Endress+Hauser Viomax CAS51D User manual

BA459C/07/EN/05.10
71114848
Operating Instructions
Viomax CAS51D
Photometric sensor for nitrate measurement

Endress+Hauser

Viomax CAS51D
Endress+Hauser 3
Table of contents
1 Safety instructions . . . . . . . . . . . . . . . . 4
1.1 Designated use . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Installation, commissioning and operation . . . . . . . . 4
1.3 Operational safety . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Return . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.5 Notes on safety icons and symbols . . . . . . . . . . . . . . 5
2 Identification . . . . . . . . . . . . . . . . . . . . 6
2.1 Nameplate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . . . . 9
3.4 Installation examples . . . . . . . . . . . . . . . . . . . . . . . 10
3.5 Post-installation check . . . . . . . . . . . . . . . . . . . . . . 14
4 Wiring . . . . . . . . . . . . . . . . . . . . . . . . 15
4.1 Connecting to the transmitter . . . . . . . . . . . . . . . . 15
4.2 Post-connection check . . . . . . . . . . . . . . . . . . . . . . 15
5 Device description . . . . . . . . . . . . . . . 16
5.1 Sensor design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.2 Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.3 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.4 Cyclic cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6 Maintenance. . . . . . . . . . . . . . . . . . . . 21
6.1 Cleaning the sensor . . . . . . . . . . . . . . . . . . . . . . . . 21
6.2 Maintenance of the optical filter and strobe lamp . 21
7 Accessories. . . . . . . . . . . . . . . . . . . . . 22
7.1 Assemblies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.2 Holder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.3 Compressed air cleaning . . . . . . . . . . . . . . . . . . . . 22
7.4 Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
7.5 Standard solutions . . . . . . . . . . . . . . . . . . . . . . . . . 23
8 Troubleshooting . . . . . . . . . . . . . . . . . 24
8.1 Troubleshooting instructions . . . . . . . . . . . . . . . . . 24
8.2 Return . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
8.3 Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
9 Technical Data. . . . . . . . . . . . . . . . . . . 25
9.1 Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.2 Performance characteristics . . . . . . . . . . . . . . . . . . 25
9.3 Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.4 Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.5 Mechanical construction . . . . . . . . . . . . . . . . . . . . 25
Index . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Safety instructions Viomax CAS51D
4Endress+Hauser
1 Safety instructions
1.1 Designated use
CAS51D is a sensor designed to measure the contents of nitrate in liquid media.
The sensor is particularly suited for use in the following applications:
• Monitoring the nitrate contents in the outlet of wastewater treatment plants
• Monitoring and optimizing the denitrification phases
• Monitoring and regulating drinking water treatment plants
• Nitrate measurement in natural bodies of water
• Monitoring the nitrate contents in aeration basins
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:
• The measurement process in the sensor uses UV light. UV light can damage the eyes. Never look
into the cuvette while the sensor is in operation.
• 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.
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.
Klären Sie vor der Rücksendung Formalitäten, z.B. das Einholen einer Identifikationsnummer, mit
Ihrer Vertriebszentrale.
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!

Viomax CAS51D Safety instructions
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1.5 Notes on safety icons and symbols
#Warning!
This symbol alerts you to hazards that can cause serious damage to the instrument or to persons 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.

Identification Viomax CAS51D
6Endress+Hauser
2 Identification
2.1 Nameplate
Compare the order code indicated on the nameplate to the product structure and your order.
The nameplate contains the following information:
• Manufacturer data
• Order code (device version)
• Extended order code
• Serial number
!Note!
To discover what sensor version you have, enter the order code on the nameplate into the search
screen at the following address:
www.products.endress.com/order-ident
2.2 Scope of delivery
The scope of delivery comprises:
• 1 CAS51D sensor (in the version ordered)
• 1 set of Operating Instructions BA459C/07/en
If you have any questions, please contact your supplier or your local sales center.
2.3 Certificates and approvals
Declaration of conformity
The product meets the requirements of the harmonized European standards. It thus complies with
the legal requirements of the EC directives.
The manufacturer confirms successful testing of the product by affixing the 4symbol.

