KROHNE H250 M40 Series Wiring diagram

Equipment protection level Gc
in protection type "increased safety" Ex ec
H250 M40
H250 M40H250 M40
H250 M40 Supplementary Instructions
Supplementary InstructionsSupplementary Instructions
Supplementary Instructions
© KROHNE 11/2019 - 4007945001 - AD H250-M40 Exec Gc R01 en

CONTENTS
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H250 M40
1 Safety instructions 3
1.1 General notes ................................................................................................................... 3
1.2 EU conformity ................................................................................................................... 3
1.3 Approval according to the IECEx scheme ........................................................................ 3
1.4 Safety instructions............................................................................................................ 4
2 Device description 5
2.1 Device description ............................................................................................................ 5
2.2 Description code............................................................................................................... 5
2.3 Marking............................................................................................................................. 6
2.4 Flammable products ........................................................................................................ 7
2.5 Equipment protection level .............................................................................................. 8
2.6 Types of protection ........................................................................................................... 8
2.7 Ambient temperature / temperature classes.................................................................. 9
2.8 Electrical data................................................................................................................. 15
3 Installation 16
3.1 Mounting ......................................................................................................................... 16
3.2 Special conditions........................................................................................................... 17
4 Electrical connections 18
4.1 General notes ................................................................................................................. 18
4.2 Power supply .................................................................................................................. 18
4.3 Inputs / outputs .............................................................................................................. 18
4.4 Grounding and equipotential bonding............................................................................ 19
5 Operation 20
5.1 Start-up........................................................................................................................... 20
5.2 Operation ........................................................................................................................ 20
5.3 Electrostatic charge .......................................................................................................20
6 Service 21
6.1 Maintenance ................................................................................................................... 21
6.2 Dismantling .................................................................................................................... 21
7 Notes 22

SAFETY INSTRUCTIONS 1
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1.1 General notes
This additional instruction applies to explosion-protected versions of variable area flowmeters
with electrical built-ins with protection type increased safety "e", equipment protection level
(EPL) Gc.
It completes the standard manual for the non explosion-protected versions.
The information given in this instruction contains only the data relevant to explosion protection.
The technical details given in the manual for the non explosion-protected versions remain
unchanged unless they will be excluded or replaced by this supplementary instruction.
1.2 EU conformity
The manufacturer declares with the EU declaration of conformity, in which the applied standard
(EN IEC 60079-0:2018 and EN 60079-7:2015) is also specified, on his own responsibility
conformity with the protection goals of directive 2014/34/EU (ATEX) for use in hazardous areas
with gas.
The EU declaration of conformity for the equipment category II 3 G is based on the EC type
examination certificate of the Physikalisch Technische Bundesanstalt (PTB):
The "X" after the certificate number refers to special conditions for safe use of the device, which
have been listed in these instructions.
If needed the EU type examination certificate can be downloaded from the manufacturer's
website.
1.3 Approval according to the IECEx scheme
Conformity of the variable area flowmeter for use in hazardous areas with gas was tested in
accordance with the "IECEx Certification Scheme for Explosive Atmospheres" according to
IEC 60079-0:2017 and IEC 60079-7:2015.
The number of the IEC certificate is:
The "X" after the certificate number refers to special conditions for safe use of the device, which
have been listed in these instructions.
If needed, the IEC certificate can be downloaded from the manufacturer's website.
PTB 11 ATEX 2012 X
PTB 11 ATEX 2012 XPTB 11 ATEX 2012 X
PTB 11 ATEX 2012 X
IECEx PTB 11. 0069 X
IECEx PTB 11. 0069 XIECEx PTB 11. 0069 X
IECEx PTB 11. 0069 X

1 SAFETY INSTRUCTIONS
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1.4 Safety instructions
If these instructions are not followed, there is a risk of explosion.
Assembly, installation, start-up and maintenance may only be performed by personnel trained in
explosion protection!
CAUTION!
The operator or his agent is responsible for observing any additional standards, directives or
laws if required due to operating conditions or place of installation.
This applies in particular to the use of easily detachable process connections when measuring
flammable media.
CAUTION!
When an equipment fault is detected the device shall be de-energised and send back to the
manufacturer for repair.

