Water dosing accuracy and stability crucial parts of water treatment, whether waste or clean. A number of chemicals are incorporated throughout these treatments that must be carefully controlled to eliminate potentially adverse effects, either to the environment or to health. Dosing involves tuning the levels of chemicals included to a batch or process stream to maintain a set concentration. This is accomplished by constantly monitoring the process using on-line instrumentation that automatically controls chemical dosing to guarantee levels are maintained without over- or under-dosing.
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Optimizing the dosing process to maintain a set concentration
One instance of a dosing process that must be cautiously regulated is fluoridation. There are a number of different global standards for fluoridation. For example, 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 put into public water supplies to help enhance dental health. Studies have revealed that the incorporation of low concentrations of fluoride of 1 mg/l can aid in decreasing the incidence of tooth decay. However, the incorporation of fluoride to water is a debatable subject, with doses over 1.5 mg/l being associated to medical disorders such as skeletal and dental fluorosis and osteoporosis.
In the UK, the incorporation of fluoride to drinking water is directed by the Code of Practice on the Technical Aspects of Fluoridation of Water Supplies 2005. Responsibility for guaranteeing compliance with the code lies with the Drinking Water Inspectorate (DWI). The DWI has the authorization to take action against any water company that is found to overshoot the permitted maximum fluoridation dose of 1.5 mg/l, the limit indicated by the Water Supply (Water Quality) Regulations 2000. It is thus vital that water companies are able to correctly monitor and control fluoride doses within the recommended limits.
The Process
Realizing dosing control stability that results in a final product that is both consistent and safe can be tough. This is particularly the case where flow rates differ rapidly and there is a substantial delay between the moment of dosing and viewing the results. These conditions can frequently leave the control system struggling to realize acceptable end product quality.
Employing one of ABB’s ControlMaster series of PID controllers, accurate and stable control can be accomplished by altering the dosage control based on the measured flow. This enables the dosing of variable flows to be regulated excellently. Furthermore, by using ABB’s ScreenMaster range of paperless recorders, operators can attain a secure record of the process that can be easily stored and retrieved for further reference to confirm that quality and legal requisites have been met.
When ABB’s ControlMaster is used along with its ScreenMaster devices, the following key benefits can be achieved:
- Accurate process control
- Process alarming
- Secure data recording
- Remote web monitoring
- Quality reporting
- Full integration with telemetry
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Dosing process overview
What ABB Products are Suitable?
ControlMaster controllers
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The ControlMaster range of PID controllers from ABB is extensively deployed in dosing applications. The CM10, CM30 and CM50 controllers offer a broad range of control functions and feature direct operator controls. All controllers with their full color TFT displays in the ControlMaster range offer Engineers with a clear and complete overview of process status and key information. These displays can be tailor-made to present specific process data, while a chart display gives short-term trending information.
ScreenMaster RVG200
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The RVG200 paperless recorder offers a versatile and secure system for data recording. It is suitable for recording the dosing concentration level and monitoring fluid flow rate and pump status. The RVG200 is capable of collecting data using Modbus™ communications, without requiring an analog input card.
RVG200 features include:
- High visibility process displays
- Intuitive and easy-to-use operation featuring touchscreen technology
- Hose down protection to IP66 and NEMA 4X
- Remote access and operation via Ethernet
- Automated process data management using ABB’s DataManager Pro PC-based historical data analysis tool
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.