Endress+Hauser OxyMax W COS 71 User manual

Quality made by
Endress+Hauser
ISO 9001
BA 286C/07/en/07.01
Nr. 51506699 OxyMax W COS 71
Sensor for Measuring
Dissolved Oxygen
Operating Instructions

OxyMax W COS 71
Endress+Hauser
Table of contents
1 Safety instructions . . . . . . . . . . . . . . . . . 2
1.1 Notes on safety conventions and icons . . . . . . 2
1.2 Designated use . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Installation, commissioning and operation . . . 2
1.4 Operational safety . . . . . . . . . . . . . . . . . . . . . . 3
1.5 Return . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.6 Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Identification . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Product structure . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Scope of delivery . . . . . . . . . . . . . . . . . . . . . . . 4
3 Installation . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 Measuring device . . . . . . . . . . . . . . . . . . . . . . 5
3.2 Installation conditions . . . . . . . . . . . . . . . . . . . 6
3.3 Installation location and position . . . . . . . . . . . 7
3.4 Sensor design and functional description . . . . 9
3.5 Post-installation check . . . . . . . . . . . . . . . . . . 11
4 Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1 Direct connection to the transmitter . . . . . . . . 12
4.2 Connection via the junction box VS . . . . . . . . 12
4.3 Post-connection check . . . . . . . . . . . . . . . . . 13
5 Commissioning . . . . . . . . . . . . . . . . . . 14
5.1 Function check . . . . . . . . . . . . . . . . . . . . . . . . 14
5.2 Polarisation . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.3 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6 Maintenance . . . . . . . . . . . . . . . . . . . . . . 17
6.1 Cleaning the outside of the sensor . . . . . . . . . 17
6.2 Regeneration . . . . . . . . . . . . . . . . . . . . . . . . . 18
7 Accessories . . . . . . . . . . . . . . . . . . . . . . . 20
7.1 Connection accessories . . . . . . . . . . . . . . . . . 20
7.2 Installation accessories . . . . . . . . . . . . . . . . . 20
7.3 Spare parts kit . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.4 Spare parts . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.5 Measurement and controlling . . . . . . . . . . . . . 20
8 Troubleshooting . . . . . . . . . . . . . . . . . . 21
8.1 Troubleshooting instructions . . . . . . . . . . . . . . 21
8.2 Sensor test . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
8.3 Spare parts . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
9 Technical data . . . . . . . . . . . . . . . . . . . . 23
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

1 Safety instructions OxyMax W COS 71
2Endress+Hauser
1 Safety instructions
1.1 Notes on safety conventions and icons
#Warning!
This symbol alerts you to hazards which could cause serious injuries as well as
damage to the instrument if ignored.
"Caution!
This symbol alerts you to possible faults which could arise from incorrect operation.
They could cause damage to the instrument if ignored.
!Note!
This symbol indicates important items of information.
1.2 Designated use
The oxygen sensor COS 71 is suitable for continuous measurement of dissolved oxygen
traces in water.
The main application is the trace measurement of dissolved oxygen in boiler feed water
of power plants.
#Warning!
•If the device is used for any application other than those described in this manual, it
may lead to unsafe and improper functioning of the measuring system and is therefore
not permitted.
•Make sure you strictly adhere to the warnings and notes in these
Operating Instructions.
•The manufacturer is not liable for damage caused by improper use or use other than
that for which it is intended.
1.3 Installation, commissioning and operation
#Warning!
•Only trained technical personnel may carry out installation, electrical connection,
commissioning, operation and maintenance of the measuring system. The technical
personnel must be authorised to do this by the system operator.
•Technical personnel must be familiar with the instructions in this manual and must
adhere to them.
•Before switching on the system, check all the connections again for correctness.
•Do not operate damaged sensors. Indicate them as being defective.
•Measuring point faults may only be remedied by authorised and trained personnel.
•If faults cannot be repaired, the measuring device must be taken out of service and
secured against unintentional commissioning.
•Repairs may only be carried out by the manufacturer or by the Endress+Hauser
service organisation.

