Endress+Hauser ISEmax CAS40D User manual

Products Solutions Services
Operating Instructions
ISEmax CAS40D
Ion-selective sensor for continuous measurement of
ammonium, nitrate and other ions
BA00491C/07/EN/05.20
71505793
2020-11-27

ISEmax CAS40D Table of contents
Endress+Hauser 3
Table of contents
1 About this document ................ 4
1.1 Warnings ............................ 4
1.2 Symbols .............................. 4
2 Basic safety instructions ............ 5
2.1 Requirements for personnel ............... 5
2.2 Designated use ........................ 5
2.3 Workplace safety ....................... 5
2.4 Operational safety ...................... 6
2.5 Product safety ......................... 6
3 Incoming acceptance and product
identification ....................... 7
3.1 Incoming acceptance .................... 7
3.2 Product identification .................... 7
3.3 Scope of delivery ....................... 8
3.4 Certificates and approvals ................ 8
4 Installation ........................ 9
4.1 Installation conditions ................... 9
4.2 Mounting the sensor ................... 10
4.3 Installation example ................... 12
4.4 Post-installation check .................. 13
5 Electrical connection .............. 14
5.1 Connecting the sensor .................. 14
5.2 Connecting additional electrodes in the
sensor .............................. 14
5.3 Ensuring the degree of protection .......... 15
5.4 Post-connection check .................. 15
6 Commissioning .................... 15
7 Operation ......................... 16
7.1 Adapting the measuring device to the process
conditions ........................... 16
8 Diagnostics and troubleshooting ... 22
9 Maintenance ...................... 23
9.1 Maintenance schedule .................. 23
9.2 Cleaning the membrane ................. 23
9.3 Replacing membrane cap and electrolyte .... 23
10 Repair ............................ 26
10.1 Spare parts .......................... 26
10.2 Return .............................. 27
10.3 Disposal ............................ 27
11 Accessories ....................... 28
11.1 Assembly holder ...................... 28
11.2 Maintenance kits ...................... 28
11.3 Electrodes ........................... 28
11.4 Standard solutions ..................... 28
11.5 Compressed air cleaning ................ 29
12 Technical data .................... 30
12.1 Input ............................... 30
12.2 Performance characteristics .............. 30
12.3 Environment ......................... 31
12.4 Process ............................. 31
12.5 Mechanical construction ................ 31
Index .................................. 33

About this document ISEmax CAS40D
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1 About this document
1.1 Warnings
Structure of information Meaning
LDANGER
Causes (/consequences)
If necessary, Consequences of
non-compliance (if applicable)
‣Corrective action
This symbol alerts you to a dangerous situation.
Failure to avoid the dangerous situation will result in a fatal or serious
injury.
LWARNING
Causes (/consequences)
If necessary, Consequences of
non-compliance (if applicable)
‣Corrective action
This symbol alerts you to a dangerous situation.
Failure to avoid the dangerous situation can result in a fatal or serious
injury.
LCAUTION
Causes (/consequences)
If necessary, Consequences of
non-compliance (if applicable)
‣Corrective action
This symbol alerts you to a dangerous situation.
Failure to avoid this situation can result in minor or more serious injuries.
NOTICE
Cause/situation
If necessary, Consequences of
non-compliance (if applicable)
‣Action/note
This symbol alerts you to situations which may result in damage to
property.
1.2 Symbols
Symbol Meaning
Additional information, tips
Permitted or recommended
Not permitted or not recommended
Reference to device documentation
Reference to page
Reference to graphic
 Result of a step

