Endress+Hauser Oxymax W COS71 Manual

TI286C/07/en/02.07
51506697
Technical Information
Oxymax W COS71
Potentiostatic amperometric three-electrode sensor
Long-term stable sensor for trace measurement
Application
Continuous measurement of the dissolved oxygen
concentration plays an important role in monitoring boiler feed
water:
• Trace quantities
Oxygen may only be present in trace quantities. Excessive
concentrations of oxygen can result incorrosion damage in the
circuit.
• Thermal resp. chemical degassing
Boiler feed water is thermally and chemically degassed to
achieve oxygen-free water. This state must be maintained in
service under process conditions.
• Laboratory measurement vs. continuous process monitoring
Spot laboratory measurements to measure oxygen involve a
risk of error due to sampling errors. Continuous measurement
directly in the process eliminates this risk and provides
reliable information about the state of the medium at any
time.
Your benefits
• Maximum measurement accuracy:
– Longterm-stable measurement thanks to potentiostatic
amperometric three-electrode system
– Long maintenance intervals
– Intelligent sensor self monitoring
• Calibration to any transmitter or location and subsequent
installation at measuring point (in digital mode with Liquisys
M COM 223/253) as calibration data is stored in the sensor
• Membrane covered sensor, i.e.:
– high O2selectivity
– Minimum maintenance effort
– Minimum calibration effort thanks to simple calibration in
air

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Function and system design
Measuring principle The oxygen molecules diffused through the membrane are reduced to hydroxide ions (OH-) at the cathode.
Silver is oxidized to silver ions (Ag+) at the anode (this forms a silver halogenide layer).
A current flows due to the electron donation at the cathode and the electron acceptance at the anode. Under
constant conditions, this flow is proportional to the oxygen content of the medium.
This current is converted in the transmitter and indicated on the display as an oxygen concentration in mg/l,
as a saturation index in % SAT or as an oxygen partial pressure in hPa.
Potentiostatic amperometric
three-electrode system
The high-impedance, current-free reference electrode plays an important role.
The formation of a silver bromide or silver chloride coating on the anode uses up the bromide or chloride ions
dissolved in the electrolyte
In the case of conventional membrane-covered sensors working with the two-electrode system, this causes an
increase in signal drift.
This is not the case with the three-electrode system:
The change in bromide or chloride concentration is registered by the reference electrode and an internal control
circuit holds the working electrode potential constant. The advantages of this principle are significantly
increased accuracy of the signal and considerably extended calibration intervals.
Measuring system A complete measuring system comprises at least:
• Oxygen sensor
• Transmitter, e.g. Liquisys M COM223/253-WX/WS
• Special measuring cable
• Assembly, e.g. flow assembly COA260 or retractable assembly COA451
Optional:
• Junction box VS (with cable extension)
a0004102
Measuring system (example)
1 Flow assembly
2 Junction box VS (optional)
3 Transmitter Liquisys M COM253
4 Oxygen sensor

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Input
Measured variable dissolved oxygen [mg/l, ppm, % SAT or hPa]
Measuring range with Liquisys M COM223/253-WX/WS:
0.001 to 20.000 mg/l
0.0 to 200.0 % SAT
0 to 400 hPa
Wiring
Electrical connection Direct connection to the transmitter (field device)
Connect the sensor directly to the transmitter (COM253-WX/WS) by using the special measuring cable with
SXP plug.
Direct connection to the transmitter (panel mounting device)
• Remove the SXP connector (transmitter side!) from the cable.
• Refer to the following table for the cable assignment and the assigned terminals for
Liquisys M COM223-WX/WS.
• Please note that the cable assignment changes depending on the sensor version (fixed cable or TOP68
connection).
a0004118
SXP plug
Terminal
COM223
Sensor with fixed cable (OMK) Sensor with TOP68 connection
(CYK71)
Core Assignment Core Assignment
87 YE +UBYE +UB
0GY0V WH0V
96 PK NTC (analog) or Com. (digital) GN Communication (digital)
97 BU NTC (analog) or Com. (digital) BN Communication (digital)
88 BN –UBKoax innen –UB
19 GN Alarm
18 WH Sensor signal

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Connection with cable extension
To lengthen the sensor connection beyond the length of the fixed cable, you require a junction box VS.
Always connect the sensor cable with the SXP plug to the junction box.
The cable extension to the transmitter then depends from the transmitter version, i.e. field device or panel
mounted device.
Performance characteristics
Response time •T
90: 0.5 minutes
•T
99: 1.5 minutes (each at 20 °C (68 °F))
Reference operating
conditions
Signal current in air1) approx. 9000 nA
Zero current zero current free
Measured value resolution 0.001 mg/l (0.001 ppm)
Maximum measured error ±1 % of measured value2)
Long-term drift with permanent polarization: < 1 % per month
Influence of medium pressure Pressure compensation not necessary
Polarization time < 60 minutes
Oxygen intrinsic consumption Approx. 900 ng/h in air at 25 °C (77 °F)
a0004129-en
Junction box VS to a field device
1 SXP plug to field device
2 SXP plug from sensor
a0004130
Junction box VS to a panel mounted device
2 SXP plug from sensor
3 Measuring cable (OMK) to the transmitter
4 Connection department of the transmitter
1
2
82 / 3.23
80 / 3.15
mm / inch
3
2
YE
GY
PK
BU
BN
GN
WH
87
0
96
97
88
19
18
4
Reference temperature: 25 °C (77 °F)
Reference pressure: 1013 hPa (15 psi)
1) For the reference operating conditions indicated
2) In accordance with IEC 746-1 at nominal operating conditions