DEVICE DESCRIPTION 2
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2.1 Device description
Variable area flowmeters measure and display the volume flow of flammable and non-
flammable gases and liquids. Depending on the device version, electrical limit switch contacts
and a 4...20 mA signal output with HART
®
communication, a Foundation Fieldbus interface or a
Profibus PA interface can be installed in the indication unit.
2.2 Description code
The safety description code consists of the following elements *:
* positions which are not needed are omitted (no blank positions)
Figure 2-1: Safety description code
1 Type series of measuring unit H250
Type series of measuring unit H250Type series of measuring unit H250
Type series of measuring unit H250
H250 - standard version, vertical upwards
H250H - horizontal orientation
H250U - vertical downwards
2 Measuring unit materials / versions
Measuring unit materials / versionsMeasuring unit materials / versions
Measuring unit materials / versions
RR - stainless steel
C - PTFE or PTFE/ceramics
HC - Hastelloy C
Ti - Titanium
F - Food
3 Heating jacket version
Heating jacket versionHeating jacket version
Heating jacket version
blank - without heating jacket
B - with heating jacket
4 Signal converter version
Signal converter versionSignal converter version
Signal converter version
M40 - aluminium housing, painted (standard)
M40S - aluminium housing with increased corrosion protection
M40R - stainless steel housing
5 High-temperature version
High-temperature versionHigh-temperature version
High-temperature version
blank - without HT extension
HT - with HT extension
6 Electrical signal output
Electrical signal outputElectrical signal output
Electrical signal output
blank - without transmitter
ESK - electrical signal output 4...20 mA (ESK4)
. . . - optionally available with counter, I/O module and display (ESK4-T) or
. . . - Foundation Fieldbus (ESK4-FF) or
. . . - Profibus PA (ESK4-PA)
7 Limit switch
Limit switchLimit switch
Limit switch
blank - without limit switches
K1 - one limit switch
K2 - two limit switches
R1 - 1 Reed switch
R2 - 2 Reed switches
8 Version
VersionVersion
Version
Ex - explosion-protected version
9 SIL version
SIL versionSIL version
SIL version
SE - SIL compliant electronic signal output
SK - SIL compliant limit switch

2 DEVICE DESCRIPTION
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2.3 Marking
The marking of the entire device is on the indication unit, where the following identification
plates can be found (refer also to designation code).
Additional markings on the housing cover:
•SN - serial number
•SO - sales order / item
•PA - order
•Vxxx - product configurator code
•AC - article code
Additional plate
The association of the housing cover to the device is confirmed by an additional plate with the
serial number on the interior of the indicator part.
Figure 2-2: Example of a nameplate
1 Device type
2 Device version
3 Identification number of the notified body ATEX & PED
4 Rating data: temperature & pressure rating
5 Data according to the pressure equipment directive
6 Marking according to the notified body
7 Electrical connection data
8 Note to observe the documentation and for disposal
9 Data matrix

DEVICE DESCRIPTION 2
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2.4 Flammable products
Atmospheric conditions:
Atmospheric conditions:Atmospheric conditions:
Atmospheric conditions:
The standard atmospheric conditions under which it may be assumed that Ex equipment can be
operated are:
•Temperature: -20...+60°C / -4...+140°F
•Pressure: 80...110 kPa (0.8...1.1 bar) / 11.6...15.9 psi
•Air with normal oxygen content, typically 21%v/v
Ex equipment operating outside the standard temperature range must be tested and certified
(e.g. for ambient temperature range -40...+65°C / -40...+149°F).
Ex equipment operating outside the standard atmospheric pressure range and standard oxygen
content is not permitted.
Operating conditions:
Operating conditions:Operating conditions:
Operating conditions:
The measuring unit of variable area flowmeters operate outside the standard atmospheric
pressure range, which means that explosion protection, regardless of the zone assignment, is
fundamentally not applicable for the measuring unit (piping).
WARNING!
Operation with flammable products is only permitted as long as no explosive fuel/air mixture
builds up inside of the piping at the same time the atmospheric conditions are exceeded.
The operator is responsible to ensure that the flowmeter is operated safely in terms of the
temperature and pressure of the products used. In case of operation with flammable products
the measuring units must be included in the periodic pressure tests of the piping.
When using the device version H250/C... (PTFE version, non-conductive) the minimum
conductivity of the media must be 10
-8
S/m, in order to avoid danger from electrostatic charge.

