Katlax wireless converters could be the right choice for SCADA based wastewater treatment plant

In a wastewater treatment plant, at each of the lift stations, an embedded controller is used to monitor high sump level, pump status, power consumption and power failure. As SCADA computers communicate with each lift station using RS232 protocol, each lift station controller is connected to a SCADA system central computer via RS232 to wireless converter. RS232 to wireless converter at each lift station and a master RS232 to wireless converter at the control centre form a "wireless" local area network (WLAN) for SCADA system communications. The 2.4 GHz ZigBee wireless converters allow the asynchronous controllers to communicate over the WLAN without any additional special communications programming. The entire system is directed by a PC-compatible computer running software.

The SCADA system central computer also communicates with another embedded controller which interfaces the wastewater treatment plant control equipment. The SCADA control computer continuously interrogates all of the remote sites through WLAN and the plant control equipment. Performance and alarm data are received, logged and reported at the control computer.

The entire network can be scanned in a few seconds. In addition to gathering data from the remote sites, the software provides a graphical display of current process data, as well as hardcopy reports containing historical information. This software is also used to program each of the remote embedded controllers. Using the software's graphical programming language, the control programs are defined and then downloaded to individual controllers for execution through WLAN. In order to provide daily, 24-hour supervision of the facilities, the Gateway Autodialer is used to report alarms when the plant offices are unattended during nights and weekends. The gateway combines a digital autodialer with an alarm and control system having full microprocessor-based operation and convenient user programmability. The gateway provides interactive monitoring and control of the controllers via the dial-up telephone network, allowing read and write access to controller data registers via any standard tone phone. It delivers these important functions via serial cable connection and without requiring the use of controller outputs or modification of control programs.

The SCADA computer is programmed to collect and reformat data from the remote sites and discern alarm information using WLAN. As alarms occur, site numbers and alarm information are relayed by control software to the Gateway using Modbus protocol.

In this installation, the Gateway is linked to the SCADA computer via a PLC, whose primary function is to convert the Modbus RTU master protocol to Modbus RTU slave protocol. In a Modbus-based link, the Gateway must act as the master. Here RS485 to Wireless Converter is used at each end to link the Gateway PLC with SCADA Computer.

(Katlax Enterprises Pvt Ltd (Interface Product Group), Pune. Telefax: 91-20-27110224. Mobile: 096897-83922. Email: sales@katlax.com)