Gossen MetraWatt METRA HIT 27EX User manual

Operating Instructions
METRA HIT⏐27EX
Milliohmmeter for deployment
in potentially explosive atmospheres 3-349-336-49
9/8.16

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1Display(LCD)
2ON|OFFkey for ON / OFF
(ON short: instrument ON → ON short: background illumination ON →
→
OFF short: background illumination OFF → OFF long: instrument OFF)
Operating mode menu: open submenus / acknowledge entries
3 DATA|CLEAR key for the functions save/delete measured value
Operating mode menu: Selection of individual menu items
against direction of flow,
increase values
4 MAN|AUTO key for manual measuring range selection
Operating mode menu: Selection of individual menu items
in direction of flow
decrease values
5MENU/ESC
Operating mode menu: Exit menu level and
return to a higher level,
exit parameters configuration
without saving data
6LEDOK blinks: valid measured value
7LEDERROR blinks: incorrect connection
8 Connector jacks *
1
2
6
4
5
8
Measurement only on
voltage-free objects!
→ chapter 5
→ chapter 3
→ chapter 4
→ chapter 7.2
→ chapter 7.3
→ chapter 7
7→ chapter 7.3
3→ chapter 6

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Symbols used in the Digital Display
1 Main display with decimal point
2 Auxiliary displays
3 : Milliohmmeter in continuous operation,
ON blinks at transmission frequency in transmission mode
4 REM: Memory mode operation, disappears after communication
via the interface is ended by means of key or switch
operation
5 ZERO: Zero balancing
6 MAN: Manual measuring range selection
7 Unit of measure (if blinking, refer to chapter 11 on page 33)
8:Low battery voltage, replace batteries
* I- Measurement input
U- Sense – for 4-wire measurement
U+ Sense + for 4-wire measurement
I+ mΩ; Ωmeasurement input
1
2
8
64 53
7

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Contents Page
1 Application .............................................................. 5
2 Safety Features and Precautions ............................ 5
3 Initial Start-Up ......................................................... 8
4 Selecting Measuring Functions and Measuring Ranges .10
4.1 Automatic Measuring Range Selection ................................10
4.2 Manual Measuring Range Selection ....................................10
4.3 Quick Measurements ......................................................... 10
5 Triple Digital Display ............................................. 11
6 Measured Value Storage ....................................... 12
6.1 Measured Value Storage – Key Function “DATA” .................12
7 Milliohm Measurement (4-Pole-Measurement) .... 14
7.1 Compensation of Cable Resistance ..................................... 14
7.1.1 Measurement with Kelvin Probe KC27 ................................14
7.2 Thermovoltage Compensation ............................................. 15
7.3 Milliohm Measurement with ≤100 mA DC [mΩ] ................. 16
8 Using the Menus – from the Initial InFO Menu to
Operating and Measuring Parameters .................. 17
8.1 Sampling rAtE ........................................................ 17
8.2 Saving Measured Values .................................................... 18
8.2.1 Memory Mode – DATA Key Function (see also chapter 6.1) ..18
8.2.2 Memory Mode Operation – STORE Menu Function ............... 19
8.3 Querying Memory Occupancy – INFO MEMO/OCCUP ....... 19
8.4 Clearing the Memory – MEMO CLEAr .............................20
8.5 Activating the Default Values ..............................................20
8.6 Transmission Mode Operation with RS 232 or USB Interface 21
9 Characteristic Values ........................................... 26
10 Maintenance ......................................................... 30
10.1 Batteries ............................................................................30
10.2 Fuses ................................................................................31
10.3 Housing and Display ........................................................... 32
10.4 Collection of Used Instruments and Environmentally
Compatible Disposal ........................................................... 33
11 System Messages ................................................. 33
12 Repair and Replacement Parts Service,
Calibration Center and Rental Instrument Service 34
13 Manufacturer’s Guarantee .................................... 35
14 Product Support .................................................... 35
15 Recalibration ......................................................... 36

