ZIROX SGM7 User manual

ZIROX Sensoren & Elektronik GmbH
Am Koppelberg 21, D-17489 Greifswald [phone], Fax: -29 E-mail: [email protected]
ZIROX Oxygen Measuring Systems
SGM7
OXYGEN MEASURING DEVICE
for the determination of oxygen concentrations
in inert and reactive gases
MANUAL
Power supply: 100…240 V, 47…63 Hz

Oxygen Monitor SGM7 Contents
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Table of contents
1 General information .................................................................................... 5
1.1 Introduction........................................................................................ 5
1.2 Copyright........................................................................................... 5
1.3 Commonly used symbols................................................................... 6
2 Application field .......................................................................................... 7
3 Safety regulations ....................................................................................... 8
4 Functional description ................................................................................ 9
4.1 Measuring principle ........................................................................... 9
4.2 General recommendations .............................................................. 10
4.3 Gas flow rate ................................................................................... 11
4.4 Accuracy of the measurement ......................................................... 11
5 Technical data ........................................................................................... 12
5.1 Characteristics................................................................................. 12
5.2 Mechanical data .............................................................................. 12
5.3 Electrical engineering / electronics................................................... 12
5.3.1 General data ........................................................................ 12
5.3.2 Interface data ....................................................................... 12
6 Composition of the oxygen monitor SGM7 ............................................. 14
6.1 General composition........................................................................ 14
6.1.1 General overview ................................................................. 14
6.1.2 Construction principle of the solid electrolyte sensor ............ 15
6.1.3 Electronic data processing ................................................... 16
6.2 Use and connecting elements.......................................................... 17
6.2.1 Current supply...................................................................... 17
6.2.2 Front .................................................................................... 17
6.2.3 Rear ..................................................................................... 18
7 Installation and initiation .......................................................................... 19
7.1 Installation conditions ...................................................................... 19
7.2 Set-up of operating state ................................................................. 19
8 Operation and parametrization................................................................. 21
8.1 Operation......................................................................................... 21
8.1.1 Switch-on and measurement indication................................ 21
8.1.2 Gas flow adjustment............................................................. 21
8.1.3 Data monitoring.................................................................... 21
8.1.4 Status and error messages .................................................. 22
8.2 Parametrization ............................................................................... 23
8.2.1 Adjustable parameters ......................................................... 23
8.2.2 Programming menus............................................................ 24
8.3 Calibration ....................................................................................... 27
8.3.1 Zero calibration .................................................................... 27

Oxygen Monitor SGM7 Contents
8.3.2 Span gas calibration............................................................. 27
8.3.3 Calibration status ................................................................. 28
8.4 Fault clearance................................................................................ 28
9 Maintenance, overhaul and storage......................................................... 29
9.1 General instructions......................................................................... 29
9.2 Replacement of the equipment fuse ................................................ 29
10 Appendix.................................................................................................... 31
10.1 Fundamentals of the use of potentiometric ZrO2 solid electrolyte
sensors for the optimal running of combustion processes......................... 31
10.2 Potentiometric ZrO2-cells for the measurement of the H2O/H2-
ratio 35
10.3 Installation instructions for Swagelok®-fittings .............................. 37
10.4 Activated carbon filter: Description and application instructions.... 38
10.4.1 Filter construction............................................................... 38
10.4.2 Application and operation of the filter ................................. 38
10.4.3 Replacing ........................................................................... 38
10.4.4 Technical data.................................................................... 39
10.5 EU Declaration of conformity ........................................................ 40
10.6 Warranty conditions...................................................................... 41
11 Your own notes and remarks ................................................................... 43

Oxygen Monitor SGM7 1 General information
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1 General information
1.1 Introduction
This manual describes composition, mode of operation and use of the oxygen
monitor SGM7 of the ZIROX GmbH.
Address of manufacturer:
ZIROX Sensoren & Elektronik GmbH
Am Koppelberg 21
D-17489 Greifswald
Tel.: ++49 0 38 34 8309-00
Fax: ++49 0 38 34 8309-29
Email: [e-mail]
The manufacturer guarantees that this manual was written in accordance
with the functional and technical features of the delivered SGM7.
This manual is not subject to the amendment service. If the manufacturer
modifies the SGM7 with the aim of making technical improvements, the user
is responsible for inserting the additional or updated pages supplied.
Proper operation of the SGM7 can only be ensured if the contents of this
manual are known. Therefore, all chapters of this manual must be read
carefully prior to operating the SGM7.
The values on the device display in this manual are examples or preset
parameters of the manufacturer. Process-specific parameters must be set by
the user.
Pages, charts and figures are numbered consecutively.
1.2 Copyright
This operation manual is copyright protected.
It must not be partially or completely reproduced, copied, or distributed,
without prior written permission of the manufacturer. The use for competitive
advantages or the distribution to third parties are not authorized either.
All rights reserved.

