEASUREMENT OF RESISTANCE USING THREE-POLE METHOD ....................... 6

2.2 MEASUREMENT OF RESISTANCE USING DOUBLE-POLE METHOD, .................... 9

2.3 MEASUREMENT OF THE RESISTANCE OF PROTECTIVE CONDUCTORS AND

EQUIPOTENTIAL BONDINGS .......................................................................... 11

2.4 CALIBRATION OF TEST LEADS ...................................................................... 13

2.4.1 Activation of Autozeroing ........................................................................... 13

2.4.2 Switching-off Autozeroing .......................................................................... 14

3 POWER SUPPLY OF THE METER ..................................................... 16

3.1 MONITORING OF THE POWER SUPPLY VOLTAGE ........................................... 16

3.2 REPLACEMENT OF BATTERIES (RECHARGEABLE BATTERIES ) ...................... 16

3.3 GENERAL PRINCIPLES REGARDING USING NI-MH RECHARGEABLE

BATTERIES ................................................................................................... 18

4 CLEANING AND MAINTENANCE ...................................................... 20

5 STORAGE ................................................................................................ 20

6 DISMANTLING AND UTILIZATION .................................................. 20

7 TECHNICAL DATA ................................................................................ 21

7.1 BASIC DATA................................................................................................. 21

7.2 SUPPLEMENTARY DATA ............................................................................... 23

7.2.1 RE Measurement .......................................................................................... 23

7.2.2 Measurement of R

CONT

................................................................................ 24

8 EQUIPMENT ........................................................................................... 24

8.1 STANDARD EQUIPMENT ............................................................................... 24

8.2 OPTIONAL EQUIPMENT ................................................................................ 24

9 MANUFACTURER ................................................................................... 26

OPERATING MANUAL MRU-20 version 3.1

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OPERATING MANUAL MRU-20 version 3.1

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1 Safety

MRU-20 meter is designed for measuring parameters important for safety of electrical installa­tions. Therefore in order to provide conditions for correct operation and the correctness of the obta­ined results, the following recommendations must be observed:
 Before you proceed to operate the meter, acquaint yourself thoroughly with this manual and ob-

serve the safety regulations and specifications defined by the producer.

 MRU-20 meter is designed to measure earth resistance and the resistance of protective conduc-

tors and equipotential bondings. Any application that differs from those specified in the present
manual may result in a damage to the device and constitute a source of danger for the user.

 The meter must be operated solely by appropriately qualified personnel members holding re-

quired certificates for carrying measurements in electric installations. Unauthorized use of the me­ter may result in its damage and may seriously endanger unauthorized user.

 Using this manual does not exclude the need to comply with occupational health and safety regu-

lations and with other relevant fire regulations required during the performance of a particular type
of work. Before starting the work with the device in special environments, e.g. potentially fire­risk/explosive environment, it is necessary to consult it with the person responsible for health and
safety.

 It is unacceptable to operate the following:

 a damaged meter which is completely or partially out of order,
 a meter with damaged test leads insulation,
 a meter stored for an excessive period of time in disadvantageous conditions (e.g. excessive

humidity).If the meter has been transferred from a cool to a warm environment of a high level
of relative humidity, do not carry out measurements until the meter is warmed up to the am­bient temperature (approximately 30 minutes).

 Before commencing measurements, make sure the test leads are connected to the appropriate

measurement sockets.

 Do not operate a meter with an open or incorrectly closed battery compartment or power it from

sources other than those specified in this manual.

 The inputs of the meter are protected electronically against overload e.g. due to having been con-

nected to a live circuit:

- for all combinations of inputs - up to 276V for 30 seconds.

 Repairs may be carried out only by an authorized service point.
 The device meets the requirements of standards EN 61010-1 and EN 61557-1, -4, -5.

Attention:
The manufacturer reserves the right to introduce changes in appearance, equi­pment and technical data of the meter.

Note:

An attempt to install drivers in 64-bit Windows 8 may result in displaying "In­stallation failed" message.