OxyMax W COS 71 1 Safety instructions
Endress+Hauser 3
1.4 Operational safety
The COS 71 sensor is operationally reliable and is made to the state of the art.
The appropriate regulations and EC directives have been met.
As the user, you are responsible for complying with the following safety conditions:
•Explosion protection regulations
•Installation instructions
•Operating instructions for the assembly and its materials
•Local prevailing standards and regulations
1.5 Return
If the device requires repair, please send the sensor clean (see Seite 17) to the
appropriate Endress+Hauser sales offices. Please use the original packaging where
possible.
Please add the filled in »Declaration of contamination« (copy the last but one page of
this manual) to the packing of the sensor and add it also to the shipping documents.
1.6 Disposal
Defective, non-repairable sensors must be disposed of.
Please keep to the local disposal regulations!

2 Identification OxyMax W COS 71
4Endress+Hauser
2 Identification
2.1 Product structure
2.2 Scope of delivery
!Note!
•Make sure the packaging is undamaged!
Inform the post office or the courier of any damage to the packing.
Keep the damaged packaging until the matter has been cleared.
•Make sure the contents are undamaged!
Inform the post office or the courier of any damage to the delivered contents.
Keep the damaged products until the matter has been cleared.
•Use the delivery papers to check that the scope of delivery is complete.
The following items are included in the delivery:
•1 oxygen sensor COS 71 with transport protection cap for membrane protection
•Accessories set COY 31-S-Z with the following contents:
–1 spare replacement cartridge COY 31-S-WP
–10 plastic ampoules containing electrolyte COY 3-F
–1 sealing kit COY 31-OR with 3 O-rings
–6 polishing sheets
•Operating Instructions BA 286C/07/en
If you have questions, please contact your supplier or your nearest
Endress+Hauser sales office (see the back page of this Operating Instructions).
Certifikate
A Version for non-hazardous area
Cable length
0 Connection cable 1,5 m
2 Connection cable 7 m
4 Connection cable 15 m
8 Cable not included (only for TOP 68 version)
9 Special version
Cable connection
F Fixed cable connection
S Cable connection via TOP 68 connector (only when using Liquisys M COM 223/253-WX/WS)
COS 71- Complete order code

OxyMax W COS 71 3 Installation
Endress+Hauser 5
3Installation
3.1 Measuring device
A complete measuring system comprises:
•Oxygen sensor OxyMax W COS 71
•Oxygen transmitter Liquisys M COM 223/253-WX/WS
Optional:
•Flow assembly FlowFit W COA 260
•Junction box VS
Fig. 3.1: Complete measuring device for COS 71 with Liquisys M COM 223/253-WX/WS
1 Junction box VS (only if cable extension required)
2 Transmitter Liquisys M COM 223/253-WX/WS
3 Flow assembly COA 260
4 Oxygen sensor COS 71
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3
4

3 Installation OxyMax W COS 71
6Endress+Hauser
3.2 Installation conditions
3.2.1 Installation dimensions
Fig. 3.2: Dimensions COS 71
fixed cable version
Fig. 3.3: COS 71 with TOP 68 plug-in head and
TOP 68 plug-in cable
220
Ø40
186
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OxyMax W COS 71 3 Installation
Endress+Hauser 7
3.3 Installation location and position
The sensor can be installed up to the horizontal in an assembly, support or a suitable
process connection (Fig. 3.4). Other angles are not permissible. Do not install the
sensor overhead.
Permissible installation .
Fig. 3.4: Permissible installation positions for the COS 71 oxygen sensor
!Note!
Make sure you comply with the instructions for installing sensors. You will find them in
the Operating Instructions for the assembly used.
Installing a
measuring point
For a complete installation of a measuring point, proceed as follows:
1. Installing the flow assembly.
2. Installing and connecting the oxygen sensor.
"Caution!
•Screw the sensor into the assembly so that the cable is not twisted.
•Avoid exerting excessive tensile force on the cable (e.g. from jerky pulling).
•Select the installation location so that there is easy access for later calibration.
#Warning!
When using metallic assemblies and installation equipment, comply with national
grounding regulations.
3.3.1 Installation example
Flow operation
Install the COA 260 flow assembly acc. to Fig. 3.5 to ensure a total height of 540 mm for
sensor installation or removal. The inlet is at the bottom of the assembly, the outlet lateral
of the assembly. If necessary use devices for cooling the medium resp. for pressure
minimisation to ensure not to exceed the maximum permissible values of 50 °C
resp. 10 bar.
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Permissible angle of installation

