Sonel MRU-21 Operation Manual

OPERATING MANUAL

Earth Resistance Meter

MRU-21

SONEL SA

ul. Wokulskiego 11

58-100 Świdnica, Poland

Version 1.04 28.04.2017

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The MRU-21 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.

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CONTENTS

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

2 SETTINGS ................................................................................................................ 6

3 MEASUREMENTS .................................................................................................. 7

3.1 EARTH RESISTANCE MEASUREMENT WITH THE THREE-LEAD METHOD ................... 7

3.2 EARTH RESISTANCE MEASUREMENT WITH THE DOUBLE-LEAD METHOD .............. 10

3.3 MEASUREMENT OF RESISTANCE OF PROTECTIVE CONDUCTORS AND

EQUIPOTENTIAL BONDING ................................................................................... 12

3.4 CALIBRATION OF TEST LEADS .............................................................................. 14

3.4.1 Turning AUTOZERO on .............................................................................. 14

3.4.2 Turning AUTOZERO off .............................................................................. 15

4 MEMORY ............................................................................................................... 16

4.1 STORING THE MEASUREMENT RESULT DATA IN THE MEMORY ............................. 16

4.2 VIEWING MEMORY DATA ..................................................................................... 18

4.3 DELETING MEMORY DATA ................................................................................... 18

4.3.1 Deleting bank data....................................................................................... 18

4.3.2 Deleting the whole memory ......................................................................... 20

4.4 COMMUNICATION WITH A COMPUTER ................................................................. 21

4.4.1 Computer connection accessories ............................................................... 21

4.4.2 Data transmission ........................................................................................ 21

5 METER POWER SUPPLY ................................................................................... 22

5.1 MONITORING OF THE POWER SUPPLY VOLTAGE ................................................... 22

5.2 REPLACEMENT OF BATTERIES ............................................................................. 22

6 CLEANING AND MAINTENANCE .................................................................... 25

7 STORAGE .............................................................................................................. 25

8 DISMANTLING AND UTILIZATION ................................................................ 25

9 TECHNICAL SPECIFICATIONS ....................................................................... 26

9.1 BASIC DATA ........................................................................................................ 26

9.2 ADDITIONAL INFORMATION ................................................................................. 28

9.2.1 RE measurement ........................................................................................... 28

9.2.2 R

CONT

measurement ...................................................................................... 29

10 EQUIPMENT ......................................................................................................... 30

10.1 STANDARD EQUIPMENT ....................................................................................... 30

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10.2 OPTIONAL ACCESSORIES ..................................................................................... 30

11 MANUFACTURER ............................................................................................... 31

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1 Safety

MRU-21 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

observe the safety regulations and specifications defined by the producer.

 MRU-21 meter is designed to measure earth resistance and the resistance of protective

conductors 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

required 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

regulations 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

connected 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.

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2 Settings

Press the SET button to select the test voltage (Un) or power supply source (SuPP). After
replacing the batteries, always set the power supply type. The correct charge indication depends on
this setting (the discharge characteristics of disposable and rechargeable batteries are different).

Turn on the meter and press SET.

Use the and buttons to select the parameter: Un or
SuPP.

Use the and buttons to change the parameters: Un
= 25V or 50V, SuPP = bAt (disposable batteries) or Acc
(rechargeable batteries).

Press ENTER to validate the changes and exit the mode, or...
...press ESC to exit the setting mode without validating the changes.

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3 Measurements

3.1 Earth resistance measurement with the three-lead method

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

Disconnect the tested
earth electrode from the
installation of the facility.

Turn on the meter.
Turn the rotary switch
to the RE 3p position.

If necessary, adjust the voltage measurement according to section 2.

2,2m

CAT IV 300V

E S H

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 tested earth electrode should be connected to E socket of the meter.
The tested earth electrode and the current electrode and the voltage electrode should be
aligned.

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The meter is ready
for measurement.
Read the
interference voltage
on the auxiliary
display.

Press START.
Perform the measurement.

Interference voltage.

Read the main
measurement result.

Resistance of earth
electrode RE.

Read the auxiliary results (sequence as
below) by pressing << and >>.

RH
Resistance of current

electrode

RS
Resistance of voltage

electrode

Additional uncertainty
caused by resistance of
the electrodes.

Measur
ement
of RE
3p

Reading
the
results.

Measur
ement
of RE
3p

Reading
the
results.

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S

Repeat the measurements (steps 3-6)
after moving the voltage a few meters ­placing it farther and closer to the
measured earth electrode. If the R

E

measurement results differ by more than
3%, the distance of the current electrode
from the tested earth electrode should be
considerably increased and the
measurements should be repeated.

