Witt MG 50-2ME User manual

Copyright WITT-GASETECHNIK GmbH & Co KG, 2016, all rights reserved
Instruction Manual for
WITT Gas Mixer
MG 50,100,200-2ME
MG 50,100,200-2ME PvDu
MG 50,100,200-2ME GB
Issue: 29.04.2016
This issue is not subject to change management

Page 2 of 27
WITT-GASETECHNIK GmbH & Co KG
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
: [phone]
www.wittgas.com
Gas Safety- & Control Equipment
D-58454 Witten
Fax: [phone]
[e-mail]
1 Table of contents
1Table of contents......................................................................................................... 2
2Notes on this manual.................................................................................................. 4
2.1 What does this manual contain?.........................................................................................................4
2.2 Structure of the manual.......................................................................................................................4
2.3 Rights to this manual...........................................................................................................................5
2.4 What symbols are used?.....................................................................................................................5
2.5 Terms (in alphabetical order) ..............................................................................................................6
3Safety instructions and precautionary measures .................................................... 8
3.1 General safety instructions..................................................................................................................8
3.2 Gas mixer with oxygen........................................................................................................................9
3.3 Liability.................................................................................................................................................9
4Description ................................................................................................................ 10
4.1 Types ................................................................................................................................................10
4.2 Applications for the gas mixer...........................................................................................................11
4.3 Functional description of the gas mixer.............................................................................................11
4.3.1 Technical data on the gas mixer............................................................................................11
4.4 Function of the alarm module............................................................................................................12
4.4.1 Technical data on the alarm module......................................................................................12
4.4.2 The terminal strip (rear)..........................................................................................................12
5Setting up and installation ....................................................................................... 13
5.1 Checking for transport damage.........................................................................................................13
5.2 Place for setting up............................................................................................................................13
5.3 Safety instructions for installation......................................................................................................13
5.4 Installation of the pipes......................................................................................................................14
5.5 Electrical installation..........................................................................................................................15
5.5.1 Connection of the floating contacts........................................................................................15
6Commissioning and operation................................................................................. 16
6.1 Safety instructions for commissioning and operation........................................................................16
6.2 Commissioning the gas mixer...........................................................................................................16
6.3 Operating the gas mixer....................................................................................................................17
6.3.1 Setting the mixing valve (24) on models MG200...................................................................17
6.4 The alarm module..............................................................................................................................18
6.4.1 Buttons and displays..............................................................................................................18
6.4.2 Inlet pressure monitoring alarm..............................................................................................18
6.5 Malfunctions and rectification............................................................................................................19
6.5.1 Malfunction table....................................................................................................................19
6.6 Taking out of operation......................................................................................................................21
6.7 Short interruption in work ..................................................................................................................21
7Servicing and maintenance...................................................................................... 22
7.1 Safety instructions for servicing and maintenance............................................................................22
7.2 Repair instructions.............................................................................................................................22
7.3 Checks and servicing tasks...............................................................................................................23
7.4 Checking inlet filters for blockages....................................................................................................24
7.4.1 Plug filters (for version MG 50, MG 100, MG 200).................................................................24
7.4.2 Screwed filters (for version MG 200, MG 500).......................................................................24
7.5 Functional check on the electrical equipment...................................................................................24
7.6 Setting the receiver pressure ............................................................................................................24
7.7 Reset of the temperature monitor for the mixed gas temperature (optional) .........................................25

Page 3 of 27
WITT-GASETECHNIK GmbH & Co KG
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8Concise instructions on operation ..........................................................................26
8.1 Switching on.......................................................................................................................................26
8.2 Switching off.......................................................................................................................................26
9Appendices................................................................................................................27

Page 4 of 27
WITT-GASETECHNIK GmbH & Co KG
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2 Notes on this manual
You have decided for a gas mixer from WITT-GASETECHNIK.
With this manual, we would like to provide you with all the information necessary for safe, correct
setting up and installation, commissioning, operation and checking of the gas mixing system.
2.1 What does this manual contain?
The operation and maintenance of the WITT gas mixer are described in this manual.
Observance of the manual helps avoid hazards, down times due to incorrect operation and to en-
sure long service and reliability of the gas mixer.
The handling of gases, particularly inflammable and/or toxic gases, requires a high degree of cau-
tion. To prevent incorrect operation this instruction manual must be fully read carefully, and under-
stood, prior to the installation and commissioning of the gas mixer. This manual must be available
to the operating personnel during the operation of the gas mixer. The operating personnel must be
familiar with the operation of the gas mixer and instructed by qualified personnel.
If unexpected malfunctions occur that you cannot rectify with the assistance of the instruction man-
ual, please contact us stating the device number on the rating plate (see also technical data, Sec-
tion 9) or fax us the first page of the technical data with a short description of the fault. Do not for-
get to state your company, your name, and your telephone number.
Our address is:
WITT-GASETECHNIK GmbH & Co KG
Salinger Feld 4-8
D-58454 Witten
Tel.: [phone]
Fax: [phone]
You can of course also send us an e-mail (servi[email protected]) or visit our homepage at
http://www.wittgas.com.
In the case of modification to the gas mixing system this instruction manual ceases to be applica-
ble!
2.2 Structure of the manual
This manual is sub-divided into several sections:
In the “Notes on this manual” section the layout of the instruction manual is explained and
the terms and symbols used explained.
In the “Safety instructions and precautionary measures” section suggestions for safe us-
age of the gas mixer are listed. You should pay particular attention to this section as failure to
observe the information given here can result in equipment damage and physical injury.
In the “Description” section the function of the WITT gas mixer is explained based on the
function scheme.
The function of the integrated alarm module is addressed in the “Function of the alarm module”
section.
In the “Set up and installation” section you will find information on the correct location for set-
ting up the gas mixer and notes on both the gas and electrical installation.
In the “Commissioning and operation” section you will learn how you must proceed so that
mixed gas is produced and how you can change the composition of the mixed gas. Here you
will also find information on how to proceed if the alarm module signals insufficient inlet pres-
sure and the possible causes of this situation. You will also learn here how you can take the
gas mixer out or operation. e.g., for servicing tasks.

