Endress+Hauser Liquiline M CM42 User manual

Products Solutions Services
CM42-MAA101EBE00
BA00382C/07/EN/16.16
Valid as of:
Firmwareversion 02.02.00
Operating Instructions
Liquiline M CM42
Two-wire transmitter for pH/ORP measurement
with Memosens glass sensors
Part 2

Endress+Hauser
CM42-MAA101EBE00
Table of contents
1 Operation via the fieldbus . . . . 4
2 Calibration and adjustment . . . 5
2.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Notes on the calibration . . . . . . . . . . . . . . 8
2.4 Calibration intervals . . . . . . . . . . . . . . . . . 8
2.5 Types of calibration . . . . . . . . . . . . . . . . . 10
2.6 Two-point calibration . . . . . . . . . . . . . . . 10
2.7 Single-point calibration . . . . . . . . . . . . . 11
2.8 Temperature adjustment . . . . . . . . . . . . 12
2.9 Calibrate . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3 Diagnostics, troubleshooting . 14
3.1 General troubleshooting . . . . . . . . . . . . . 14
3.2 Diagnostic information on local display 18
3.3 Diagnostic information via fieldbus . . . 22
3.4 Adapting the diagnostic information . . 22
3.5 Pending diagnostic messages . . . . . . . . . 23
3.6 Diagnostic list . . . . . . . . . . . . . . . . . . . . . . 23
3.7 Logbooks . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.8 Simulation, Resetting the measuring device
24
3.9 Change sensor . . . . . . . . . . . . . . . . . . . . . 26
3.10 Sensor type change . . . . . . . . . . . . . . . . . 27
3.11 Sensor status . . . . . . . . . . . . . . . . . . . . . . 28
3.12 Output state . . . . . . . . . . . . . . . . . . . . . . . 29
3.13 Device information . . . . . . . . . . . . . . . . . 29
3.14 Sensor information . . . . . . . . . . . . . . . . . 29
3.15 Firmware history . . . . . . . . . . . . . . . . . . . 30
4 Maintenance. . . . . . . . . . . . . . . 31
5 Repair. . . . . . . . . . . . . . . . . . . . . 32
5.1 Spare parts . . . . . . . . . . . . . . . . . . . . . . . . 32
5.2 Replacing modules . . . . . . . . . . . . . . . . . . 34
5.3 Return . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.4 Disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
6 Accessories . . . . . . . . . . . . . . . . 35
6.1 Installation kits . . . . . . . . . . . . . . . . . . . . 36
6.2 Weather protection . . . . . . . . . . . . . . . . . 36
6.3 Firmware update and upgrade . . . . . . . . 36
6.4 Data management . . . . . . . . . . . . . . . . . . 36
6.5 Measured value simulation . . . . . . . . . . . 37
6.6 Communication-specific accessories . . . 37
7 Technical data. . . . . . . . . . . . . . 38
7.1 Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.2 Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.3 Protocol-specific data . . . . . . . . . . . . . . . . 39
7.4 Electrical connection . . . . . . . . . . . . . . . . 40
7.5 Performance characteristics . . . . . . . . . . 41
7.6 Environment . . . . . . . . . . . . . . . . . . . . . . . 42
7.7 Mechanical construction . . . . . . . . . . . . . 42
Index. . . . . . . . . . . . . . . . . . . . . . 43

Operation via the fieldbus CM42-MAA101EBE00
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1 Operation via the fieldbus
The device supports HART communication via current output 1. Here, digital data are
transmitted in addition to the current. Most process control systems have HART inputs that can
process the data further directly. Process values, the status of the process values and the device
status are transmitted.
The device can also be configured via HART. The device driver enables access to the complete
Setup and Diagnostics menu with few exceptions.
You have the following options for configuration:
• The process control system directly supports the use of DDs (Device Descriptions) and DTMs
(Device Type Managers) or
• you use an additional HART master, e.g. a handheld terminal or FieldCare in conjunction with
a modem.
The interface offered by the DDs and DTMs largely corresponds to the menu structure of local
operation.
It is not possible to access all the tables and the calibration with DDs or DTMs. In addition, it is
not possible to access the logbooks with a handheld terminal.
A detailed description of the commands and features supported by the device is provided in
SD01325C under "Document/Manuals/Software" and then "Special Documentation (SD)" on
www.endress.com/cm42.