2 DEVICE DESCRIPTION
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2.5 Equipment protection level
Variable area flowmeters are designed according to IEC 60079-0 and IEC 60079-7 in
equipment protection level (EPL) Gc for use in zone 2.
The inside of the measuring unit is also approved for zone 2.
2.6 Types of protection
The variable area flowmeter is designed with protection type "Increased safety" according to
IEC 60079-7. Explosion protection is ensured in that there are no contacts or hot surfaces with a
sparking effect during operation.
The identification for equipment category II 3 G or the equipment protection level (EPL) Gc is:
II 3G
II 3GII 3G
II 3G (ATEX only)
Ex ec IIC T6...T2 Gc
Ex ec IIC T6...T2 GcEx ec IIC T6...T2 Gc
Ex ec IIC T6...T2 Gc
The marking contains the following information:
INFORMATION!
Definition of zone 2:
This is an area in which an explosive atmosphere as a result of the mixture of flammable
substances in the form of gas, steam or mist with air is not expected to occur under normal
operation. If, however, such an atmosphere does occur it only lasts for a brief period of time.
II
IIII
II Explosion protection, group II
3
33
3Equipment category 3
G
GG
GGas explosion protection
Ex ec
Ex ecEx ec
Ex ec Explosion protection through increased safety, protection level "ec"
IIC
IICIIC
IIC Gas group, suitable for gas groups IIC, IIB and IIA
T6...T2
T6...T2T6...T2
T6...T2 Temperature class range, suitable for temperature classes T6...T1
Gc
GcGc
Gc EPL, suitable for zone 2
Table 2-1: Description of the marking
INFORMATION!
The temperature class of the device depends on the product temperature.

DEVICE DESCRIPTION 2
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2.7 Ambient temperature / temperature classes
Due to the influence of the product temperature, variable area flowmeters with built-in electrical
equipment (electric variants) are not assigned to any fixed temperature class. The temperature
class of these devices is rather a function of the product temperature and ambient temperature
that is present and the specific device version. The classification is outlined in the following
tables.
The tables take into account the following parameters:
•built-in equipment
•Ambient temperature T
amb
•Product temperature T
m
•Nominal size DN
•Standard or high temperature version (HT)
•Standard or heating jacket version
•Heat resistance of the connecting cable
When using more than one built-in equipment, the data of the most unfavourable equipment
should be used.
For certain device versions, lower values apply due to differing boundary conditions (e.g. liner
materials). In this regard, pay special attention to the pressure and temperature indications on
the device nameplate.
INFORMATION!
The maximum permissible product temperatures listed in the tables are valid under
the following conditions:
• The measuring device is installed and operated in accordance with the manufacturer's
installation instructions.
• It must be ensured that the measuring device is not heated by the effects of additional heat
radiation (sunshine, adjacent plant parts) and thus operated above the permissible ambient
temperature range.
• Insulation must be limited to the piping.
Unobstructed ventilation of the indicator part must be ensured.
For this purpose, the variant with a projecting indicator (HT version) is preferable.
• For device versions with a heating jacket the temperature of the heating medium does not
exceed the maximum permissible product temperature.