Note:

The earth resistance measurement can be made when the interference voltage
does not exceed 24V. The voltage is measured up to 100V, but above 50V is
indicated as dangerous. The meter must not be connected to voltages
exceeding 100 V.

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

- If resistance of the test probes is too high, RE earth electrode measurement will include an additional
uncertainty. Particularly high measurement uncertainty 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 poorly conductive). In such a
case, the ratio of resistance of the probes to resistance of the tested earth electrode is very high and
consequently, uncertainty of measurement that depends on this ratio is also very high. Then, you can
make a calculation according to the formulas given in item 9 to estimate the influence of
measurement conditions, or you can use the graph also included in the appendix. This uncertainty is
also displayed in [%] as an additional result. It is calculated on the basis of measured valued. If such

additional uncertainty exceeds 30% the symbol is displayed 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, one should always be aware of the uncertainty included in the measurement.

- Factory calibration includes the resistance of the 2.2 m test lead (supplied).

Additional information displayed by the meter

and

Excessive interference voltage (> 24V). The measurement is
not possible.
Disconnect the source of interference or try another location of
the probes.

and

and continuous

audio signal 

Interference voltage exceeds 50V!
Disconnect the meter immediately!

Disconnect the voltage source before you reconnect the
meter.

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and

and continuous

audio signal 

Interference voltage exceeds 100V!
Disconnect the meter immediately!

Disconnect the voltage source before you reconnect the
meter.

with the

electrode

(electrodes) name

and

Interruption in measuring circuit or resistance of test probes
higher than 60 kΩ.
Check connections in the test circuit or reduce the probe
resistance by driving it into the soil again.

(in the field

below Cell) and

measurement result

and

Uncertainty of the RE measurement caused by probes
resistance exceeds 30%. Reduce the probe resistance by
driving it into the soil again or by dampening the soil in its
immediate vicinity.

>1,99kΩ

The RE measuring range is exceeded.

>50kΩ

Test probes resistance above 50kΩ (but below 60kΩ).

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

and and

long audio signal



Measured voltages or currents are too low in relation to the
noise, or highly unstable measurement result. (The

symbol is displayed instead of the result).

and

Maximum allowed temperature inside the meter is exceeded.

3.2 Earth resistance measurement with the double-lead method

Turn on the meter.
Turn the rotary switch
to the RE 2p position.

If necessary, adjust the voltage measurement according to section

2.

2,2m

1,2m

CAT IV 300V

E H

Connect the tested
facility to the E and H
terminals.

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The meter is ready
for measurement.
Read the interference
voltage on the
auxiliary display.

Press START.
Perform the measurement.

Interference voltage.

Read the measurement
result.

Measured resistance.

Note:

- Factory calibration includes the resistance of the 1.2 m and 2.2 m test leads (supplied).

Additional information displayed by the meter

and

Excessive interference voltage (> 24V). The measurement is
not possible.
Disconnect the source of interference.

and

and continuous

audio signal 

Interference voltage exceeds 50V!
Disconnect the meter immediately!

Disconnect the voltage source before you reconnect the
meter.

and

and continuous

audio signal 

Interference voltage exceeds 100V!
Disconnect the meter immediately! (The symbol is

displayed instead of the interference voltage).
Disconnect the voltage source before you reconnect the
meter.

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and

Interruption in the test circuit.

>1,99kΩ

The RE measuring range is exceeded.

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

and and

long audio signal



Measured voltages or currents are too low in relation to the
noise, or highly unstable measurement result. (The

symbol is displayed instead of the result).

and

Maximum allowed temperature inside the meter is exceeded.

3.3 Measurement of resistance of protective conductors and

equipotential bonding

NOTE

Calibrate the test leads when measuring very small resistance values or when using
test leads different than the supplied 1.2 m and 2.2 m.

Turn on the meter.
Turn the rotary switch
to the R

CONT

position.

2,2m

1,2m

CAT IV 300V

E

S

Connect
the tested
facility
to the S
and E
terminals.

The meter is ready
for measurement.

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Press START.
Perform the measurement.

Read the measurement
result.

Note:

- The test current flows in one direction. To obtain the result for both directions, switch the test leads
and perform the measurement again, then calculate the arithmetic mean of both results.

Additional information displayed by the meter

and

Excessive interference voltage (> 3Vrms). The measurement
is not possible.
Disconnect the source of interference.

and

and continuous

audio signal 

Interference voltage exceeds 50V!
Disconnect the meter immediately!

Disconnect the voltage source before you reconnect the
meter.

> 199Ω

The R

CONT

measuring range is exceeded.