Cause: Windows 8 by default blocks drivers without a digital signature.
Solution: Disable the driver signature enforcement in Windows.

OPERATING MANUAL MRU-20 version 3.1

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2 Measurements

2.1 Measurement of resistance using three-pole method

The three-pole measuring method is the basic type of resistance-to-earth measurement.

Disconnect earth
electrode being
tested from the
installation of
the building.

Turn on the meter.
Set the rotational func­tion selector
set at RE 3p position.

Using Un button
set test voltage
on 25V or 50V.
After 5 sec. the
meter returns to
the measure­ment mode.
You can also
confirm the
choice by
pressing the
START push­button.

ES H

2,2m

The current electrode (driven into earth) should be connected to H socket of the meter.
The voltage electrode (driven into earth) should be connected to S socket of the meter.
The earth electrode being tested should be connected to E socket of the meter.
The earth electrode being tested and the current electrode and the voltage electrode should
be located one line

OPERATING MANUAL MRU-20 version 3.1

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The meter is ready for
measurement.
Value of interference
voltage is displayed
on the auxiliary di­splay

Press START button.
Carry out the measurement.

Value of interference vol­tage.

Read out main results:
earth electrode resistan-

ce RE.

Auxiliary results may be read
after pushing SEL push-button.

RH
resistance of current

electrode

RS
resistance of voltage

electrode

Measu-
rement
RE 3p

Read the
results

Measu-
rement
RE 3p

Read the
results

OPERATING MANUAL MRU-20 version 3.1

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Value of additional
uncertainty caused by
resistance of the
electrodes.

S

Repeat the measurements (points 3-6) shi­fting the voltage electrode several meters:
the electrode should be shifted farther and
closer to the earth electrode being tested.
If RE measurement results differ from each
other by more than 3%, the distance of the
current electrode from the earth electrode
being tested should be considerably in­creased and the measurements should be
repeated

Note:

Measurement of resistance-to-earth may be carried out if voltage of interferen­ces does not exceed 24 V. Voltage of interferences is measured up to the level
of 100 V but above 50 V it is signaled as dangerous The meter must not be
connected to voltages exceeding 100 V.

- Particular attention should be paid to quality of connection between the object being tested and the
test lead – the contact area must be free from paint, rust, etc.

- If resistance of test probes is too high, RE earth electrode measurement will be burdened with addi­tional uncertainty. Particularly high uncertainty of measurement occurs when a small value of resi­stance-to-earth is measured with probes that have a weak contact with earth (such a situation occurs
frequently when the earth electrode is well made and the upper soil layer is dry and slightly conduc­tive). In such a case, the ratio between resistance of the probes and resistance of the earth electrode
tested is very high and consequently, uncertainty of measurement that depends on this ratio is also
very high. Then according to guidelines defined in section 7 it is possible to calculate the effect of
measurement conditions - or to use the attached chart. This uncertainty is also displayed in [%] as an
additional result. It is calculated on the basis of measured valued. If such additional uncertainty exce-

eds 30% the following symbol is displayed with the measurement result . You can improve the
contact between the probe and soil, for example, by dampening with water the place where the probe
is driven into earth, driving the probe into earth in a different place or using a 80 cm-long probe.
Check also the test leads for possible insulation damage and for corroded or loosened connection be­tween the banana plug and the test lead. In majority of cases the measurement accuracy achieved is
satisfactory. However, you should always be aware of the uncertainty included in the measurement.

- Calibration performed by the manufacturer takes into account the resistance of supplied measure­ment lead of 2.2 m

OPERATING MANUAL MRU-20 version 3.1

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Additional informations displayed by the meter

and

Interference voltage is too high (> 24V) – the measure­ment is impossible.
Turn off the source of interferences or try arrange probes
differently

and

and continuous audio

signal 

Interference voltage is above 50V!
Immediately disconnect the meter!

Before re-connecting, turn off the source of voltage.

and

and continuous audio

signal 

Interference voltage is above 100V!
Immediately disconnect the meter!

