Endress+Hauser Oxymax COS22 Series User manual

BA446C/07/EN/01.11
71098071
Operating Instructions
Oxymax COS22
Dissolved oxygen sensor

Notes for using this manual
Warning instructions and their meaning
The structure, signal words and safety colors of the signs comply with the specifications of ANSI Z535.6
("Product safety information in product manuals, instructions and other collateral materials").
Cross reference symbols
Safety message structure Meaning
DANGER
!
Cause (/consequences)
Consequences if safety
message is not heeded
►Corrective action
This symbol alerts you to a dangerous situation.
Failure to avoid the situation will result in a fatal or serious injury.
WARNING
!
Cause (/consequences)
Consequences if safety
message is not heeded
►Corrective action
This symbol alerts you to a dangerous situation.
Failure to avoid the situation can result in a fatal or serious injury.
CAUTION
!
Cause (/consequences)
Consequences if safety
message is not heeded
►Corrective action
This symbol alerts you to a dangerous situation.
Failure to avoid this situation can result in minor or medium injury.
NOTICE
Cause/situation
Consequences if safety
message is not heeded
►Action/note
This symbol alerts you to situations that can result in damage to
property and equipment.
È ä 1 This symbol indicates a cross reference to a defined page (e.g. p. 1).
È å 2 This symbol indicates a cross reference to a defined figure (e.g. fig. 2).

Endress+Hauser
Table of contents
1 Safety instructions . . . . . . . . . . 4
1.1 Designated use . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Installation, commissioning and operation . 4
1.3 Operational safety . . . . . . . . . . . . . . . . . . . 5
1.4 Return . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 Identification . . . . . . . . . . . . . . 6
2.1 Order code . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Scope of delivery . . . . . . . . . . . . . . . . . . . . 6
2.3 Certificates and approvals . . . . . . . . . . . . . . 6
3 Installation . . . . . . . . . . . . . . . . 7
3.1 Incoming acceptance, transport, storage . . . 7
3.2 Installation conditions . . . . . . . . . . . . . . . . 7
3.3 Installation instructions . . . . . . . . . . . . . . . 8
3.4 Installation examples . . . . . . . . . . . . . . . . 10
3.5 Post-installation check . . . . . . . . . . . . . . . 12
4 Wiring . . . . . . . . . . . . . . . . . . 13
4.1 Connection to the transmitter . . . . . . . . . 13
4.2 Post-connection check . . . . . . . . . . . . . . . 13
5 Function . . . . . . . . . . . . . . . . . 14
5.1 Measuring principle . . . . . . . . . . . . . . . . . 14
5.2 Calibration . . . . . . . . . . . . . . . . . . . . . . . . 15
6 Commissioning. . . . . . . . . . . . 18
6.1 Function check . . . . . . . . . . . . . . . . . . . . 18
6.2 Polarization . . . . . . . . . . . . . . . . . . . . . . . 18
6.3 Calibration . . . . . . . . . . . . . . . . . . . . . . . . 19
7 Maintenance. . . . . . . . . . . . . . 20
7.1 Maintenance tasks . . . . . . . . . . . . . . . . . . 20
7.2 Maintenance intervals . . . . . . . . . . . . . . . 20
7.3 Cleaning the sensor . . . . . . . . . . . . . . . . . 21
7.4 Wear parts and consumables . . . . . . . . . . 21
8 Accessories. . . . . . . . . . . . . . . 25
8.1 Connection accessories . . . . . . . . . . . . . . 25
8.2 Installation accessories . . . . . . . . . . . . . . . 25
9 Trouble-shooting. . . . . . . . . . . 26
9.1 Trouble-shooting instructions . . . . . . . . . . 26
9.2 Spare parts and consumable material . . . . . 27
9.3 Return . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
9.4 Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . 27
10 Technical data . . . . . . . . . . . . . 28
10.1 Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
10.2 Performance characteristics . . . . . . . . . . . . 28
10.3 Environment . . . . . . . . . . . . . . . . . . . . . . 29
10.4 Process . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
10.5 Mechanical construction . . . . . . . . . . . . . . 31
Index. . . . . . . . . . . . . . . . . . . . 33