Page 5 of 27
WITT-GASETECHNIK GmbH & Co KG
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Information on servicing tasks that you can perform yourself is given in the “Servicing and
maintenance“ section. Here you will also find notes on what you should check if, at some
point, a feature does not function correctly.
The “Concise operating instructions” provide you with information on the operation of the
gas mixer in short steps.
As an appendix to this manual you will find the technical data on the WITT gas mixer, the
schemes given in the technical data, along with drawings and a list of symbols. This provides a
short overview on the function and the controls on the gas mixer. You will also find the num-
bers for the symbols on the function scheme on the components themselves. With the aid of
the list of symbols and function scheme, you can identify components in the gas mixer.
2.3 Rights to this manual
This manual is the copyright of WITT-GASETECHNIK GmbH & Co KG.
Without the prior written agreement of WITT-GASETECHNIK GmbH & Co KG the manual is not
permitted to be duplicated or used in a manner contrary to the company’s due interests.
It is only permitted to pass this manual on to third parties in conjunction with the provision of the gas
mixer.
2.4 What symbols are used?
The attention symbol indicates hazards for man or the system.
It is imperative that these instructions are observed and followed.
The word “Caution!” is placed in front of information indicating risk of injury- and potentially
fatal hazards.
The word “Attention!”is placed in front of hazards for the system.
Note!
The pointing hand marks general notes that explain operating procedures.
The “dot” marks actions to be performed.
This symbol is used for a list.
This symbol indicates that you should turn the page.
This symbol indicates sections that only apply to the PvDu and GB versions.
PvDu
GB

Page 6 of 27
WITT-GASETECHNIK GmbH & Co KG
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2.5 Terms (in alphabetical order)
In this section the terms necessary to understand this manual are explained.
*These terms are explained in more detail in the following text.
Alarm module :
The alarm module is on the separate control housing. It signals insuf-
ficient gas inlet pressure* and indicates the corresponding gas.
Constant pressure (Pm) :
The individual gases are reduced to the constant pressure by the
constant pressure regulator unit*. The constant pressure is the pres-
sure of the individual gases from the dome or double dome loaded
pressure regulators.
Constant pressure
regulator unit :
The constant pressure regulator unit comprises dome or double dome
loaded pressure regulators and a p
ilot pressure regulator*. The gases
to be mixed are regulated to the required constant pressure* by the
constant pressure regulator unit.
Dome loaded pressure
regulator :
A dome loaded pressure regulator functions similarly to a spring-
loaded pressure reg
ulator, however in this case the force from the
spring is replaced by the pilot gas pressure on a membrane. If several
dome loaded pressure regulators are subjected to the same pressure-
regulated pilot gas, then the same constant pressure* is established a
t
each of the dome loaded pressure regulators.
Double dome loaded
pressure regulator :
A double dome loaded pressure regulator* can be considered as two
single dome loaded pressure regulators*. Both chambers in the dome
loaded pressure regulator are subje
cted here to a gas, the pilot gas*;
this results in exactly the same pressures being established at the
outlets of the dome loaded pressure regulator. Together with the pilot
pressure regulator*, the dome and double dome loaded pressure
regulators in a gas mixer form the constant pressure regulator unit*.
Gas inlet pressure (Pv) :
The pressure provided by the supplies for the individual gases is
termed the gas inlet pressure. A differentiation is made between static
and dynamic pressure. If no mixed gas is
produced, no gas flows. The
pressures now present at the inlet to the gas mixer are static pres-
sures. However, if mixed gas is produced, the gas inlet pressure
drops to the dynamic pressure as a function of the sizing of the gas
supply.
The static pressu
re is always higher that the dynamic pressure. The
static pressure (without mixed gas production) must not exceed the
maximum permitted inlet pressure. The dynamic pressure (during the
production of mixed gas) must not drop below the minimum required
gas inlet pressure (in the case that inlet pressure monitoring is acti-
vated, this would result in the triggering of the alarm).
Inlet pressure
monitoring :
The inlet gas pressure monitoring comprises pressure switches*
or
pressure transmitter* and an alarm mo
dule*. It is used to check for the
minimum gas inlet pressure required. The inlet pressure is only moni-
tored to check if the inlet pressure drops below the min. inlet pressure
given in the technical data.
Mixed gas output (QM) : The mixed gas output is t
he mixed gas flow that the gas mixer can
produce in the normal operating state (P=1
bar; T=15 °C). The mixed
gas output will depend on the mixture this value relates to air.

