METREL MI 3205 User manual

TeraOhm XA 5 kV
MI 3205
Instruction manual
Version 1.1; Code No. 20 752 446

2
Distributor:
Manufacturer:
METREL d.d.
Ljubljanska cesta 77
1354 Horjul
Slovenia
web site: http://www.metrel.si
e-mail: [email protected]
Mark on your equipment certifies that this equipment meets the requirements of the EU
(European Union) concerning safety and electromagnetic compatibility regulations
© 2015 METREL
No part of this publication may be reproduced or utilized in any form or by any means
without permission in writing from METREL.

MI 3205 TeraOhm XA 5kV Table of contents
3
Table of contents
1General Description ............................................................................................ 5
1.1 Features........................................................................................................ 5
2Safety and operational considerations ............................................................. 6
2.1 Warnings and notes...................................................................................... 6
2.2 Battery and charging of Li-ion battery pack................................................... 8
2.2.1 Precharge .............................................................................................. 9
2.2.2 Li – ion battery pack guidelines............................................................ 11
2.3 Standards applied....................................................................................... 12
3Instrument description ..................................................................................... 13
3.1 Instrument casing ....................................................................................... 13
3.2 Operator’s panel ......................................................................................... 13
3.3 Accessories ................................................................................................ 15
3.3.1 Test leads ............................................................................................ 15
3.4 Display organization.................................................................................... 16
3.4.1 Measurement result window ................................................................ 16
3.4.2 Measurement control window .............................................................. 17
3.4.3 Message window ................................................................................. 18
3.4.4 Battery, time and communication indication ........................................ 19
3.4.5 Measurement result line ...................................................................... 20
3.4.6 Graphical presentation of measured data............................................ 20
3.4.7 Backlight operation .............................................................................. 20
4Main menu ......................................................................................................... 21
4.1 Instrument Main menu ................................................................................ 21
4.2 Custom tests............................................................................................... 22
4.2.1 Creating custom test............................................................................ 22
4.3 Memory menu............................................................................................. 23
4.3.1 Saving results ...................................................................................... 23
4.3.2 Recalling results .................................................................................. 24
4.3.3 Deleting results.................................................................................... 25
4.3.4 Deleting custom test ............................................................................ 25
4.3.5 Clearing complete memory content ..................................................... 26
4.4 Settings menu............................................................................................. 26
4.4.1 Language selection.............................................................................. 27
4.4.2 Initial Settings selection ....................................................................... 27
4.4.3 Time selection...................................................................................... 27
4.4.4 Date selection...................................................................................... 27
4.4.5 Transfer mode ..................................................................................... 28
4.4.6 Contrast selection ................................................................................ 28
4.4.7 Warning sound..................................................................................... 28
4.4.8 Graph selection.................................................................................... 28
4.4.9 Break Down selection .......................................................................... 29
4.4.10 Instrument info..................................................................................... 29
4.5 Help Menu .................................................................................................. 29
5Measurements ................................................................................................... 30
5.1 General information about high voltage testing........................................... 30
5.1.1 The purpose of insulation tests............................................................ 30
5.1.2 DC vs. AC testing voltage.................................................................... 30

MI 3205 TeraOhm XA 5kV Table of contents
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5.1.3 Typical insulation tests......................................................................... 30
5.1.4 Electrical representation of insulating material .................................... 31
5.2 Some application examples ........................................................................ 32
5.2.1 Basic Insulation resistance test ........................................................... 32
5.2.2 Voltage dependence test – Step Voltage Test..................................... 32
5.2.3 Time dependence test – Diagnostic Test............................................. 32
5.2.4 Withstanding Voltage Test................................................................... 34
5.3 Guard terminal ............................................................................................ 35
5.4 Averaging options ....................................................................................... 36
5.4.1 The purpose of averaging.................................................................... 36
5.4.2 Example of averaging .......................................................................... 37
5.5 Measurement menu.................................................................................... 38
5.6 Insulation Resistance Measurement........................................................... 39
5.6.1 Set Limit............................................................................................... 41
5.7 Diagnostic test ............................................................................................ 42
5.7.1 Dielectric Absorption Ratio (DAR)........................................................ 44
5.7.2 Polarization Index (PI) ......................................................................... 44
5.7.3 Dielectric Discharge Testing (DD)........................................................ 45
5.8 Step Voltage testing.................................................................................... 47
5.9 Withstanding Voltage Test .......................................................................... 49
6Communication ................................................................................................. 51
7Maintenance ...................................................................................................... 52
7.1 Batteries insertion and replacement ........................................................... 52
7.2 Cleaning...................................................................................................... 54
7.3 Periodic calibration...................................................................................... 54
7.4 Service........................................................................................................ 54
8Technical specifications................................................................................... 55
8.1 General data ............................................................................................... 58
Appendix A – Remote Control ............................................................................... 59