1..3Vrms interference voltage during the R

CONT

measurement.
Measurement is slightly unstable. The results may include an
additional uncertainty.

and and

long audio signal



Measurement is highly unstable.

and

Maximum allowed temperature inside the meter is exceeded.

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3.4 Calibration of test leads

In order to eliminate the impact of the resistance of test leads on the measurement result, the
compensation (autozeroing) of resistance may be performed. This is made with the AUTOZERO
function in the Rcont measurement.

3.4.1 Turning AUTOZERO on

Turn on the meter.
Turn the rotary switch
to the the R

CONT

ZERO

position.

CAT IV 300V

E S

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

Press START.
Perform autozeroing.

Autozeroing
completed.

Note:

- Remember that the resistance of crocodile clips and crocodile-banana connections is added to the
resistance of the test leads.

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3.4.2 Turning AUTOZERO off

Turn on the meter.
Turn the rotary switch
to the the R

CONT

ZERO

position.

CAT IV 300V

E S

Disconnect the test
leads.

Press START.

Autozeroing is off.
During the
measurements, the
meter will compensate
the resistance of the
supplied 1.2 m and 2.2
m leads.

NOTE
It suffices when the compensation for given test leads is performed only once.
It is remembered when the meter is turned off.

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4 Memory

The MRU-21 meters feature memory that can store 990 single measurement results The whole
memory is divided into 10 memory banks, with 99 cells in each bank. Each measurement result can
be stored in a memory cell marked with a selected number and in a selected memory bank. Thanks to
this, the user of the meter can, at his/her option, assign memory cell numbers to individual
measurement points and the memory bank numbers to individual facilities. The user can also perform
measurements in any sequence and repeat them without losing other data.

Memory of measurement result data is not deleted when the meter is switched off. Thanks to
this, the data can be later read or sent to a computer. The number of a current memory cell or
memory bank is not changed either.

Note:

- One cell can contain the results of a single measurement.

- After each entry of the measurement result to the cell, its number is automatically incremented.

- It is recommended to delete the memory after reading the data or before performing a new series of
measurements that may be stored into the same memory cells as the previous ones.

4.1 Storing the measurement result data in the memory

Press ENTER after completion of
the measurement.
The meter is in the memory
storing mode.

Cell is empty.

Use the and symbols to select the
bank...

or use the and symbols to select the
cell.

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Press ENTER again. The screen (shown below)
appears for a moment, accompanied by three
short beeps, and then the meter returns to
display the last result of the measurement.

An attempt to overwrite a result causes
the warning symbol to appear.

lub

Press ENTER to overwrite the
result or ESC to abort.

Note:

- Stored in the memory is a complete set of results (main result and supplementary results), as well
as the test voltage for RE.

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4.2 Viewing memory data

Turn on the meter.
Turn the rotary switch
to the MEM position.

The content of the last saved
cell appears.

Use the and symbols to select the
bank...

or use the and symbols to select the
cell.

Press << or >> to view additional results.

4.3 Deleting memory data

4.3.1 Deleting bank data

Turn on the meter.
Turn the rotary switch
to the the MEM
position.

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Set the bank number
to be deleted.
Set the cell number
before “1”...

...the cell number
disappears, and
appears the symbol

indicating the

readiness to delete.

Press ENTER .

The “?” and
symbols appear,
asking you to
confirm deletion.

lub

Press ENTER to start deleting or ESC
to abort.

The deletion
progress is
shown on the
display as
dashes (each
dash means
25%). When
deletion is
complete, the
meter
generates
three short
beeps and
sets the cell
number to "1".

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4.3.2 Deleting the whole memory

Turn on the meter.
Turn the rotary switch
to the MEM position.

Set the bank number
between “0” and “9”...

...the bank number
disappears, and
appears the symbol

, indicating the

readiness to delete.

Press ENTER .

The “?” and
symbols appear,
asking you to
confirm deletion.

lub

Press ENTER to start deleting or
ESC to abort.

The deletion
progress is shown
on the display as
dashes (each dash
means 25%).

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When deletion is
complete, the
meter generates
three short beeps
and sets the bank
number to "0" and
the cell number to
"1".

4.4 Communication with a computer

4.4.1 Computer connection accessories

What is necessary in order to operate the meter with a computer is additional accessories,
namely a cable for serial transmission and appropriate software. If this package has not been
purchased along with the meter, it can be bought from the manufacturer or an authorized distributor
where detailed software information is also available.

4.4.2 Data transmission

If the rotary switch is in the MEM position, after detecting the USB connection with a computer the
meter automatically goes to the data transmission mode and displays the following screen.

