ZIROX SGM7.2 User manual

ZIROX Sensoren & Elektronik GmbH Greifswald
Am Koppelberg 21, D-17489 Greifswald ++49 3834 8309 -00, Fax: -29 e-mail: [email protected]
ZIROX®-Oxygen Measuring Systems
SGM7.2
Oxygen measuring device for inert
and reactive gases
Manual

SGM7.2
Manual
Oxygen measuring device
for the determination of oxygen concentrations
in inert and reactive gases
Range: 2 · 105... 10-20 Vol.-ppm Power supply: 100…240 V, 47…63 Hz
HB_SGM72_Rehm_eng.DOC 2

Oxygen Monitor SGM7.2 Contents
Table of contents
1General Information...................................................................................... 5
1.1 Introduction......................................................................................... 5
1.2 Copyright............................................................................................. 5
1.3 Safety symbols and terms................................................................... 6
2Application Field........................................................................................... 7
3Safety Regulations........................................................................................ 8
4Functional Description................................................................................. 9
4.1 Measuring principle............................................................................. 9
4.1.1 General recommendations.................................................... 10
4.1.2 Gas flow quantity .................................................................. 11
4.1.3 Precision of the measuring ................................................... 11
5Technical Data............................................................................................. 12
5.1 Characteristics.................................................................................. 12
5.2 Mechanical data................................................................................ 12
5.3 Electrical engineering/electronics ..................................................... 12
5.3.1 General data......................................................................... 12
5.4 Interface data.................................................................................... 13
6Construction of the Oxygen Monitor SGM7.2 .......................................... 15
6.1 Principle construction........................................................................ 15
6.1.1 General overview.................................................................. 15
6.1.2 Construction principle of the solid electrolyte sensor............ 15
6.1.3 Electronic measured-value processing.................................17
6.2 Using and connection elements........................................................ 18
6.2.1 Power supply ........................................................................ 18
6.3 Front side.......................................................................................... 18
6.3.1 Rear side............................................................................... 19
7Placement and putting into operation ......................................................20
7.1 Installation conditions........................................................................ 20
7.2 Setting up of the operating state....................................................... 20
8Operation and parameter setting .............................................................. 22
8.1 Operation.......................................................................................... 22
8.1.1 Switch on and measurement indication................................ 22
8.1.2 Gas flow adjustment ............................................................. 22
8.1.3 Measuring value monitoring.................................................. 22
8.1.4 Status and error messages................................................... 23
8.2 Parameter Setting............................................................................. 24
8.2.1 Adjustable Parameter ........................................................... 24
8.2.2 Programming menus............................................................. 25
8.3 Calibration......................................................................................... 28
8.3.1 Zero Gas Calibration............................................................. 28
HB_SGM72_Rehm_eng.DOC 3

Oxygen Monitor SGM7.2 Contents
8.3.2 Span Gas Calibration............................................................ 28
8.3.3 Calibration state.................................................................... 29
8.4 Trouble Shooting............................................................................... 29
9Maintenance, overhaul and storage.......................................................... 30
9.1 General Hints.................................................................................... 30
9.2 Replace the equipment fuse............................................................. 30
10 Anhang......................................................................................................... 31
10.1 Fundamentals of the use of potentiometric ZrO2 solid electrolyte
sensors for the optimal guidance of combustion processes ...................... 31
10.2 Mounting Hints for Swagelok®-Fittings........................................... 35
10.3 Charcoal Filter: Description and Using Hints................................. 36
10.3.1 Filter Construction............................................................... 36
10.3.2 Application and Operation of the filter................................. 36
10.3.3 Replacing............................................................................ 36
10.3.4 Technical Data.................................................................... 36
10.4 EU Declaration of Conformity ........................................................ 37
10.5 Warranty Conditions ...................................................................... 38
11 Remarks and Own Notes............................................................................ 39
HB_SGM72_Rehm_eng.DOC 4