Safety instructions
4Endress+Hauser
1 Safety instructions
1.1 Designated use
The oxygen sensor is suitable for continuous measurement of dissolved oxygen in water.
The specific suitability depends on the sensor design:
• COS22-1 (standard, measuring range 0.01 to 60 mg/l)
– Measuring, monitoring and regulating the oxygen content in fermenters
– Monitoring the oxygen content in biotechnology facilities
• COS22-3 (trace measurement, measuring range 0.001 to 10 mg/l, preferred operational range
0.001 to 2 mg/l), also suitable for high CO2partial pressure
– Monitoring inertization equipment in the food industry
– Monitoring the residual oxygen content in carbonated fluids of the beverage industry
– Trace measurement in industrial applications such as inertizations
– Monitoring the residual oxygen content in boiler feedwater
– Monitoring, measuring and regulating the oxygen content in chemical processes
NOTICE
Molecular hydrogen
Hydrogen causes sensitivity in other substances and leads to false low readings or, at the worst, total
failure of the sensor.
►Do not use the sensor in media containing hydrogen.
Any other use than the one described here compromises the safety of persons and the entire measuring
system and is not permitted.
The manufacturer is not liable for damage caused by improper or non-designated use.
1.2 Installation, commissioning and operation
Please note the following items:
• Installation, commissioning, operation and maintenance of the measuring system must only be
carried out by trained technical personnel.
Trained personnel must be authorized for the specified activities by the system operator.
• Electrical connection must only be carried out by a certified electrician.
• Technical personnel must have read and understood these Operating Instructions and must adhere
to them.
• Before commissioning the entire measuring point, check all the connections. Ensure that electrical
cables and hose connections are not damaged.
• Do not operate damaged products and secure them against unintentional commissioning. Mark the
damaged product as being defective.
• Measuring point faults may only be rectified by authorized and specially trained personnel.
• If faults can not be rectified, the products must be taken out of service and secured against
unintentional commissioning.
• Repairs not described in these Operating Instructions may only be carried out at the manufacturer’s
or by the service organization.

Safety instructions
Endress+Hauser 5
1.3 Operational safety
The sensor has been designed and tested according to the state of the art and left the factory in perfect
functioning order.
Relevant regulations and European standards have been met.
As the user, you are responsible for complying with the following safety conditions:
• Installation instructions
• Local prevailing standards and regulations.
1.4 Return
If the sensor has to be repaired, please return it cleaned to the sales center responsible.
Please use the original packaging, if possible.
Before returning the device, please clarify all formalities - such as obtaining an identification number -
with your sales center.
Please enclose the completed "Declaration of Hazardous Material and De-Contamination" (copy the
second last page of these Operating Instructions) with the packaging and the transportation documents.
No repair without completed declaration!

Identification
6Endress+Hauser
2 Identification
2.1 Order code
To find out the version of your device, enter the order code indicated on the nameplate in the
search screen at the following address: www.products.endress.com/order-ident
2.2 Scope of delivery
The following items are included in the delivery:
• Oxygen sensor with tap water filled cap for membrane protection
• Electrolyte, 1 bottle, 10 ml (0.34 fl.oz.)
• Brief Operating Instructions
• Operating Instructions on CD
If you have any questions, please contact your supplier or your local sales center.
2.3 Certificates and approvals
The manufacturer declares the FDA compliance of the materials used.
Ask your local sales center for the certificates.
Product FDA certificate for
COS22-****22 Membrane, O-rings, process sealing
COS22Z-*2*2 Membrane, O-rings, process sealing
COS22-****23 Membrane, O-rings
COS22Z-*2*3 Membrane, O-rings

Installation
Endress+Hauser 7
3 Installation
3.1 Incoming acceptance, transport, storage
• Make sure the packaging is undamaged!
Inform the supplier about any damage to the packaging.
Keep the damaged packaging until the matter has been settled.
• Make sure the contents are undamaged!
Inform the supplier about damage to the contents. Keep the damaged products until the matter has
been settled.
• Check that the order is complete and agrees with your shipping documents.
• The packaging material used to store or to transport the product must provide shock protection and
humidity protection. The original packaging offers the best protection. Also, keep to the approved
ambient conditions (see "Technical data").
• If you have any questions, please contact your supplier or your local sales center.
3.2 Installation conditions
3.2.1 Angle of installation
The sensor must be installed with an inclination angle of at least 10 ˚to the horizontal in an assembly,
support or a corresponding process connection. Other inclination angles are not permitted. Do not
install the sensor overhead.
Observe the instructions for installing sensors in the Operating Instructions for the assembly used.
a0005584-en
Fig. 1: Permitted angle of installation
10° 10° Not permissible!
Not permissible!
Permissible angle of installation