Page 7 of 27
WITT-GASETECHNIK GmbH & Co KG
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Mixing valve : Mixing valves are only used in gas mixers for more than two gases.
The percentage portion of the related gas type is set on the mixing
valves. It must be noted that the total of all portions set must always
add up to 100%.
Non-return valve : The non-
return valves prevent the gases from each individual phase
flowing back into the other gases.
Outlet pressure (Ph) : The outlet pressure is the mixed gas pressure in the mixed gas re-
ceiver on the outlet of the gas mixer.
Pilot gas :
One of the gases used in the mixing process is defined as the pilot
gas and is used as the m
edium to be applied to the dome loaded
pressure regulators (via the pilot pressure regulator). If the supply of
the pilot gas is lost, the production of gas mixture is also lost com-
pletely. The pilot gas must therefore always be connected with suffi-
cient g
as inlet pressure, even if it is not used in the mixing process
itself.
Pilot pressure regulator :
The pressure to be applied to the dome loaded pressure regulator* is
adjusted on the pilot pressure regulator. In the dynamic condition, the
pilot pressure is slightly higher than the constant pressure.
Pressure switch /
Pressure transmitter :
The pressure switches or pressure transmitter
monitor the required
gas inlet pressures for the gases supplied. Together with the alarm
module, this then forms the inl
et pressure monitoring*. The pressure
switches only monitor the minimum inlet pressure required, and not
the maximum inlet pressure.
Proportional mixing
valve :
A proportional mixing valve is only found on gas mixers for two gases.
Here the percentage po
rtion of the gas named on the adjusting knob
is set. If the portion of a gas is increased, then portion of the other gas
is automatically reduced.
Receiver pressure (Pb) :
The receiver pressure is the pressure of the mixed gas in the mixed
gas receiver. It fluctuates between the minimum and maximum re-
ceiver pressure that is set on the pressure switch.
Supply gas :
All gases that are mixed including the pilot gas are termed supply
gases.

Page 8 of 27
WITT-GASETECHNIK GmbH & Co KG
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Gas Safety- & Control Equipment
D-58454 Witten
Fax: [phone]
[e-mail]
3 Safety instructions and precautionary measures
It is imperative that the following safety instructions and precautionary measures are observed and
followed. They are intended to avoid hazards that can arise during the use of the system.
In addition, the applicable national health and safety regulations and safety regulations from the
trade associations are to be observed. For example, in Germany:
Health and safety regulations from the trade associations
a) DGUV Regulation 1 Grundsätze der Prävention (principles of prevention)
b) DGUV Regulation 3 Elektrische Anlagen und Betriebsmittel
(Electrical Systems and Equipment)
c) BGR 500 Sec. 2.33 Gase (Gases)
d) BGR 500 Sec. 2.32 Sauerstoff (Oxygen) - if used as a supply gas
The Pressure Devices Regulations and appropriate technical regulations
a) TRB 600 Aufstellung der Druckbehältern (Installation of Pressurised Vessels)
b) TRB 404 Ausrüstung der Druckbehälter, Ausrüstungsteile
Equipment for Pressurised Vessels, Equipment Parts)
c) TRB 700 Betrieb von Druckbehältern (Operating Pressurised Vessels)
must be observed.
No claim is made that this list is absolute.
Along with the instruction manual and the health and safety regulations applicable in the country
and place of use, recognised engineering regulations for safe and correct working are to be ob-
served.
The operating organisation must ensure that only authorised persons work on or with the system.
The gas mixer is built to the state of the art and is safe to operate. Hazards can be produced by the
gas mixer if it is used incorrectly by untrained personnel, or is not used for the purpose intended.
3.1 General safety instructions
Caution!
Only persons who have been instructed on the operation of the system and who have read
and understood this manual are permitted to use the system.
Observe national technical regulations on the handling of gases, e.g. applicable health and
safety regulations.
Any unauthorised modifications or changes to the system are forbidden for safety reasons.
Malfunctions arising during operation may only be rectified by trained personnel.
Maintenance- and repair tasks may only be performed by trained personnel.
During all maintenance- and repair tasks ensure that the gas mixer is isolated from mains elec-
tricity (also observe external voltage, e.g. via floating contacts) and is de-pressurised.
All supply pipes to and from the gas mixer are to be designed for the maximum permitted gas
pressure. If this is not possible for the system following the gas mixer, then it must be ensured
that the maximum permitted pressure for the following system cannot be exceeded by means
of the installation of suitable fittings, e.g., bursting discs or safety valves.
The material for the gas pipes (pipes from the gas supply to the inlets on the gas mixer), all fit-
tings installed there (e.g. shut-off valves, gauges, etc.) and all sealing elements there must be
designed for the related type of gas.
The material for the gas outlet pipe (pipe from the outlet on the gas mixer to the load), all fit-
tings installed there (e.g. shut-off valves, gauges, etc.) and all sealing elements there must be
designed for all the related types of gas.
The maximum gas inlet pressures in the technical data must not be exceeded. If necessary
this is to be ensured by the installation of safety valves or bursting discs.
Check the connections and joints for leaks to atmosphere at regular intervals (e.g. at every
commissioning) with inert gas and document this check. For this purpose only use suitable
leak detection methods. Never check using a naked flame! If you find leaks, rectify them im-
mediately; the applicable safety regulations are to be observed during this process.