MI 3205 TeraOhm XA 5kV General Description
5
1 General Description
1.1 Features
TeraOhm XA 5kV (MI 3205) is a portable battery (Li-ion) or mains powered test
instrument with excellent IP protection: IP65 (case closed), IP54 (case open), intended
for diagnosing of Insulation Resistance by using high test voltages of up to 5 kV. It is
designed and produced with the extensive knowledge and experience acquired through
many years of working in this field.
Available functions and features offered by the TeraOhm XA 5kV meter:
Wide measuring range (10 kΩ... 15 TΩ);
Insulation Measurement;
Step Voltage Test;
Withstanding Voltage Test (DC) up to 5 kV;
Polarization Index (PI);
Dielectric Absorption ratio (DAR);
Dielectric Discharge ratio (DD);
Graph R(t);
Adjustable test voltage (50 V...5 kV) 50 V and 100 V step;
Programmable timer;
Automatic discharge of test object after completion of measurement;
Capacitance measurement;
Input AC current noise rejection 1 mA@300 V (4 mA max);
High voltage breakdown detection;
Limit status;
Additional averaging (filters) of the result (5, 10, 30, 60)
Bluetooth, USB and RS232 communication;
High power Li-ion battery pack (14.8V, 4.4Ah);
High overvoltage category CAT IV / 600 V.
A 320x240 dot matrix LCD offers easy-to-read results and all associated parameters.
The operation is straightforward and clear to enable the user to operate the instrument
without the need for special training (except reading and understanding this Instruction
Manual).
Test results can be stored on the instrument. PC software HVLink PRO that is supplied
as a part of standard set enables transfer of measured results to PC where can be
analyzed or printed.

MI 3205 TeraOhm XA 5kV Safety and operational considerations
6
2 Safety and operational considerations
2.1 Warnings and notes
In order to maintain the highest level of operator safety while carrying out various tests
and measurements Metrel recommends keeping your TeraOhm XA 5kV instruments in
good condition and undamaged. When using the instrument, consider the following
general warnings:
The symbol on the instrument means »Read the Instruction manual with
special care for safe operation«. The symbol requires an action!
The symbol on the instrument means “Hazardous voltage may be
present at the test terminals!”.
If the test equipment is used in a manner not specified in this user manual,
the protection provided by the equipment could be impaired!
Read this Instruction manual carefully, otherwise the use of the instrument
may be dangerous for the operator, the instrument or for the equipment
under test!
Do not use the instrument or any of the accessories if any damage is
noticed!
Consider all generally known precautions in order to avoid risk of electric
shock while dealing with hazardous voltages!
Do not use the instrument in supply systems with voltages higher than
300 V!
Service intervention or adjustment is only allowed to be carried out by
competent authorized personnel!
Use only standard or optional test accessories supplied by your distributor!
Hazardous voltages exist inside the instrument. Disconnect all test leads,
remove the power supply cable and switch off the instrument before
opening the battery compartment.
All normal safety precautions must be taken in order to avoid risk of electric
shock while working on electrical installations!