Before re-connecting, turn off the source of voltage.

with the name of
an electrode (or elec-

trodes) and

Interruption in measuring circuit or resistance of test pro­bes is higher than 60kΩ.
Please check connections in the measuring circuit or re­duce the resistance of the measuring probe by its reposi­tioning.

and the measure-

ment result and

Uncertainty of RE measurement introduced by the resi­stance of test probes exceeds 30%. Reduce the resistan­ce of the probe by its repositioning, or increase the damp­ness of the ground in the direct vicinity of the probe.

>1,99kΩ

RE measuring range is exceeded .

>50kΩ

Resistance of test probes is higher than 50kΩ (but lower
than 60kΩ).

Interference voltage is above 10V or unstable measure­ment result or measured voltages or currents are low in re­lation to noise.

and

and

long audio signal



Measured voltages or currents are too low in relation to
noise or very unstable measurement result. (Symbol

is displayed instead of the result.)

and

Acceptable temperature inside the meter is exceeded.

2.2 Measurement of resistance using double-pole method,

Turn on the meter.
Set the rotational function se­lector at RE 2p position.

OPERATING MANUAL MRU-20 version 3.1

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UsingUn button
set test voltage
on 25V or 50V.
After 5 sec. the
meter returns
to the measu­rement mode.
You can also
confirm the
choice by
pressing the
START push­button.

E H

2,2m

1,2m

Connect the measured
object to terminalsE
and H of the meter.

The meter is ready for
measurement.
Value of interference
voltage is displayed
on the auxiliary di­splay.

Press START button.
Carry out the measurement.

Value of interference vol­tage.

Read out test results:
The value of measured

resistance.

Note:

- Calibration performed by the manufacturer takes into account the resistance of supplied measure­ment leads of 1.2 m and 2.2 m

OPERATING MANUAL MRU-20 version 3.1

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Additional informations displayed by the meter

and

Interference voltage is too high (> 24V) – the measure­ment is impossible.
Turn off the source of interferences.

and

and continuous audio

signal 

Interference voltage is above 50V!
Immediately disconnect the meter!

Before re-connecting, turn off the source of voltage.

and

and continuous audio

signal 

Interference voltage is above 100V!
Immediately disconnect the meter. (symbol displayed in-

stead of voltage value).
Before re-connecting, turn off the source of voltage.

and

Interruption in measuring circuit.

>1,99kΩ

RE measuring range is exceeded.

Interference voltage is above 10V or unstable measure­ment result or measured voltages or currents are low in re­lation to noise.

and

and

long audio signal



Measured voltages or currents are too low in relation to no­ise or very unstable measurement result. (Symbol is

displayed instead of the result.)

and

Acceptable temperature inside the meter is exceeded.

2.3 Measurement of the resistance of protective conductors and
equipotential bondings

Attention:

When carrying out measurements of very low resistance, or when using leads other
than original (1.2 m and 2.2 m) the calibration of test leads must be performed.

Turn on the meter.
Set the rotational function se­lector at R

CONT

200mA posi-

tion.

OPERATING MANUAL MRU-20 version 3.1

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E S

2,2m

1,2m

Connect the
measured object
to terminals S and
E of the meter.

The meter is ready
for measurement.

Press START button.
Carry out the measurement.

Read out the result.

Note:

- test current flows unidirectionally. To obtain results of a bidirectional current flow, the measurement

should be repeated with replaced test leads and then respective arithmetic mean should be calculated
from both measurements.

OPERATING MANUAL MRU-20 version 3.1

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Additional informations displayed by the meter

and

Interference voltage is too high (> 3Vrms) – the measure­ment is impossible.
Turn off the source of interferences.

and

and continuous audio

signal 

Interference voltage is above 50V!
Immediately disconnect the meter!

Before re-connecting, turn off the source of voltage.

> 199Ω

R

CONT

measuring range is exceeded.

