RTU Input / Output Signals

The DFA Remote Terminal Unit (RTU) monitors and transmits values as input or output signals from I/O devices such as meters, pressure transducers, pump starter auxiliary contacts, etc. from within the SCADA System.

Signals created from a device such as a water meter and sent to the RTU are called input signals. Signals created within the RTU and sent elsewhere such as the System Control Computer (SCC) or another RTU are called output signals.

Signals are of the following types:
  • Digital - ON/OFF discrete signal such as an equipment contact closure wired to the isolated inputs of the RTU and is generally read as 0 or 1 in value. These values could be a RUN status from a pump starter auxiliary contact, pressure switch, etc.

  • Analog - A continuous signal that changes smoothly over a given range is brought into the RTU via a 4 to 20 milliamp signal. These are real values such as water levels, pressure or turbidity and are not discrete signals such as ON / OFF.

  • Counter - Pulse signals from Flow meters or similar occurrence meters which count the number of times an event occurs.
The RTU transmits digital, analog or counter data values
Remote Terminal Unit (RTU)