MI 3205 TeraOhm XA 5kV Safety and operational considerations
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Warnings related to measurement functions:
Working with the instrument
Use only standard or optional test accessories supplied by your distributor!
Equipment under test must be switched off (i.e. de-energized) before test leads
are connected to the equipment.
Always connect accessories to the instrument and to the test object before
starting high voltage measurement. Do not touch test leads or crocodile clips
during measurement. Only hand-held part of high voltage test lead with tip is
allowed to be touched (held) during measurement.
Do not touch any conductive parts of equipment under test during the test, risk of
electric shock!
Make sure that the tested object is disconnected (mains voltage disconnected)
before starting the Insulation Resistance measurement!
In case of a capacitive test object (long tested cable etc.), automatic discharge of
the object may not be done immediately after finishing the measurement –
“Please wait, discharging” message will be displayed.
Do not connect test terminals to an external voltage to prevent any damage to the
test instrument!
Handling with capacitive loads
Note that 40 nF charged to 1 kV or 8 nF charged to 5 kV are hazardous live!
Never touch the measured object during the testing until it is totally discharged.
Warnings related to Batteries:
Use only batteries provided by the manufacturer.
Never dispose of the batteries in a fire as it may cause them to explode or
generate a toxic gas.
Do not attempt to disassemble, crush or puncture the batteries.
Do not short circuit or reverse polarity the external contacts on a battery.
Keep the battery away from children.
Avoid exposing the battery to excessive shock/impacts or vibration.
Do not use a damaged battery.
The Li – ion battery contains safety and protection circuit which, if
damaged, may cause the battery to generate heat, rupture or ignite.
Do not leave a battery on prolonged charge when not in use.
If a battery has leaking fluids, do not touch any fluids.
In case of eye contact with fluid, do not rub eyes. Immediately flush eyes
thoroughly with water for at least 15 minutes, lifting upper and lower lids,
until no evidence of the fluid remains. Seek medical attention.

MI 3205 TeraOhm XA 5kV Safety and operational considerations
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2.2 Battery and charging of Li-ion battery pack
The instrument is designed to be powered by rechargeable Li-ion battery pack or with
mains supply. The LCD contains an indication of battery condition and the power source
(upper left section of LCD). In case the battery is too weak the instrument indicates this
as shown in Figure 2.1.
Symbol:
Indication of low battery.
Figure 2.1: Battery test
The battery is charged whenever the power supply is connected to the instrument. The
power supply socket is shown in Figure 2.2. Internal circuit controls (CC, CV) charging
and assures maximum battery lifetime. Nominal operating time is declared for battery
with nominal capacity of 4.4 Ah.
Figure 2.2: Power supply socket (C7)
The instrument automatically recognizes the connected power supply and begins
charging.
Symbol:
Indication of battery charging
Figure 2.3: Charging indication
Battery and charging characteristic Typical
Battery type VB 18650
Charging mode CC / CV
Nominal voltage 14,8 V
Rated capacity 4,4 Ah
Max charging voltage 16,7 V
Max charging current 1,2 A
Max discharge current 2,5 A
Typical charging time 4 hours

MI 3205 TeraOhm XA 5kV Safety and operational considerations
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Typical charging profile which is also used in this instrument is shown in Figure 2.4.
Figure 2.4: Typical charging profile
where:
VREG ............................... Battery charging voltage
VLOWV.............................. Precharge threshold voltage
ICH................................... Battery charging current
ICH/8................................. 1/8 of the charging current
2.2.1 Precharge
On power up, if the battery voltage is below the VLOWV threshold, the charger applies 1/8
of the charging current to the battery. The precharge feature is intended to revive deeply
discharged battery. If the VLOWV threshold is not reached within 30 minutes of initiating
precharge, the charger turns off and a FAULT is indicated.
Figure 2.5: No battery indication
Note:
As a safety backup, the charger also provides an internal 5-hour charge timer for
fast charge.

MI 3205 TeraOhm XA 5kV Safety and operational considerations
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Typical charging time is 4 hours in the temperature range of 5°C to 60°C.
TLTF TCOOL TWARM THTF
Current
Figure 2.6: Typical charging current vs temperature profile
where:
TLTF................................. Cold temperature threshold (typ. -15°C)
TCOOL .............................. Cool temperature threshold (typ. 0°C)
TWARM ............................. Warm temperature threshold (typ. +60°C)
THTF ................................ Hot temperature threshold (typ. +75°C)
The charger continuously monitors battery temperature. To initiate a charge cycle, the
battery temperature must be within the TLTF to THTF thresholds. If battery temperature is
outside of this range, the controller suspends charge and waits until the battery
temperature is within the TLTF to THTF range.
If the battery temperature is between the TLTF and TCOOL thresholds or between the
TWARM and THTW thresholds, charge is automatically reduced to ICH/8 (1/8 of the charging
current).