Page 9 of 27
WITT-GASETECHNIK GmbH & Co KG
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Gas Safety- & Control Equipment
D-58454 Witten
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Also check cables for damage, as well as the supply pipes to the gas mixer and the gas mixer
to the load for leaks.
When using toxic or corrosive gases, for your safety continuously monitor the atmosphere in
the workplace using a gas warning system.
The gas mixer must be used in a well ventilated area. If there is any doubt regarding the venti-
lation then the area should be monitored for minimum oxygen levels and maximum CO2or
flammable gas levels if they are part of the mixture.
A wrong gas mixture may be generated either when the gas mixing unit is started or possibly
as a result of a functional fault during operations, or as a result of the process in the down-
stream system, and for this reason the downstream consumer must be suitable for operations
with wrong gas mixtures. If this is not the case, the gas mixture must be permanently moni-
tored at a suitable place by an analyser to prevent the gas mixture entering a wrong area with-
out having been monitored.
The use of the gas mixer for a purpose other than that intended involves safety risks. Usage for a
purpose other than that intended includes, for example:
Use with gases other than those listed in the technical data.
Operation of the gas mixer with liquids.
The use of the gas mixer in ambient temperatures outside the temperature range specified in
the technical data.
The use of the gas mixer with gases at temperatures outside the temperature range specified
in the technical data.
The installation and operation of the gas mixer in areas with an explosion hazard.
In the case of unauthorised, unapproved changes, modifications, or conversions to the gas mixer,
the guarantee is void.
3.2 Gas mixer with oxygen
Caution!
In the case of the usage of oxygen, the German health and safety regulations BGR 500 Sec.
2.32 must be observed. In particular, the following applies:
The supply pipe for oxygen may only be installed in the connection provided for this purpose.
The oxygen connection must be kept oil-free and grease-free, and also free of soiling.
A vent pipe must be fitted to the safety valve on the receiver (if fitted); this must be designed
such that any gas escaping can flow out without hazard. The vent pipe must be designed such
that the required mass flow rate can be reliably and safely drawn off and the function of the
safety valve is not impaired.
A wrong gas mixture (e.g. pure oxygen) may be generated either when the gas mixing unit is
started or possibly as a result of a functional fault during operations, or as a result of the pro-
cess in the downstream system, and for this reason the downstream consumer must be suita-
ble for operations with wrong gas mixtures (e.g. pure oxygen). If this is not the case, the gas
mixture must be permanently monitored at a suitable place by an analyser to prevent the gas
mixture entering an undefined range without having been monitored.
Observe the maximum control pressure in the technical data.
3.3 Liability
The liability for the function of the unit passes in all cases to the owner or operating organisation as
far as the unit is operated by persons who do not belong to WITT Service, is incorrectly maintained
or repaired, or if the unit is used in a manner that does not comply with the intended usage of the
unit, or is contrary to the applicable regulations.
WITT-GASETECHNIK GmbH & Co KG is not liable for damages arising from failure to observe
these instructions.

Page 10 of 27
WITT-GASETECHNIK GmbH & Co KG
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4 Description
4.1 Types
The MG series comprises as standard the types MG 50, MG 100, MG 200 and MG 500. The differ-
ences between the types lie in the mixed gas outputs.
The gas mixer is specified in more detail by further additions. Please see the information in the en-
closed technical data for the specification of your gas mixer (see Section 9).
MG
50
100
200
500
-2
-3
-4
ME
GB
PvDu
PmDü
A
Ex
Ex Ex-Version (ATEX)
A Analysis
GB Inlet pressure monitoring,
solenoid valve closes on alarm
PvDu Inlet pressure monitoring
PmDü Pilot pressure monitoring
ME elec. pressure switch / solenoid valve
combination
Number of gases
Mixed gas output
Big gas mixer (Gross-Mischer)