2 DEVICE DESCRIPTION
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Using a heat-resistant connecting cable
•HT version - high-temperature version with projecting indicator
•The permitted ambient temperature range is indicated on the nameplate; depending on the
device version it is
T
amb
= -40...+65°C / -40...+149°F or T
amb
= -25...+65°C / -13...+149°F.
•The minimum product temperature is -40°C/-40°F.
Lower product temperatures are possible, provided they do not fall below the permitted
temperature of the indicator (see reference point observation).
Heating jacket T
m
1
without with HT version T
amb
≤40 T
amb
≤60 T
amb
≤65
DN15, DN25, DN50 DN15, DN25 220 105 75
x - 175 95
DN80, DN100 DN50, DN80 165 90 75
x - 155 90
Table 2-2: Temperature table in °C
1Maximum value of the product temperature for the use of a standard connecting cable. For higher product
temperatures a connecting cable with a temperature resistance of 90°C is required.
Heating jacket T
m
1
without with HT version T
amb
≤104 T
amb
≤140 T
amb
≤149
DN15, DN25, DN50 DN15, DN25 428 221 167
x - 347 203
DN80, DN100 DN50, DN80 329 194 167
x - 311 194
Table 2-3: Temperature table in °F
1Maximum value of the product temperature for the use of a standard connecting cable. For higher product
temperatures a connecting cable with a temperature resistance of 194°F is required.

DEVICE DESCRIPTION 2
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Maximum permissible product temperature T
m
[°C]
Heating
jacket
TK T6 T5 T4 T3 T2, T1
without
with HT
version
T
amb
[°C] 
≤40 ≤60 ≤65 ≤60 ≤65 ≤40 ≤60 ≤65 ≤40 ≤60 ≤65
ESK4
DN15
DN25
DN50
DN15
DN25 85 100 90 135 135 200 160 140 235 160 140
x85 100 100 135 135 200 200 200 300 300 270
DN80
DN100 DN50 DN80 85 100 85 135 130 200 150 130 220 150 130
x85 100 100 135 135 200 200 200 300 300 255
ESK4-T
DN15
DN25
DN50
DN15
DN25 85 90 70 135 120 200 140 120 220 140 120
x85 100 85 135 135 200 200 200 300 290 225
DN80
DN100 DN50 DN80 85 85 70 130 115 200 130 115 200 130 115
x85 100 80 135 135 200 200 200 300 270 215
ESK4-FF / ESK4-PA
DN15
DN25
DN50
DN15
DN25 70 60 not adm. 135 125 200 150 125 235 150 125
x85 60 135 135 200 200 200 300 300 240
DN80
DN100 DN50 DN80 65 60 135 120 200 140 120 220 140 120
x85 60 135 135 200 200 200 300 300 225
K1/K2
DN15
DN25
DN50
DN15
DN25 85 100 100 135 135 200 200 180 290 205 180
x85 100 100 135 135 200 200 200 300 300 300
DN80
DN100 DN50 DN80 85 100 100 135 135 200 185 170 260 185 170
x85 100 100 135 135 200 200 200 300 300 300
Table 2-4: Maximum permissible product temperatures in °C

2 DEVICE DESCRIPTION
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Maximum permissible product temperature T
m
[°F]
Heating
jacket
TK T6 T5 T4 T3 T2, T1
without
with HT
version
T
amb
[°F] 
≤104 ≤140 ≤149 ≤140 ≤149 ≤104 ≤140 ≤149 ≤104 ≤140 ≤149
ESK4
DN15
DN25
DN50
DN15
DN25 185 212 194 275 275 392 320 284 455 320 284
x185 212 212 275 275 392 392 392 572 572 518
DN80
DN100 DN50 DN80 185 212 185 275 266 392 302 266 428 302 266
x185 212 212 275 275 392 392 392 572 572 491
ESK4-T
DN15
DN25
DN50
DN15
DN25 185 194 158 275 248 392 284 248 428 284 248
x185 212 185 275 275 392 392 392 572 554 437
DN80
DN100 DN50 DN80 185 185 158 266 239 392 266 239 392 266 239
x185 212 176 275 275 392 392 392 572 518 419
ESK4-FF / ESK4-PA
DN15
DN25
DN50
DN15
DN25 158 140 not adm. 275 257 392 302 257 455 302 257
x185 140 275 275 392 392 392 572 572 464
DN80
DN100 DN50 DN80 149 140 275 248 392 284 248 428 284 248
x185 140 275 275 392 392 392 572 572 437
K1/K2
DN15
DN25
DN50
DN15
DN25 185 212 212 275 275 392 392 356 554 401 356
x185 212 212 275 275 392 392 392 572 572 572
DN80
DN100 DN50 DN80 185 212 212 275 275 392 365 338 500 365 338
x185 212 212 275 275 392 392 392 572 572 572
Table 2-5: Maximum permssible product temperatures in °F