ISEmax CAS40D Basic safety instructions
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2 Basic safety instructions
2.1 Requirements for personnel
• Installation, commissioning, operation and maintenance of the measuring system may
be carried out only by specially trained technical personnel.
• The technical personnel must be authorized by the plant operator to carry out the
specified activities.
• The electrical connection may be performed only by an electrical technician.
• The technical personnel must have read and understood these Operating Instructions
and must follow the instructions contained therein.
• Faults at the measuring point may only be rectified by authorized and specially trained
personnel.
Repairs not described in the Operating Instructions provided must be carried out only
directly at the manufacturer's site or by the service organization.
2.2 Designated use
The ion-selective sensor is designed for measuring tasks in the activated sludge basin and
in the inlet to the activated sludge basin of municipal sewage treatment plants.
The following parameters can be monitored and regulated depending on the device
version:
• Nitrate
• Ammonium
• Potassium (also to compensate ammonium)
• Chloride (also to compensate nitrate)
• pH value
• ORP
Use of the device for any purpose other than that described, poses a threat to the safety of
people and of the entire measuring system and is therefore not permitted.
The manufacturer is not liable for damage caused by improper or non-designated use.
2.3 Workplace safety
As the user, you are responsible for complying with the following safety conditions:
• Installation guidelines
• Local standards and regulations
Electromagnetic compatibility
• The product has been tested for electromagnetic compatibility in accordance with the
applicable international standards for industrial applications.
• The electromagnetic compatibility indicated applies only to a product that has been
connected in accordance with these Operating Instructions.

Basic safety instructions ISEmax CAS40D
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2.4 Operational safety
Before commissioning the entire measuring point:
1. Verify that all connections are correct.
2. Ensure that electrical cables and hose connections are undamaged.
3. Do not operate damaged products, and protect them against unintentional operation.
4. Label damaged products as defective.
During operation:
‣If faults cannot be rectified:
products must be taken out of service and protected against unintentional operation.
LCAUTION
Cleaning not switched off during calibration or maintenance activities
Risk of injury due to medium or cleaning agent!
‣If a cleaning system is connected, switch it off before removing a sensor from the
medium.
‣If you wish to check the cleaning function and have therefore not switched off the
cleaning system, wear protective clothing, goggles and gloves or take other appropriate
measures.
2.5 Product safety
The product is designed to meet state-of-the-art safety requirements, has been tested, and
left the factory in a condition in which it is safe to operate. The relevant regulations and
international standards have been observed.

ISEmax CAS40D Incoming acceptance and product identification
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3 Incoming acceptance and product
identification
3.1 Incoming acceptance
1. Verify that the packaging is undamaged.
 Notify the supplier of any damage to the packaging.
Keep the damaged packaging until the issue has been resolved.
2. Verify that the contents are undamaged.
 Notify the supplier of any damage to the delivery contents.
Keep the damaged goods until the issue has been resolved.
3. Check that the delivery is complete and nothing is missing.
 Compare the shipping documents with your order.
4. Pack the product for storage and transportation in such a way that it is protected
against impact and moisture.
 The original packaging offers the best protection.
Make sure to comply with the permitted ambient conditions.
If you have any questions, please contact your supplier or your local Sales Center.
3.2 Product identification
3.2.1 Nameplate
The nameplate provides you with the following information on your device:
• Manufacturer identification
• Order code
• Extended order code
• Serial number
• Ambient and process conditions
• Input and output values
• Safety information and warnings
‣Compare the information on the nameplate with the order.
3.2.2 Product identification
Product page
www.endress.com/cas40d
Interpreting the order code
The order code and serial number of your product can be found in the following locations:
• On the nameplate
• In the delivery papers
Obtaining information on the product
1. Go to www.endress.com.
2. Call up the site search (magnifying glass).
3. Enter a valid serial number.
4. Search.
 The product structure is displayed in a popup window.

Incoming acceptance and product identification ISEmax CAS40D
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5. Click on the product image in the popup window.
 A new window (Device Viewer) opens. All of the information relating to your
device is displayed in this window as well as the product documentation.
3.3 Scope of delivery
The scope of delivery comprises:
• 1 sensor, version as ordered
• 1 socket wrench
• 1 tube silicone grease
• 1 Operating Instructions
3.4 Certificates and approvals
3.4.1  mark
Declaration of Conformity
The product meets the requirements of the harmonized European standards. As such, it
complies with the legal specifications of the EU directives. The manufacturer confirms
successful testing of the product by affixing to it the  mark.
3.4.2 EAC
The product has been certified according to guidelines TP TC 004/2011 and TP TC
020/2011 which apply in the European Economic Area (EEA). The EAC conformity mark
is affixed to the product.