Oxygen Monitor SGM7.2 1 General Information
1 General Information
1.1 Introduction
This operation manual describes the design, function and
operation of the oxygen monitor SGM7.2 of the ZIROX GmbH.
Address of manufacturer:
ZIROX Sensoren & Elektronik GmbH
Am Koppelberg 21
D-17489 Greifswald
Phone: ++49 38 34 8309 -00
Fax: ++49 38 34 8309 -29
e-mail: [email protected]
www.zirox.de
The manufacturer assures that this operation manual has
been written in accordance with the functional and technical
features of the delivered SGM7.2.
This operation manual is not subject to the amendment service.
If the manufacturer modifies the SGM7.2 with the aim of making
technical improvements the user is responsible to insert the
additional or updated pages supplied.
Secure and proper function of the SGM7.2 can only be
guaranteed when the contents of this manual are known.
Therefore, all chapters of this manual must be read carefully
before installation and operation of the SGM7.2.
The values shown on the device display in this manual are
samples or presettings of the manufacturer. The process
specific values must be set by the user.
1.2 Copyright
This operation manual is copyright protected.
It may not be partially or totally reproduced, copied, or
distributed, without prior written admission from the
manufacturer, neither are unauthorized use for the purposes of
competition or the handing over of the manual to third parties
permitted.
All rights reserved.
HB_SGM72_Rehm_eng.DOC 5

Oxygen Monitor SGM7.2 1 General Information
1.3 Safety symbols and terms
Symbol for direct imminent hazards
This symbol is shown with recommendations for industrial
safety if a direct danger to the life and health of persons
exists.
If these recommendations are not thoroughly observed, fatal injuries
may result.
Symbol for indirect imminent hazards
This symbol informs about situations where indirect hazards occur.
Degree and intensity of the damage depend on the triggering
actions and the behavior of the persons involved.
Disregard of these hints may result in damage to or destruction
of the entire SGM7.2 or single components, other property, as
well as minor injuries.
Symbol for proper usage
This symbol can be found where the observance of instructions,
regulations, and proper order of actions/events is important.
Not observing these hints may result in damage or
destruction of the SGM7.2 or its single components.
HB_SGM72_Rehm_eng.DOC 6

Oxygen Monitor SGM7.2 2 Application Field
2 Application Field
The protective gas monitor SGM7.2 serves for the continuous
measuring of the oxygen concentration in industrial, laboratory
and protective gases as well as during mixing, production and
processing 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 mixtures is possible.
The SGM7.2 is a modification of the SGM7 for using in soldering
applications.
As
agreed
use
The main application area of the SGM7.2 is the monitoring of technical protecting
gases.
The introduction of explosive gas mixtures, high concentrations of
halogens or sulphuric gases (e.g. SO2) into the SGM7.2 is not
permitted.
The contact of the SGM7.2 with silicon- or phosphorus containing
components is also not permitted.
The SGM7.2 Functions
• measures and indicates the oxygen concentration in a measured
gas continuously
• indicates deviations of the oxygen concentration in the measured
gas from a rated 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 given in the "Technical Data" must be strictly
observed.
Any other use is treated as non-authorized use.
HB_SGM72_Rehm_eng.DOC 7

Oxygen Monitor SGM7.2 3 Safety Regulations
3 Safety Regulations
The following regulations for industrial safety give basic
information about possible hazards during handling and
operation of the buffer gas monitor SGM7.2. Therefore, they
must be observed and strictly followed by the operation and
service staff.
• Secure and proper function of the SGM7.2 can only be
guaranteed when the contents of this manual are known.
Therefore, all chapters of this manual must be read
carefully before installation and operation of the SGM7.2.
• The SGM7.2 may only be used for applications stated as
authorized (see chapter 2).
• The SGM7.2 may only be installed, operated, and
maintained by trained staff.
• In any case, the SGM7.2 must be connected to the main
supply with a socket with earth connection by the supplied
cable.
Explosive gas mixtures, halogens in high concentration, and
gases containing sulfur (e.g. SO2) are not permitted to be
measured by this SGM7.2.
Due to the high operation temperature of the sensor, the SGM7.2
produces much heat.
It has to take care that the piece of equipment is not covered so
strongly that it will be come to overheatings.
Vertical installation is not permitted to avoid possible damages
to the device by localization of heat.
Switch off and disconnect the device from the power supply
before opening the housing cover of the SGM7.2.
Special safety recommendations for possible hazards during
special work or sequences of work are given in the relevant
text.
HB_SGM72_Rehm_eng.DOC 8