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2 Calibration and adjustment
The calibration provides important information on the condition of your sensor and the
quality of the pH measurement.
pH glass electrodes
In addition to the slope that has an ideal value of approx. -59 mV/pH at 25 °C, the change in the
zero point also provides important information to the user. It is an indicator of the condition of
the gel-like layer of the pH glass and could point to a blockage in the reference system. Suitable
maintenance would involve cleaning or regenerating the sensor.
To perform a quick test, simply immerse the sensor in a buffer solution with the same pH value
as the internal buffer (e.g. pH 7). 0 mV would be an ideal value. The greater the deviation from
the ideal value, the poorer the condition of the sensor (±20 mV is still acceptable in most
situations).
2.1 Definitions
Calibration (as per DIN 1319):
A calibration is defined as a set of operations that establish the relationship between the
measured value or expected value of the output variable and the related true or correct value of
the measured variable (input variable) for a measuring system under specified conditions.
A calibration does not alter the performance of the measuring device.
Adjustment
An adjustment corrects the value displayed by a measuring device, in other words the
measured/displayed value (the actual value) is corrected so that the reading agrees with the
correct, set value.
The value determined during calibration is used to calculate the correct measured value and
saved in the sensor.
2.2 Terminology
2.2.1 Zero point and slope
Using a mathematical function, the transmitter converts the input signal of the sensor y (raw
measured value) to the measured value x. In many cases, this function is a simple linear of the
form y = a + b .x.
The linear element "a" is usually equivalent to the zero point and the factor "b" is the slope of the
line and is often known as the sensor slope.

Calibration and adjustment CM42-MAA101EBE00
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The Nernst equation, which is used to calculate the pH value, is a typical linear relationship:
pH = -lg(aH+), aH+ ... activity of the hydrogen ions
Ui... raw measured value in mV
U0... zero point (=voltage at pH 7)
R ... universal gas constant (8.3143 J/molK)
T ... temperature [K]
F ... Faraday constant (26.803 Ah/mol)
The slope of the Nernst equation (-2.303RT/F) is known as the Nernst factor and has the
value -59.16 mV/pH at 25 °C.
2.2.2 Delta slope
The device determines the difference in the slope between the calibration that is currently valid
and the last calibration. Depending on the sensor type, this difference is an indicator of the
condition of the sensor. The smaller the slope, the less sensitive the measurement, and the
accuracy deteriorates particularly in the low measuring range.
Depending on the operating conditions, users can define limit values that represent the still
tolerable absolute values of the slope and/or slope differentials. If the limit values are exceeded,
maintenance must be performed on the sensor at the very least. The sensor must be replaced if
the insensitivity problems persist after maintenance has been carried out.
a0013593
Fig. 1: Linear function
aZeropoint
bSlope
U=U
i0
-2.303 RT
FpH

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2.2.3 Delta zeropnt.
The device determines the difference between the zero points of the last and second-last
calibration. A shift in the zero point does not alter the sensitivity of the measurement. However,
if the offset is not corrected this can falsify the measured value.
As with the slope, you can also define and monitor limit values for the offset. If the limit values
are exceeded, this means that maintenance must be performed on the sensor.
a0013594
Fig. 2: Delta slope
Blue Last calibration
Red Calibration currently valid
 bDeltaslope
a0013595
Fig. 3: Delta zeropnt.
a1 Zero point of the second-last calibration
a2 Zero point of the last calibration
 aDeltazeropnt.

