Water dosing accuracy and stability are a vital part of the water treatment, whether waste or clean. Different chemicals are added all through these treatments that should be carefully controlled to eliminate potentially harmful effects, either to the environment or to health. Dosing involves tuning the levels of chemicals included to a process stream or batch in order to maintain a set concentration. This is accomplished by continuously monitoring the process through on-line instrumentation that automatically controls chemical dosing to ensure that the levels are maintained without under- or over-dosing.
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Optimizing the dosing process to maintain a set concentration.
One instance of a dosing process that should be carefully regulated is fluoridation. There are a number of various international standards for fluoridation. For instance, in the U.S., the decision to fluoridate is authorized by the local municipality or state and in some parts of the world, fluoride is added to public water supplies in order to help enhance dental health.
Studies have revealed that the integration of low concentrations of 1 mg/l fluoride can assist in decreasing the incidence of tooth decay. However, integration of fluoride to water is a debatable subject, with doses above 1.5 mg/l being associated to medical disorders such as skeletal and dental fluorosis and osteoporosis.
In the UK, the integration of fluoride to drinking water is governed by the Code of Practice on the Technical Aspects of Fluoridation of Water Supplies 2005. The authority for ensuring compliance with the code lies with the Drinking Water Inspectorate (DWI). The DWI has the authority to take action against any water company that is found to go beyond the permitted maximum fluoridation dose of 1.5 mg/l, the limit stated by the Water Supply (Water Quality) Regulations 2000. Therefore, it is important that water companies are able to accurately monitor and control fluoride doses within the recommended limits.
The Process
It can be difficult to achieve dosing control stability that produces a final product that is both consistent and safe. This is particularly the situation where flow rates differ rapidly and there is a considerable delay between the moment of dosing and viewing the results. Often, these conditions can leave the control system struggling to attain acceptable end product quality.
One of ABB’s ControlMaster series of PID controllers can be used to achieve accurate and stable control by altering the dosage control based on the measured flow. This allows the dosing of variable flows to be regulated effectively. In addition, by employing ABB’s ScreenMaster range of paperless recorders, operators can achieve secure record of the process that can be easily stored and recovered for further reference in order to confirm that legal and quality requirements have been met.
When ABB’s ControlMaster and ScreenMaster devices are used together, they can provide the following key benefits:
- Accurate process control
- Full integration with telemetry
- Process alarming
- Quality reporting
- Remote web monitoring
- Secure data recording
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Dosing process overview.
What ABB Products are Suitable?
ControlMaster controllers
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ABB’s ControlMaster range of PID controllers is extensively deployed in dosing applications. The CM10, CM30, and CM50 controllers provide a broad range of control functions and feature direct operator controls. All controllers with their full color TFT displays in the ControlMaster range provide engineers with a comprehensive and clear overview of process status and key information. These displays can be customized to show particular process data, while a chart display offers short-term trending information.
ScreenMaster RVG200
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The RVG200 paperless recorder offers a secure and versatile solution for data recording. It is perfect for recording the level of dosing concentration and monitoring fluid flow rate and pump status. The RVG200 can collect data using Modbus™ communications, without the requirement for an analog input card.
RVG200 features include:
- Automated process data management using ABB’s DataManager Pro PC-based historical data analysis tool
- High visibility process displays
- Hose down protection to NEMA 4X and IP66
- Easy-to-use and intuitive operation featuring touchscreen technology
- Remote access and operation through Ethernet
Acknowledgements
MODBUS is a registered trademark of the Modbus-IDA organization
This information has been sourced, reviewed and adapted from materials provided by ABB Measurement & Analytics.
For more information on this source, please visit ABB Measurement & Analytics.