Installation
8Endress+Hauser
3.2.2 Mounting location
• Select the installation location so that there is easy access for later calibration.
• Make sure that upright posts and assemblies are secured safely and vibration-free.
• Select an installation location which produces a typical oxygen concentration.
3.3 Installation instructions
3.3.1 Measuring system
A complete measuring system comprises:
• A digital oxygen sensor Oxymax COS22
• A transmitter, e.g. Liquisys COM223/253F
• An appropriate measuring cable, e.g. COK21
• Optional: an assembly, e.g. fixed installation assembly CPA442, flow assembly CPA240 or retractable
assembly CPA475
a0006653
Fig. 2: Example of a measuring system with COS22
1 Oxygen sensor COS22
2 Retractable assembly CPA475
3 Measuring cable COK21
4 Transmitter Liquisys COM253F
1
2
3
4
CAL REL
REL1
REL1
ALARM
REL2
REL2
E

Installation
Endress+Hauser 9
3.3.2 Installing a measuring point
WARNING
!
Electrical voltage
In the event of a fault, non-grounded metallic assemblies may be under voltage and then are not
touchable.
►When using metallic assemblies and installation equipment, observe the national grounding
provisions.
For a complete installation of a measuring point, proceed as follows:
1. Install a retractable or a flow assembly (if used) into the process.
2. Connect the water supply to the rinse connections (if you use an assembly with cleaning function).
3. Install and connect the oxygen sensor.
NOTICE
Installation errors
Cable breakage, loss of the sensor, unintended unscrewing of the membrane cap
►Do not install the sensor suspended from the cable.
►Screw the sensor into the assembly so that the cable is not twisted.
►Mounting or dismounting the sensor: hold the sensor body, only turn the threaded plug-in head
while screwing the sensor in or out of the assembly. Otherwise you could unscrew the sensor’s
membrane cap. It will remain in the assembly resp. in the process then.
►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.

Installation
10 Endress+Hauser
3.4 Installation examples
3.4.1 Fixed installation (CPA442)
The CPA442 fixed installation assembly allows a sensor to be easily adapted to almost any process
connections from Ingold nozzles to Varivent or Triclamp connections.
This type of installation is very suitable for tanks and larger pipes. The sensor achieves a defined
immersion depth in the medium in an easy manner.
3.4.2 Flow assembly
CPA240
The CPA240 flow assembly offers up to three installation slots for sensors with a shaft diameter of 12
mm (0.47"), a shaft length of 120 mm (4.72") and a process connection Pg 13.5.
It is very suitable for use in pipes or at hose connections.
During trace measurement in particular, ensure the assembly is completely vented to avoid measuring
errors.
a0005720
Fig. 3: CPA240 flow assembly with protective hood
a0005721
Fig. 4: Bypass installation
1 Main line
2Mediumremoval
3, 6 Manually actuated or solenoid valves
4 Sampling
5 Flow assembly with installed sensor
7 Medium return

Installation
Endress+Hauser 11
Flow assembly for water treatment applications
The compact stainless steel assembly (see "Accessories") offers space for a 12-mm sensor with a length
of 120 mm. The assembly has a low sampling volume and, with the 6-mm connections, it is best suited
for residual oxygen measurement in water treatments and boiler feedwater. The flow comes from
below.
a0014081
Fig. 5: Flow assembly
1 Built-in sensor
2Drain
3 Wall mount (clamp D29)
4Inflow
12
3
4