ISEmax CAS40D Installation
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4 Installation
4.1 Installation conditions
4.1.1 Dimensions
50 (1.97)
Ø112 (4.41)
198 (7.8)
50.6 (1.99)
610 (24.0)
100 (3.94) 43 (1.69)
364 (14.3)
8
A0015207
 1 Dimensions in mm (inch)
4.1.2 Mounting location
Choose a mounting location that can be easily accessed at a later stage.
‣Ensure that upright posts and assemblies are fully secured and vibration-free.

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4.2 Mounting the sensor
4.2.1 Electrode installation
NOTICE
Electrode protection caps not used or incorrectly used
Drying out of pH electrode or damage to ion-selective membrane
‣Remove the protection cap from the pH electrode before immersing the sensor in the
medium.
‣Set the protection cap aside.
‣If you remove the sensor from the medium for more than 20 minutes, place the
protection cap filled with 1‑3 M KCl solution back on the pH electrode. This prevents
the electrode from drying out.
‣pH electrodes that have dried out due to incorrect storage can be made ready for
measurement again by leaving them in 3 M KCl solution for up to 12 hours.
‣The ion-selective electrodes do not have a protection cap. Never put one of these caps
on the electrodes.
All electrodes are installed and wired in the factory in accordance with the version
ordered.
Installing an additional electrode (optional)
A0015225
 2 Release protection
guard
A0015226
 3 Remove coupling
nut
A0015227
 4 Release cable
SW17
A0015229
 5 Remove electrode
1. Release the protection guard and remove (→  2,  10).
2. Unscrew the coupling nut (→  3,  10).
3. Remove the electrode holder from the sensor.
4. Release the electrode cable on a dummy electrode (placeholder, must be present to
ensure tight sealing →  4,  10).
5. Remove the dummy electrode using a socket wrench, AF17 (→  5,  10).
6. Install the new electrode in the free space.
7. Tighten the electrode hand-tight with the socket wrench, AF17.
8. Connect the electrode connector.
9. Pay attention to the color coding of the electrodes and the labeling of the cable. Refer
to the following table for this purpose →  11.
10. Carefully push the electrode holder and the air hose back into the sensor.
11. Screw on the coupling nut followed by the protection guard.

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NOTICE
Air bubbles
Air bubbles may accumulate in the electrodes following transportation and if they have
been stored in a horizontal position. These air bubbles cause measuring errors.
‣Before installing the sensor, eliminate any air bubbles e.g. by shaking gently.
‣Then make sure to hold the sensor in an upright position (electrodes facing
downwards) at all times until the sensor is installed at the measuring point.
Electrode identification
Electrode Color of membrane ring and marking on screw head 1) Cable identification
Ammonium RD 1, 2 or 3
Nitrate BU
Potassium YE
Chloride GN
pH (incl. reference) No marking R
Temperature No marking T
1) color codes as per IEC 757
4.2.2 Installing at the measuring point
NOTICE
Compressed air
Damage to the relay!
‣The compressed air supply must not exceed 3.5 bar (50 psi).
‣The compressed air must be supplied through an air filter (5 µm). This filter is already
installed in the optional cleaning unit →  29.
Installing at the measuring point
1. Install additional electrodes in the sensor if necessary.
2. Connect the electrodes to the suitable cable connector.
3. NOTICE
Sensor too deep in the medium, tension in sensor cable.
Failure of sensor due to penetration of medium or damage to cable!
‣Do not use the cable to suspend the sensor into the medium. Use a suitable
holder.
‣Never use the cable to pull the sensor out of the medium.
‣Never immerse the sensor completely in the medium.
Suspend the sensor from the chain on the holder.
4. Adjust the chain length and the cross bearer for the holder in such a way that the
sensor is immersed approx. 0.5 m (1.64 ft) in the medium and is
approx. 0.5 m (1.64 ft) from the basin rim.
5. Route the cables in such a way that no mechanical damage or interference influences
can arise from other cables.
6. Connect the optional cleaning unit to the transmitter and the pressure hose (OD 8) to
the sensor.