Interference voltage with value of 1..3Vrms during R

CONT

measurement. Obtained test results may be burdened with
additional uncertainty.

and

and

long audio signal



Very unstable measurement result.

2.4 Calibration of test leads

In order to eliminate the impact of the resistance of test leads on measurement result, the com­pensation (autozeroing) of resistance may be performed. Therefore measurement function R

CONT

has

its sub-function called AUTOZERO.

2.4.1 Activation of Autozeroing

Turn on the meter.
Set the rotational function se­lector at R

CONT

ZERO posi-

tion.

E S

Short the test leads by
putting crocodile clips
on exposed ends of the
test leads.

Press START button.
Perform Autozeroing.

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Autozeroing
performed.

Note:

- remember that the resistance of crocodile clips and crocodile-banana connections is added to the

resistance of the test leads.

2.4.2 Switching-off Autozeroing

Turn on the meter.
Set the rotational function se­lector at R

CONT

ZERO posi-

tion.

E

S

Open out the test leads.

Press START button.

Autozeroing was turned
off by the user.
During measurements
the meter will compensa­te the resistance of origi­nal test leads (1.2m and
2,2m.)

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Attention:
It is sufficient to perform single compensation for the test leads. It is stored in
memory even after turning off the meter.

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3 Power supply of the meter

3.1 Monitoring of the power supply voltage

The level of the charge of the batteries or rechargeable batteries is currently indicated by the

symbol in the right upper corner of the display:

Batteries (or rechargeable batteries) charged
Batteries (or rechargeable batteries) low.

Batteries (or rechargeable batteries) need charging!

Note:
 The symbol displayed on the display indicates insufficient power supply voltage and the need

to charge or replace batteries.

 Measurements carried out with insufficient meter power supply voltage are distorted with additio-

nal errors which are impossible to ascertain by the user and thus they cannot constitute a basis
for a conclusion of correctness of the tested earthing.

3.2 Replacement of batteries (rechargeable batteries)

MRU-20 Meter is powered by eight batteries or rechargeable batteries R6 (it is recommended to
use alkaline batteries). Batteries (rechargeable batteries) are inserted into a container in the bottom
part of the casing.

WARNING:
Before replacing the batteries (or rechargeable batteries), disconnect the test
leads from the meter.

In order to replace batteries or the set of rechargeable batteries it is necessary to do the following:

1. Remove all the test leads from the measurement circuit and turn the meter off,

2. Remove the battery compartment (in the bottom of the case) after loosening three screws,

3. Replace all batteries (rechargeable batteries). New batteries or rechargeable batteries must be
inserted observing the correct polarity ("-" on the springy part of the contact plate). Incorrect posi­tion of batteries will not damage the meter or batteries, but the meter with incorrectly inserted bat­teries will not work.

4. Insert the battery compartment and fix it with screws.

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After replacing batteries/ rechargeable batteries the meter, af­ter switching it on, will operate in power supply selection
mode.

Selected power supply: rechar­geable batteries.

Pressing SEL push-button will change the power supply to
batteries.

Another pressing of the push-button will switch
the selection again to rechargeable batteries.

OPERATING MANUAL MRU-20 version 3.1

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Pressing START push-button will confirm the choice
and the meter will be ready for measurement.

NOTE!
After replacing batteries (rechargeable batteries), set the type of power supply
in order to enable correct display of battery charging level (charging characte­ristics of batteries and rechargeable batteries are different).

NOTE!
If batteries leak inside the battery compartment the meter should be serviced.

Rechargeable batteries should be charged in an external charger.

3.3 General principles regarding using Ni-MH rechargeable batte­ries

- If you do not use the device for a prolonged period of time, then it is recommended to remove the

rechargeable batteries and store them separately.

- Store the rechargeable batteries in a dry, cool and well ventilated place and protect them from direct

sunlight. Ambient temperature in case of prolonged storage should not exceed 30°C. If the recharge-
able batteries are stored for a long time in a high temperature, then occurring chemical processes
may reduce their lifetime.