Installation
12 Endress+Hauser
Retractable assembly (CPA475 or CPA450)
The assembly is designed for installation on tanks and pipes. Suitable nozzles must be available for this.
Install the assembly at places with constant flow. The minimum pipe diameter is DN 80 (3").
a0005722-de
Fig. 6: Permissible and impermissible sensor installation positions with retractable assembly
1 Ascending pipe, best position
2 Horizontal pipe, sensor top down, impermissible due to air cushion or foam bubble forming
3 Horizontal pipe, lateral installation with permissible installation angle (acc. to sensor version)
5 Down pipe, impermissible
NOTICE
Incorrect measurements
Sensor not in the medium all the way, buildup, overhead installation
►Do not install the assembly at places where air cushions or foam bubbles can be formed.
►Avoid deposits on the sensor membrane and/or remove them regularly.
►Do not install the sensor overhead.
3.5 Post-installation check
►Sensor and cable undamaged?
►Compliance with permissible sensor installation position?
►Is the sensor installed in an assembly and is not suspended from the cable?
►Avoid moisture by rain by putting the protective cap on the assembly?
5
3
41
2
3
4
2
Detail A,
(top view)
Detail A, rotated
(side view)
90°

Wiring
Endress+Hauser 13
4Wiring
WARNING
!
Device is energized
Improper connection can cause injury or death.
►The electrical connection must only be carried out by a certified electrician.
►Technical personnel must have read and understood the instructions in this manual and must
adhere to them.
►Prior to beginning any wiring work, make sure voltage is not applied to any of the cables.
4.1 Connection to the transmitter
The electrical connection between the sensor and the transmitter uses the multi-core special measuring
cable COK21.
4.2 Post-connection check
a0005583-en
Fig. 7: Special measuring cable COK21
Instrument status and specifications Remarks
Are the sensor, assembly, junction box or cable damaged? Visual inspection
Electrical connection Remarks
Are the installed cables strain-relieved and not twisted ?
Long enough length of cable core stripped and correct in terminal? Check seating (pull slightly)
Are all the screws terminals properly tightened ? Tighten
Are all the cable entries installed, tightened and sealed ? For cable entries lateral: cable loops downwards
for water to be able to drip off.
Are all the cable entries installed downwards or lateral ?
PK
GN / YE
BN
YE
BU
S
12
90
91
11
Assignment Terminal
External shield
Cathode
Anode
NTC temp. sensor
Active internal shield
(NTC temp. sensor)

Function
14 Endress+Hauser
5 Function
5.1 Measuring principle
5.1.1 Amperometric measuring principle
The oxygen molecules that diffuse through the membrane are reduced at the cathode into hydroxide
ions (OH-). At the anode, silver is oxidized into silver ions (Ag+) (this forms a silver halide 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, μg/l, ppm, ppb or Vol%,
as a saturation index in % SAT or as an oxygen partial pressure in hPa.
5.1.2 Sensor design
5.1.3 Polarization
When the sensor is connected to the transmitter, a fixed voltage is applied between the cathode and
anode. The polarization current this creates can be identified on the transmitter with a display that is
initially high, but decreases with time. The sensor cannot be calibrated until the display is calibrated.
Reference value for nearly complete polarization of a sensor that was previously stored for a long time:
• COS22-*1: 2 hours
• COS22-*3: 12 hours
After this time, even measurements close to the determination limit are useful.
The necessary polarization time is reduced for sensors that were in use a short time before.
a0011868
Fig. 8: Exploded view
1
2
3
4
Plug-in head
Pressure ring
Sensor shaft
O-ring 8.5 x 1.5 mm
5
6
7
Membrane body
Shaft cover
Glass body with cathode and anode
8
9
Process sealing 10.77 x 2.62 mm
Process connection Pg 13.5