Oxygen Monitor SGM7.2 4 Functional Description
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 remarkable temperature independent oxygen
concentration.
The NERNST-equation is used as a basis for determining the
oxygen concentration in gases with the oxygen monitor SGM7.2. NERNST-
Equation
U
RT
F
p
pOair
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 measured gas in Pa.
The sensor of the SGM7.2 is based on the conductivity of
oxide ions in a special ceramic substance (zirconium
dioxide) with stabilising additives. The conductivity of these
oxide ions increases exponentially with the temperature and
it is sufficiently high for temperatures above 600°C.
The gas to be measured passes through the ceramic oxide
ion conductor which is a gas-tight pipe. The ceramic pipe is
situated axially symmetric in a thermally well-insulated
heater. The electrodes of the galvanic sensor are made from
platinum. The electrode on the outside of the pipe,
surrounded by dry air, is used as a reference electrode with
a constant, known electrode potential.
HB_SGM72_Rehm_eng.DOC 9

Oxygen Monitor SGM7.2 4 Functional Description
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
is valid:
Equation
for Oxygen
Concentrati
on
ϕ
O2=20,64 · e(-46,42 · U
T)(II)
ϕ
O2 – oxygen concentration in the measured 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.-%.
4.1.1 General recommendations
The oxygen may be in free or bound form inside the measuring gas1.
Thereby, the following dependencies are valid:
– for free oxygen
UT~
UT
~1– for bound oxygen
The equation (II) for calculating the oxygen concentration is
valid for measured gases with free oxygen as well as for
reducing gas mixtures in which oxygen only exists in bound
form (e.g. in H2/H2O- or CO/CO2-mixtures).
In reducing gas mixtures, 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.
1It has to be distinguished between different conditions of the oxygen in the measuring gas:
Free oxygen: There are the oxygen molecules in the gas independently without every relationship
relation to the other gas components (inert gases such as N2or Ar)
Bound oxygen: There aren't any free oxygen molecules, but only in bound form e.g. as steam in
the gas. At higher temperatures a dissociation is carried out and oxygen molecules then are
availably. Since the dissociation degree increases with the temperature, the measurement result is
also dependent on the temperature.
Circumstances permitting free oxygen can react with perhaps available burning gasses at the hot
platinum electrode, a reducing gas then can be also in the result through what.
HB_SGM72_Rehm_eng.DOC 10

Oxygen Monitor SGM7.2 4 Functional Description
4.1.2 Gas flow quantity
At lower quantities, the measurement results become
distorted by contamination effects of the gas pipes
(leakages, permeability, desertions). If the gas flow trough
the sensor is too much, asymmetric cooling of the sensor
electrodes may cause additional measuring errors.
The constant flow of the measuring gas will be ensured by
internal pump. It can be chosen between High (40 l/h) and
Low (5-10 l/h).
4.1.3 Precision of the measuring
The manufacturer guarantees a measuring error of less than
5% (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 pipe has no
leakages or permeability’s.
For measurements of oxygen concentrations less than 10
ppm, the following aspects must be taken into account
during evaluation:
• composition of the measured gas (e.g. presence of
burning gases)
• specific characteristics of the production process (e.g.
material used)
• temperature of the measured gas.
To reduce the measuring error at low oxygen concentrations,
the following advice must be considered:
• The measuring gas must be taken from a location where
the measuring gas has a homogeneous concentration of
its substances.
• The pipe from the measuring point to the SGM7.2 must
be as short as possible in order to avoid a change in the
chemical balance in the pipe.
• All gas inlet and outlet pipes must be free of leakages.
• For measurements of oxygen concentrations of less
than
1000 ppm, the use of steel pipes is necessary.
• If the measured 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 measured gas should be
filtered by an active charcoal filter before entering the
SGM7.2.
HB_SGM72_Rehm_eng.DOC 11