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1 Application
METRA HIT⏐27EX is a milliohmmeter with 4-pole measure-
ment, which is designed for deployment in potentially
explosive environment.
In accordance with directive 2014/34/EU the device is
approved for being used in explosive, gaseous atmo-
spheres (IIA T4) with ambient temperatures between –
10 °C and +50 °C.
The device conforms to the following standards:
– EN 60079-0:2012 + A11:2013
– EN 60079-11:2012
It bears CE certification number, type INERIS 05ATEX0040,
which has been conferred by the Ineris certification authority.
2 Safety Features and Precautions
You have selected an instrument which provides you with
high levels of safety.
This instrument fulfills the requirements of the applicable
EU guidelines and national regulations. We confirm this
with the CE marking. The relevant declaration of conformity
can be obtained from GMC-I Messtechnik GmbH.
The METRA HIT⏐27EX is manufactured and tested in
accordance with safety regulations IEC 61010–1:2010 /
EN 61010–1:2011/VDE 0411–1:2011/EN 60079-0:2009 and
EN 60079-0:2012/EN 60079-11:2012. When used for its
intended purpose, safety of the operator, as well as that of
the instrument, is assured. Their safety is however not
guaranteed, if the instrument is used improperly or handled
carelessly.
In order to maintain flawless technical safety conditions, and to
assure safe use, it is imperative that you read the operating
instructions thoroughly and carefully before placing your instru-
ment into service, and that you follow all instructions contained
therein.
Use for Intended Purpose:
– The milliohmmeter described herein is a portable
instrument which can be held in one hand during mea-
surements.
– The milliohmmeter may only be operated with the
included or with type-tested batteries, as specified in
the Characteristic Values.
– The milliohmmeter may only be operated with closed
housing. The instrument must be removed from the
potentially explosive environment before opening the
housing to replace batteries or fuses.
– Only the type-tested fuses specified in the Characteris-
tic Values may be used.
– The milliohmmeter may only be used to perform such
measurements as described in chapter 7.
– The limits of the overload capacity may not be
exceeded. Refer to the “Characteristic Values” on
page 26 for overload values and overload duration.

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– Measurements may only be performed within the indi-
cated ambient conditions. See page 29 for operating
temperature range and relative humidity.
– The instrument may not be used in a dusty atmo-
sphere.
– No maintenance operation may be performed in
potentially explosive atmospheres (cleaning, replace-
ment of batteries, opening the device, etc.)
Observe the following safety precautions:
•Type-tested Housing
The milliohmmeter may not be operated with open
housing.
In a potentially explosive atmosphere the housing may
not be opened. In this case, there is no protection
against explosions.
•Type-tested Batteries
Use the included or other type-tested batteries with
identical technical features only, see Characteristic Val-
ues.
Before use, please make sure that the housing cover is
closed. There is no protection against explosions when
the housing is open.
Batteries may only be replaced outside the potentially
explosive environment. No spare batteries may be
brought into the potentially explosive environment.
•Operation by qualified electricians
The instrument may only be operated by persons who
are capable of recognizing shock hazards and taking
the appropriate safety precautions. Shock hazards
exist anywhere, where voltages of greater than 33 V
(RMS) may occur.
•Shock Hazards
Avoid working alone when taking measurements
which involve shock hazards. Be certain that a second
person is present.
•Measurement Cables
Make sure that all measurement cables are in faultless
condition, e.g. undamaged insulation, no interruptions
in cables and plugs, etc.
•Unexpected Voltages
Be prepared for the occurrence of unexpected volt-
ages at devices under test (e.g. defective devices, after
inspecting the winding resistance of contactor relays,
etc.). For example, capacitors can still be dangerously
charged.
Perform measurements on voltage-free objects only.
•Type-tested Fuses (cannot be replaced by the user)
Only use type-tested fuses, as specified in the Charac-
eristic Values. There is no protection against explo-
sions when other fuses are used.
In order to prevent major damage to the instrument
when interference voltage is applied (within the admis-
sible limit values), the mΩ/Ω measuring circuit is
equipped with a fuse F1 which makes these measur-

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ing circuits highly resistive for the duration of the over-
load when high currents occur as a result of a distur-
bance. Another fuse F2 is located in the path between
batteries and instrument.
•Dusty Atmosphere
The instrument may not be used in a dusty atmosphere.
Meanings of symbols on the instrument:
Warning concerning a source of danger
(attention: observe documentation!)
Ground
Continuous, doubled or reinforced
insulation
Indicates EC conformity
Symbol for explosion protection:
Electrical equipment for intended use in
potentially explosive environments per
EN 60079-11
This device may not be disposed of with the
trash. Further information regarding the WEEE
mark can be accessed on the Internet at
www.gossenmetrawatt.com by entering the
search term ’WEEE’.
Repair, Parts Replacement and Balancing
When the instrument is opened, voltage conducting parts
may be exposed. The instrument must be disconnected
from the measuring circuit before the performance of
repairs, the replacement of parts, or balancing. If
balancing, maintenance or repair of a live open instrument
is required, this may only be carried out by trained
personnel who are familiar with the dangers involved.
Defects and Extraordinary Strains
If it may be assumed that the instrument can no longer be
operated safely, it must be removed from service and
secured against unintentional use. This applies particularly
for potentially explosive environments.
Safe operation can no longer be relied upon,
• If the instrument or the test probes are damaged
• If the instrument no longer functions
• If the limits of the overload capacity have been
exceeded, e.g. after the fuse has blown
• After long periods of storage under unfavorable condi-
tions (e.g. humidity, dust, or excessive temperature),
see „Ambient Conditions“ on page 29.
!