- NiMH rechargeable batteries are usually last for 500-1000 charging cycles. This rechargeable batte-

ries reach their maximum capacity after being formatted (2-3 charge and discharge cycles). The most
important factor which influences the lifetime a rechargeable battery is the level of its discharging. The
deeper the discharge level, the shorter lifetime of a rechargeable battery.

- The memory effect is limited in case of NiMH rechargeable batteries. These rechargeable batteries

may be charged at any point with no serious consequences. However, it is recommended to dischar­ge them completely every few cycles.

OPERATING MANUAL MRU-20 version 3.1

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- During storage, Ni-MH rechargeable batteries are discharged at the rate of approximately 30% per

month. Storing rechargeable batteries in high temperatures may increase this rate even to 60%. In
order to prevent excessive discharge of rechargeable batteries, after which it would be necessary to
format them, it is recommended to charge the accumulators from time to time (even if not used).

- Modern quick-chargers detect both too low and too high temperature of rechargeable batteries and

they react to this situation adequately. When the temperature is too low, charging is prevented as it
may irreparably damage rechargeable batteries. Increased temperature of rechargeable batteries is a
signal to stop charging and it is a typical phenomenon. However charging at high ambient temperatu­res reduces the lifetime of batteries and causes faster increase of their temperature, preventing char­ging to the full capacity.

- Remember that in the case of quick charging, rechargeable batteries are charged to approximately

80% of their capacity; better results may be obtained if the process of charging is continued: the
charger goes then to the phase of charging with a low current and after next couple of hours the re­chargeable batteries are charged to their full capacity

- Do not charge or use rechargeable batteries in extreme temperatures. Extreme temperatures reduce

the lifetime of batteries and rechargeable batteries. Avoid locating devices powered by rechargeable
batteries in very hot places. The nominal working temperature must be absolutely observed.

OPERATING MANUAL MRU-20 version 3.1

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4 Cleaning and maintenance

NOTE!

Apply only maintenance methods specified by the manufacturerin this manual.

The casing of the meter and its case may be cleaned with a soft, damp cloth using all-purpose
detergents. Do not use any solvents or cleaning agents which might scratch the casing (powders, pa­stes, etc.).
Clean the probes with water and dry it. Before the probes are stored for a prolonged period of time
it is recommended to grease them with any machine lubricant.
The reels and test leads should be cleaned with water and detergents, and then dried.

The electronic system of the meter does not require maintenance.

5 Storage

The following recommendations must be observed to ensure proper storing of the device:

 Disconnect all the test leads from the meter.
 Clean the meter and all its accessories thoroughly.
 Wind the long test leads onto the reels.
 If the meter is to be stored for a prolonged period of time, the batteries must be removed from the

device.

 in order to prevent total discharge of the rechargeable batteries during prolonged storage, charge

them from time to time.

6 Dismantling and utilization

Worn-out electric and electronic equipment should be collected selectively, i.e. it must not be di­sposed with waste of another kind.

Worn-out electronic equipment should be sent to a collection point in accordance with regulations

related to Waste Electrical and Electronic Equipment.

Before the equipment is sent to a collection point, do not attempt to dismantle any elements.
Observe the local regulations concerning disposal of packages, worn-out batteries and accumula-

tors.

OPERATING MANUAL MRU-20 version 3.1

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7 Technical data

 Specified accuracy relates to terminals of the meter.
 „m.v.” abbreviation indicated standard measured value.