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Connecting an optional cleaning unit or an external compressed air supply
1.
Remove the watertight dummy plug from the sensor's compressed air connection.
2. Push against the black ring for this purpose.
3. Remove the plastic dummy plug.
4.
Plug the compressed air hose (OD 8) belonging to the cleaning unit or compressed air
supply into the compressed air connection.
5. Only optional cleaning unit:
Connect the cleaning unit to the transmitter (for more information, see the
Operating Instructions for the transmitter).
4.3 Installation example
A complete measuring system comprises:
• Sensor CAS40D
• Ion-selective electrode(s) for ammonium, nitrate, potassium or chloride
• pH glass electrode, Orbisint CPS11-1AS2GSA
• Temperature sensor, CTS1
• Transmitter Liquiline CM44x
Optional:
• Assembly holder, e.g. CYH112
• Weather protection cover: absolutely essential if mounting the transmitter outdoors!
• Compressed air generator (if no compressed air available on site)

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1 2
4
5
63
A0015206
 6 Example: measuring system on basin rim
1 Sensor cable
2 Wastewater assembly holder, secure to rail, with transverse pipe and chain
3 Liquiline CM44x transmitter (in graphic: wall-mounted with weather protection cover)
4 Rail
5 Sensor CAS40D with ion-selective electrodes
6 Connection for optional compressed air cleaning (not in graphic)
4.4 Post-installation check
1. After mounting, check all the connections to ensure they are secure and leak-tight.
2. Check all cables and hoses for damage.
3. Verify that the cables are routed in such a way that they are free from
electromagnetic interference influences.

Electrical connection ISEmax CAS40D
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5 Electrical connection
LWARNING
Device is live!
Incorrect connection may result in injury or death!
‣The electrical connection may be performed only by an electrical technician.
‣The electrical technician must have read and understood these Operating Instructions
and must follow the instructions contained therein.
‣Prior to commencing connection work, ensure that no voltage is present on any cable.
5.1 Connecting the sensor
When connecting to the Liquiline CM44x transmitter, there are two options:
1. M12 plug (version: fixed cable, M12 plug)
 The wiring for the M12 socket is inside the device. Only the sensor plug is
connected to the socket.
2. Direct connection of the fixed cable to the plug-in terminals (version: fixed cable,
ferrules)
85 86 85
1
2
86
97 88 8798
Sensor 1
PK
GY
GN
YE
BN
WH
1
A0018019
 7 Connection e.g. at
sensor module 2DS
1 Sensor with M12 plug
64
1
NC
2
3
5
7
46
2
NC
1
7
5
3
A0018021
 8 Plug assignment Above:
socket Below: plug
1 PK (24 V)
2 GY (Shield 24 V)
3 BN (3 V)
4 WH (Shield 3 V)
5 GN (Memosens)
6 YE (Memosens)
7,
NC
Not connected
N L 43 42 41 86 85 86 85
98 97 88 87
32 31 32 31
PK
GY
GN
YE
Sensor
PE
A0012460
 9 Connection e.g. at basic module
The maximum cable length is 100 m (328 ft).
5.2 Connecting additional electrodes in the sensor
All electrodes are connected in the factory prior to delivery.
Installing and connecting additional electrodes
‣Install the electrode (→  10).
Then reset the electrode configuration at the transmitter.

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5.3 Ensuring the degree of protection
Only the mechanical and electrical connections which are described in these instructions
and which are necessary for the required, designated use, may be carried out on the device
delivered.
‣Exercise care when carrying out the work.
Otherwise, the individual types of protection (Ingress Protection (IP), electrical safety, EMC
interference immunity) agreed for this product can no longer be guaranteed due,
for example to covers being left off or cable (ends) that are loose or insufficiently secured.
5.4 Post-connection check
Device status and specifications Notes
Are the sensor and cable free from damage on the outside? Visual inspection
Electrical connection Notes
Does the supply voltage of the connected transmitter match the data
on the nameplate?
Visual inspection
Are the installed cables strain-relieved and not twisted?
Is the cable type route completely isolated on site? Power cables / signal lines
Are all cable entries installed, tightened and sealed? In the case of lateral cable entries:
Cable loops facing downwards to allow
water to drip off.
Are all cable entries facing downwards or mounted laterally?
6 Commissioning
Select the correct pH electrode at the transmitter.
1. Path in the transmitter menu: Setup/Inputs/ISE/1 (R) pH
2. Reference electrode: Specify the pH electrode version, Standard or Salt ring.
The version of the pH electrode can only be found on the electrode's nameplate
(CPS11-1AS*** = Salt ring, CPS11-1AT*** = Standard).
Sensors from 2019 onwards are always delivered with pH electrodes with salt storage
(salt ring).