Viomax CAS51D Installation
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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 Dimensions
a0013193
Fig. 1: Dimensions CAS51D-**A2 (2 mm gap)
a0013208
Fig. 2: Dimensions CAS51D-**A1 (8 mm gap)
50
(1.97)
mm (inch)
40
(1.57)
388 (15.28) 69 (2.72)
NPT “¾
G1
2 (0.08)
8 (0.31)
12 (0.47)
20
(0.79)
14.5 (0.57)
NPT “¾
G1
69 (2.72)
394 (15.51)
8 (0.31)
40
(1.57)
mm (inch)
14 (0.55)
20 (0.79)
12 (0.47)
14.5 (0.57)

Installation Viomax CAS51D
8Endress+Hauser
3.2.2 Mounting location
• Select a mounting location that can also be easily accessed later on.
• Make sure upright posts and assemblies are securely fastened and free from vibrations.
• Select a mounting location where the nitrate concentration is representative of the application.
• Do not install the sensor above aeration discs. Oxygen bubbles can accumulate on the cuvette and
distort the measured value.
3.2.3 Orientation
• Flow assembly
Horizontal installation with bushes on a panel.
• Immersion operation in an open basin
– Suspended vertically from a chain
– Horizontal, fixed installation
3.2.4 Installation instructions
For correct measurement to take place, the windows of the cuvette have to be clear of any
sedimentation. This is best achieved by the cleaning unit (accessory) which uses compressed air for
cleaning.
With horizontal orientations, mount the sensor in such a way that the cuvette is located at the side.

Viomax CAS51D Installation
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3.3 Installation instructions
3.3.1 Measuring system
A complete measuring system comprises:
• Nitrate sensor Viomax CAS51D
• Transmitter Liquiline
• Assembly Flexdip CYA112 and holder system Flexdip CYH112
a0013215
Abb. 3: Measuring system with immersion assembly (example)
1
2
3
4
5
Holder system Flexdip CYH112
Transmitter Liquiline
Weather protection roof
Assembly Flexdip CYA112
Nitrate sensor Viomax CAS51D
a0013333
Abb. 4: Measuring system with immersion assembly (example)
1
2
3
4
5
Transmitter Liquiline
Weather protection roof
Holder system Flexdip CYH112
Assembly Flexdip CYA112
Nitrate sensor CAS51D
1
2
3
1
4
5
2
3
4
1
5

Installation Viomax CAS51D
10 Endress+Hauser
3.4 Installation examples
3.4.1 Immersion operation
Fixed installation with wastewater assembly
This type of installation is particularly suitable for strong or turbulent medium flow (>0.5 m/s
(1.6 ft/s)) in the basin or channels.
A cleaning unit (accessory) that uses compressed air significantly extends the maintenance intervals
for the sensor.
a0013347
Fig. 5: 90° installation secured on railing
1 Viomax CAS51D nitrate sensor
2 Flexdip CYA112 wastewater assembly
3 Flexdip CYH112 holder
4 Railing
a0013215
Fig. 6: 90° installation with upright post
1 Flexdip CYH112 holder
2 Liquiline transmitter
3 Weather protection cover
4 Flexdip CYA112 wastewater assembly
5 Viomax CAS51D nitrate sensor
1
2
3
4
1
2
3
1
4
5

Viomax CAS51D Installation
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Installation with chain retainer
The chain retainer is particularly suitable for applications that require a sufficient distance between
the mounting location and the edge of the aeration basin. As the assembly is freely suspended, any
vibration of the upright post is practically ruled out.
The swinging movement of the chain retainer enhances the self-cleaning effect of the cuvette.
A cleaning unit (accessory) that uses compressed air significantly extends the maintenance intervals
for the sensor.
a0013348
Fig. 7: Chain retainer on railing
1 Flexdip CYA112 wastewater assembly with Viomax
CAS51D nitrate sensor
2 Chain
3 Flexdip CYH112 holder
4 Railing
a0013351
Fig. 8: Chain retainer on upright post
1 Flexdip CYH112 holder
2 Liquiline transmitter
3 Weather protection cover
4 Flexdip CYA112 wastewater assembly
5 Viomax CAS51D nitrate sensor
1
2
3
4
1
2
3
1
4
5
4

Installation Viomax CAS51D
12 Endress+Hauser
Cleaning unit
a0013292
Fig. 9: CAS51D sensor with cleaning unit
1 8 mm adapter (only for 6 mm gland)
2 6 mm or 6.35 mm (¼") gland
3.4.2 Bypass operation
Flow assembly for clear water
a0013352
Fig. 10: Sensor with flow assembly
1 Sensor holder
2 Viomax CAS51D nitrate sensor
3 Medium inlet
4 Flow assembly
5 Medium outlet
6 Liquiline transmitter
20.5
(0.81)
300 (11.81)
1
2
mm (inch)
12134
5
6