To transmit data, follow the instructions of the software.

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5 Meter power supply

5.1 Monitoring of the power supply voltage

The charge level of the batteries or rechargeable batteries is indicated by the symbol in the right

upper corner of the display on a current basis:

Batteries charged
Batteries discharged

Replace or recharge the batteries!

Note:
 The symbol on the display means insufficient power supply voltage and the need to replace

or recharge the batteries.

 Measurements performed with an insufficient supply voltage feature additional errors which the

user is unable to evaluate. Consequently, such measurements cannot prove that the tested
earthing system is correct.

5.2 Replacement of batteries

The MRU-21 is powered by four R14 disposable or rechargeable batteries (alkaline batteries are
recommended). The disposable or rechargeable batteries are placed in the compartment at the
bottom of the enclosure.

WARNING:

Before replacing the batteries, disconnect the test leads from the meter.

To replace the batteries:

 remove all test leads from the sockets and turn the meter off,
 remove the four screws of the battery compartment (in the lower part of the enclosure),
 remove the compartment and take off the lid (use a tool),
 remove and replace all batteries, observing the correct polarity when putting new batteries ("-" on

the spring). Reverse polarity will not damage the meter or the batteries, but the meter will not
work.

 put on the lid, place the compartment and secure it with 4 screws.

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After replacement of batteries, the meter when turned on,
starts in the power supply selection mode.

Selected power supply:
rechargeable batteries:

Use the and symbols to select the power
supply: bAt (disposable batteries) or Acc
(rechargeable batteries).

Press ENTER to validate the choice
The meter goes to the measurement readiness mode.

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NOTE!
After replacing the batteries, always set the power supply type. The correct
charge indication depends on this setting (the discharge characteristics of
disposable and rechargeable batteries are different).

NOTE!
Have the meter serviced in case of battery leakage inside the compartment.

Batteries must be recharged in an external charger.

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6 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.

7 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.

8 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

accumulators.

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9 Technical specifications

 The specified accuracy relates to the meter terminals.
 "m.v" means a standard measured value.

9.1 Basic data

Measurement of resistance to earth RE

Measurement method: technical, conforming with IEC 61557-5.
Measuring range acc. to IEC 61557-5: 0.50 ... 1.99kfor Un=50V

0.68 ... 1.99kfor Un=25V

Display range

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-lead method, the meter displays the uncertainty caused by the probes resistance.

Such uncertainty can be also evaluated using the following diagram:

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

Electrodes resistance and measurement uncertainty

Additional uncertainty caused by r

esistance of probes [%]

Voltage electrode resistance Rs[]

resistanceEarth

resistance electrodeCurrent



E

H

R

R

OPERATING MANUAL MRU-21 version 1.04

27

Measurement of resistance of auxiliary earth electrodes RH, R

S

Display range

Resolution

Measurement 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: about 100k

Display range

Resolution

Measurement uncertainty

0...100V

1V

(2% m.v. + 3 digits)

R

CONT

measurement
Measurement method: technical
Measuring range according to IEC 61557-4: 

Display range

Resolution

Measurement uncertainty

0.00...9.99

0.01

(2% m.v. + 3 digits)

10.0...99.9

0.1

100...199

1

Note: Guaranteed are only the values with tolerances or limits. Values without tolerances are for
information only.

Other technical specification

a) type of insulation .................................................. double, PN-EN 61010-1 and IEC 61557 compliant

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

c) degree of protection of enclosure acc. to PN-EN 60529 ............................................................. IP54

d) maximum interference voltage for the RE measurement .............................................................. 24V

e) maximum interference voltage for the R

CONT

measurement ........................................................... 3V

f) maximum measured interference voltage .................................................................................. 100V

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

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

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

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

k) R

CONT

test current (with shorted terminals for U

BAT

 6,0V) .................................................... 200mA

l) maximum voltage at open terminals for R

CONT

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

m) meter power supply .................................. R14 alkaline disposable or rechargeable batteries (4 pcs)

n) number of RE measurements ............................................ > 1000 (5, 2 measurements per minute)

o) dimensions ........................................................................................................... 288 x 223 x 75 mm

p) weight with batteries ....................................................................................................... about 1,4 kg

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

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

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

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

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

v) reference humidity ................................................................................................................ 40...60%

w) time to AUTO-OFF ............................................................................................................. 5 minutes

x) the product meets the EMC requirements acc. to PN-EN 61326-1:2006 and PN-EN 61326-2-2:2006

y) quality standard ............................. development, design and manufacturing are ISO 9001 compliant

OPERATING MANUAL MRU-21 version 1.04

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9.2 Additional information

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

conditions and for metrological laboratories for the purpose of calibration.