Operation ISEmax CAS40D
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7 Operation
7.1 Adapting the measuring device to the process
conditions
7.1.1 Calibration
Factory calibration
Before being delivered, the sensor is checked in the factory and precalibrated with regard
to the sensor slope and zero point.
Since the correct calibration state depends on the medium matrix (ionic strength,
concentration of interference ions etc.), users must always calibrate the sensor themselves
after commissioning in order to adjust the zero point so that it suits the users' particular
application conditions. The manual offset is set to zero upon delivery. If a compensation
electrode is not used for automatic interference ion compensation, the offset must be set
before the first calibration is performed if working with ammonium and nitrate electrodes.
Calibration recommendations
Application Variables to be calibrated Recommended calibration types
Commissioning Zero point, manual offset 1-point calibration
Maintenance Slope Data entry
Set the slope specified on the manufacturer's certificate in the
transmitter
Zero point 1-point calibration
Routine calibration Zero point 1-point calibration
Types of calibration
• pH electrode:
• 2-point calibration (recommended)
• 1-point calibration
• Ion-selective electrodes:
• 1-point calibration (recommended)
• Data entry
• 2-point calibration
• Standard addition ("Expert" only)
• ORP sensor:
1-point calibration
• Temperature adjustment by entering a reference value
Calibration parameters
When determining ion concentrations potentiometrically, the electrochemical measuring
cell consists of the ion-selective electrode and a reference electrode. This cell supplies a
voltage within the "linear" or preferably "NERNST" range which is proportional to the
logarithm of the concentration (or activity) of the ions to be determined. The slope and
zero point calibration parameters refer to this logarithmic relationship, which gives these
parameters a completely different meaning in this measurement method compared with
other measurement methods.

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Slope
The slope is specified as a %, based on the theoretical slope according to Nernst.
Example: 98% slope = 59.16 mV/pX . 0.98 = 57.98 mV/pX
The slope affects the linearity of the measurement.
If the slope set at the transmitter is less than or greater than the actual slope of the ion-
selective electrode, measured errors can occur due to non-linearities. The greater the
concentration range in which the measured values vary, the greater the possible non-
linearities. If, on the other hand, the measured values only vary in a small range, even
larger slope errors will not result in discernible non-linearities. The slope is determined in
the factory for every ion-selective electrode and every membrane cap and is indicated on
the manufacturer's certificate supplied with the device. The user simply has to enter the
slope data to communicate the supplied slope value to the transmitter. As the slope only
changes marginally while the unit is in operation, the user does not normally have to
perform a calibration. The slope is a property of the ion-selective electrode. Therefore the
reference electrode does not affect the slope.
Slope of ion-selective electrodes
Electrode Maximum Minimum
Ammonium 110% 90%
Nitrate 90%, typically 98 - 100%
Potassium 90%
Chloride
If the calibrated slope is outside the table values, the calibration conditions must be taken
into account. Check if the manual offset or calibration of the compensation electrode is
correct.
Zero point
The zero point determines the sensitivity of the measurement. If the configured zero point
is too low or too high in relation to the actual zero point of the ion-selective electrode
system, all the measured values are either too high or too low by a certain percentage. The
zero point depends on the internal solution used by the ion-selective electrode and the
reference electrode. As a result of the ion-selective electrode and the reference electrode
aging, the zero point gradually changes over time and must be calibrated periodically. The
zero point depends on both the ion-selective electrode and the reference electrode.
Typical zero points
Electrode Typical zero point 1)
Ammonium 1.1
Nitrate 1.4
Potassium 3.55
Chloride -0.5
1) for new reference electrode (electrode aging affects the zero point)
Sequence for calibration/adjustment of measuring point
Some measured values from other electrodes or sensors are used for measured value
compensation of ion-selective electrodes:
• Measured value of temperature sensor for temperature compensation
• pH measured value for pH compensation of ammonium (optional)
• Potassium or chloride measured value for compensation of interference ions in the case
of ammonium or nitrate (optional)