3 Installation OxyMax W COS 71
8Endress+Hauser
Please pay attention to the following notes if the assembly is used in a pressure system
with reflow (Fig. 3.6) instead of free outlet:
"Caution!
For pressures > atmospheric pressure
•Pressurisation and work at a constant overpressure up to 10 bar poses no problems.
•Rapid pressure loss at the measuring point leads to air degassing in the electrolyte
due to the sudden reductions in solubility. This could lead to a swelling of the sensor
membrane.
Avoid this problem by keeping up the pressure on the sensor. In the case of rapid
pressure loss e.g. during maintenance work on the pipeline close all the valves
(manual mode: manually actuated valves, automatic mode: solenoid valves, see Fig.
3.6, Pos. 4 and 5) of the assembly.
Fig. 3.5: Flow assembly COA 260 Fig. 3.6: Bypass installation with manually
actuated valves or solenoid valves
1 Cap 1 Main line
2 Pressing screw 2 Medium return
3 Intermediary 3 Flow assembly COA 260
4 Flow vessel 4, 5 Manually actuated or solenoid valves
6 Flow assembly COA 250-A
6 Medium removal
Ø60
400
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1
2
3
4
Required
total height
for sensor
installation or
removal
540 mm
1
23
4
5
6
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OxyMax W COS 71 3 Installation
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3.4 Sensor design and functional description
The following figures show an enlarged side view (Fig. 3.8) and a top view (Fig. 3.9) of
the sensor head.
3.4.1 Design
The sensor consists of the following
function units:
•Sensor body with integrated
sensor electronics
•Sensor head with gold cathode,
counter electrode and
reference electrode
•Membrane cap with electrolyte
•Protection basket
The electrical connection is either done by
a fixed cable (1) or by a TOP 68 plug-in
connection.
The threaded connection G 1 (2) is
designed for installing the sensor in an
assembly.
The protection basket (4) is screwed on.
The membrane cap screwed onto the
sensor head is filled with electrolyte. The
screw connection seals it from the
medium.
The membrane which is in contact with the
medium is seated tightly in the membrane
cap (pretensioned in the factory).
The gold cathode (5), the counter elec-
trode (Ag/AgBr, 8), the reference electrode
(Ag / AgBr, 9) and two internal temperature
sensors are located inside the sensor
head.
Fig. 3.7: Design of the sensor COS 71
1 Sensor cable
2 Threaded connection G 1
3 Sensor body
4 Protection basket
5 Gold cathode
6 Membrane
7 Electrolyte
8 Counter electrode
9 Reference electrode
Fig. 3.8: Sensor head with membrane cap
(Side view with cut-away view of
membrane cap)
Fig. 3.9: Sensor head (top view with membrane
cap removed)
1 Screw thread for protection basket 6 Membrane cap
2 Sealing ring 7 Counter electrode
3 Screw thread for membrane cap 8 Reference electrode
4 Electrolyte 9 Gold cathode
5 Membrane
1
3
4
5
6
7
8
2
9
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1
2
3
4
5
6
7
8
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3 Installation OxyMax W COS 71
