RTU stands for Remote Terminal Unit, sometimes also called Remote Telemetry Unit or Remote Telecontrol Unit.
A RTU is a microprocessor based device that monitors and controls field devices, that then connects to plant control or SCADA (supervisory control and data acquisition) systems.
If you do a search on the definition of a RTU, you may find many results that state a RTU is much more powerful than a PLC as the RTU can have several inputs and outputs. Well, as you know, so can the PLC.
The RTU does have some potential benefits over the PLC, which we will discuss.
Price Point
On the price point, the winner right now is the PLC.
PLCs have a lower price point but many consider the RTU to be a much more rugged system which would lead you to believe that spending more initially will equal out in the end.
Process Control
As far as process control, the RTU is probably on equal ground with the PLC. Both controllers can have multiple different types of I/O, different communications modules, and programming of processes that may require little to no operator intervention.
Where the RTU is considered to have some advantages is in environment tolerances, backup power options, and autonomy.
Programming Advantage
Let’s first discuss a programming advantage that the RTU may have over the PLC.
A PLC requires specific software and specific skills and knowledge of ladder logic, structured text, function block, etc.
A RTU can sometimes be programmed through a simple web interface. In other instances, the RTU comes with setup software that can help you to configure input streams to output streams as well as communications.
There are also many RTU’s that have preprogrammed modules that can just be applied for the desired function.
This advantage can quickly be turned into a disadvantage.
Some RTUs may be programmed with languages such as Basic, Visual Basic and C#. Of course, these languages require a special skill set just as the PLCs do.
Some RTUs are even programmed in the same languages that PLCs are programmed with such as Ladder Logic and Structured Text.
Environmental Tolerances
A definite advantage is in the environmental tolerances of a RTU.
RTU’s are widely used in environments with extreme temperatures and located in remote locations.
And when I say remote, I don’t mean within a few feet or few hundred feet, I mean miles down dirt roads, on top of mountains, on off shore oil rigs, that kind of remote.
Imagine using a RTU on an off shore oil rig. Getting reliable communications would be both essential and difficult. With the use of the stated communications, sending and receiving data from these very remote locations is a breeze.
Some RTU’s have a backup battery and charging circuit, such as solar power, that will allow the RTU to continue to operate even when AC power is lost.
Of course, PLC’s can have a UPS backup which adds the same benefit but the charging circuit is a definite plus.
The advantages that were described here can easily be mitigated with the new PLC and PAC (programmable automation controller) systems. Just about every category of advantage can be found in other options.
The biggest advantage is the environmental tolerances, those are hard to compete with.
So all and all, there aren’t a lot of differences between modern RTUs and PLCs.
The ever changing technologies do a remarkable job of leveling the playing field.
With so much love and excitement,
The RealPars Team
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