Technical article
One for all
The new generation of conductivity transmitters by Endress+Hauser
Marc Buttmann
Process control through conductivity measurement is a widely found in todays process industry. As similar the available measuring principles are as different are the applications: From pure water production for the pharmaceutical industry to concentration control of acids and caustic it provides a reliable measuring point with little service requirements.
In many cases conductivity loops in one plant have different task and thus have to be equipped with instruments of different models or even different suppliers. With the introduction of the new Mycom S CLM153 Endress+Hauser offers one instrument for all common conductivity applications that allows standardization for the user. Together with a wide selection of conductivity sensors complete solutions are offered to the customer.
Fig. Mycom S CLM153
Pure water applications
Pure water is a crucial process variable in many industries. The pharmaceutical industry requires pure water of a certain purity as base of injectable drugs or to clean and rinse their pipes, fermentors or bioreactors. The most known standard for purity is the USP24 standard (United States Pharacopeia).
It defines water pure enough to be used if the raw conductivity is less a limit at a defined temperature. As the temperature changes the limit changes as well. The authors of this standard realized that with the common compensation of raw conductivities to a 25°C value uncertainties will be introduced to the instruments output through the algorithm used in manufactures instruments to calculate the compensated conductivity. By requiring both outputs without internal calculation it is ensured that only the sole accuracy of the two measuring inputs conductivity and temperature determines the end result. As an additional safety function the pairs conductivity and temperature are monitored and if the limit according to USP is exceeded an alarm relay becomes active. This allows to back up the central control system in case of failures.
The Mycom S CLM153 is able to measure down to the theoretical conductivity of pure H2O at 56nS/cm at 25°C with a 0,1 cm-1 sensor. The resolution is at 1 nS/cm which can be even lower if other sensors are used with cell constants of 0,01 µS/cm like the CLS15.
If automatic temperature compensation is required the Mycom S CLM153 offers different principles like linear compensation, pure water compensation, NaCl compensation or a user table.
Filter applications
Filter control is one of the most common applications found: Since conductivity is the measure of the concentration of all ions in the liquid this is an ideal parameter to control reverse osmosis filters or ion exchangers.
Usually it is sufficient to monitor the outlet of the filters. In the case the filter performance drops and it has to be regenerated the conductivity of the process stream rises.
More accurate is achieved by controlling both the inlet and the outlet and evaluating the difference between.The Mycom S CLM153 offers two totally independent sensor inputs with each assigned to an analog current output. Additionally it provides the possibility to apply mathematical functions like substraction, multiplication, division and sum of the two readings. Also the result of these functions can be assigned a separate analog output.
Concentration applications
The concentration of acids or caustic can be determined using conductivity. Since both acid and caustic change, i.e. increase the concentration of ions in the liquid through dissociation of compounds and therefore also change the conductivity it is a direct measure for the concentration.
The Mycom S CLM153 comes with 4 preset tables and 4 more tables that can be user set. By changing to the % display mode the instrument uses an internal look up table to convert the conductivity sensor input.
In applications like CIP (Clean in Place), mostly found in the sanitary industry, often several cleaning agents are used and it is of advantage to switch from one table to the other while the process is running. This allows to control the concentration of each of the agents separately and avoids multiple measuring points.
The Mycom S CLM153 provides remote inputs that change the complete data set in use: the display mode (µS/cm, mS/cm or %), the temperature compensation and the current output range.
Considering the wide measuring range in concentration applications from pure water in the few µS/cm range to highly concentrated acids at more than 400000µS/cm the Mycom S CLM153 also features an innovative auto range function for the output signal. The current output range is always selected to the best resolution. The range currently used is indicated by relay outputs for back calculation in the control system.
Quality control
The Mycom S CLM153 offers different features to ensure the highest accuracy and reliability of the system, specifically important in applications where product specifications have to be tightly met: A sensor check system monitors the wiring and sets an alarm if the sensor is disconnected and product will leave the plant without the necessary quality control.
The most common cause of inaccuracy of contacting conductivity sensors, the polarisation at high conductivities, is monitored and compensated. If the measuring range is exceeded and the systems reading will not match the specified accuracies an alarm is set.
A Process Check System (PCS) sets an alarm if the sensor input is invariable over a period of time. This indicates a disconnected sample line or a coated or blocked sensor. The limits both for the sensor input variance and the time period can be selected by the user.
A redundancy measurement makes use of a second sensor input. Installed close to the first sensor, the system assumes similar readings. If the difference between the two inputs becomes too big the alarm is set.
Safety:
Besides all the self check systems build in the new Mycom S CLM153 to assure a safe operation there is still the possibility that the set up menu is changed during the running process. To avoid access of unauthorized personnel the operating menu is a divided in 3 levels: Display, Maintenance and Specialist level. Each of these levels are password protected.
New features
The Mycom S CLM153 incorporates some new technologies that will change the make the users life easier and increase the reliability of the measuring point:
This new generation of conductivity transmitters comes with an optional DAT module, a data storage module that can be plugged into the terminal compartment and that down- and uploads data to and from the instrument. These data can be edited and stored on a computer by means of an adapter that is connected to the serial interface. The Software package PARAWIN is used to set the system up within a windows based menu. One DAT modul can be used at multiple measuring points and thus minimizes start up times for larger installations. Not only for the start up phase this new technology offers advantages to the customer. Since all internal data are accessable through the DAT module recording and archiving of instrument data like calibration history, sensor performance data, measurement log book and min/max records is easily possible at the computer.
Bild Parawin Oberfläche
Operating the instrument thought the key pads has become easier as well: The back lit graphic display offers online help pages with every function. This will allow the user to navigate through the clear text menu without operating manual.
To visualize the data history new screen functions have beed introduced as well: A graph for the primary and the secondary sensor input, i.e. conductivity and temperature, helps specifically during the set up of process parameters and control loops.
Bild Bildschirm im Schreiber Modus
An internal log book stores the last 500 measuring data points for the records. The frequency of these data poinst can be selected to expand the time recorded.
The Mycom S CLM153 comes with a wide selection of control features, from easy limit switches and 2-point controllers to PID controllers. An analog output via the 4-20mA signal as well as a binary output using a relay in puls frequency and puls length mode can be connected to external devices like valves or motors.
A current input terminal for additional parameters like flow allows feed forward control to optimize the control loop.
The relays can also be assigned NAMUR standards to indicate alarm, warning and failure status.
To fulfill the requirement of the chemical industry ATEX, FM, CSA and TIIS approvals are available.
The common communication protocols Profibus PA, Profibus DP, Fieldbus and Hart will be available as option. The new CLM153 generation will be fully compliant to FDT Standards.
Modular design:
The new Mycom S CLM153 has been developed according to the modular electronic design introduced to the Endress+Hauser Analysis transmitters 3 years ago. By developing modules that are used in different instrument families the number of electronic board variants is reduced and, at the same time, production volume is increased. Upgrades in Software or Hardware are widely introduced at the same time and ensure that all instruments are of the newest generations. Stock is reduced to a minimum and production costs can be optimized. Time to market for new instruments is minimized since already existing module designs can be reused.
Bild Modulare Elektronik
The modular concept also allows to define upgrade kits that can be installed by authorized service personnel on site. This is specifically important if an existing installation has to be upgraded with digital communication or new control functions require additional relays.