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3.4.2 Functional description
Polarisation
When the sensor is connected to the transmitter, a fixed external voltage is applied
between the cathode and anode. The resulting polarisation current is indicated on a
display on the transmitter. The current starts high but then drops over time. The sensor
can only be calibrated when the display is stable.
Membrane
The oxygen dissolved in the medium is conveyed to the membrane by the incoming
flow. The membrane is only permeable for dissolved gases. Other substances
dissolved in the liquid phase e.g. ionic substances, will not penetrate through the
membrane. Therefore, medium conductivity has no impact on the measuring signal.
Only the white membrane cap with a 25 µm membrane (fast response time) is used for
the sensor COS 71. Do not use the black membrane cap with 50 µm membrane
(for sensor COS 31 resp. COS 41).
Amperometric measuring principle
The oxygen molecules diffused through the membrane are reduced to hydroxide ions
(OH-) at the gold cathode. Silver is oxidised to silver ions (Ag+) at the anode (this forms
a silver bromide layer, AgBr).
A current flows due to the connected electrode release at the gold cathode and
accepted at the anode. In equilibrium, this flow is proportional to the oxygen content of
the medium.
This current is converted in the measuring instrument 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 three-electrode system
Unlike the two-electrode system the anode of the three-electrode system is splitted in a
current-carrying counter electrode and a currentless reference electrode. The latter
shows an essentially better potential stability due to its high resistance wiring. A closed
control loop inside the sensor electronics together with the three-electrode system
results in correct adjustment of the oxygen specific working potential at the gold
cathode. In case of advanced electrolyte consumption or in case of high measuring
current the loop tuning remains reliable. The advantages are an essentially better signal
accuracy and an extension of the calibration intervals.
Adaptive control of polarisation voltage (ACPV)
The potential of the working electrode versus the reference electrode is continuously
changed depending on the measured current value. The ACPV function calculates an
optimum polarisation voltage from the instantaneous sensor current and controls it. This
leads to an effective minimisation of the oxygen independent zero current. The
advantages are a better signal resolution and a linearity of the calibration function also
with very small oxygen concentrations.
Self control
Continuous resistance measurement between the measuring chamber and the medium
leads to immediate identification of leakages of the membrane or of the measuring
chamber locking. This provides a high protection from measuring errors, from escaping
of the electrolyte or from penetration of the medium into the electrolyte.
This function is not available in media with very low conductivity.

