Control refers to the processing of input variables (e.g. setpoints, sensor or operator inputs) in order to influence the output variables (e.g. valve positions, pump output) via a control element (e.g. PLC, switch or relay). In contrast to closed-loop control, there is no continuous feedback of the output variables; instead, the controller works strictly according to defined instructions.
Components of a control system
A control system typically comprises the following elements:
- Input devices: Sensors, switches or control panels that record the input variables or specify them manually.
- Control element: The central unit that implements the control logic (e.g. PLC - programmable logic controller or relay control).
- Output devices: Actuators such as valves, dosing pumps or drives that execute the control command.
- Power supply: Ensures the operation of the control components.
Table of contents
Technical background and control types
Types of control
Various types of control are used in industrial water and wastewater treatment, depending on the requirements of the process:
- Time control: Control is based on a fixed schedule, e.g. cyclical backwashing of filters.
- Logic operation control: Logic operations (AND, OR, NOT) determine the sequence, e.g. for safety functions that monitor several states.
- Sequential or sequence control: The control takes place sequentially in several steps, e.g. when filling, stirring and emptying a neutralization tank.
- Event-driven control: External signals (e.g. fill level, pressure) trigger control commands, e.g. opening a valve in the event of overfilling.
Programmable logic controller (PLC)
The PLC is the most common control technology in water treatment. It enables flexible and customizable control sequences through programming. Advantages of the PLC:
- High reliability and precision.
- Easy adaptability to process changes.
- Integration with SCADA and DCS systems for monitoring and data logging.
Photo: Our switchgear with ALMA Controle software developed in-house - system technology, control cabinet planning & programming - everything from a single source (process: CP system ALMA CHEM MCW)
Application areas of the control unit in water and wastewater technology
In water and wastewater treatment, control technology solutions are of central importance in order to operate the complex and often highly variable processes safely and efficiently. The control system takes on the central task of linking all system components with each other and ensuring smooth communication between sensors, actuators and process control systems. The use of programmable logic controllers (PLCs) enables flexible, precise and reliable automation of the systems.
PLC-based control systems
Programmable logic controllers (PLCs) are at the heart of modern automation technology and have become indispensable in water and wastewater technology. They perform tasks such as
- Control of operating processes: From the dosing of chemicals to the control of pumps and valves.
- Safety monitoring: Detection of limit value violations and initiation of emergency measures.
- System monitoring and optimization: Acquisition and processing of measurement data to analyze operating conditions and optimize processes.
Integrating the control system into process control systems such as SCADA makes it possible to monitor, control and document the entire system centrally.
Holistic approach: system planning, control cabinet construction and programming
A particularly great advantage in the implementation of control solutions in water and wastewater technology lies in the combination of system design, control cabinet planning and PLC programming. Close integration of these areas ensures optimum interaction between the systems, which eliminates frequent sources of error such as communication problems at interfaces.
Our strengths in interaction:
- System design: Automation is integrated into the overall concept as early as the planning stage of the system processes.
- Control cabinet construction: The precise planning and construction of the control cabinets takes into account all the requirements of the PLC and the sensors/actuators.
- Programming: The programming of the PLC is specially adapted to the individual requirements of the system and designed for smooth communication.
This holistic approach results in an error-free, well-coordinated control solution that not only works efficiently, but is also easy to maintain and scalable.
PLC manufacturers and programming languages
The market-leading suppliers of PLC systems provide reliable and flexible control solutions that have been specially developed for industrial applications. The most important manufacturers include:
Siemens
With its SIMATIC S7 series and TIA Portal programming software, Siemens is one of the leading suppliers of PLC systems. The platform enables intuitive programming and offers comprehensive functions for process automation. Siemens solutions are particularly popular in large systems and complex applications.
Beckhoff Automation
With its CX controllers and TwinCAT software, Beckhoff offers flexible and PC-based automation solutions. The high degree of openness and scalability make Beckhoff particularly interesting for systems that require individual adaptations.