DEVICE DESCRIPTION 2
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Maximum permissible product temperature T
m
[°C]
Heating jacket TK T6 T5 T4...T1
without with HT version T
amb
[°C] 
≤40 ≤60 ≤65 ≤60 ≤65
DN15...DN100 DN15...DN80 with /
without
ESK4 / ESK4-T 40 65 65 65 65
ESK4-FF / ESK4-PA 40 60 not adm. 65 65
K1/K2 40 65 65 65 65
Table 2-6: Maximum permissible product temperatures for painted measuring units in °C
Maximum permissible product temperature T
m
[°F]
Heating jacket TK T6 T5 T4...T1
without with HT version T
amb
[°F] 
≤104 ≤140 ≤149 ≤140 ≤149
DN15...DN100 DN15...DN80 with /
without
ESK4 / ESK4-T 104 149 149 149 149
ESK4-FF / ESK4-PA 104 140 not adm. 149 149
K1/K2 104 149 149 149 149
Table 2-7: Maximum permissible product temperatures for painted measuring units in °F

2 DEVICE DESCRIPTION
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Reference point observation
Reference point observationReference point observation
Reference point observation
The permissible product and ambient temperatures may be exceeded or undershot as long as
the permissible temperature range of the reference point of the display is not exceeded.
The following table contains the permissible maximum values at the reference point.
In this consideration, it should be noted:
•Reference point is the connection of the equipotential bonding conductor of the M40 indicator.
•The temperatures at the reference point are to be determined in the most unfavourable
operating situation.
•The required measuring uncertainty is max. 2 K.
•Measuring conditions and results are to be permanently recorded in a suitable format.
•The measuring unit should be insulated properly.
•At temperatures above 70°C / 158°F, a heat-resistant cable must be used.
Version of
indicator
Component Permitted temperature range at reference point T [°C] according to
temperature class
TK T6/T5 T4 ... T1
M40./../K./... SC3,5-...
SJ3,5-... -25 ... +70 -25 ... +90
SB3,5-... -25 ... +70 -25 ... +70
I7S23,5-... -40 ... +70 -40 ... +90
M40./../ESK/K./... SC3,5-...
SJ3,5-... -25 ... +60 -25 ... +80
SB3,5-... -25 ... +60 -25 ... +70
I7S23,5-... -40 ... +60 -40 ... +80
M40./../ESK/... ESK4A
ESK4-T
ESK4-FF
ESK4-PA
-40 ... +60 -40 ... +80
Table 2-8: Permissible temperatures at reference point of indicator in °C
Version of
indicator
Component Permitted temperature range at reference point T [°F] according to
temperature class
TK T6/T5 T4 ... T1
M40./../K./... SC3,5-...
SJ3,5-... -13 ... +158 -13 ... +194
SB3,5-... -13 ... +158 -25 ... +158
I7S23,5-... -40 ... +158 -40 ... +194
M40./../ESK/K./... SC3,5-...
SJ3,5-... -13 ... +140 -13 ... +176
SB3,5-... -13 ... +140 -13 ... +158
I7S23,5-... -13 ... +140 -40 ... +176
M40./../ESK/... ESK4A
ESK4-T
ESK4-FF
ESK4-PA
-40 ... +140 -40 ... +176
Table 2-9: Permissible temperatures at reference point of indicator in °F