OxyMax W COS 71 3 Installation
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3.5 Post-installation check
After installing the sensor, carry out the following checks:
Checks Remarks
Membrane OK (visual inspection)? Replace membrane if there is a leak.
Compliance with permissible sensor installation position? see Chapter 3.3
Sensor installed tightly in flow assembly? Avoid leakages.
Right flow set ? See Technical data in chapter 9.

4Wiring OxyMax W COS 71
12 Endress+Hauser
4Wiring
4.1 Direct connection to the transmitter
The sensor COS 71 is connected to the transmitter using a special measuring cable with
SXP plug-in head (fig).
To connect the sensor to a field instrument COM 253-WX/WS plug in the sensor
plug-in head into the SXB plug-in of the transmitter.
To connect the sensor to a panel mounting instrument COM 223-WX/WS cut the SXP
plug-in head (to restore the plug-in head follow the instructions of chapter 4.2 ). Find the
termination of the measuring cable, the colours of the cable cores and the pin No. of the
transmitter terminal block in the following table.
4.2 Connection via the junction box VS
To extend the sensor connection beyond the length of the fixed cable, use a junction
box VS. The extension to a field instrument COM 253-WX/WS is done by the
measuring cable OMK with SXP plug-in head.
The connection to a panel mounting instrument COM 223-WX/WS is done at the
terminal block of the transmitter. Find the pin assignment and the colours of the cable
cores in the table from the chapter »Direct connection to the transmitter«.
The extension of the sensor cable via the junction box VS and the two variants of
connection (field instrument and panel mounting instrument) to the transmitter are given
in figs. 4.2 and 4.3 on page 13.
Fig. 4.1: SXP plug-in head
PIN Fixed cable version (OMK) TOP 68 plug-in connection (CYK 71) PIN
COM 223
Colour Assignment Colour Assignment
1yellow+U
Byellow + UB87
2greyOV whiteOV 0
3 pink NTC (analogue) or communic. (digital) green Communication (digital) 96
4 blue NTC (analogue) or communic. (digital) brown Communication (digital) 97
5brown–UBCoax in. –UB88
6 green Alarm 19
7 white Sensor signal 18
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OxyMax W COS 71 4 Wiring
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Junction box VS
4.3 Post-connection check
After wiring up the electrical connection, carry out the following checks:
Fig. 4.2: Cable extension to a field instrument
COM 253-WX/WS via junction box VS
Fig. 4.3: Cable extension to a panel mounting
instrument COM 253-WX/WS via junction
box VS
1 SXP plug-in head to COM 253-WX/WS 3 OMK cable to COM 223-WX/WS
2 SXP plug-in head of COS 31
Instrument status and specifications Remarks
Are the sensor, assembly, junction box or cable damaged ? Visual inspection
Electrical connection Remarks
Does the supply voltage of the transmitter match the specifications on the
nameplate ?
230 V / 115 V / 100 V AC
24 V AC / DC
Are the installed cables strain-relieved and not twisted ?
Is the cable type route completely isolated ? Power cable/weak current cable
Are the power supply and signal cable correctly connected to the
transmitter ?
Are all the screws terminals properly tightened ? Use the connection diagram of
COM 2x3.
Are all the cable entries installed, tightened and sealed ?
Are all the cable entries installed downwards or lateral ?
For cable entries lateral: cable loops downwards for water to be able to
drip off.
82
80
1
2
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2
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5 Commissioning OxyMax W COS 71
14 Endress+Hauser
5 Commissioning
5.1 Function check
Before the first commissioning, make sure of the following points:
•That the sensor was correctly installed (Post-installation check, see Chapter 3.5)
•That the electrical connection is correct (Post-connection check, see Chapter 4.3)
#Warning!
Danger of medium escaping.
Before applying compressed air to the assembly, make sure the connections of the
cleaning facility are correctly fitted. Otherwise, the assembly may not be used.
5.2 Polarisation
The sensor was tested in the factory for perfect functionality and is supplied ready for
operation.
To prepare for calibration, proceed as follows:
•Remove the sensor protective cap.
•Place the externally dry sensor in atmospheric air.
The air should be saturated with water vapour. Therefore, install the sensor as close
to the water surface as possible. When calibrating the sensor membrane, make sure
the membrane remains dry.
Therefore, avoid any direct contact with the water surface.
•Connect the sensor to the transmitter and switch on the transmitter.
The polarisation is automatically proceeded. Within the first 30 seconds the sensor
builds up an analogue or a digital transmission protocol depending on the used
transmitter. During this time all displayed measuring values are 0. Having built-up the
transmission protocol, a measuring value can be displayed.
•The polarisation time takes about 1 hour.
Polarisation starts high, then drops gradually. You will recognise the end of polarisation
when the display stabilises and remains practically constant.
"Caution!
When you remove the sensor from the medium, protect the sensor from strong sunlight.
Make sure you comply with the instructions for comissioning and calibration in the
Operating Instructions of the transmitter.