Viomax CAS51D Installation
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Mounting
a0013290
Fig. 11: Dimensions
Mount the sensor along with the flow assembly as follows:
1. Slide the flow assembly over the sensor.
2. Align the sensor in such a way that the cuvette is in the direction of flow (check the position
through the window in the assembly)
3. Secure the position of the assembly with the two thread adapter nuts.
4. Mount the sensor horizontally on a panel on directly on the wall. Use the bushes supplied.
Connecting the flow assembly
a0013361
Fig. 12: Flow assembly in the bypass
1 Main pipe
2Mediumreturn
3 Medium outlet
4 Viomax CAS51D nitrate sensor
5 Manual or solenoid valves
6 Flow assembly
7 Medium inlet
8 Medium sampling
Connect the flow assembly as illustrated in Abb. 12 or Abb. 13. This fills the assembly from below
and ensures the assembly is self-venting.
The minimum flow rate must be 250 ml/h (0.066 gal/hr).
Consider the extended response time!
Ø 6.5
0.26
86
(3.39)
30
(1.18)
100
(3.94)
mm (inch)
70
(2.76)
**
1
2
3
5
6
4
8
57

Installation Viomax CAS51D
14 Endress+Hauser
a0013434
Fig. 13: Flow assembly with open outlet
1 Basin
2 Filter unit
3 Viomax CAS51D nitrate sensor
4 Flow assembly
5 Medium outlet
6 Medium inlet
7Pump
8Openoutlet
3.5 Post-installation check
• Sensor and cable undamaged?
• Cap 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?
34
12
5
6
7
8

Viomax CAS51D Wiring
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4 Wiring
#Warning!
• 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 Connecting to the transmitter
The sensor will be connected to the transmitter as follows:
• With the M12 plug (version: fixed cable, M12 plug) or
• With the fixed cable connected to the terminal strips (version: fixed cable, end sleeves):
a0012460
Fig. 14: Sensor connection
The maximum cable length is 100 m (328 ft).
4.2 Post-connection check
Device condition and specifications Notes
Is damage visible on the outside of the sensor, assembly, junction box or
cable?
Visual inspection
Electrical connection Notes
Does the transmitter supply voltage match the specifications on the
nameplate?
Are the installed cables strain-relieved and not twisted?
Is the cable type route completely isolated at the mounting location? Power cables / signal cables
Are the cable cores stripped sufficiently and installed correctly in the
terminal?
Check if seated correctly (pull gently)
Are all the screw terminals firmly tightened? Tighten
Are all the cable entries installed, firmly tightened and leak-tight? For lateral cable entries, make sure the
cable loops downwards to ensure water
can drain off.
Are all the cable entries mounted on the side or pointing downwards?
Are the power supply and signal cables connected correctly? If detected by the CM44x:
Periodic flashing in the cuvette (audible
and visible)

Device description Viomax CAS51D
16 Endress+Hauser
5 Device description
5.1 Sensor design
The sensor is designed for the continuous in-situ measurement of process values. One version of the
sensor measures the amount of nitrate in the medium.
The sensor is designed as a 40 mm sensor that can be operated directly and completely in the
process without the need for further sampling (in situ).
As an open measuring cell, the cuvette is the central component of the system. This is the area in
which the measuring light can interact with the medium.
All the necessary modules are contained in the sensor:
• Power supply
• High-voltage generation for the strobe lamp
• Cuvette
• Detectors detect the measuring signals, digitize them and process them to form a measured value.
• The sensor controller is responsible for controlling the internal processes and transmitting the
data.
All the data - including the calibration data - are stored in the sensor. The sensor can thus be
precalibrated and used at a measuring point, calibrated externally, or used for several measuring
points with different calibrations.
5.2 Function
5.2.1 Measuring principle
The light from a pulsed, high-stability strobe lamp (item 5) passes through the measurement section
(items 3 and 4).
The beam splitter (item 2) directs the light beam to the two receivers (items 1 and 6). A filter is
arranged upstream of each receiver. The filter upstream of the measuring receiver (item 1) only lets
through light in the measuring wavelength range, while the filter upstream of the reference receiver
(item 6) only lets through light in the reference wavelength range.
a0013213
Fig. 15: Principal mode of operation of the nitrate sensor
1 Measuring receiver with filter
2 Beam splitter
3Cuvette
4Lens
5 Strobe lamp
6 Reference receiver with filter
12345
6