DEVICE DESCRIPTION 2
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2.8 Electrical data
Electrical equipment Nominal voltage Nominal current
Limit switch K1 / K2, OC output 10...30 VDC 5...100 mA per switch
Limit switch K1 / K2, NAMUR output 8VDC ≤1 / ≥3mAperswitch
Signal output ESK4 14...30 VDC 4...20 mA with HART
®
communication
Switching output ESK4-T, OC output < 30 VDC 1...100 mA per circuit
Switching output ESK4-T, NAMUR
output 8VDC ≤1 / ≥3 mA per circuit
Signal input ESK4-T, input < 30 VDC ≤2mA
ESK4-FF Foundation Fieldbus
transmitter 19...32 VDC 16 mA
ESK4-PA Profibus transmitter 29...32 VDC 16 mA
Table 2-10: Electrical data
1Further information and instructions for operation of the ESK4-FF transmitter are provided in separate supplementary instructions.
2Further information and instructions for operation of the ESK4-PA Profibus transmitter are provided in separate supplementary
instructions.

3 INSTALLATION
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3.1 Mounting
Mounting and setup must be carried out according to the applicable installation standards by
qualified personnel trained in explosion protection. The information given in the manual and the
supplementary instructions must always be observed.
Variable area flowmeters must be installed in such a way that
•there is no danger from mechanical impact effects.
•no external forces are affecting the indication unit.
•the device is accessible for any necessary visual inspections and can be viewed from all sides.
•the nameplate is clearly visible.
•it can be operated from a location with secure footing.
Take special note of the installation position for the H250/H/... with horizontal flow
direction:
In order to comply with thermal parameters and measuring accuracy, flowmeters for horizontal
installation are to be installed in the pipeline so that the indicator is located on the side of the
measuring tube. The maximum product and ambient temperatures indicated as well as the
measuring accuracy are based on lateral installation of the indicator.
Figure 3-1: Installation position for the H250/H/... with horizontal flow direction
CAUTION!
The manufacturer is not liable for any damage resulting from improper use or use other than the
intended purpose. This applies in particular to hazards due to insufficient corrosion resistance
and suitability of the materials in contact with product.
DANGER!
Components made of titanium in oxygen applications
Components made of titanium in oxygen applicationsComponents made of titanium in oxygen applications
Components made of titanium in oxygen applications
Variable area flowmeters with titanium components are NOT
NOTNOT
NOT suitable for use in explosion-
protected areas in conjunction with oxygen applications (products with an oxygen content which
is significantly above the oxygen content in the earth's atmosphere)!

INSTALLATION 3
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3.2 Special conditions
Equipotential bonding
Connect the connection parts for the equipotential bonding of the H250 measuring unit and the
M40 indicator to the equipotential bonding system of the hazardous area.
Wetted parts made of titanium
When dealing with device versions with wetted parts made of titanium (TI option), use the
protected installation to prevent sparking due to external impact and friction between titanium
and other materials.
Flammable products
In case of operation with flammable products the measuring units must be included in the
periodic tests of the pipelines and fittings.
IP protection
Use the cable entries and blind plugs supplied or similar types to guarantee an adequate IP
protection class.
Unused cable entries are to be closed.
Electrostatics
To minimise danger due to electrostatic discharge, the variable area flowmeters type
H250/M40...-Ex and indicators type M40...-Ex may not be used in areas in which there are
processes that generate strong charges.
Observe additional information regarding electrostatics.
For further information refer to
Electrostatic charge on page 20.
Thermal data
Observe the maximum ambient and product temperatures.
INFORMATION!
The ground terminal on the gate of the cable entry of the display guarantees an electrostatic
connection of the device and complies with the requirements of an equipotential bonding
connection.