Function
Endress+Hauser 15
5.1.4 Membrane body
The oxygen dissolved in the medium is transported to the membrane by the necessary flow. The
membrane is permeable for dissolved gases only. 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.
The sensor is shipped with a standard membrane body, which can be used for all common applications.
The membrane is pretensioned at the factory and can be installed immediately.
Electrolytes are version-specific and cannot be mixed in a single application!
5.2 Calibration
Calibration is a means of adapting the transmitter to the characteristic values of the sensor.
Normally, sensor calibration is seldom necessary. It is necessary after:
• First commissioning
• Replacing a membrane or electrolyte
• Long breaks in operation without power supply
Within the framework of system monitoring and supervision, for example, the calibration can also be
cyclically monitored (at typical time intervals, depending on operating experience) or renewed.
5.2.1 Types of calibration
You can carry out single-point or two-point calibration for the sensor.
In most applications, single-point calibration suffices in the presence of oxygen (=calibration of
measured value at air).
The additional calibration of the zero point (two-point calibration) improves the precision of the
measurement results in the trace range. Calibrate the zero point with nitrogen (minimum 99.995%) or
with water free from oxygen, for example. In doing so, make sure the measured value has settled
correctly (20 to 30 minutes) to avoid incorrect measurements in the trace range at a later stage.
The available types of calibration depend on the transmitter used. Refer to your transmitter's
Operating Instructions to find out which types of calibration are supported.
The following section only describes the calibration in air (saturated with water vapor) as the easiest
method of calibration and therefore the recommended method.
However, this type of calibration is only possible if the air temperature is ≥–5 ˚C (23 ˚F).
5.2.2 Calibration in air
1. Remove the sensor from the medium.
2. Clean the outside of the sensor with a damp cloth.
3. 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.
4. If the measured value display on the transmitter is stable, carry out the calibration in accordance
with the Operating Instructions of the transmitter.
5. Place the sensor in the medium again.

Function
16 Endress+Hauser
Make sure you comply with the instructions for calibration in the Operating Instructions of the
transmitter.
5.2.3 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 ambient temperature for the sensor (air temperature for "air" calibration method,water
temperature for "air-saturated water" calibration type)
– 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 (407 inH2O) for an approximate calculation.)
2. Define:
– the saturation value Sacc. to the first table
– the factor Kacc. to the second table
T
[˚C(˚F)]
S
[mg/l=ppm]
T
[˚C(˚F)]
S
[mg/l=ppm]
T
[˚C(˚F)]
S
[mg/l=ppm]
T
[˚C(˚F)]
S
[mg/l=ppm]
0 (32) 14.64 11 (52) 10.99 21 (70) 8.90 31 (88) 7.42
1 (34) 14.23 12 (54) 10.75 22 (72) 8.73 32 (90) 7.30
2 (36) 13.83 13 (55) 10.51 23 (73) 8.57 33 (91) 7.18
3 (37) 13.45 14 (57) 10.28 24 (75) 8.41 34 (93) 7.06
4 (39) 13.09 15 (59) 10.06 25 (77) 8.25 35 (95) 6.94
5 (41) 12.75 16 (61) 9.85 26 (79) 8.11 36 (97) 6.83
6 (43) 12.42 17 (63) 9.64 27 (81) 7.96 37 (99) 6.72
7 (45) 12.11 18 (64) 9.45 28 (82) 7.82 38 (100) 6.61
8 (46) 11.81 19 (66) 9.26 29 (84) 7.69 39 (102) 6.51
9 (48) 11.53 20 (68) 9.08 30 (86) 7.55 40 (104) 6.41
10 (50) 11.25
Altitude
[m (ft)]
KAltitude
[m / ft]
KAltitude
[m / ft]
KAltitude
[m / ft]
K
0 1.000 550 (1800) 0.938 1050 (3450) 0.885 1550 (5090) 0.834
50 (160) 0.994 600 (1980) 0.932 1100 (3610) 0.879 1600 (5250) 0.830
100 (330) 0.988 650 (2130) 0.927 1150 (3770) 0.874 1650 (5410) 0.825
150 (490) 0.982 700 (2300) 0.922 1200 (3940) 0.869 1700 (5580) 0.820

Function
Endress+Hauser 17
3. Calculate the factor L:
4. Calculate the calibration value C:
C = S .K .L
Example
• Air calibration at 18˚C (64 ˚F), altitude 500 m (1650 ft) above sea level, air pressure 1009 hPa (405
inH2O)
• S = 9.45 mg/l, K = 0.943, L = 0.996
Calibration value C = 8.88 mg/l.
You do not need factor K from the table if your device returns the absolute air pressure Labs
(location-dependent air pressure) as the measured value.
Thus, the formula for calculation is: C = S .Labs.
200 (660) 0.977 750 (2460) 0.916 1250 (4100) 0.864 1750 (5740) 0.815
250 (820) 0.971 800 (2620) 0.911 1300 (4270) 0.859 1800 (5910) 0.810
300 (980) 0.966 850 (2790) 0.905 1350 (4430) 0.854 1850 (6070) 0.805
350 (1150) 0.960 900 (2950) 0.900 1400 (4600) 0.849 1900 (6230) 0.801
400 (1320) 0.954 950 (3120) 0.895 1450 (4760) 0.844 1950 (6400) 0.796
450 (1480) 0.949 1000 (3300) 0.890 1500 (4920) 0.839 2000 (6560) 0.792
500 (1650) 0.943
L=
relative air pressure during calibration
-------------------------------------------------------------------------
1013 hPa
Altitude
[m (ft)]
KAltitude
[m / ft]
KAltitude
[m / ft]
KAltitude
[m / ft]
K

