SCADA Design, Installation, and Service
What is a SCADA System?
A typical fresh water system may consist of one or more pumping and storage facilities. The water for the fresh water supply is obtained through several methods. Well pumps extract water from under ground aquifers. Surface water is collected from lakes and rivers. Water is purchased from a water provider who obtains water using either of the previous methods mentioned. A pumping facility may consist of one or more water pumps for collecting water and/or maintaining delivery system pressure. These pumps would be controlled based on the water elevation in overhead tanks, water elevation in ground storage tanks, or water pressure in the delivery system grid.
Typical wastewater treatment systems consist of a main treatment facility and one or more wastewater collection stations called lift stations. The lift stations simply pump the wastewater from a low lying location to the treatment facility. Wastewater moves through the plant undergoing several purification processes and is released into rivers or streams when completed.
Environmental Protection Agencies regulate water quality. Strict guidelines must be followed by the water provider in order to assure high water quality. These guidelines dictate types of chemical treatment required for water quality improvement as well as acceptable limits on water born contaminants. These agencies also regulate the quality of purified wastewater that is released into the environment.
What Does ACS Do?
ACS designs these SCADA system control schemes in accordance with engineer and/or customer specifications. Upon customer request ACS will solely engineer the system control scheme. A typical SCADA system consists of a central monitoring and control station and one or more remote stations. The central station will collect data from these remote stations via dedicated telephone line modem links and/or radio modem links. The central station will also send data to these remote stations via these same links. The trend in the market is towards state of the art “Human Machine Interface” (HMI) software running on a desktop computer at the central station. This software communicates with a programmable logic controller (PLC). The PLC then communicates with the remote stations via the above mentioned links. The PLC is “intelligent” and will maintain basic system control in the event of a computer failure. The central station can utilize only a PLC for control and employ a simple graphic interface for control setting adjustment and system monitoring. The remote stations are primarily PLC based and can be programmed to provide basic system control in the event of a communications failure. The remote PLC can employ a simple graphic interface for control setting adjustment and system monitoring giving the operator a view of the entire SCADA system from these remote locations.
ACS configures all of the software components of a SCADA system. This includes the “Human Machine Interface” (HMI) graphics, “Programmable Logic Controller” (PLC) functions, operator reports and system failure alarming. These elements are developed based on customer specifications and have basic similarities from job to job however; variations exist between customers and must be addressed. The HMI graphics portray the water supply or wastewater treatment system to the operator and must be clear, intuitive and simple. The HMI collects and archives system events, alarms and data from the PLC. This data can be reviewed to assess system efficiency. This data is also used for system reporting. The data is shared with third party software that is configured for report printing. The PLC carries out logical repetitive control iterations and communicates with both the HMI computer and the remote stations. The PLC must be configured to collect and organize the system data. Proper organization insures efficient communications between the HMI computer and the remote stations. The PLC at the remote station can be programmed for local control in the event of a communications failure. It is primarily responsible for the collection and organization of the remote station data and transmission of the data to the central station PLC. ACS is mindful of governmental regulations controlling water quality as well as safe electrical system installations.