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3InitialStart-Up
Insert Batteries
Warning!
Remove the instrument from the potentially explo-
sive environment before opening.
Only use the included type-tested batteries, as in-
dicated in the Characteristic Values.
Refer to chapter 10.1 regarding correct battery installation.
Note!
As a result of internal voltage monitoring, the instru-
ment may respond as follows if the battery voltage
level is low:
– Cannot be switched on
– Shuts back down immediately
– Shuts back down immediately when a load is
applied in the mΩrange.
If this is the case, replace the batteries.
Warning!
Never replace the batteries in potentially explosive
atmospheres.
Switching the Instrument On Manually
➭Press the ON|OFF key.
As long as the key is held depressed, all of the seg-
ments at the LCD are illuminated. The LCD is shown
on page 2. Power-up is acknowledged with a brief
acoustic signal.
The instrument is ready for use as soon as
the key is released.
Switching the Instrument On with a PC
After transmission of a data frame from the PC, the mil-
liohmmeter is switched on. See also chapter 8.6.
Switching the Instrument On Automatically
The milliohmmeter is switched on automatically in the
transmission and memory modes.
Note!
Electrical discharge and high frequency interference may cause
incorrect displays to appear, and may disable the measuring
sequence. In such cases, switch the instrument off and back on
again in order to reset. If the problem persists, briefly dislodge
the batteries from the connector contacts.
Setting Time and Date
See chapter 8 on page 17.
Switching the Instrument Off Manually
➭Press the ON|OFF key until OFF is shown on the display.

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Shutdown is acknowledged with two, brief acoustic sig-
nals.
Switching the Milliohmmeter Off Automatically – „SLEEP MODE“
The instrument is switched off automatically if none of the
keys are activated for approximately 10 minutes. Shut-
down is acknowledged with a brief acoustic signal.
Transmission mode: In this case, checking is first performed
to determine whether or not the sampling rate has been set
to a value of greater than 10 s. The instrument is switched
off after 10 minutes, but the instrument is reactivated 10 s
before data is to be saved to memory. The instrument is
then switched back off again.
In the transmission mode, the instrument can be manually
activated with the ON|OFF key. After activation of this type,
the instrument returns to the “SLEEP MODE”.
If the instrument is to be fully shut down, it must first be
activated and then switched off with the ON|OFF key. This
ends both memory mode and transmission mode
operation.
We recommend setting the instrument to continuous
operation for transmission mode operation.
The continuous operation mode is not effected by auto-
matic shutdown.
Disabling Automatic Shutdown
The instrument can be set to continuous operation.
➭Press and hold the MENU/ESC key and then switch the
instrument on by pressing the ON|OFF key. Continuous
operation is indicated at the display with the symbol.
Switching LCD Illumination On and Off
➭Briefly press the ON|OFF key after the instrument has al-
ready been switched on.
Illumination is switched off automatically after approxi-
mately 2 minutes.
Note: Electrical discharge and high frequency interference
may cause incorrect displays to appear, and may disable
the measuring sequence. In such cases, switch the instru-
ment off and back on again in order to reset.
If the problem persists,
1 leave the potentially explosive environment,
2 disconnect the instrument from the measuring circuit before open-
ing and refer to chapter 10.1 „Batteries“,
3 Briefly dislodge the batteries from the connector contacts.

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4 Selecting Measuring Functions and Measuring
Ranges
4.1 Automatic Measuring Range Selection
The milliohmmeter is equipped with auto-ranging for all
measuring ranges. Auto-ranging is active as soon as the
instrument is switched on. The instrument automatically
selects the measuring range which allows for highest pos-
sible resolution for the applied quantity.
The instrument automatically switches to the next highest
or next lowest measuring range for the following measured
quantities:
4.2 Manual Measuring Range Selection
Auto-ranging can be deactivated and measuring ranges
can be selected manually in accordance with the following
table.
The manual mode is deactivated by pressing and holding
the MAN|AUTO key (approx. 1 s) or by switching the instru-
ment off and then back on again.
Note!
If the red ERROR LED lights up and OL is shown
on the display during manual measuring range
selection, you should switch to the next higher
range.
4.3 Quick Measurements
If you wish to perform quicker measurements than those
possible with the automatic measuring range selection
function, make sure to establish the appropriate measuring
range and to perform the following two functions:
•bymanual measuring range selection, i. e. by selecting
the measuring range with the best resolution, see
chapter 4.2.
or
Measuring Ranges Reso-
lution
Switching to next
highest range
at +(... d + 1 d)
Switching to next
lowest range
at +(... d –1 d)
300 mΩ, 3 Ω, 30 Ω4 ¾ 31 000 2 800
30 mΩ3 ¾ 3 100 280

MAN|
AUTO
Function
Acknow-
ledgement
Dis-
play
Acoust.
Signal
short Manual mode active:
utilized measuring range is fixed MAN 1 x
short Range switching sequence for:
mΩ:30mΩ→300 mΩ→3Ω→30 Ω→30 mΩ→… MAN 1 x
long Return to automatic range selection —2 x