MI 3205 TeraOhm XA 5kV Safety and operational considerations
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2.2.2 Li – ion battery pack guidelines
Li – ion rechargeable battery pack require routine maintenance and care in their use and
handling. Read and follow the guidelines in this user manual to safely use Li – ion
battery pack and achieve the maximum battery life cycles.
Do not leave batteries unused for extended periods of time (self – discharge).
When a battery has been unused for 6 months, check the charge status see chapter
3.4.4 Battery, time and communication indication. Rechargeable Li – ion battery pack
have a limited life and will gradually lose their capacity to hold a charge. As the battery
loses capacity, the length of time it will power the product decreases.
Storage:
Charge or discharge the instruments battery pack to approximately 50% of
capacity before storage.
Charge the instrument battery pack to approximately 50% of capacity at least
once every 6 months.
Store the instrument at temperatures between 5 °C and 20 °C.
Transportation:
Always check all applicable local, national, and international regulations before
transporting a Li – ion battery pack.
Handling Warnings:
Use only batteries provided by the manufacturer.
Do not disassemble, crush, or puncture a battery in any way.
Do not short circuit or reverse polarity the external contacts on a battery.
Do not dispose of a battery in fire or water.
Keep the battery away from children.
Avoid exposing the battery to excessive shock/impacts or vibration.
Do not use a damaged battery.
The Li – ion battery contains safety and protection circuit which, if
damaged, may cause the battery to generate heat, rupture or ignite.
Do not leave a battery on prolonged charge when not in use.
If a battery has leaking fluids, do not touch any fluids.
In case of eye contact with fluid, do not rub eyes. Immediately flush eyes
thoroughly with water for at least 15 minutes, lifting upper and lower lids,
until no evidence of the fluid remains. Seek medical attention.

MI 3205 TeraOhm XA 5kV Instrument description
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2.3 Standards applied
The TeraOhm XA 5kV instrument is manufactured and tested in accordance with the
following regulations:
Electromagnetic compatibility (EMC)
EN 61326 Electrical equipment for measurement, control and laboratory
use – EMC requirements Class A
Safety (LVD)
EN 61010 - 1 Safety requirements for electrical equipment for measurement,
control and laboratory use – Part 1: General requirements
EN 61010 - 2 - 030 Safety requirements for electrical equipment for measurement,
control and laboratory use – Part 2-030: Particular requirements
for testing and measuring circuits
EN 61010 - 031 Safety requirements for hand-held probe assemblies for electrical
measurement and test.
Some further recommendations
IEEE 43 – 2000 Recommended Practice for Testing Insulation Resistance of Rotating
Machinery:
1 MΩ+ 1 MΩ/ 1000 V rating of equipment for insulation systems prior to 1970;
5 MΩfor random wound motors under 600 Volts;
100 MΩfor form wound motors over 600 Volts, and armatures;
IEC 60439-1 Low-voltage switchgear and control gear assemblies - Part 1:
Type-tested and partially type-tested assemblies:
Scope of the insulation resistance test: alternative method for verification of
dielectric properties by insulation resistance measurement;
Description: a d.c. test voltage (500 V) is applied to the insulation and its
resistance is measured. Insulation is proper, if its resistance is high enough (1000
Ω/ V of circuit rated voltage);
IEC 61558 Isolating transformers and safety isolating transformers:
Test voltage: 500 V, measurement period: 1 min;
Minimum insulation resistance for basic insulation: 2 MΩ;
Minimum insulation resistance for supplementary insulation: 5 MΩ;
Minimum insulation resistance for reinforced insulation: 7 MΩ;
Li – ion battery pack
IEC 62133 Secondary cells and batteries containing alkaline or other non-
acid electrolytes - Safety requirements for portable sealed
secondary cells, and for batteries made from them, for use in
portable applications.
Note:
Immunity to radiated RF fields (Field strength: 10V/m, Modulation: AM, 80%, 1 kHz)
Voltage Range Operational conditions Disturbance < 5 % Disturbance > 5 %
50 V 100 MΩ300 MHz ÷ 900 MHz 900 MHz ÷ 1 GHz
Note about EN and IEC standards:
Text of this manual contains references to European standards. All standards of
EN 6XXXX (e.g. EN 61010) series are equivalent to IEC standards with the same
number (e.g. IEC 61010) and differ only in amended parts required by European
harmonization procedure.