Page 11 of 27
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4.2 Applications for the gas mixer
The gas mixer is used for the intermittent generation of gas mixture from two different gases.
A receiver (see technical data section 9) must be connected after the gas mixer, if not already pro-
vided. It is possible to continuously draw mixed gas from 0 to the maximum mixed gas output (see
technical data Section 9) without any change to the precision of the mixing.
The gas mixer is only suitable for the application area specified in the technical data (Section 9).
The information in Section 3 of this manual and the related safety instructions are to be observed.
4.3 Functional description of the gas mixer
Note!
The functional description is given with the aid of the enclosed function schemes (see Sec-
tion 9). You will also find the numbers for the symbols on the function scheme on the com-
ponents themselves. With the aid of the list of symbols and the function scheme, you can
identify components in the gas mixer.
The individual gases are supplied separately to the system via the correspondingly marked gas
connections with filters (1,2) and inlet pressure monitoring (PvDu and GB version).
A mixed gas receiver with safety valve is connected after the gas mixer. Please see the technical
data (Section 9) for the volume. If this is not the case, the customer is obliged to install an appro-
priate mixed gas receiver after the gas mixer; it is to be possible to continuously draw gas mixture
from 0 to the max. gas mixture output from the mixed gas receiver.
In the case of the PvDu and GB versions, the unit is equipped with inlet pressure monitoring that is
automatically activated when the power supply to the unit is switched on.
If the inlet pressure for one of the gases drops below the permitted minimum pressure, then the
green LED for this gas goes out on the alarm module (81). In addition the alarm is also indicated on
the LCD display. In the case of the GB version the solenoid valve (27) also closes and the audible
alarm device (84) emits an audible warning signal.
Note!
The production of mixed gas is only interrupted on the GB version.
By means of a constant pressure regulator unit, comprising the pressure regulator (13) and the pi-
lot pressure regulator (15), the gases to be mixed are set to a constant pressure. This ensures that
the mixture ratio remains constant with reducing pilot gas pressure, however the mixed gas flow is
reduced.
Note!
In the case of the loss of the pilot gas, the production of mixed gas is automatically
interrupted.
The required mixture ratio is set at the proportional mixing valve (24) in vol.-%.
The mixed gas then flows through a pressure switch or pressure transmitter / solenoid valve com-
bination (29,27) into the receiver. The receiver pressure can be read on the gauge (28).
If the receiver pressure drops to the minimum due to the drawing of gas, the solenoid valve (27) in
the outlet on the gas mixer opens and the receiver is filled with mixed gas to the maximum receiver
pressure. For the factory setting of the receiver pressure, please see the technical data (Section 9).
In the case of the MG100 and MG 200 versions is inside the mixer a metering valve (30) for open-
ing the connection to a separate analyser (if supplied).
Optionally a temperature monitor is located in the mixed gas outlet (see chapter 7.7).
4.3.1 Technical data on the gas mixer
Please see the enclosed data sheet for the technical data on the gas mixer (see Section 9).
PvDu
GB

Page 12 of 27
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[e-mail]
4.4 Function of the alarm module
The alarm module is used together with the pressure switches or pressure transmitters to monitor
the inlet pressures on a maximum of three gas inlets. An alarm is present if the pressure drops be-
low the minimum inlet gas pressure on at least one of the three gas inlets (see technical data). An
alarm is indicated on the LCD display and a floating contact switches.
In the case of the GB version the solenoid valve (27) also closes and the audible alarm device (84)
emits an audible warning signal.
Note!
For more information see separate manual of the alarm module.
4.4.1 Technical data on the alarm module
Parameter
Connection Number
MIN
TYPE
MAX
Unit
Power supply
230 V
X1:1, X1:2 180 230 240 V (AC)
Powert consumption
5.0
VA
Working temperature
0
50
Degrees C
Rating of the floating
contacts X1:4, X1:5, X1:6 250 2
24
2
V (AC)
A
V (DC)
A
Rating of the +24 V
connection
– mA
4.4.2 The terminal strip (rear)
Power supply
GND / alter-
nating signal
Alarm relay connections
Digital inputs
Output
Neutral
wire
Phase
On alarm
alternating
signal
Centre
contact
No
alarm
Alarm
IN 1
IN 2
IN 3
+24V
N
L1
C
NO
NC
X1:
1
2
3
4
5
6
7
8
9
10
Note!
In case of an alarm the connection X1:3 switches cyclically.
PvDu
GB

Page 13 of 27
WITT-GASETECHNIK GmbH & Co KG
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Gas Safety- & Control Equipment
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Fax: [phone]
[e-mail]
5 Setting up and installation
In this section you will find information on the correct location for setting up the mixer, and notes on
both the gas and electrical installations.
5.1 Checking for transport damage
Note!
Never transport the system in a tilted position.
Perform a visual inspection for external damage and damage to cables (nicks, damage to
the insulation).
The gas mixer system is supplied ready to use. It must be correctly transported.
5.2 Place for setting up
Note!
Never subject the system to direct sunlight or sources of large amounts of heat.
Note!
Do not operate the system in an environment with increased electromagnetic activity (out-
side the standardised limits).
Note!
Observe the safety distances when setting up.
The gas mixer housing must remain accessible for servicing work.
Place the undamaged unit on a solid surface in a place protected from the weather and se-
cured against accidents.
During setting up observe the ambient conditions stated in the technical data (Section 9)
(e.g., ambient temperature, safety zone, humidity, dust, altitude).
5.3 Safety instructions for installation
Caution!
Prior to initial commissioning and after changes, repairs, or expansion of the system / unit,
the safety checks required by DGUV Regulation 3 (reference to DIN VDE 0100, DIN VDE
0701, DIN VDE 0702, etc.) are to be performed and logged. The checks encompass the in-
spection, testing, and measuring of the effectiveness of protective measures (e.g. emergen-
cy stop devices, interlocks, pressure switches, etc.)
If the operating organisation is not in a position to perform a check, a check in accordance
with DIN VDE 0702 can be performed by WITT Service.
Caution!
In accordance with DGUV Regulation 3 a protective earth connection (PE connection) of
protection class 1 must be provided.
Caution!
Following initial commissioning and after changes, repair, or expansion of a system / unit,
the connections and joints are to be checked for leaks to atmosphere with inert gas (docu-
ment this check). For this process only use suitable leak testing procedures (never test with
a naked flame). If you find leaks, rectify them immediately; the applicable safety regulations
are to be observed during this process.
Caution!
All supply pipes to and from the gas mixer are to be designed for the maximum permitted
gas pressure. If this is not possible for the system downstream of the gas mixer, then it
must be ensured that the maximum permitted pressure for the downstream system cannot
be exceeded by means of the installation of suitable fittings, e.g., bursting discs or safety
valves.