Oxygen Monitor SGM7 1 General information
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1.3 Commonly used symbols
Symbol for imminent danger:
This symbol refers to imminent danger to persons’ life and health.
In case of disregard fatal injuries may result.
Symbol for indirect danger:
This symbol indicates indirect danger.
The degree of the damage depends on the circumstances and the
actions of the persons involved.
In case of disregard destruction or damage of the SGM7, its single
components or other material assets as well as minor injuries may
result.
Symbol for proper handling:
This symbol appears where the manual refers to the adherence to
rules, instructions and proper operation.
In case of disregard damage or destruction of the SGM7 or its single
components may result.
danger
NOTE
attention

Oxygen Monitor SGM7 2 Application field
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2 Application field
The protective gas monitor SGM7 serves the continuous measuring of the
oxygen concentration in industrial, laboratory and protective gases as well
as in the process of mixing and producing of special forming gases in
industry. The measuring of the free oxygen concentration in inert gases and
also the measuring of bound oxygen in gas compounds is possible.
The main application fields of the oxygen monitor are:
• processes for mixing and producing of forming gases;
• production processes of welding and soldering, especially gas-
shielded arc welding in steel and container production as well as plant
construction
• production processes of electronic components under buffer gas.
The introduction of explosive gas compounds, high concentrations of
halogens or sulphuric gases (e.g. SO2) into the SGM7 is not permitted.
The contact of the SGM7 with siliconic or phosphoric compounds is not
permitted either.
The SGM7 Functions
• measures and indicates the oxygen concentration in a measuring gas
continuously;
• indicates any deviations of the oxygen concentration in the measuring
gas from an adjustable set value;
• monitors the course of a particular production process under buffer
gas;
• checks the purity of buffer gases and determines whether the
requested protective effect of the buffer gas is reached.
The requirements and limit values provided in "Technical data" must be
strictly observed.
Any other use is treated as non-authorized use.

Oxygen Monitor SGM7 3 Safety regulations
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3 Safety regulations
The following regulations for industrial safety provide basic information about
potential danger during the operation of the buffer gas monitor SGM7. Therefore,
they must be observed and strictly followed by the responsible staff.
• A failure-free and functional operating of the SGM can only be
guaranteed with knowledge of this manual. Therefore, all chapters of
this manual must be read carefully before the installation and initiation
of the SGM7.
• The SGM7 is to be used for the functional operation only (see chapter
2).
• The SGM7 is to be installed, operated, and serviced by trained staff
only.
• The SGM7 is to be connected to an isolated ground socket (Schuko-
socket) with the supplied cable.
Explosive gas compounds, halogens in high concentration, and sulphuric
gases (e.g. SO2) are not permitted to be measured by this SGM7.
Due to the high operation temperature of the sensor, the SGM7 produces a
lot of heat.
Make sure the device does not overheat because of covering.
A vertical installation may cause heat accumulation and damage to the
device.
Switch off and disconnect the device from the power supply before opening
the housing cover of the SGM7.
Special safety instructions for potential danger during certain working
processes are given in relevant text passages.