Commissioning
18 Endress+Hauser
6 Commissioning
6.1 Function check
Before first commissioning, check if:
• the sensor is correctly installed
• the electrical connection is correct.
If using an assembly with automatic cleaning, check the correct connection of the cleaning agent (e.g.
water or air).
WARNING
!
Escaping process medium
Risk of injury from high pressure, high temperatures or chemical hazards
►Before applying compressed air to an assembly with cleaning facility, make sure the connections are
correctly fitted.
►Do not install the assembly in the process if you cannot make the correct connection reliably.
6.2 Polarization
NOTICE
Incorrect measurements due to ambient influences
►Be absolutely certain to avoid direct sunlight on the sensor.
►Make sure you comply with the instructions for commissioning in the Operating Instructions of the
transmitter.
The sensor has been tested at the factory for proper function and is shipped in ready-to-operate
condition.
To prepare for the calibration, carry out the following steps:
1. Pull off the sensor protection cap.
2. Expose the sensor, which should be dry on the outside, to the air atmosphere. The air should be
saturated with water vapor. Therefore, install the sensor as close as possible to a surface of water.
However, the sensor membrane must remain dry during calibration. Therefore, avoid direct
contact with the surface of water.
3. Connect the sensor to the transmitter.
4. Switch on the transmitter.
When the sensor is connected to the transmitter, the polarization takes place automatically after
the power-up of the transmitter.
5. Wait for the polarization time to run out.

Commissioning
Endress+Hauser 19
6.3 Calibration
Calibrate the sensor (air calibration) immediately after the polarization time has elapsed.
The calibration intervals depend heavily on:
• The application and
• The installation position of the sensor.
The following methods help you determine how long the calibration intervals should be:
1. Check the sensor one month after its being put into operation by taking it out of the fluid, drying
it and then measuring the oxygen saturation index at air after 10 minutes.
Decide using the results:
a. Ifthemeasuredvalueisnotat100±2%SAT,youhavetocalibratethesensor.
b. Otherwise, double the length of time to the next inspection.
2. Proceed as per Point 1 after two, four and/or eight months. In this way, you can determine the
optimum calibration interval for your sensor.
Be sure to calibrate the sensor at least once a year.

Maintenance
20 Endress+Hauser
7 Maintenance
7.1 Maintenance tasks
The following tasks are mandatory:
• Cleaning the sensor
• Replace wear parts or consumables:
– Electrolyte
– Membrane body
– Sealing ring
• Check the measuring function:
1. Remove the sensor from the medium.
2. Clean and dry the membrane.
3. After about 10 minutes, measure the oxygen saturation index in air (without recalibration).
4. The measured value should be at 100 ± 2 % SAT
• Recalibration (if desired or required)
7.2 Maintenance intervals
Maintenance cycles depend to a great extent on the operating conditions.
The following rule of thumb applies:
• Constant conditions, e.g. power plant = long cycles (1/2 year)
• Greatly varying conditions, e.g. daily CIP cleaning = short cycles (1 month or shorter)
The following method helps you determine the necessary intervals:
1. Inspect the sensor one month after commissioning.
Take it out of the medium and dry it.
2. After 10 minutes, measure the oxygen saturation index in air.
Decide using the results:
a. If the measured value is not at 100 ±2 %SAT, you have to maintain the sensor.
b. Otherwise, double the length of time to the next inspection.
3. Proceed similarly after two, four and/or eight months. In this way, you can determine the
optimum maintenance interval for your sensor.
Particularly for widely varying process conditions, damage of the membrane can occur even within
a maintenance cycle. You can recognize this by implausible sensor behavior.