OxyMax W COS 71 5 Commissioning
Endress+Hauser 15
5.3 Calibration
Calibration is a means of adapting the transmitter to the characteristic values of the sen-
sor. As no zero calibration is required for the sensor COS 71, a single-point calibration
is carried out in the presence of oxygen.
There are three basic types of calibration:
•In air (preferably saturated water vapour, e.g. near the water surface)
•In air-saturated water
•By entering a reference measured value in the transmitter
(sensor remains in the medium).
Following only the calibration in air is discribed because it is the easiest and that’s why
it is the recommended method of calibration.
Calibration in air is only possible if air temperature ≥ –5 °C.
The sensor requires calibration after:
•first commissioning
•replacing a membrane or electrolyte
•cleaning the gold cathode
•long breaks in operation without power supply
•typical time intervals dependent on operating experience
5.3.1 Calibration in air
To calibrate the sensor in air, proceed as follows:
•Remove the sensor from the medium.
•Clean the outside of the sensor with a damp cloth. Then dry the sensor membrane e.g.
by using a tissue.
•If the sensor is removed from a closed pressure system with a process pressure great-
er than atmospheric pressure:
–open the membrane cap to equilibrate the pressure and clean the cap if necessary.
–Change the electrolyte filling and close the membrane cap again.
–Wait for the polarisation time to end.
•Then wait while the sensor adjusts to the temperature of the ambient air. This takes
about 20 minutes. Check that the sensor is not in direct sunlight during this time.
•If the measured value display on the transmitter is stable, carry out the calibration in
accordance with the Operating Instructions of the transmitter.
•Place the sensor in the medium again. Do not keep the sensor in air for a longer time.
!Note!
Make sure you comply with the instructions for calibration in the Operating Instructions
of the transmitter.
5.3.2 Calculation example for the calibration value
As a check, you can calculate the expected calibration value (transmitter display) as
shown in the following example.
Salinity is 0%.
1. Determine:
•The sensor temperature (ambient air)
•The altitude above sea level.
•The current air pressure (rel. air pressure to sea level) at the time of calibration.
(If undeterminable, use 1013 hPa for an approximate calculation.)
2. Define:
•The saturation value Sacc. to Table 1 on page 16
•The factor Kacc. to Table 2 on page 16

5 Commissioning OxyMax W COS 71
16 Endress+Hauser
3. Determine:
•L = [rel. air pressure at calibration] : [1013 hPa]
•M=1.02 for calibration in air
M=1.00 for calibration in air-saturated water
4. Calculate the calibration value:
Calibration value = S • K • L • M
Example:
•Air calibration at 18°C, altitude 500 m above sea level, air pressure 1022 hPa
•S = 9.45 mg/l, K = 0.943, L = 1.0089, M = 1.02
Calibration value = 9.17 mg/l
Table 1:
Saturation value S as a factor of temperature
(taken at an air pressure of 1013 hPa)
Table 2:
Correction factor K as a factor of mean altitude
(above sea level)
°CS [mg/l] °CS [mg/l] °CS [mg/l] °CS [mg/l]
0 14.64 11 10.99 21 8.90 31 7.42
1 14.23 12 10.75 22 8.73 32 7.30
2 13.83 13 10.51 23 8.57 33 7.18
3 13.45 14 10.28 24 8.41 34 7.06
4 13.09 15 10.06 25 8.25 35 6.94
5 12.75 16 9.85 26 8.11 36 6.83
6 12.42 17 9.64 27 7.96 37 6.72
7 12.11 18 9.45 28 7.82 38 6.61
8 11.81 19 9.26 29 7.69 39 6.51
9 11.53 20 9.08 30 7.55 40 6.41
10 11.25
Altitude
[m]
KAltitude
[m]
KAltitude
[m]
KAltitude
[m]
K
0 1.000 550 0.938 1050 0.885 1550 0.834
50 0.994 600 0.932 1100 0.879 1600 0.830
100 0.988 650 0.927 1150 0.874 1650 0.825
150 0.982 700 0.922 1200 0.869 1700 0.820
200 0.977 750 0.916 1250 0.864 1750 0.815
250 0.971 800 0.911 1300 0.859 1800 0.810
300 0.966 850 0.905 1350 0.854 1850 0.805
350 0.960 900 0.900 1400 0.849 1900 0.801
400 0.954 950 0.895 1450 0.844 1950 0.796
450 0.949 1000 0.890 1500 0.839 2000 0.792
500 0,943