Oxygen Monitor SGM7 4 Functional description
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4 Functional description
4.1 Measuring principle
In industry and laboratories the measurement of the oxygen concentration in
gases is often required. Mostly, it is measured in gases which have a
considerable, temperature-independent oxygen concentration.
The NERNST equation is used as a basis for determining the oxygen
concentration in gases with the oxygen monitor SGM7.
NERNST
equation
U
RT
F
p
p
O air
O meas gas
=4
2
2
ln ,
, .
(I)
U – cell voltage in V
R – molar gas constant, R = 8.314 J/(mol · K)
T – measuring temperature in K
F– Faraday-constant, F = 9.648 · 104C/mol
pO2,air – partial pressure of the oxygen at the reference electrode
in dry air in Pa
pO2,meas.gas – partial pressure of the oxygen at the measuring electrode
in the measuring gas in Pa.
The sensor of the SGM7 is based on the conductivity of oxide ions in a
special ceramic substance (zirconium dioxide) with stabilizing additions. The
conductivity of these oxide ions increases exponentially with the temperature
and reaches a sufficiently high temperature above 600°C.
The gas to be measured passes through the ceramic oxide ion conductor
which is a gas-tight tube. The ceramic tube is situated axially symmetrically
in a thermally well-insulated heater. The electrodes of the galvanic sensor
are made from platinum. The electrode on the outside of the tube,
surrounded by dry air, is used as a reference electrode with a constant,
known electrode potential. (composition see chapter 6.1.2)

Oxygen Monitor SGM7 4 Functional description
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Based on the assumption that the total pressures of the gases are almost
the same at both electrodes (in this case the volume concentrations may be
used in the calculation instead of the partial pressures) and replacing the
parameters by numbers in equation (I) the following equation applies:
Equation
for oxygen
concentr.
ϕ
O2=20.64 · e (-46.42 · ) (II)
ϕ
O2 – oxygen concentration in the measuring gas in vol%
U – potential difference in mV
T – measuring temperature in K
20.64 – oxygen concentration in air with a relative humidity of
50% in vol%.
4.2 General recommendations
The oxygen may be in free or bound form inside the measuring gas1. (see
chapter 10.1)
Thereby, the following dependencies are valid:
– for free oxygen
– for bound oxygen
The equation (II) for calculating the oxygen concentration is valid for
measuring gases with free oxygen as well as for reducing gas compounds in
which oxygen only exists in bound form (e.g. in H2/H2O- or CO/CO2-
compounds).
1Different conditions of oxygen in the measuring gas must be distinguished:
Free oxygen: Oxygen molecules in the gas are independent without a bond to other gas components
(inert gases such as N2or Ar).
Bound oxygen: Free oxygen molecules do not exist in the gas, only in bound form e.g. as water
vapor. Higher temperatures cause a dissociation and oxygen molecules are available. Since the
dissociation degree increases with the temperature, the measurement result depends on the
temperature.
Possibly, free oxygen can react with potential burnable gases at the hot platinum electrode. The result
can be a reducing gas.
U
T
U T~
U
T
~1
In reducing gas compounds, the oxygen partial pressure is inversely
proportional to the temperature. For converting the measured value at the
measuring temperature into other temperatures special thermodynamic
equations are required.

Oxygen Monitor SGM7 4 Functional description
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4.3 Gas flow rate
For exact measurements a flow rate between 5 and 10 l/h of the measuri
ng
gases must be ensured (see also chap. 8.1.2)
Contamination effects of the gas tubes (leaks, permeability, desorption) may
cause falsified measuring result if the flow rate is too low.
Asymmetric cooling of the sensor electrodes may cause falsified measuring
results if the flow rate is too high.
The gas flow rate is measured by a pressure difference sensor. The SGM7
displays an error message when the limit values are over- or underrun.
However, the measuring will be continued.
4.4 Accuracy of the measurement
The manufacturer guarantees a measuring error of less than 3% (relative
error) only with measurements of oxygen concentrations within a range of 2
· 105 ... 10 ppm. For measurements of oxygen concentrations of 10 ... 10-3
ppm the relative error is less than 5% if the gas inlet tube has no leaks or
permeability.
For measurements of oxygen concentrations less than 10 ppm, the following
aspects must be taken into account during evaluation:
• composition of the measuring gas (e.g. presence of burning gases)
• specific characteristics of the production process (e.g. material used)
• temperature of the measuring gas.
To reduce the measuring error in low oxygen concentrations, the following
conditions must be provided:
• The measuring gas must be extracted where a formation of layers can
be avoided.
• The tube from the measuring point to the SGM7 must be as short as
possible in order to avoid a change in the chemical balance in the tube.
• All gas inlet and outlet tubes must be free of leaks.
• For measurements of oxygen concentrations of less than 1000 ppm,
the use of steel tubes is necessary.
• If the measuring gas contains reducing components (e.g. alcohol), the
concentration of free oxygen cannot be determined correctly as
chemical reactions occur at the electrode. In such cases the measuring
gas should be filtered by an active carbon filter before entering the
SGM7. (see chapter 10.4)
NOTE
NOTE

