Neil Saunders, Sales Manager and water industry specialist at Bürkert Fluid Control Systems, assesses the requirements for process control and how best to meet current and future requirements
Process control is vital to ensure the integrity of the water supply chain and as the technology in this area advances so it is important, if you are involved in the design, installation and operation of the process control equipment, including the panels, that you are fully aware of the latest developments.
Water is a finite resource and so the efficient management of this resource is crucial to maintaining supplies and a key driving factor behind industry investment. Much of the water that we all use every day is actually on a continuous loop, constantly being processed after use so that it can be returned to the environment before it is extracted again, treated and reused.
This process is heavily dependent upon precise process control, monitoring and data recording to ensure that all the regulatory standards are maintained as well as ensuring that the environment and the general population is protected.
Sewage treatment consists of four main processes: screening, primary filtration, secondary filtration and tertiary treatment. On entering a sewage treatment works, dirty water passes through screens to remove paper, wood and other large articles that could damage machinery or block pipe systems.
Control of chemical dosing
Before the waste water progresses to the next treatment stage, iron or aluminium salts are added to assist in the removal of phosphorus, while the biological processes will remove the nitrogen, both of which originate from industrial and agricultural practices.
The process of chemical dosing has to be very carefully controlled and monitored with records being kept to ensure compliance with local water quality standards. The remaining processes involve further settlement and filtration before the water can be returned to the local water course, from where it may be extracted to undergo further purification. The water is very carefully dosed with aluminium sulphate, a coagulant, which helps to bind the impurities together to form particles.
This process requires careful monitoring of the pH levels as well as effective mixing in order to be efficient. Removing taste and odour, as well as disinfection, are all carefully carried out to ensure that the final product which appears from the tap is potable and meets all the necessary regulations.
In general, the water treatment industry prefers to operate a centralised control system for each site, making it quicker and easier for operators to assess the equipment and processes on the site. With such a wide array of sensors, valves and pumps installed around the site, the most efficient controller will be one that is capable of multiple tasks while still being simple to operate.
Controller maximises compatibility
One example would be Bürkert's type 8619 multiCELL transmitter/controller, which is ideal for a wide range of applications in water treatment using pH, conductivity and flow sensors, ORP and temperature measurements. The major advantage of this controller is its versatility, being compatible with most common sensors as well as its modular design allowing additional hardware and software to be added easily.
Each controller can be configured for a range of sensors as well as having up to six pre-configured I/O boards to accommodate any signal requirements. In addition, the multiCELL can be configured as a datalogger, using the built-in SD card slot for data storage. This SD card slot can also be used to save sensor parameters and control application settings to allow the same settings to be replicated in another multiCELL controller; ensuring accurate transfer of control parameters between sites.
The multifunction controller has been designed with both the installer and the operator in mind — the wide range of features and the modular design allows the system to be customised to the clients' exact requirements, while the easy, intuitive user interface can be configured in four different views to display the most relevant information to a particular application. Different users can configure different views, depending on the area of control they are interested in.
Designing a system such as this essentially allows costs to be reduced in the processing applications; a systems engineer can, in many instances, replace an entire control cabinet with one neat controller with a built-it display. The relative costs of a separate enclosure, rack mounted plc, I/O, cabling, power supply, HMI etc. can effectively be replaced with just one multiCELL unit — not great news for the panel building industry you would think, but cutting costs and streamlining installs is the name of the game and this type of knowledge can prove invaluable.
Furthermore, the advantage of this modular expansion facility is that multiCELL users only pay for the features that they actually require and since the multiCELL provides a single controller/transmitter across a wide range of applications, inventory and training costs are also both minimised. In the long term, the total cost of ownership is greatly reduced when compared to those systems currently in use. This unit is designed specifically to be panel mounted, either internally, or on a door or bulkhead — so a panel can be downsized, but technologically up-sold.
Controller with communications options
Similar principles have also been used in the design of the mxCONTROL multifunction controller, type 8620, which has the additional benefits of Ethernet or modem communication as well as the ability to control digital dosing pumps. The flexible programming capabilities enable integrators and end users to make fast program modifications during commissioning, future upgrades and maintenance.
Again, there is an SD card slot for data logging and saving parameter settings to save time when installing a number of units across different sites. By using a simple user interface, easily configured control programs and common sensors the whole process from design to implementation is streamlined for efficiency, reducing training time, parts inventory and overall cost of ownership.
Both solutions allow direct connection to existing SCADA systems and other methods of site-wide monitoring and supervisory control, so adding connectivity to PH sensors and flow meters for example can add to the automation efficiency of a plant, while supporting the case put forward by the panel builder or integrator for a smarter solution. As this area of process control develops, so it is important to be able to understand the client's difficulties with legacy equipment to allow the best solutions to be designed and implemented.
By using in-depth knowledge of process control and working with the end user, the panel builder and the installer it is possible to create a package that works for all concerned and delivers a simple to use, efficient and cost-effective solution.