4 ELECTRICAL CONNECTIONS
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4.1 General notes
The built-in equipment is connected electrically in the indication unit.
The connection terminals enable connection to a wire size of 0.25...2.5 mm².
The connecting cables should be selected according to the applicable installation standards and
the maximum operating temperature.
•Before connecting or disconnecting the electric connecting cable of the device, ensure that
all of the cables leading to the signal converter are de-energised relative to each other and to
the reference potential of the hazardous area. This also applies to grounding conductors (FE)
and equipotential bonding conductors (PA).
•The connecting cables must be fixed and laid so they are sufficiently protected against
damage.
•Not used cores must be securely connected to the earth potential of the hazardous area or
carefully insulated against each other and against earth (test voltage ≥500 V
eff
).
•Lay cables so as to ensure that there is sufficient distance between surfaces of the
measuring unit and the connecting cable.
•If the blind plugs / cable entries supplied separately on customer request, the influence of
the components on the IP protection class of the housing or the thermal data must be
validated.
Recommendation:
IP protection class: ≥IP66/68 according to IEC 60529
Temperature range: -40...+90°C / -40...+194°F
•The outer diameter of the connecting cable must be within the sealing range of the cable
entry (7...12 mm / 0.28...0.47").
•Unused cable entries are to be closed (>IP66/67). Supplied plugs should be replaced with
suitable connecting cables.
•Tighten the signal circuit terminals with a tightening torque of 0.5...0.6 Nm.
Ensure that the gaskets and incised gasket ring are tight.
4.2 Power supply
The variable area flowmeter does not require a separate power supply.
The required supply for the built-in electronics is provided via the 4...20 mA current output or the
bus connection.
4.3 Inputs / outputs
The signal circuits of the variable area flowmeter may only be connected to downstream devices
or circuits that satisfy the requirements of protective extra-low voltage (PELV). The terminal
assignment of the built-in electrical equipment is described in the manual.
Only circuits that are suitable for operation in zone 2 hazardous areas may be connected.
Outside of the variable area flowmeter, measures must be taken for the circuits to prevent the
rated voltage from being exceeded by more than 40% due to temporary faults.

ELECTRICAL CONNECTIONS 4
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4.4 Grounding and equipotential bonding
The signal converter shall be connected to the equipotential bonding system of the hazardous
area via the internal or external grounding connection on the signal converter housing.
The measuring unit and the signal converter are electrically connected via an equipotential
bonding connection.
Any existing cable shields should be connected to ground according to applicable installation
regulations. A terminal in the terminal compartment permits a short way grounding of the cable
shields.
Alternatively, the equipotential bonding of the signal converter can also take place by way of the
measuring tube incorporated into the equipotential bonding of the hazardous area.
The measuring tube can be incorporated into the equipotential bonding system of the hazardous
area using the U-clamp mounted on the flange if present, or suitable conductive connections
(gaskets, etc.).
Figure 4-1: Grounding connections
1 Grounding connection on the indicator
2 Outer grounding connection

5 OPERATION
20
H250 M40
www.krohne.com 11/2019 - 4007945001 - AD H250-M40 Exec Gc R01 en
5.1 Start-up
Start-up is only permitted when the variable area flowmeter:
•is correctly installed in the system and connected.
•has been checked for the proper state with regard to its installation and connection
requirements.
•has been properly sealed in the electronic compartment or there is no explosive atmosphere
present.
The operator of the system has to check prior to start-up, if the start-up was in compliance with
the national regulations for checks.
If the device needs to be configured due to the existence of an explosive atmosphere, this can be
done using the supplied programming magnets for versions M40/ESK/ with display. There is no
need to open the housing as it can be done through the glass window of the electronics
compartment or digitally via the signal output (HART
®
interface or Bus interface).
5.2 Operation
Variable area flowmeters must be operated in such a way that they remain within the maximum
and minimum permissible temperatures and pressures and the electrical limit values.
Variable area flowmeters may only be operated if the equipment parts necessary for safety are
effective in the long run, and are not rendered inoperable during operation.
During operation it is only permitted to open the indicator if no explosive atmosphere is present.
5.3 Electrostatic charge
In order to avoid ignition hazards due to electrostatic charge, variable area flowmeters
may not be used in areas with:
•processes that generate strong charges,
•mechanical friction and cutting processes,
•spraying of electrons (e.g. in the vicinity of electrostatic painting systems) or
•pneumatically conveyed dust is exposed.
WARNING!
Ignition risks caused by pressure surges, impact or friction must particularly be avoided when
titanium measuring units are used.
WARNING!
Electrostatic charging of the housing surface by friction must be avoided. The devices must not
be dry cleaned.