Rockwell Automation (Allen-Bradley)
With the ControlLogix and CompactLogix systems, Rockwell Automation offers robust PLC solutions that are primarily used in international applications and the process industry. Programming is carried out using the powerful Studio 5000 software.
Schneider Electric
The Modicon series from Schneider Electric in combination with the EcoStruxure Control Expert software is specially designed for energy-efficient control solutions. Schneider PLC systems are often used in medium-sized water and wastewater plants.
WAGO
With its 750 and 760 PLC systems, WAGO offers a particularly compact and modular solution that is suitable for small and medium-sized systems. The open architecture and support of protocols such as Modbus, BACnet or OPC UA enable easy integration into existing systems. Programming is carried out using the e!COCKPIT software or on the basis of CODESYS, which allows flexible adaptation to different application requirements.
ABB
With its AC500 series, ABB supplies state-of-the-art PLC solutions that are characterized by their robustness and flexibility. ABB's PLC systems are particularly suitable for use in demanding industrial environments. They are programmed using Automation Builder, a powerful platform that offers comprehensive functions for process automation, energy monitoring and integration.
Photo: Our switchgear with ALMA Controle software developed in-house - system technology, control cabinet planning & programming - everything from a single source (process: ALMA OSMO reverse osmosis system)
Integration of control in process control systems
The integration of control systems into process control systems (PCS) or SCADA systems (Supervisory Control and Data Acquisition) is a decisive step towards mastering the complexity of modern water and wastewater plants. This integration enables centralized monitoring and control of all plant components, promotes transparency of operating states and optimizes the efficiency and safety of plant operation.
Functions and advantages of process control systems
1. visualization
One of the biggest advantages of a DCS or SCADA system is the ability to graphically display control sequences and system statuses in real time.
- Interactive process images: All relevant data, such as fill levels, pressures, temperatures, pH values or flow rates, are displayed in clear graphics. Operators can react quickly to deviations.
- Alarm messages: Critical states are highlighted in color and alarms provide real-time information about potential faults. This makes it easier to diagnose faults and speeds up troubleshooting.
- Simulations: Many DCSs allow simulations to be carried out to test processes before they are put into practice.
2. data logging
The recording and storage of process data in a central database is a central component of modern process control systems.
- Historical data analysis: Long-term data such as COD values, flow rates or energy consumption can be evaluated in order to recognize trends and identify potential for optimization.
- Report generation: Automatically generated reports enable transparent documentation of operating statuses and serve as proof to authorities or customers.
- Maintenance planning: By analyzing operating data, maintenance intervals can be planned on the basis of actual load (predictive maintenance), which reduces downtimes.
3. remote control
DCS and SCADA systems make it possible to monitor and control systems remotely via networks, including the Internet.
- Remote access: Operators or service technicians can access the system from any location, carry out diagnostics and adjust control parameters.
- Cost efficiency: Remote access reduces the need for on-site visits and enables a rapid response to faults.
- Security measures: Encrypted connections and user rights management ensure that only authorized persons have access to critical system data and controls.
Technical integration of control system and DCS/SCADA
The PLC and process control system are usually connected via industrial protocols that ensure reliable and standardized data exchange. Frequently used protocols are:
- Modbus (TCP/RTU): Widely used in water and wastewater technology, especially for pump and valve control.
- OPC UA (Unified Architecture): Enables platform-independent communication between control systems and control systems with integrated safety architecture.
- PROFINET/Profibus: Particularly suitable for fast communication within systems, e.g. for real-time control.
Implementation typically takes place via central controllers (e.g. Siemens SIMATIC or ABB AC500), which record all relevant data from sensors and actuators and forward it to the DCS/SCADA system.
Conclusion
The control system is an indispensable tool in industrial water and wastewater technology. It offers a simple and reliable way of coordinating system components and automating processes. Especially in systems with constant conditions or clearly defined processes, the control system is a cost-efficient and effective solution. For complex or dynamic processes that require constant adaptation, control is often supplemented by closed-loop control. A deep understanding of control principles is essential in order to operate systems efficiently, safely and economically.
For further information on our products, please feel free to contact us at any time!