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For this reason, there is a sequence for calibration and adjustment that must be followed
in order to achieve a reliable measurement:
1. Temperature adjustment (precalibrated in the factory, therefore not necessary for
initial calibration)
2. Calibration and adjustment of pH electrode
3. Depending on whether compensation electrodes are used:
Calibration and adjustment of ion-selective compensation electrodes (potassium,
chloride)
4. If no compensation electrodes are used:
A correct manual offset is configured for the ammonium and nitrate electrode
5. Calibration and adjustment of ion-selective measuring electrodes (ammonium,
nitrate)
Calibration
The following minimum concentrations apply for 1-point and 2-point calibration:
• 6.4 mg/l ammonium or 5 mg/l ammonium-nitrogen
• 22.1 mg/l nitrate or 5 mg/l nitrate-nitrogen
• 20 mg/l potassium
• 100 mg/l chloride
The values are benchmarks which may change over time due to the influence of
interference ions or the aging of ion-selective electrodes. If the calibration concentrations
are too low, the measured values will be incorrect.
Stability criterion
The factory setting on the transmitter is "weak". The measured value of an ion-selective
electrode only reaches adequate stability after approx. 4 min.
‣Wait for a stable measuring signal before starting calibration.
Data entry
The zero point and the slope of the ion-selective electrode system can be entered directly
and modified using the "Data entry" method.
When installing an ion-selective electrode or membrane cap in the sensor:
1. Set the electrode slope for the slot using "Data entry". The electrode slope is indicated
on the manufacturer's certificate.
2. Calibrate the zero point.
1-point calibration
In the case of 1-point calibration, the zero point of the ion-selective electrode system is
calibrated in a solution with a known concentration.
• Enter the reference value either before or after the measured value is recorded.
• Set the slope and the manual offset correctly or carry out a calibration of the
compensation electrodes for ammonium and nitrate.
Two ion-selective electrodes can be calibrated simultaneously (ammonium and nitrate
or potassium and chloride) with the Liquiline CM44x transmitter.
1. Suspend the sensor into a vessel or into a process with a known concentration.
 Experience shows that at 7 mg/l good values are produced during calibration for
ammonium and nitrate.
2. Start the 1-point calibration in the transmitter menu.
 Select whether or not the measured value of the reference medium is known.
3. Wait for the signal (mV value) to stabilize (approx. 4 min for new membrane caps).

