Campbell Scientific systems are seeing increased use in Supervisory Control and Data Acquisition (SCADA) applications. These systems typically consist of two components: a "Supervisory" component comprised of a central control computer and software, and a "Control And Data Acquisition" component made up of Remote Terminal Units (RTUs).  The RTUs make measurements, report back to, then execute commands from, the Supervisory component.

SCADA systems are used in a number of industrial process and control applica­tions. This article reflects our recent efforts toward water and wastewater treat­ment plants.

The Supervisory Component

In Campbell Scientific systems, the Supervisory component consists of a PC-compatible computer running CSI’s Real-Time Data Monitoring (RTDM) and PC208W software.  Alternatively, Wonderware, Intellution, or other soft­ware augmented by Modicon’s Modbus software can be used.  Our RTDM soft­ware runs on Windows 95, 98, NT and allows the operator in the treatment plant to monitor graphical screens with animat­ed objects such as wet well levels, screens, grit chambers, centrifuges, chem­ical dosage rates, tank levels, pumps, clar­ifiers, digesters, filters, oxidation ditch weir levels, aerators, UV disinfectors, and chlorine and ozone injectors.

Operators watch the computer screen to view status and acknowledge alarms in the plant and/or at remote sites. Remote lift stations, reservoirs, and pumping sta­tions send data to RTDM via dial up leased phone lines, radio, or wide area network T1 links.

Control And Data Acquisition Component (the RTUs)

Our RTUs are the CR510, CR10X, orCR23X dataloggers, depending on the measurement and control capabilities needed at each locale.

Using Modbus with our SCADA Systems

Since its introduction by Modicon in 1979, Modbus has proven to be reliable, economical, and popular in worldwide SCADA networks. Modbus is a master/slave protocol that permits the Supervisory computer to communicate with the RTUs (slaves). This protocol is used by many manufacturers of PLCs (Programmable Logic Controllers) and RTUs. To operate in these systems Campbell Scientific RTUs must be equipped with a Modbus operating system (contact an applications engineer).

Before the release of RTDM, Campbell Scientific successfully installed CR10X RTUs in several customer SCADA sites, some of which use Wonderware’s Intouch software as the Modbus master.

Modbus is RS-232, RS-485, and TCP/IP compatible over direct line, leased line, fiber optics, telephone, radio, microwave, satellite, Ethernet and internet connections.

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