Powering Telemetry & SCADA Systems

Image

Remote terminal units (RTUs) provide telemetry and actuation in a supervisory control and data acquisition (SCADA) system. RTUs can interface with sensors and actuators directly or through programmable logic controllers (PLCs). RTUs can communicate with the SCADA server using wired links (such as RS-232 and RS-485) and wireless radio links. RTUs typically  are powered from a 12 or 24 VDC isolated AC-DC converter which filters power line faults and disturbances for higher system safety, availability and high stability in wired and radio communications. These AC-DC converters need to work at wide temperatures from subfreezing to over 60-70 °C when RTU cabinets are installed outdoors; they must be able to start operating without hesitation at subfreezing temperatures and must continue operating at high temperatures without need for forced cooling for better system reliability. Aimtec AC-DC converters such as AMEC40-MAZ or AMES40-MAZ (for DIN-rail or panel mount) are designed to start operating without hick-cups down to -40 °C and work at temperatures as high as 85 °C with only free air convection.

 

RTUs powered from batteries and solar power systems can use DC-DC converters to isolate the source of input power. DC-DC converters with 9-36 V input range (such as AM20EW-NZ) can work with 12-24 V batteries while converters with 40-160 V input range (such as  AM20EW-110-NZ) fit 48-120(125) V battery stacks. The isolation barrier in the DC-DC converters provide additional protection against wiring faults or disturbances conducted from external battery banks or solar power sources.

 

RTU communication line interfaces (i.e. RS-232, RS-485) and analog/digital input/output sections (to sensors and actuators) expose an RTU to external disturbances. DC-DC converters in an RTU add further isolation and protection from external conditions. DC-DC converters tap the 12-24 VDC bus and produce isolated 5, 12, 15 or 24 V (unipolar or bipolar) for the line interface circuits and input/output circuits. These low-power circuit sections typically consume less than 3 W and can be powered by AM3TIW-RZ converters with 9-36 V input range. The AM3TIW-RZ includes overload and continuous short-circuit protections which help protect against damage from ground reference shifts, external wiring faults or load shorts and shield the input power source from potentially
excessive high currents.