9.2.1 RE measurement

9.2.1.1 Additional uncertainty caused by resistance of auxiliary earth electrodes:

0%

RH and RS ≤ 100

7.5%

(RH ≥ 5k or RS ≥

5k) and RE ≥ 500

 

%105,1

004,0

5,7

28























H

E

H

dod

R

R

R



RS ≥ 5k and RE ≤

500

 

%105,1

004,0

150

100000

28



























H

E

H

S

S

dod

R

R

R

R

R



remaining cases

The meter displays RE, RH and RS in [.This uncertainty is calculated by the meter and

displayed as ER.

9.2.1.2 Additional uncertainty caused by serial interference voltage

RE

Uwy

Additional uncertainty []

0.00…9.99
25V

(0.01RE + 0.012)Uz  0.007U

z

2

50V

(0.01RE + 0.012)Uz  0.003U

z

2

10.0…99.9

25V. 50V

(0.001RE + 0.05)Uz  0.001U

z

2

100…1.99k

(0.001RE + 0.5)Uz  0.001U

z

2

9.2.1.3 Additional uncertainty caused by ambient temperature

± 0.25 digit/°C for Uwy = 50V, ± 0.33 digit/°C for Uwy = 25V

9.2.1.4 Additional uncertainties according to IEC 61557-5

Working uncertainty or

influencing factors

Reference conditions or

operating range

Designation

Additional

uncertainty

Position

Reference position

±90°

E1

0

Power supply voltage

U

nom

÷ U

min

E2

0

Storage temperature

0 ÷ 35°C

E3

acc. to

formula

from 9.2.1.3

Serial interference voltage

3V

E4

acc. to

formula

from 9.2.1.2

Resistance of probes and

auxiliary earth electrodes

From 0 to 100RE, but ≤

50kΩ

E5

acc. to

formula

from 9.2.1.1

Working uncertainty





2

5

2
4

2

3

2

2

2

1

15,1 EEEEEAB 

where A = measurement uncertainty

OPERATING MANUAL MRU-21 version 1.04

29

9.2.2 R

CONT

measurement

9.2.2.1 Additional uncertainty caused by ambient temperature

±0.15%/°C

9.2.2.2 Additional uncertainties according to IEC 61557-4

Working uncertainty or

influencing factors

Reference conditions or

operating range

Designation

Additional

uncertainty

Position

Reference position

±90°

E1

0

Power supply voltage

U

nom

÷ U

min

E2

0

Storage temperature

0 ÷ 35°C

E3

±0.15%/°C

Working uncertainty





2

3

2

2

2

1

15,1 EEEAB 

where A = measurement uncertainty

OPERATING MANUAL MRU-21 version 1.04

30

10 Equipment

10.1 Standard equipment

Standard set of equipment supplied by the manufacturer includes:

 MRU-21 meter – WMPLMRU21,
 set of test leads:

 30m lead on the reel (red) with banana plugs – WAPRZ030REBBSZ,
 15m lead on the reel (blue) with banana plugs – WAPRZ015BUBBSZ,
 2.2m lead (black) with banana plugs– WAPRZ2X2BLBB,
 1.2m lead (blue) with banana plugs – WAPRZ1X2BUBB,
 K01 crocodile clip, black – WAKROBL20K01,
 K02 crocodile clip, blue – WAKROBU20K02,

 30cm test probe (2 pcs.) – WASONG30,
 carrying case for the meter and accessories ,
 harness (2 pcs, long and short) -WAPOZSZEKPL,
 USB cable – WAPRZUSB,
 LR14 batteries, (4 pcs),
 SONEL CD,
 operating manual,
 warranty card,
 calibration certificate

10.2 Optional accessories

Additionally, the following items that are not included in the scope of standard equipment can be

purchased from the manufacturer or the distributors:

WAPRZ025BUBBSZ

 25m test lead (blue)

WAPRZ050YEBBSZ

 50m test lead

WAZACIMA1

 vise

LSWPLMRU21

 calibration certificate

OPERATING MANUAL MRU-21 version 1.04

31

WASONG80

 80cm test probe

WAFUTL3

 cover for the 80cm test probe

11 Manufacturer

The manufacturer of the device and provider of warranty and post-warranty service:

SONEL S.A.

ul. Wokulskiego 11

58-100 Świdnica

Poland
tel. [phone]
fax [phone]

E-mail: [email protected]

Web page: www.sonel.pl

NOTE

Service repairs must be performed solely by the manufacturer.

OPERATING MANUAL MRU-21 version 1.04

32