Oxygen Monitor SGM7.2 5 Technical Data
5 Technical Data
5.1 Characteristics
Description ............................................. Protective gas monitor SGM7.2
Application.............................................. Measuring of the oxygen concentration
in gases
Measuring range .................................... 1 Vol.-ppm…20.6 Vol.-% O2, down to
10-20 Vol.- ppm possible (reducing
conditions, see chap. 4.2),
up to 100 Vol.-% on request
Accuracy at normal pressure.................. Relative measuring error < 5%
Measuring gas throughput...................... 5…10 l/h
Max. permitted pressure of the gas........ 20 mbar over pressure
Max. permitted temp. of the gas............. 80 ° C
Δp 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
Mass....................................................... 3 kg
Gas input................................................ Swagelok®3 mm (at charcoal filter
Swagelok®6 mm)
Gas output.............................................. Tube nipple 4 mm
5.3 Electrical engineering/electronics
5.3.1 General data
Power supply
Voltage........................................ 100…240 V AC, 47…63 Hz
Power consumption .................... 20 VA
Heating measuring cell ............... 24 V DC, approx. 10 W
(controlled internally)
Keyboard and display
Keyboard................................................ 3 buttons
Text indication ........................................ LCD dot matrix
HB_SGM72_Rehm_eng.DOC 12

Oxygen Monitor SGM7.2 5 Technical Data
5.4 Interface data
Serial Interface RS-232
Transfer rate .................................. max. 19200 Baud, adjustable
Stop bits......................................... 1
Data bits......................................... 8
Parity.............................................. none
Handshake..................................... without
MD
TXD
RXD
Pin-Configuration Connector SUB-D 9-pol. F:
Table 1: Serial Interface Protocol (CR = Carriage Return)
Command Returned Data Description
M2CR M2x.xxExxCR Oxygen concentration in ppm
A1CR A1xxxCR Cell voltage in mV
A2CR A2xxxCR Measuring cell temperature in °C
Table 2: Error Indication
Error code Description
Error0 Transmission error
Error1 Warm up
Error2 Cell temperature to low
Error3 Thermocouple defect
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
Table 3: Properties limit value switch
Load Resistive load (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 load 1 mA at 5 V DC
HB_SGM72_Rehm_eng.DOC 13

Oxygen Monitor SGM7.2 5 Technical Data
5.4.1 Pump Controlling
A more powerful pump is integrated at the SGM7.2. It can be also controlled via
RS232:
Table 4: pump controlling via RS232
Command from PC Answer of SGM7.2 Remark
P0CR P0CR pump off
P1CR P1CR pump low
P2CR P2CR pump high
pCR pXCR scan pump state
X=0 pump off
X=1 pump low
X=2 pump high
Control input for pump relay: 24 V DC (internal inverse-polarity protection and
free wheeling diode)
Table 5: Pin config. for 7-pol. Socket and connection cable with plug (1,5m long)
Pin Description Cable colour
1 limit relay NC contact blue
2 limit relay NO contact brown
3 limit relay central contact green
4 pump control white
5 pump control grey
6 output + pink
7 output - yellow
HB_SGM72_Rehm_eng.DOC 14

Oxygen Monitor SGM7.2 6 Construction
6 Construction of the Oxygen Monitor SGM7.2
6.1 Principle construction
6.1.1 General overview
The SGM7.2 is a transportable device. The in principle structure of the
SGM7.2 shows Figure 3.
Fig. 1: Principle construction of the SGM7.2
The measuring gas get into the sensor due to little overpressure at the inlet or
an 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.
6.1.2 Construction principle of the solid electrolyte sensor
12 567 34
Measurig Gas
1 Keramikrohr
2 Keramische Abdeckung der
Referenzelektrode
3 Messelektrode
4 Referenzelektrode
5 Thermoelement
6 Anschlussdraht der
Referenzelektrode
7 Anschlussdraht der
Messelektrode
Fig. 2: Design of the solid electrolyte sensor
HB_SGM72_Rehm_eng.DOC 15