MI 3205 TeraOhm XA 5kV Instrument description
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3 Instrument description
3.1 Instrument casing
The instrument is housed in a plastic box that maintains the protection class defined in
the general specifications.
3.2 Operator’s panel
The operator’s panel is shown in Figure 3.1 below.
Figure 3.1: The operator’s panel
Keypad Section:
1 START / STOP Start or stop measurement.
2 ON / OFF
Switches the instrument power on or off.
The instrument automatically turns off 15 minutes after the
last key was pressed (Hard OFF – hold key for 8 s).
3 MEM Store / recall / clear tests in memory of the instrument.
4 SELECT To enter set-up mode for the selected function or to select
the active parameter to be set.
5,6 Select an option upward, downward.
7,8 Decrease, increase the selected parameter.
9 ESC Exit the selected mode.

MI 3205 TeraOhm XA 5kV Instrument description
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10 ☼Turn the display backlight ON or OFF.
Instrument’s RESET (hold key for 5 s or more).
Display Section:
20 High voltage warning light (red).
Terminal Section:
11 + Rx Positive high voltage output terminal.
12,13 GUARD Guard input terminals.
14 - Rx Negative high voltage output terminal.
Power and Communication Section:
19 C7 Input power supply socket (C7)
18 USB USB communication port (standard USB connector - type B)
18 RS232 RS232 communication port (standard RS232 9-pin D
female)
Warnings!
Maximum allowed voltage between any test terminal and ground is 600 V!
Maximum allowed input voltage between test terminals is 50 V! Use original
test accessories only!

MI 3205 TeraOhm XA 5kV Instrument description
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3.3 Accessories
The accessories consist of standard and optional accessories. Optional accessories can
be delivered upon request. See attached list for standard configuration and options or
contact your distributor or see the METREL home page: http://www.metrel.si.
3.3.1 Test leads
The standard length of high voltage shielded test lead with tip is 2 m. The standard
length of high voltage shielded test leads with (red, black) banana connectors is 3 m;
optional lengths are 8 m and 15 m. For more details see attached list for standard
configuration and options or contact your distributor or see the METREL home page:
http://www.metrel.si.
All test leads are made of high voltage shielded cable, because shielded cable provides
higher accuracy and immunity to disturbance of measurements that can occur in
industrial environments.
High voltage shielded test leads with High voltage alligator clips.
Application notes:
This test leads are designed for diagnostic
testing of insulation. They can also be used
for hand held testing with test voltages up to
5 kV d.c..
Insulation ratings:
High voltage banana connectors (red,
black): 5 kV d.c. (reinforced insulation);
Alligator clips (red, black): 5 kV d.c.
(reinforced insulation);
Guard banana connector (green): 600
V CAT IV (reinforced insulation);
Cable (yellow): 12 kV (shielded).
Figure 3.2: HV test leads with alligator clips
Guard test lead with alligator clips
Insulation ratings:
Guard test lead with banana
connectors (green): 600 V CAT IV
(reinforced insulation);
Alligator clip (green): 600 V CAT IV
(reinforced insulation)
Figure 3.3: Guard lead with alligator clip

MI 3205 TeraOhm XA 5kV Instrument description
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3.4 Display organization
Figure 3.4: Typical function display and graph screen
1 Measurement result window
2 Measurement control window
3 Messages window
4 Battery, time and communication indication
5 Measurement result line
6 Graphical presentation of measured data
3.4.1 Measurement result window
Measurement window shows all relevant data during measurement campaign.
Figure 3.5: Measurement window
Measured Insulation
resistance
Is shown in the center of a screen with the largest font. During
measurement campaign this result is refreshed every few
seconds. When the measurement is completed result is hold on
screen, until new measurement is started.
Bar graph Graphically represents measured insulation resistance in respect
to the measurement range. It also displays limit value if it is
enabled.
UShows the output voltage. During measurement campaign this
result is refreshed every few seconds. When the measurement is
completed result is hold on screen, until new measurement is
started.
IShows the input current. During measurement campaign this
result is refreshed every few seconds. When the measurement is
completed result is hold on screen, until new measurement is
started.