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Installation
Angle of installation The sensor can be installed up to the horizontal in an assembly, support or a suitable process connection.
Other angles are not permissible. Do not install the sensor overhead.
a0004087
Angle of installation
A Permissible installation positions: 0 ... 180 °
!Note!
Make sure you comply with the instructions for installing sensors. You will find them in the Operating
Instructions for the assembly used.
Environment
Ambient temperature range –5 to 50 °C (20 to 120 °F)
Storage temperature filled with electrolyte: –5 to 50 °C (20 to 120 °F)
without electrolyte: –20 to 60 °C (0 to 140 °F)
Ingress protection • Fixed cable versions:
IP 68 (10 m (33 ft) water column at 25 °C (77 °F) in 30 days)
• Top 68 plug-in head versions:
IP 68 (1 m (3.3 ft) water column at 50 °C (122 °F) in 7 days)
Process
Process temperature –5 to 50 °C (20 to 120 °F)
Process pressure max. 10 bar (145 psi) permissible overpressure
Underpressure operation is not permissible.
A

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Mechanical construction
Design, dimensions
Weight with cable length 7 m (23 ft): 0.7 kg (1.5 lbs.)
with cable length 15 m (49 ft): 1.1 kg (2.4 lbs.)
with TOP68 plug-in connection: 0.3 kg (0.66 lbs.)
Material
Process connection G1
Maximum cable length max. 100 m (328 ft) (including cable extension)
Membrane thickness approx. 25 μm
Electrolyte Alkaline electrolyte
a0004083-en
Fixed cable version
a0004084-en
TOP68 version
Sensor shaft:
Membrane cap:
Cathode:
Anode/Reference electrode:
stainless steel1.4571, AISI 316Ti
POM
Silver
Silver / Silver bromide

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Ordering information
Product structure
Scope of delivery The following items are included in the delivery:
• Oxygen sensor with transport protection cap for membrane protection
• Accessories set with the following contents:
– 2 replacement cartridges (replacement membrane caps)
– 10 plastic ampoules containing electrolyte
– 1 sealing kit with 3 O-rings
–6abrasivesheets
• Operating Instructions (on CD only)
• Brief Operating Instructions (paper version)
Accessories
!Note!
In the following sections, you find the accessories available at the time of issue of this documentation.
For information on accessories that are not listed here, please contact your responsible service.
Assemblies (selection) Retractable assembly Cleanfit COA451
• manually driven retractable assembly, stainless steel, with ball valve, for oxygen sensors;
• ordering acc. to product structure (Technical Information TI368C/07/en)
Flow assembly COA260
• for plate or wall mounting, for oxygen trace measurements
• ordering acc. to product structure (Technical Information TI310C/07/en)
Zero solution • 3 units to produce 3 x 1 liter oxygen-free solution
• order no. 50001041
Measuring cable COK31 special measuring cable
• for sensors COS31, COS61 and COS71 with TOP68 plug-in head
• Order numbers:
– Cable length 1.5 m (4.9 ft): 51506820
– Cable length 7 m (23 ft): 51506821
– Cable length 15 m (49 ft): 51506822
Measuring cable OMK
• for use as extension cable between junction box VS and transmitter, not terminated
• sold by the metre - order no. 50004124
Junction box VS junction box
• With plug-in socket and 7-pole plug
• For cable extension from sensor (COS71, COS61, COS31, COS3 with SXP connector) to transmitter, IP 65;
• Order no. 50001054
Certificate
A Ex free version
Cable length
0 Cable length: 1.5 m (4.9 ft)
2 Cable length: 7 m (23 ft)
4 Cable length: 15 m (49 ft)
8 Without Cable (TOP 68 version only)
9 Special design to customer specifications
Cable connection
F Fixed cable connection
S Cable connection using TOP 68 plug (with COM223/253-WX/WS only)
COS71- Complete order code

Transmitter Liquisys M COM 223/253
• Transmitter for oxygen measurement
• field or panel-mounted housing
•Hart
®or Profibus available
• Ordering acc. to product structure, see Technical Information (TI 199C/07/en)
Instruments International
Endress+Hauser
Instruments International AG
Kaegenstrasse 2
4153 Reinach
Switzerland
Tel.[phone]
Fax[phone]
www.endress.com
[email protected]
TI286C/07/en/02.07
51506697
Printed in Germany / FM+SGML 6.0 / DT