SCADA (Supervisory Control And Data Acquisition) systems are crucial elements of many water distribution and wastewater collection systems, allowing centralized personnel to perform remote monitoring and control of widely dispersed equipment, generally pumping stations. Although the most common configurations use radio as the means of communicating with RTUs (Remote Terminal Units), other communication schemes are possible. These include direct lines, leased telephone lines, and dial-up telephone lines.

Our experience with SCADA systems is extensive, covering all types of communication schemes and systems as large as 100 RTUs. Our system design process involves four key steps: the radio survey, analysis and design, build and test, field testing and training.

Radio Survey

When a system is intended to use radio communications, we will do a survey to assure paths, elevations, and frequencies for all sites in the network will meet operational standards for proper performance. Key steps in the survey are as follows:

• Obtain the geodetic coordinates for each site and establish the relevant digital elevation model to be used
• Using terrain analysis computer software, generate a path analysis and check it against the USGS topographical maps
• Select a propagation method and model with which to do the necessary calculations
• Based on the factors developed in the previous steps, determine the expected receive signal level and compare that against acceptable minimums
• Specify a selection of either licensed radio or spread spectrum, based on a comparison of the system requirements to the strengths and weaknesses of both approaches
• Perform a field radio test to confirm the calculations and frequency selection performance