Viomax CAS51D Device description
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Within the measurement section - i.e. the open path through the cuvette - parts of the light interact
with the medium.
While the medium in the cuvette (water and particles) attenuates the light across the entire
spectrum, another factor comes into play in the measuring wavelength range, as nitrate in the
medium takes some of the energy from the light and causes additional attenuation of the light beam.
The ratio of the light signal of the measuring wavelength to the reference wavelength is used to
calculate the nitrate measured value. If only water and turbidity is present, both signals are
attenuated to the same extent and the ratio remains constant. If the medium contains nitrate, the
signal for the measuring wavelength is attenuated more and the ratio changes. This change in the
ratio can be converted to determine the concentration of nitrate. This dependency is non-linear.
Conclusion: Long measurement paths are required for high resolutions. This is achieved with the
8-mm cuvette for clear water measurements. If turbidity values are high, longer measurement paths
result in the total absorption of light, and the measured values are not valid. For media with high
turbidity values (activated sludge applications), the sensor with the 2 mm cuvette returns good,
reliable measured values.
5.2.2 Nitrate measurement
Nitrate ions absorb UV light in the range from approx. 190 to 230 nm. Nitrite ions have a similar
absorption rate in the same range.
In the cuvette, the nitrate and nitrite ions absorb the UV light in the measuring wavelength range
in proportion to the nitrate and nitrite concentration, while the UV light in the reference channel
remains virtually unchanged.
Interference factors such as turbidity, fouling or organic hydrocarbons are eliminated by
mathematical means.
The signal ratio between the reference channel and the measuring channel is used as the
measurement result. This ratio is converted to the concentration of nitrate using the calibration
curve programmed into the sensor.
5.2.3 Cross-interference
The following directly affect the measuring range:
• Total solids (TS) and turbidity
• Sludge properties
• Color
•COD
•Temperature
•Nitrite
Trends:
• Higher percentage of TS and turbidity reduces the upper end of the measuring range, i.e. the
measuring range is smaller.
• The same percentage of TS and turbidity but different colors results in different measuring
ranges/measured values.
• COD rates greater than 100 mg/l have a direct effect if nitrate concentrations below 1 mg/l.
The following can be deduced from the interdependencies cited above:
• An increase in the turbidity value in the medium does not affect the measured value.
• Organic substances in the sludge floc absorb light in the measuring wavelength and simulate the
presence of nitrate. Sludge floc transported through the cuvette can thus cause an increase in the
measured value.
• High concentrations of COD in the medium can increase the measured value.
• Nitrite absorbs light in a similar wavelength range as nitrate and is measured along with the
nitrate. The rate is constant: 1.0 mg/l nitrite is indicated as 0.8 mg/l nitrate.

Device description Viomax CAS51D
18 Endress+Hauser
5.3 Calibration
Calibration helps to adjust the precalibrated sensor more precisely to the given situation.
Types of calibration:
• The sensor measures the concentration of nitrate in a medium. The actual value is determined by
external wet-chemical analysis (e.g. photometric measurement with a reaction indicated by a
change in color). This value is then assigned.
• You specify a parent solution with a known nitrate concentration (e.g. one prepared in the
laboratory). This parent solution can be designed as a single-point or multi-point system by
diluting the solution.
In addition to the factory calibration data, which cannot be modified, the sensor has six other data
records to be used for storing calibrations. Each calibration data record can contain up to five
calibration points.
Single-point calibration causes a change in the slope. This type of calibration is used if the
concentration of nitrate in the medium only changes to a limited extent.
Two-point calibration causes a change in the slope and the zero point. This type of calibration is
used if the concentration of nitrate in the medium changes to a large extent.
Both types of calibration are based on the data record stored internally in the device.
Calibration at three or more points always causes the measuring curve to be recalculated.
5.3.1 Factory calibration
The sensor is precalibrated on leaving the factory. As such, it can be used in a wide range of
applications (e.g. clear water measurement) without the need for additional calibration. The factory
calibration is based on a three-point calibration.
The factory calibration cannot be deleted and can be retrieved at any time. All other calibrations -
performed as customized calibrations - are referenced to this factory calibration.
5.3.2 Stability criterion
During the calibration process, the measured values returned by the sensor are checked to ensure
they remain constant. The stability criterion defines the maximum amount the measured values
may deviate during calibration and still be accepted.
The data comprise:
• The maximum permissible deviation in temperature measurement
• The maximum permissible deviation in the measured value in %
• The minimum timeframe in which these values must be maintained
If the signal values or temperatures deviate more than is permitted in a maximum timeframe of
60 seconds, this calibration point becomes invalid and a warning is issued.
The stability criteria monitor the quality of the individual calibration points in the course of the
calibration. The aim is to achieve the best possible calibration quality in a short timeframe while
taking external conditions into account.
For high-precision calibrations in the laboratory, the measured value windows can be kept as small
as possible and the time selected can be as long as possible.
For calibrations in the field under tough weather and environmental conditions, the measured value
windows selected can be large and the timeframe short.
!Note!
The stability criteria have a direct impact on the quality of the calibration, and thus on the quality
of the subsequent measured values.