Oxygen Monitor SGM7.2 6 Construction
The measuring cell (sensor) consists of a tube made of
zirconium dioxide (2/1) with two platinum electrode. The
measuring electrode is inside the tube (2/3). The reference
electrode (2/4) is located at the outer side of the tube. It
has a constant electrode potential regarding the
surrounding air. The measuring gas is flowing through the
ceramic tube. The electrodes and the ceramic tube form a
galvanic solid electrolyte measuring cell.
Measuring Cell
(Sensor)
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 due to chemical
unbalances. A thermocouple (2/5) inside the measuring cell
determines the actual electrode temperature. A heater
control assures a constant temperature.
Sensor Heater
The heated measuring cell produces warmth energy.
Therefore the SGM7.2 must not covered.
HB_SGM72_Rehm_eng.DOC 16

Oxygen Monitor SGM7.2 6 Construction
6.1.3 Electronic measured-value processing
The following block circuit diagram illustrates the in principle construction of the
electronic measured-value 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
11
0
-2
30
V
/50
-
60
H
z
Analog out
Fig. 3: Block circuit diagram of the SGM7.2
HB_SGM72_Rehm_eng.DOC 17

Oxygen Monitor SGM7.2 6 Construction
6.2 Using and connection elements
6.2.1 Power supply
The SGM7.2 will be connected to the power supply by
securely attached line cord.
6.3 Front side
The indication and operating devices are at the front of the
SGM7.2. Depending on the size the measured values are
shown either in vol -% or in vol -ppm on a display.
A green or orange light serves as operating indication
depending on chosen limit value and actually measuring
value. A red light points out certain operating or warning
conditions (see chap. 8.1.4).
A keyboard is located on the right side of the front panel. It
serves for the device programming.
Fig. 4: Front side of the SGM7.2
HB_SGM72_Rehm_eng.DOC 18

Oxygen Monitor SGM7.2 6 Construction
6.3.1 Rear side
The gas inlet and outlet, the analog output and limit value
relay (connection for pump control relay included), the
RS232-Interface, the pump switch and the power switch will
be found at rear panel.
The gas inlet is connected with the charcoal filter. The inlet
of the filter is located at the front side.
The line cord is attached to the device. It can not be
disconnected.
Fig. 5: Rear side of the SGM7.2
HB_SGM72_Rehm_eng.DOC 19

Oxygen Monitor SGM7.2 7 Placement
7 Placement and putting into operation
7.1 Installation conditions
The protective gas monitor must be put in a dry and mainly dust-
free place on a stable, flat pad.
• A socket has to be in the immediate proximity of the
installation place of the SGM7.2, if possible as a separate
electrical circuit, protected with a 10 A fuse.
• No heat sources or appliances which produce strong
magnetic fields (e.g. electro motors, transformers) should be
put in the proximity of installation place.
• The working position of the SGM7.2 is horizontal.
A vertical placement is not permitted because of possible
damaging of the gas monitor by heat concentration.
Penetration of liquids into the SGM7.2 can lead to serious
damages or to the complete destruction of the device.
7.2 Setting up of the operating state
If the SGM7.2 has been brought from a cold place to a place of
operation with higher temperature or relative humidity a waiting
period of at least two hours should be attended before switching
on the SGM7.2, in order to compensate the temperature
difference.
1. Put the SGM7.2 on the desired place, regarding the hints in
chapter 7.1.
2. Build the connections from the measurement place to the gas
inlet and outlet of the SGM7.2. Check the connections for
leaks.
3. If a pressure limitation is necessary, place a needle valve
directly in front of the gas inlet (can be delivered by
manufacturer of the SGM7.2).
4. If the measuring gas contains so much water vapor, that the
danger of condensing water in a cold connecting pipe exists, a
water trap must be installed before inflow of the measuring gas
into the SGM7.2 (The penetration of water into the hot measuring
cell can destroy it and therefore must be absolutely prevented.)
5. Connect the SGM7.2 to the power supply.
HB_SGM72_Rehm_eng.DOC 20