7.1 Basic data

Measurement of resistance-to-earth RE

Measurement method: technical, according to IEC 61557-5
Test range according to IEC 61557-5: 0,50 ... 1,99k for Un=50V
0,68 ... 1,99k for Un=25V

Ranges

of display

Resolution

Basic uncertainty

0,00...9,99

0,01

(2% m.v. + 3 digits)

10,0...99,9

0,1

100...999

1

1,00...1,99k

0,01k

 In the three-pole method, the uncertainty caused by resistance of probes is calculated and di-

splayed by the meter. It can also be estimated using the following chart:

0,0010

0,0100

0,1000

1,0000

10,0000

100,0000

1 10 100 1000 10000 100000

Rezystancja elektrody napięciowej Rs[]

Błąd dodatkowy od rezystancji elektrod [%]

RH/RE=0,3

RH/RE=1

RH/RE=3

RH/RE=10

RH/RE=30

RH/RE=100

RH/RE=300

RH/RE=1000

RH/RE=3000

uziemienia aRezystancj

ądowejpr elektrody aRezystancj



E

H

R

R

Influence of the resistance of electrodes on measurement uncertainty

Voltage electrode resistance Rs[]

Additional uncertainty caused by r

esistance of probes [%]

resistanceEarth

resistance electrodeCurrent



E

H

R

R

OPERATING MANUAL MRU-20 version 3.1

22

Measurement of auxiliary electrodes resistance RH, R

S

Ranges

of display

Resolution

Basic uncertainty

000...999

1

(5% (RS + RE + RH) + 3 digits)

1,00...9,99k

0,01k

10,0...50,0k

0,1k

Measurement of interference voltages

Internal resistance: approx. 100k

Range

Resolution

Basic uncertainty

0...100V

1V

(2% m.v. + 3 digits)

Measurement of R

CONT

Measurement method: technical
Test range according to IEC 61557-4: 0,13…199 

Display range

Resolution

Basic uncertainty

0,00...9,99

0,01

(2% m.v. + 3 digits)

10,0...99,9

0,1

100...199

1

Note: Only values containing tolerances or boundary values are considered as guaranteed data. Va­lues without tolerances are for informational purposes only.

Other technical data

a) type of insulation .................................................... double, according to EN 61010-1 and IEC 61557

b) measurement category .................................................................. IV 300V according to EN 61010-1

c) degree of housing protection acc. to EN 60529 .......................................................................... IP54

d) maximum voltage of interferences at which RE measurement is performed ................................. 24V

e) maximum voltage of interferences at which R

CONT

measurement is performed .............................. 3V

f) maximum measured voltage of interferences ............................................................................ 100V

g) frequency of RE test current .................................................................................................... 125 Hz

h) test voltage RE .................................................................................................................. 25V or 50V

i) test current RE .......................................................................................................................... 20mA

j) maximum resistance of test electrodes ..................................................................................... 50k

k) R

CONT

measuring current (with shorted terminals for U

BAT

 9,0V) .......................................... 200mA

l) maximum voltage on open terminals for R

CONT

............................................................................ 13V

m) power supply of the meter ........... alkaline batteries or NiMH rechargeable batteries, size AA (8 pcs)

n) number of RE measurements ..................................................... > 1000 (5, 2 measurements /min.)

o) dimensions ............................................................................................................... 260x190x60 mm

p) weight of the meter with batteries ................................................................................ approx. 1.3 kg

q) display ............................................................................................................... LCD with a backlight

r) working temperature ......................................................................................................... -10..+55C

s) nominal temperature........................................................................................................... +23 ± 2C

t) storage temperature ...................................................................................................... -20C..+70C

u) relative humidity .................................................................................................................... 20..90%

v) relative humidity nominal ................................ ................................................................ ....... 40..60%

w) altitude (above sea level) ....................................................................................................... <2000m

x) time of automatic switch-off ................................................................................................ 5 minutes

y) electromagnetic compatibility ..................................... according to EN 61000-6-3 and EN 61000-6-2

z) quality standard, execution, design and manufacturing are ISO 9001 compliant

OPERATING MANUAL MRU-20 version 3.1

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7.2 Supplementary data

Data on additional uncertainties are useful mainly when the meter is used in non-standard condi-

tions and for meteorological laboratories during calibration.

7.2.1 RE Measurement

7.2.1.1 Additional uncertainty caused by resistance of auxiliary electrodes

 

%105,1

004,0

150

100000

28



























H

E

H

S

S

dod

R

R

R

R

R



RS < 5k

 

%105,1

004,0

5,7

28























H

E

H

dod

R

R

R



RS ≥ 5k

RE, RH and RS are values indicated by the meter in [.The above uncertainty is calculated by the

meter and displayed as ER.