Viomax CAS51D Device description
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5.3.3 Calibration in the process
Calibration is performed in the process by comparing the values to an external standard method. A
sample of the process medium is taken and analyzed in the laboratory for nitrate. Colorimetric
measurement with a cuvette test is common practice and is a standard method in accordance with
DIN 38405 Part 9.
!Note!
• Drinking water can contain larger concentrations of nitrate and is not suitable as a blank value.
Use fully deionized water as your blank value.
• During calibration, make sure the sample is homogeneous.
• When calibrating, start with a low concentration and increase the concentrations gradually.
• Clean and dry the sensor after a calibration. Make sure there is no residue in the cuvette. In this
way, you avoid mixing the different samples and changing the concentration of nitrate.
Performing the calibration
1. Select a data record.
2. Put the sensor into the medium.
3. During calibration, make sure the medium is as homogeneous as possible.
4. Start the calibration for the measuring point.
5. Save the data for the measuring point. For this purpose, enter the measured value that is
roughly expected. The plausibility of the data is checked before the data are saved. The data
are not saved if the values are not plausible. You might have to adapt the stability criterion to
the ambient conditions.
6. Take a sample of your medium and measure it with a reference electrode.
7. Start the calibration again. Select the same data record and edit the data record with the result
of the reference method.
• Processes with relatively high nitrate values
Take, measure and calibrate a sample with a high concentration. To ensure the measured value
obtained is correct, the concentration of nitrate should not drop below a value of 0.1 mg/l.
• Processes with very different nitrate values
At time A, take a sample with a high concentration, and measure and calibrate the sample. At
time B - which can by all means be a few days after time A - take a sample with a low
concentration, and measure and calibrate the sample.
• Calibration with the addition of standard
If the sludge parameters tend to be constant, you can perform the calibration with a sample with
a low concentration of nitrate and then add standard to the sample.
Take a larger sample (bucket) and analyze some of it by colorimetric means. Calibrate this value
in the sensor.
Now add standard to the sample, check the sample in the laboratory and calibrate the value in
the sensor.
Additional calibration points, recalibration
Points can be added to an existing calibration. The maximum number of points per data record is
also limited to 5 here.
In this way, different media or concentrations can be included in the calibration at different times.

Device description Viomax CAS51D
20 Endress+Hauser
5.3.4 Calibration in the laboratory
Calibration is performed in the laboratory using ready-prepared parent solutions with different
concentrations.
!Note!
Please note that drinking water can contain larger concentrations of nitrate and is not suitable as a
blank sample. Use fully deionized water as your blank sample.
Make a serial dilution of a parent solution, putting the range of dilutions in beakers (prepared
internally or purchased from a specialist shop). Immerse the sensor in the beakers in succession and
calibrate the sensor to the set concentrations. In this way, you can calibrate up to 5 points.
!Note!
Note the following to avoid incorrect calibration resulting from nitrate carryover:
• Always go from a low concentration to a high concentration.
• Clean and dry the sensor after a calibration. Make sure there is no residue in the cuvette. In this
way, you avoid mixing the different samples and changing the concentration of nitrate.
5.4 Cyclic cleaning
Compressed air is most suitable for cyclic automatic cleaning. There is a connection for compressed
air on every sensor. The optional cleaning unit is either ready-supplied or can be retrofitted, and
operates effectively at a rate of 20 l/min (5.4 US gal/min).
Recommended settings for the cleaning unit:
Cyclic cleaning can also be performed manually at set intervals.
Type of fouling Cleaning interval Cleaning duration
Severe fouling with rapid buildup 5 min 10 s
Low degree of fouling 10 min 10 s