Page 14 of 27
WITT-GASETECHNIK GmbH & Co KG
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Caution!
The material for the gas pipes (pipes from the gas supply to the inlets on the gas mixer), all
fittings installed there (e.g. shut-off valves, gauges, etc.) and all sealing elements there must
be designed for the gas to be used.
Caution!
The material for the gas outlet pipe (pipe from the outlet on the gas mixer to the point of
use), all fittings installed there (e.g. shut-off valves, gauges, etc.) and all sealing elements
there must be designed for all the gas to be used.
Caution!
The gases to be mixed must only be supplied via the gas inlet connections with the corre-
sponding markings.
Caution!
The maximum gas inlet pressures in the technical data must not be exceeded. If necessary
this is to be ensured by, e.g., the installation of safety valves or bursting discs.
5.4 Installation of the pipes
Install the separate filter (if supplied) as near as possible at the gas mixer.
Consider the flow direction!
Attention!
Ex factory the gas mixers are equipped with gas inlet filters. The filters are built in or are de-
livered separately (usually from MG200 upwards). The filters protect the gas mixers and in-
crease their life-span. The filters are designed for normal industrial use with clean gases
and purged and cleaned pipe system.
If higher soiling is expected additional fine filter must be installed by customer. These filters
must be designed for the pressure and gas flow necessary for the mixing system. Willingly
we offer adequate components to you.
Install the pipes necessary for the gas supply in a correct manner.
Observe following safety instructions:
Caution!
The pipes must be un-pressurised during connection.
Attention!
It is to be ensured the pipes ahead of the system are appropriately sized to ensure the ade-
quate supply of the individual gases to be mixed (inside diameter at least as large as the
connections, see technical data Section 9).
Attention!
It must be possible to shut off the gas supply pipes before the gas mixer.
Attention!
All supply and outlet pipes must be free of oil and grease, and free of other contamination
(e.g. dust, etc.). If necessary all pipes are to be blown out using nitrogen or clean, oil-free air
prior to connection to the gas mixer.
Note!
A mixed gas receiver with safety valve is connected after the gas mixer. Please see the
technical data (Section 9) for the volume. If this is not the case the customer must connect
an appropriate mixed gas receiver after the gas mixer!
Install the pipe from the outlet of the mixed gas receiver to the point of use taking the shortest
path.
Attention!
It must be possible to shut off the gas before the point of use.
Install a suitable vent pipe on the outlet of the safety valve on the receiver.
In the case of the use of flammable gases and/or toxic gases, ensure that the gas is piped
away safely (e.g. above the roof).

Page 15 of 27
WITT-GASETECHNIK GmbH & Co KG
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Note!
It is sensible to install a vent pipe with a shut-off valve after or at the gas receiver so that in-
correctly mixed gas can be blown off on initial commissioning, on changes to the gas mix-
ture and during servicing and repairs, without the need for the gas to flow over the normal
point of use.
It also necessary to ensure that the gas is piped off safely here (e.g. above the roof). The
vent pipe is to be appropriately sized!
5.5 Electrical installation
Establish the connection to the mains using the plug.
The installation of the electrical connections as per the electrical circuit diagram must be per-
formed in accordance with VDE 0100.
Observe following instructions:
Note!
The usage of cables that are not approved can result in irreparable damage to the cables in
the case of heavy mechanical loading. In the case of cables that are not twisted or screened,
signal processing may be imprecise.
Note!
Protect the cables from mechanical loads (e.g. using a suitable cable duct). Excessive me-
chanical loading can result in irreparable damage to the cable.
Note!
It is imperative that the supply voltage in the technical data is provided.
Note!
Do not yet switch on the power supply.
5.5.1 Connection of the floating contacts
AC voltages up to 250 V, 2 A and DC voltages up to 24 V, 2 A can be connected to the alarm relay
connections. X1:4 is the centre contact for the relay contacts. If there is no alarm, the centre con-
tact is connected to X1:5. In the case of an alarm the centre contact is switched to X1:6.
PvDu
GB

