Wireless communications have seen wide applications in the water industry since it is often cost prohibitive to run hard wire to remote locations. Licensed radio communications (VHF and UHF) have been the predominant method used for remote site monitoring. However, limited availability of RF frequencies, licensing delays, and annual licensing costs have been a bottleneck to more widespread use of wireless SCADA and telemetry in water and sewer systems. Unlicensed radio communications offer a solution to this bottleneck.
Unlicensed RF bands
The FCC and Industry Canada have allocated sections of the RF spectrum for unlicensed communications systems. These include the 902-928 Mhz band and the 2.4 Ghz band. These bands are offered on a "no interference - no protection" basis. Equipment operating in the 902-928 Mhz and 2.4 Ghz bands use spread-spectrum technology where the transceivers hop through a pseudo-random pattern of frequencies (frequency hopping) or simultaneously broadcast on multiple frequencies (direct sequence).
Unlicensed RF bands
With these techniques, only transceivers in a system with the same pseudo-random pattern or coding are able to receive from transceivers with the same coding. In this way, different systems can coexist without a unique licensed frequency.
Unlicensed RF bands
License free wireless communications can be an alternative to leased telephone company lines, which typically cost from $50 to $500 per month depending on line distances. As an example, it is possible to install radio equipment at a cost of $1,500 to replace a leased line that had cost $200 per month, yielding a payback of less than a year.
SCADALink System
Bentek Systems has incorporated the 902-928 Mhz Spread Spectrum technology in its SCADALink 900-MB RTU/Radiomodem. Recognizing that there are many SCADA and telemetry applications with limited I/O (input/output) requirements that cannot justify a traditional RTU & radiomodem system, Bentek has integrated I/O with a radiomodem in a single unit which can be configured to operate as a wireless modem, wireless RTU, or wireless control cable replacement (End to End I/O telemetry where control signals at one end are duplicated at the other end).
SCADALink System
With 4 inputs (DI/AI) and 4 outputs (DO/AO), the units are suited for many water and sewer applications.
SCADALink System
For water system applications with minimal points of measurement and control, the SCADALink 900-MB is all the equipment that may be required at the site. For larger applications, it can be used for data communications to PLCs, RTUs, or a computer host.
SCADALink System
A common application is to transfer a single level measurement from a reservoir or water tower back to a pump/lift station to control a pump. This can be a stand alone application in a water system with no centralized SCADA monitoring system or it could be used in an application where the pump control is independent of the SCADA system. In one such application, a pair of SCADALinks were used in end to end mode to telemeter water levels a half-mile to a pump station where a PLC started and stopped pumps based on the reservoir level.