7.2.1.2 Additional uncertainty caused by serial interference voltage

RE

Additional uncertainty []

0,00...9,99

±(0,01RE + 0,012)Uz ± 0,003U

z

2

10,0...99,9

±(0,001RE + 0,05)Uz ± 0,001U

z

2

100...1,99k

±(0,001RE + 0,5)Uz ± 0,001U

z

2

7.2.1.3 Additional uncertainty caused by ambient temperature:

± 0,25 digits /°C

7.2.1.4 Additional uncertainties according to IEC 61557-5

Operational uncertainty or

significant parameter

Reference conditions or

range of use

Designation

Additional

uncertainty

Position

Reference

position ±90°

E1

0

Supply voltage

U

nom

÷ U

min

E2

0

Temperature

0 ÷ 35°C

E3

according to

the formula

defined in

7.2.1.3

Serial

interference voltage

3V

E4

according to

the formula

defined in

7.2.1.2

Resistance of probes and

auxiliary earth electrodes

From 0 to 100RE, but ≤

50kΩ

E5

according to

the formula

defined in

7.2.1.1

Operational uncertainty





2

5

2

4

2

3

2

2

2

1

15,1 EEEEEAB 

where A = basic uncertainty

OPERATING MANUAL MRU-20 version 3.1

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7.2.2 Measurement of R

CONT

7.2.2.1 Additional uncertainty caused by ambient temperature:

±0,15%/°C

7.2.2.2 Additional uncertainties according to IEC 61557-4

Operational uncertainty or

significant parameter

Reference conditions or

range of use

Designation

Additional

uncertainty

Position

Reference

position ±90°

E1

0

Supply voltage

U

nom

÷ U

min

E2

0

Temperature

0 ÷ 35°C

E3

according to

the formula

defined in

7.2.2.1

Operational uncertainty





2

3

2

2

2

1

15,1 EEEAB 

where A = basic uncertainty

8 Equipment

8.1 Standard Equipment

Standard set of equipment supplied by the manufacturer includes:

 MRU-20 meter – WMPLMRU20,
 AA batteries (8 pcs)
 set of test leads:

 lead (30m), red, on a reel, ended with banana plugs – WAPRZ030REBBSZ,
 lead (15m) on a reel, ended with banana plugs – WAPRZ015BUBBSZ,
 lead (2.2m), black, ended with banana plugs– WAPRZ2X2BLBB,
 lead (1.2m) blue, ended with banana plugs WAPRZ1X2REBB,
 crocodile clip, blue K02 – WAKROBU20K02,
 crocodile clip, black K01 – WAKROBL20K01,

 earth contact test probe (rod) 30cm (2 pcs) – WASONG30,
 carrying case for the meter and its equipment – WAFUTL4,
 harness for the meter – WAPOZSZE2,
 operating manual,
 calibration certificate.

8.2 Optional Equipment

Additionally, the following items not included in the scope of standard equipment may be purcha-

sed from the manufacturer or the distributors:

OPERATING MANUAL MRU-20 version 3.1

25

WAPRZ025BUBBSZ

 Test lead, 25m (blue)

WAPRZ050YEBBSZ

 Test lead 50m

WAPOZSZP1

 reel for winding test leads

WASONG80

 earth contact test probe (rod) (80 cm)

WAFUTL3

 probe protective cover 80cm

 cramp

LSWPLMRU20

 calibration certificate

OPERATING MANUAL MRU-20 version 3.1

26

9 Manufacturer

The manufacturer of the device, which also provides guarantee and post-guarantee service is the
following company:

SONEL S.A.

ul. Wokulskiego 11

58-100 Świdnica

Poland
tel. [phone]
fax [phone]

E-mail: [email protected]

Web page: www.sonel.pl

Attention:

Service repairs must be realized only by the manufacturer.