Page 16 of 27
WITT-GASETECHNIK GmbH & Co KG
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Gas Safety- & Control Equipment
D-58454 Witten
Fax: [phone]
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6 Commissioning and operation
Here you will learn how you must proceed so that mixed gas is produced and how you can change
the mixture. You will also learn here how you can take the gas mixer out of operation, e.g., for ser-
vicing tasks.
Note!
If malfunctions occur during commissioning or operation, try to rectify the fault with the aid
of the malfunction table (Section 6.5.1).
If it is not possible to rectify the fault, please take the system out of operation and inform
the responsible customer service department at the manufacturer.
6.1 Safety instructions for commissioning and operation
Caution!
The system may only be operated by persons who have been instructed on the operation of
the system and who have read and understood this manual.
Attention!
Always open the gas supply pipes slowly.
A sudden pressure rise can damage the device.
Note!
Also observe the general safety instructions in Section 3.1.
6.2 Commissioning the gas mixer
Note!
Ensure that the system is not pressurised and shut-off the pipe to the point of use.
The pilot pressure regulator must be released!
On models MG200 see the special hints for setting the proportional mixing valve in Sec. 6.3.1.
If fitted, open the vent pipe.
Open the gas supply pipe for the gas that is not used as the pilot gas adjust the inlet pressure
(see technical data) and observe the inlet pressure gauge.
Open the gas supply pipe for the gas that is used as the pilot gas adjust the inlet pressure (see
technical data) and observe the inlet pressure gauge.
On the proportional mixing valve now set the required mixed gas composition in vol.-%.
Again check the inlet pressures to the gas mixer.
Turn the pilot pressure regulator to the pilot pressure (see technical data) and observe the pilot
pressure gauge at the front.
Note!
The pressure regulators are secured. If settings should be made proceed as follows:
The pressure is reduced by turning the knob anti clockwise, and increased by turning the
knob clockwise.
First pull the black setting knob, then turn the knob to make the correct setting.
If the setting is made, push the black setting knob back to lock the setting.
Connect to the power supply and switch on the gas mixer using the master switch on the front.
The solenoid valve in the outlet opens and gas flows until the maximum receiver pressure is
reached in the mixed gas receiver connected after the gas mixer. For the factory setting of the
receiver pressure, please see the technical data (Section 9).
Note!
If changes of the receiver pressure are necessary, please refer to the instructions in Section
7.6. If the pressure ratios are altered the mixed gas output also changes.
Note that the pressure drop above the constant pressure regulator unit and above the mix-
ing valve must be at least 1 bar.

Page 17 of 27
WITT-GASETECHNIK GmbH & Co KG
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The inlet pressure monitoring is now activated automatically.
In case of an alarm, see Section 6.4.2.
If all OK LEDs illuminate during operation, the gas mixer operates fully automatically.
Open the metering valve (30) inside the mixer for the connection to a separate analyser (if
supplied).
You can now close the vent pipe (if fitted) after the receiver.
All pressures should then be checked during operations.
Attention, it is imperative that the following is observed!
Check the connections and joints for leaks to atmosphere after commissioning and at regu-
lar intervals with inert gas and document this check.
For this process only use suitable leak testing procedures (never test with a naked flame). If
you find leaks, rectify them immediately; the applicable safety regulations are to be ob-
served during this process.
Remove the covers of the housing to check the inside components.
6.3 Operating the gas mixer
Once you have placed the gas mixer in operation, as described in Section 6.2, and checked for
leaks to atmosphere, proceed as follows:
Open the pipe to the point of use.
After a short period the required mixed gas will be present in the pipe to the point of use.
The gas mixer now operates automatically and generates mixed gas as required.
If an analyser is connected the mixing ratio is displayed. The gas mixer functions correctly
when the mixing ratio corresponds with the default value.
Mixed gas can be drawn at any flow between 0 and the maximum mixed gas output.
While the system is in operation you can:
Change the mixture ratio by turning the proportional mixing valve.
6.3.1 Setting the mixing valve (24) on models MG200
Attention!
Don´t try to set the proportional mixing valve (24) if the pilot / receiver pressure is above
5 barg. If you have to change the mixture ratio proceed as follows:
First lower the pilot pressure to about 4 barg.
Let the mixed gas flow away until the pilot / receiver pressure reaches that pressure.
Set the desired mixed gas composition to the desired composition.
Re set the pilot pressure to the desired pressure.
PvDu
GB

Page 18 of 27
WITT-GASETECHNIK GmbH & Co KG
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Gas Safety- & Control Equipment
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Fax: [phone]
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6.4 The alarm module
The layout of the alarm module is shown in the following figure:
6.4.1 Buttons and displays
On the front of the alarm module there are three membrane buttons, three green ON LEDs, three
green OK LEDs and a LCD display.
If the alarm module is configured appropriate monitoring of the gas inlet pressures can be switched
off and on by pressing the buttons.
After switching the device on check whether the inlet pressure monitoring for the different gases is
activated. The three ON LEDs indicate which inlet pressures are monitored. If the ON LED is illu-
minated, then the related inlet is monitored.
In addition this is also indicated on the LCD display. Two of the four monitored inputs are indicated
alternating at a time.
The OK LEDs indicate the state of the gas pressures to be monitored. If the OK LEDs are illumi-
nated, then the associated gas pressure is adequate and there is no alarm condition.
Note!
In the event of alarm, only the channels marked with the gas types are of importance. Chan-
nels that are not occupied have no function.
6.4.2 Inlet pressure monitoring alarm
Note!
Inlet pressure monitoring is activated when the power supply is connected.
This is signalled by a green ON LED on the alarm module above the gas type label. If the inlet
pressures are adequate, a further OK LED is illuminated per gas phase used.
If the gas inlet pressure in one of the supply pipes drops during operation, there is an alarm. An ac-
cording error message is shown on the LCD display. On the GB version the solenoid valve in the
mixed gas outlet closes and the mixed gas production is interrupted.
At the same time the green OK LED goes out for the gas type for which the inlet pressure has
dropped below the minimum.
A connected alarm device (e.g. audible alarm device or alarm lamp) also announces the alarm.
Check admission pressure and, if necessary, readjust.
If necessary, check the gas supply.
Actual pressures
Gas1
8,7 bar
Gas2
11,8 bar
Gas1 Gas2 –
Buttons
ON-LED
OK-LED
LCD display