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4. Start calibration process.
 Accept the calibration.
2-point calibration
In the case of 2-point calibration, the zero point and the slope of the ion-selective
electrode system are determined using 2 solutions whose concentrations are known. The
two concentrations in the two solutions should be in the upper and lower measuring
range. When using 2-point calibration, the manual offset must already be set correctly, as
non-linearities would otherwise not be corrected by the 2-point calibration.
With 2-point calibration, the concentration should at least double. In this case, the
change in the mV signal is approx. 1/3 of the slope in mV.
1. Suspend the sensor into a vessel or into a process with a known concentration.
 Experience shows that at 7 mg/l good values are produced during calibration for
ammonium and nitrate.
2. Start the 2-point calibration in the transmitter menu.
 Select whether or not the measured value of the reference medium is known.
3. Wait for the signal (mV value) to stabilize (approx. 4 minutes for new membrane
caps).
4. Start calibration process.
5. Clean sensor and quickly wipe it dry.
 Suspend the sensor into the vessel with the second concentration.
6. Wait for the signal (mV value) to stabilize (approx. 4 minutes for new membrane
caps).
7. Start calibration process.
 Accept calibration.
Potassium and chloride compensation
Depending on the selectivity of the ion-selective electrode vis-à-vis other ions
(interference ions), and the concentration of these ions, such ions could also be interpreted
as part of the measuring signal and thus cause measuring errors. When measuring in
wastewater, the potassium ion which is chemically similar to the ammonium ion can cause
higher measured values. High concentrations of chloride may result in the measured
values for nitrate being too high. To reduce measuring errors resulting from such cross-
interference, the concentration of the potassium or chloride interference ion can be
measured and compensated for with a suitable additional electrode. As an alternative to
using compensation electrodes, a manual offset can be entered.
If compensation electrodes are used, there is no need to set a manual offset.
• Use of the potassium electrode for compensation:
For concentrations > 40 mg/l (> 40 ppm) with simultaneously fluctuating values of
± 20 mg/l (± 20 ppm)
• Use of the chloride electrode for compensation:
For concentrations > 500 mg/l (> 500 ppm) with simultaneously fluctuating values of
± 100 mg/l (± 100 ppm)
Manual offset
Constant systematic measured errors, which occur over the entire concentration range, can
be corrected by setting a suitable manual offset. Here, the set offset is added to the
measured value. To correct the measured error, a suitable negative value (often ranging
from - 0.2 to 2 mg/l (- 0.2 to 2 ppm) for municipal wastewater) must be set as the manual
offset for the specific ion-selective electrodes.
Using the offset for potassium or chloride values that do not fluctuate.
When determining ammonium, a manual offset of -1 mg/l NH4-N (-1 ppm NH4-N) should
be set per 20 mg/l (20 ppm) of potassium for complete compensation. When determining

Operation ISEmax CAS40D
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nitrate, the manual offset should be - 1 mg/l NO3-N (-1 ppm NO3-N) per
200 mg/l (200 ppm) chloride. It is normally not necessary to set a manual offset when
using ion-selective electrodes for potassium and chloride, as the effect of interference ions
on the measured value for potassium or chloride is too small. The offset value can be left at
zero.
Checking the calibration
1. Take 3 liters (0.79 US gal.) of sample from the wastewater treatment plant outlet.
2. Provide a bucket with drinking water.
3. Transfer exactly 2 liters (0.53 US gal.) of the sample into a suitable vessel.
4. Immerse the sensor into the sample.
5. Make sure there is convection in the solution (use a magnetic stirrer with a magnetic
stir bar or constantly move the sensor slightly by hand).
 After a few minutes the measured value should match the reference measured
value (laboratory value) within the normal tolerance for measured value
fluctuations.
6. Have some of the sample analyzed in the laboratory for the parameter to the
calibrated.
7. Gradually increase the concentration of the ion to be measured in the sample.
Preferably use a microliter pipette to add defined volumes to the standard solution.
8. After waiting 5 to 10 minutes, note down the stable measured value.
 The increase in the measured value should be as expected. The increase in
concentration is calculated using the following formula: concentration increase =
volume added x standard concentration x molar mass of parameter / (volume
presented + total volume added).
9. Immerse the sensor in a bucket with drinking water.
10. Check the concentration and the raw values.
 Typically, the values for ammonium are close to 0 mg/l for raw values of -170
mV or less. With 3 mg/l of nitrate, a raw value of at least +150 mV or higher
should be achieved.
Example
In 5 individual steps, 0.5 ml of 1M ammonium nitrate standard solution are added each
time to 2 liters of sample solution. The molar mass of NH4-N and NO3-N is 14 g/mol in
each case. As the volume added is so small, the increase in the volume of sample solution
can be disregarded. Each time standard solution is added, the concentration of NH4-N and
NO3-N produced increases by
0.5 ml * 1 mol/l * 14 g/mol / 2000 ml = 3.5 mg/l (3.5 ppm).
If the measured values do not increase as expected or are systematically too high or too low,
implement the measures shown in the table.
Problem Reason Action
Measured values are always too high
by the same amount
Manual offset setting is
not negative or not
negative enough
‣Make manual offset more negative.
Measured values are always too low by
the same amount
Manual offset setting is
too negative
‣Reduce the manual offset setting
based on the amount.
Measured values are always too high
by a certain percentage
Zero point setting is too
low
‣Calibrate the zero point.
Measured values are always too low by
a certain percentage
Zero point setting is too
high