Calibration and adjustment CM42-MAA101EBE00
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2.3 Notes on the calibration
The following rules apply for all parameters:
• Calibrate in a way that reflects conditions in the process.
– If the process medium is constantly moving, also move the calibration solution accordingly
(e.g. use a magnetic stirrer if calibrating in the laboratory).
– If your medium is relatively stationary, calibrate in solutions that are also stationary.
• Make sure that the samples are homogeneous for reference measurements, sample
calibration etc.
• Use the same menu settings as those in the process to perform the calibration.
Example: If you automatically compensate for the temperature effect during pH
measurement, switch on automatic temperature compensation for the calibration also.
It is advisable to perform the laboratory calibration using the "Memobase Plus" database
soware (→"Accessories"). This improves the availability of your measuring points and all
the calibration and sensor data records are stored securely in the database.
2.4 Calibration intervals
2.4.1 Specifying the intervals
The service life of a pH glass electrode is limited. This is due, in part, to the deterioration and
aging of the pH-sensitive membrane glass. This aging causes the gel-like layer to change and
become thicker over time.
Symptoms of aging include:
• Higher membrane resistance
• Slow response
• Decrease in the slope
A change in the reference system (e.g. due to contamination, i.e. unwanted redox reactions at
the reference electrode) or electrolyte solution dissolving away in the reference half cell can
change the reference potential, which, in turn, causes a zero point shift in the measuring
electrode.
To ensure a high level of accuracy, it is important to readjust the pH sensors at set intervals.
The calibration interval depends heavily on the area of application of the sensor, as well as the
required level of accuracy and reproducibility. The calibration interval can vary between daily
and once every few months.
Defining the calibration interval for the process
1. Check the sensor with a buffer solution, e.g. pH 7.
Proceed as specified in Step 2 only if the value deviates from the set point. No
calibration/adjustment is necessary if the value is within the defined deviation tolerance
range (see the Technical Information for the sensor).
2. Calibrate and adjust the sensor.

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3. After 24 hours, check again with the buffer solution.
• If the deviation is within the permitted tolerance range, increase the checking interval
by doubling it for example.
• If the deviation is larger, you must shorten the interval.
4. Continue to proceed as defined in Steps 2 and 3 until you have identified the suitable
interval.
Monitoring the calibration
‣Define the limit values for monitoring the slope and zero point differentials (SETUP/Sensor
pH/ORP/Sensor diagnostics/Diagnostic limits).
These limit values depend on the process and must be determined by empirical means.
During calibration a diagnostics message is displayed if the defined warning limits have been
exceeded. You then have to service the sensor by cleaning the sensor or reference, or by
regenerating the glass membrane.
You have to replace the sensor if warning messages continue to be displayed despite the
maintenance measure.
2.4.2 Monitoring the calibration interval
If you have established calibration intervals for your process, you can also have the device
monitor them.
Two functions are available to monitor the calibration interval:
1. Calibration timer (SETUP/Sensor pH/ORP/Sensor diagnostics/Diagnostic limits/Calibration
timer)
You specify the calibration interval and the controller generates a diagnostics message
once the set time has elapsed. You then recalibrate the sensor or replace it with a
precalibrated sensor.
The timer is reset with the new calibration.
2. Calibration validity (SETUP/Sensor pH/ORP/Sensor diagnostics/Diagnostic
limits/Calibration expired)
You set time limits to specify how long a calibration should be regarded as valid.
Memosens sensors save all the calibration data. In this way it is easy to see whether the
last calibration took place in the specified timeframe and is therefore still valid. This is
particularly advantageous when working with precalibrated sensors.

Calibration and adjustment CM42-MAA101EBE00
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2.5 Types of calibration
2.5.1 pH measurement
The following types of calibration are possible:
• Two-point calibration
– With calibration buffers
– Entry of data for the slope, zero point and temperature
• Single-point calibration
– Entry of a reference value
– Sample calibration with laboratory comparative value
• Temperature adjustment by entering a reference value
If using a combined sensor (CPS16D/CPS76D/CPS96D) you must calibrate both the pH
electrode and the ORP electrode to get reliable rH values, for example.
2.5.2 Measuring the ORP
The following types of calibration are possible:
• Two-point calibration with medium samples (only ORP %)
• Single-point calibration with calibration buffer (only ORP mV)
• Data entry of an offset (only ORP mV)
• Temperature adjustment via reference value
2.6 Two-point calibration
2.6.1 General information
Two-point calibration is the preferred method for pH sensors, particularly in the following
applications:
• Municipal and industrial wastewater
• Natural waters and drinking water
• Boiler feedwater and condensates
• Beverages
Calibrating with buffers with pH 7.0 and 4.0 is recommended for most applications.
Alkaline buffer solutions have the disadvantage that carbon dioxide from the air can alter the
pH value of the buffer on the long term. If calibrating with alkaline buffers it is best to do so in
closed systems, such as flow assemblies or retractable assemblies with a rinse chamber, to
minimize the effect of air.
2.6.2 With calibration buffers
pH measurement
You use calibration buffers to perform two-point calibration. The quality buffers supplied
by Endress+Hauser are certified and measured in an accredited laboratory. The