Page 19 of 27
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Fax: [phone]
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6.5 Malfunctions and rectification
6.5.1 Malfunction table
Malfunction Cause Remedy
•No production of mixed gas •Gas supply closed
•Power supply interrupted
•Main fuse is defective
•Solenoid valve faulty
•Gas outlet closed
•The temperature monitor
(18, optional) has
closed the solenoid
valve (27) by reason of
too low mixed gas tem-
perature
•Open gas supply
•Check connection to the
mains or connect to the
mains
•Check, replace if necessary
•Contact
WITT-GASETECHNIK
•Open gas outlet
•Safety system for the down-
stream connected system.
For cancelling the lock see
Sec. 7.7
•
Mixed gas output drops or is
too low
•Cross-section of the
supply pipe too small
•Filter in the inlet blocked
•The inlet pressure has
dropped below the min.
•Cylinder regulators are
designed for flow setting,
not pressure-setting
•See instructions on
installation, Sec. 5.4.
•Clean filters in the inlet or
replace if necessary
(see Sec. 7.4)
•Increase inlet pressures
(see tech. data, Sec. 9)
•Install regulators with pres-
sure setting/indicator
•Gas consumption too high •Leaks in the system •Rectify leaks
•Pressure indication on the
manometer too high
•Solenoid valve does not
close
•Solenoid valve faulty.
Contact
WITT-GASETECHNIK
•Receiver pressure switch /
transmitter faulty. Contact
WITT-GASETECHNIK
•Pressure indication on the
manometer too low
•Too much mixed gas
drawn
•Solenoid valve does not
open
•The inlet pressure has
dropped below the min.
•Reduce amount of mixed gas
drawn
•Solenoid valve faulty.
Contact
WITT-GASETECHNIK
•Receiver pressure switch /
transmitter faulty. Contact
WITT-GASETECHNIK
•Increase inlet pressures
(see tech. data, Sec. 9)

Page 20 of 27
WITT-GASETECHNIK GmbH & Co KG
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Gas Safety- & Control Equipment
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Malfunction Cause Remedy
•Incorrect mixture •Gas supply pipe mal-
function
•The inlet pressure has
dropped below the min.
•Clean filters in the inlet or
replace if necessary
(see Sec. 7.4)
•Check inlet pressures
(see tech. data, Sec. 9)
•Incorrect mixture •Incorrect setting of pro-
portion.
•Solenoid valve leaks. A
very low flow is still
passing through the so-
lenoid valve, filling the
receiver up to control
pressure
•
Receiver pressure / max.
switching point setting to
high
•Receiver pressure is
correctly set, but sole-
noid valve does not cut-
off the mixed gas flow at
max. receiver pressure
set-point
•Incorrect pressure drop
between inlet-, control-,
max. receiver pressure
under flowing conditions
•Alter setting due to require-
ment
•Isolate mixed gas line down-
stream of the receiver and
observe receiver pressure
gauge. If receiver pressure
exceeds set max. value
(switching point) check cor-
rect setting of pressure switch
first
•Solenoid valve faulty.
Contact
WITT-GASETECHNIK
•See manual, alter setting of
pressure switch, according to
data indicated in manual. If
pressure switch does not al-
low correct setting, replace.
•Solenoid valve faulty.
Contact
WITT-GASETECHNIK
•Follow manual, alter pressure
settings, if necessary
•Solenoid valve opens/
closes in very high frequen-
cy (less than 2-3 sec.)
•Size of mixed gas re-
ceiver does not fit with
mixer capacity
•Restrictions between
mixer and receiver or in-
correct pipe-diameter
•Mixed gas consumption
is slightly beneath mixed
gas max. capacity
•Observe recommendation of
manual, install receiver of
suitable size
•Check pipe and pipe-
diameter and install tube with
sufficient diameter
•Increase inlet pressure/ con-
trol pressure to achieve high-
er capacity
•No lights on alarm
module
•No power supply
•Alarm module faulty
•Check connection to the
mains or connect to the
mains
•Contact
WITT-GASETECHNIK
Note!
In the case of other malfunctions contact us or an authorised centre to have the unit
checked.
The gas mixer is only permitted to be placed back in operation after it has been checked
and repaired by us or an authorised centre.