OxyMax W COS 71 6 Maintenance
Endress+Hauser 17
6 Maintenance
Maintenance work must carried out at regular intervals. To ensure that it is carried out,
we recommend you to enter the maintenance dates into an operations logbook or in an
operations calendar in advance.
The following activities must be carried out:
•Cleaning the sensor
In particular when the membrane is soiled (see Chapter 6.1).
•Check the measuring function
A simple inspection of the measuring function is to remove the sensor from the
medium. Clean and dry the membrane. After about 10 minutes, measure the oxygen
saturation index in air (without recalibration). The measured value should be near to
102% SAT (display of O2saturation with COM 2x3 by pressing 4 times O- key).
•Replace a defective membrane or one which cannot be cleaned any more.
•Recalibration (see Chapter 5.3.1)
6.1 Cleaning the outside of the sensor
The measurement can be corrupted by sensor fouling or malfunction, e.g.:
•Coatings on the sensor membrane
→cause longer response times and a reduced slope.
•Soiling or poisoning of the electrolyte
→causes longer response times and false measurement.
To ensure reliable measurement, the sensor must be cleaned at regular intervals. The
frequency and intensity of the cleaning operation depend on the measuring medium.
Clean the sensor:
•before every calibration
•at regular intervals during operation as necessary.
•before returning it to Endress+Hauser for repairs.
Depending on the type of soiling, proceed as follows:
"Caution!
After cleaning, rinse the sensor with copious amounts of clean water.
Type of soiling Cleaning measure
Salt deposits Immerse the sensor in drinking water or in 1-5% hydrochloric acid
for a few minutes. Afterwards, rinse it with copious amounts of water.
Dirt particles on the sensor body
(not the membrane)
Clean the sensor body mechanically with water and a suitable brush.
Dirt particles on the membrane cap or
the membrane
Clean the membrane with water and a soft sponge.

6 Maintenance OxyMax W COS 71
18 Endress+Hauser
6.2 Regeneration
Parts of the sensor will suffer wear and tear during operation.
Suitable action can restore normal operating functionality.
This action includes:
#Warning!
Before beginning regeneration, switch off the power supply at the transmitter.
6.2.1 Cleaning the gold cathode
The gold cathode only needs to be cleaned when it is visibly soiled or there is a coating
of silver on it.
To clean it, proceed as follows:
•Unscrew the membrane cap from the membrane body.
•Carefully clean the gold surface in two stages with the polishing sheet (contained in
scope of supply) until the (silver) coating is fully removed. Use the green sheet first
and then the yellow sheet.
•Clean the electrode with drinking or distilled water.
•Fill the membrane cap with fresh electrolyte COY 3-F and screw it back onto the mem-
brane body (up to the stop).
"Caution!
The counter electrode and the reference electrode are covered with a brown silver
bromide layer at the factory. Do not clean the counter electrode or the reference
electrode under any circumstances!
If the coating is removed as a result of operation, the sensor is unusable and must be
sent in for recoating. In this case, contact your E+H sales office.
6.2.2 Replacing the sealing ring
Replacing the sealing ring (see Fig. 3.8 on page 9, Pos. 2) is only necessary when it is
visibly damaged. For replacement, use only the supplied sealing rings COY 31-OR.
6.2.3 Replacing the electrolyte
During measuring operations the electrolyte COY 3-F is slowly used up because of
electrochemical reactions. No reactions occur in de-energised state and the electrolyte
is not used up.
The theoretical life time of an electrolyte filling for use in air-saturated drinking water at
20°C is max. 2 months. That’s why do not keep the sensor on air for a longer time (e.g.
before or after calibration). With a concentration of 1 mg/l dissolved oxygen the life time
of an electrolyte filling is approx. 1.5 years, it prolongs with less concentrations
accordingly.
If the sensor is used in other media than ultrapure water the electrolyte life time can be
shortened by diffused, dissolved gases such as H2S, NH3or high concentrations of
CO2.
Action Cause
Cleaning the gold cathode
(Chap. 6.2.1)
Soiled or silver-plated gold cathode
Replacing the sealing ring
(Chap. 6.2.2)
Visual damage to the sealing ring
Replacing the electrolyte
(Chap. 6.2.3)
unstable or implausible measuring signal or electrolyte soiling
Replacing the membrane cap
(Chap. 6.2.4)
Uncleanable membrane
Damaged membrane (hole or overstretch)