MI 3205 TeraOhm XA 5kV Instrument description
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CShows the capacitance measured at the output terminals. Value
of capacitance is measured during the final discharge of the test
object.
R1, R2, R3 Show resistances measured at Timer1, Timer2 and Timer3.
When the measurement is completed result is hold on screen,
until new measurement is started (appears only in Diagnostic
Test).
R1, R2, R3,R4, R5 Show resistances measured at steps one to five. When the
measurement is completed result is hold on screen, until new
measurement is started (appears only in Step Voltage Test).
U1, U2, U3, U4, U5 Show voltages measured at steps one to five. When the
measurement is completed result is hold on screen, until new
measurement is started (appears only in Step Voltage Test).
DAR Show the Dielectric Absorption Ratio. When the measurement is
completed result is hold on screen, until new measurement is
started (appears only in Diagnostic Test).
PI Show the Polarization Index. When the measurement is
completed result is hold on screen, until new measurement is
started (appears only in Diagnostic Test).
DD Show the Dielectric Discharge result. When the measurement is
completed result is hold on screen, until new measurement is
started (appears only in Diagnostic Test).
fShows frequency of the measured voltage (appears only in True
RMS Voltmeter).
tShows test time (mm:ss).
3.4.2 Measurement control window
Control window permit user to modify control measurement parameters.
Figure 3.6: Control window
Un Allows user to set the desired test voltage.
Timer1 Allows user to set the desired measurement duration in
Insulation Resistance test.
Delay for starting DAR measurement in Diagnostic test.
(mm:ss) – step 1 s (max time 99 min).

MI 3205 TeraOhm XA 5kV Instrument description
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Timer2 Delay for starting PI measurement (mm:ss) – step 1 s (max time
99 min).
Timer3 Allows user to set the desired measurement duration (mm:ss) –
step 1 s (max time 99 min).
DD Allows user to enable or disable Dielectric Discharge
measurement.
Itrgg Allows user to set the desired trigger level – step 100 μA (max
current 5 mA).
Tstart Allows user to set the start test voltage time (mm:ss) – step 1s
(max time 99 min).
Tend Allows user to set the constant end test voltage time (mm:ss) –
step 1 s (max time 99 min).
Ustart Allows user to set the desired start test voltage.
Uend Allows user to set the desired end test voltage.
Tramp Allows user to set the duration of the test ramp (mm:ss) – step 1
s (max time 99 min).
HI Lim Allows user to set the high limit (value is evaluated at the end of
the measurement).
AVG Allows user to set the additional averaging of the result (OFF, 5,
10, 30, 60).
3.4.3 Message window
In the message field warnings and messages are displayed.
Figure 3.7: Message window

MI 3205 TeraOhm XA 5kV Instrument description
19
High voltage is present on measuring terminals (> 50 V rms).
Test result can be saved.
AC noise is present on the measuring terminals (+ Rx, - Rx).
A Breakdown or Over voltage event has accrued.
Instrument is overheated. Measurement process is disabled.
Graph is enabled.
Graph logging is enabled (internal Flash memory).
Internal Flash memory is full (graph logging is disabled).
Measurement result is within defined limits.
Measurement result is out of defined limits.
3.4.4 Battery, time and communication indication
These symbols indicate the charge condition of a battery, charger connection and
communication status. Time indication is also present.
Battery capacity indication.
Low battery.
Recharge the battery.
Recharging in progress (if mains supply cable is connected).
Time indication (hh:mm).
USB communication is enabled.
Bluetooth communication is enabled.
Note:
Date and time is attached to each stored result.

MI 3205 TeraOhm XA 5kV Instrument description
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3.4.5 Measurement result line
RShows Insulation resistance. During measurement campaign this
result is refreshed every few seconds. When the measurement is
completed it represents Insulation resistance at cursor position.
U Shows the output voltage. During measurement campaign this
result is refreshed every few seconds. When the measurement is
completed it represents output voltage at cursor position.
tShows test time (mm:ss). When the measurement is completed
it represents time at cursor position.
Note:
Averaging in measurement result line is disabled during measurement campaign
in all functions regardless of settings.
3.4.6 Graphical presentation of measured data
Figure 3.8: Graph screen
Measured or averaged Insulation resistance values in relation to time of measurement
are represented in this two dimensional R/t diagram. Online plotting, during
measurement, can also be observed. When the measurement is completed cursor is
attached to the graph for detail analysis.
3.4.7 Backlight operation
After turning the instrument ON the LCD backlight is automatically turned ON. It can be
turned OFF and ON by simply clicking the ☼(LIGHT) key.
Note:
If you press and hold the Light (☼) key for approximately 5 s the instrument will
RESET!