Oxygen Monitor SGM7 5 Technical data
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5 Technical data
5.1 Characteristics
Description............................................. Protective gas monitor SGM7
Application............................................. Measuring of oxygen concentration
in gases
Measuring range.................................... 1 vol-ppm…20.6 vol% O2, down to
10-20 vol-ppm possible (reducing
conditions, see chapter 4.2),
up to 100 vol% on request
Accuracy at normal pressure ................. Relative measuring error < 5%
Measuring gas flow rate......................... 5…10 l/h
Max. permitted pressure of the gas........ 20 mbar over pressure
Max. permitted temp. of the gas............. 80 ° C
∆p over measuring cell........................... Approx. 1 kPa (100 mm WS) at 10 l/h
Working conditions ................................ 10…45 °C, rH < 80 % at 20 °C
Storage conditions................................. -20…60 °C, rH < 95 % at 20 °C
Degree of protection .............................. IP40
5.2 Mechanical data
Dimensions............................................ 135 x 100 x 240 mm
Weight ................................................... 3 kg
Gas inlet ................................................ Swagelok®3 mm (at carbon filter
Swagelok®6 mm)
Gas outlet .............................................. Tube nipple 4 mm
5.3 Electrical engineering / electronics
5.3.1 General data
Current supply
Voltage....................................... 100…240 V AC, 47…63 Hz
Current consumption .................. 20 VA
Heater measuring cell................. 24 V DC, approx. 10 W
(controlled internally)
Keypad and display
Keypad .................................................. 3 keys
Text display ........................................... LCD dot-matrix
5.3.2 Interface data
Serial interface RS-232
Transfer rate.................................. Max. 19200 Baud, adjustable
Stop bits ........................................ 1

Oxygen Monitor SGM7 5 Technical data
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Data bits ........................................ 8
Parity............................................. None
Handshake .................................... None
Pin assignment connector SUB-D 9-pol. F:
Chart 1: Serial interface protocol (CR = Carriage Return)
Command Display Description
M2CR M2x.xxExxCR Oxygen concentration in ppm
A1CR A1xxxCR Cell voltage in mV
A2CR A2xxxCR Measuring cell temperature in °C
Chart 2: Error indication
Error code Description
Error0 Transmission error
Error1 Warm up
Error2 Cell temperature too low
Error3 Thermocouple defective
Error6 System error
Analog output
Current signal .........................0/4 - 20 mA, potential-free, range adjustable,
apparent Ohmic resistance max. 500 Ohm
Alternative voltage signal........0/2 - 10V (on request), potential-free,
range adjustable
Chart 3: Pin assignment for 4-pol. socket
Pin Description
1 Iout – (optional Uout – )
2 Iout + (optional Uout + )
3 Alarm relay (potential-free contact)
4 Alarm relay (potential-free contact)
Chart 4: Limit value relay
Charge Resistive charge (cosϕ= 1)
Max. switching voltage 125 V AC, 60 V DC
Max. switching current 1A
Max. switching power 62.5 VA, 30 W
Min. permissible charge 1 mA at 5 V DC
MD
TXD
RXD

Oxygen Monitor SGM7 6 Composition
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6 Composition of the oxygen monitor SGM7
6.1 General composition
6.1.1 General overview
The SGM7 is a transportable device. The general composition of the SGM7
is shown in fig. 1.
Fig. 1: General composition of the SGM7
The measuring gas gets into the sensor by means of little overpressure at
the inlet or the optional pump ingests the measuring gas. In the first case,
the optional pressure reducer or needle valve at the gas inlet can be used to
control the gas flow. If the pump is installed, the gas flow is controlled by a
flow control of the pump.

Oxygen Monitor SGM7 6 Composition
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6.1.2 Construction principle of the solid electrolyte sensor
1 2 567 3 4
Measurig Gas
Fig. 2: Composition of the solid electrolyte sensor
The measuring cell (sensor) consists of a tube made of zirconium dioxide
(2/1) with two platinum electrodes. The measuring electrode is inside the
tube (2/3). The reference electrode (2/4) is located on the outside of the tube
and has a constant electrode potential. The electrodes and the ceramic tube
form a galvanic solid electrolyte measuring cell.
Measuring cell
(sensor)
In order to gain a higher oxide ion conductivity of the zirconium dioxide tube,
the sensor is heated to 750°C. This also avoids interfering reactions with
combustible components of the measuring gas at the electrode caused by
chemical unbalances. A thermocouple (2/5) inside the measuring cell
determines the actual electrode temperature. A regulator ensures a constant
temperature.
Sensor heater
The heated measuring cell produces thermal energy. Therefore, the SGM7
must not be covered.
1 Ceramic tube
2 Ceramic cover of reference
electrode
3 Measuring electrode
4 Reference electrode
5 Thermocouple
6 Connecting wire of
reference electrode
7 Connecting wire of
measuring electrode

Oxygen Monitor SGM7 6 Composition
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6.1.3 Electronic data processing
The following block diagram illustrates the data processing.
Sensor
Amplifier for
Cell Voltage
Heater
Control Microcontroller
Sensor Surveillance
Pow er
Supply
1.0 A
0.8 A
Amplifier for
Thermocouple
Display
Keyboard
DC-Output
Relay Outputs
RS-232
110
-
230 V/50
-
60 Hz
Analog out
Fig. 3: Block diagram of the SGM7

Oxygen Monitor SGM7 6 Composition
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6.2 Use and connecting elements
6.2.1 Current supply
The SGM7 is firmly connected with the current supply by a connecting cable.
6.2.2 Front
The indicators and control elements are located on the front of the SGM7.
Depending on the size, the measured values are displayed either in vol% or
in vol–ppm (from 1 % in vol%, below that in vol-ppm).
A green or orange light serves as operating indication depending on the
chosen limit value and actual measuring value. A red light points out certain
operating or warning conditions.
A keypad is located on the right side of the front panel. It serves the
programming of the device.
Fig. 4: Front of the SGM7

Oxygen Monitor SGM7 6 Composition
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6.2.3 Rear
The gas inlet and outlet, the analog output, the RS232-interface and the
power switch are located on the rear panel. The line cord is permanently
fixed with the device. It cannot be disconnected.
Fig. 5: Rear of the SGM7

Oxygen Monitor SGM7 7 Installation
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7 Installation and initiation
7.1 Installation conditions
The protective gas monitor must be set up in a dry and mainly dust-free place
on a stable, flat surface.
• A socket, preferably as a separate electrical circuit, must be available
in immediate proximity of the installation place, protected with a 10 A
fuse.
• No heat sources or appliances which produce strong magnetic fields
(e.g. electric motors, transformers) should be put in the proximity of the
installation place.
• The SGM7 operates in horizontal position.
A vertical placement
may cause damage by heat accumulation and is not
permitted.
A liquid entry can lead to severe damage or to the complete destruction
of the device.
7.2 Set-up of operating state
A temperature compensation is required after the transportation of the device
from cold surroundings to a site with higher ambient temperature or humidity.
A waiting time of about 2 hours before switching-on must be considered.
1. Install the SGM7 in the favored place (see chapter 7.1).
2. Connect point of measurement and places of gas inlet and outlet of the
SGM7. Pay attention to leak-tightness.
3. If a pressure limit is required, install a needle valve directly in front of the
gas inlet (available from manufacturer of the SGM7).
4. If the amount of water vapor in the measuring gas is likely to cause a
condensation of water in a cold gas pipe, a water trap must be installed
in front of the gas inlet. (The penetration of water into the hot measuring
cell can destroy it and therefore must be absolutely prevented.)
5. Connect the SGM7 to the power supply.
On long transport routes and at unfavorable temperatures the material
of the connecting tubes must rule out any oxygen permeability. The
manufacturer recommends the following materials in dependence on
the measuring conditions:
Material of the
connecting
tubes
NOTE
NOTE

Oxygen Monitor SGM7 7 Installation
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Low temperature of measuring gas..................Thick-wall PVC-hose
Higher temperature of measuring gas Tygon R 3603 (supplier
e.g. Novodirekt Kehl)
Oxygen concentration of < 100 ppm ................Stainless steel tube.
Silicone can cause measuring inaccuracies because of its oxygen
permeability. Therefore, the manufacturer advises against a usage.
The measuring gas can also flow through the SGM7 when it is off.
For using Swagelok®-fittings please note the manufacturer’s advice in the
appendix of this manual!
NOTE