PLC vs RTU vs IED

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Difference Between PLC, RTU, & IED

PLCs and RTUs are both electronic devices; their functionalities overlap with each other. RTCs are sold with PLC-like features, and PLCs are sold with RTC-like features. Many vendors sell proprietary alternatives and different associated environments to run these programs since the industry made the functional language running RTUs and PLCs standard.



RTU                                                                                    

“RTU” stands for “Remote Terminal Units.” They are also referred to as “Remote Telemetry Units.” An RTU is an electronic device which is controlled by a microprocessor. The main function of an RTU is to interface the SCADA to the objects present physically. “SCADA” stands for “supervisory control and data acquisition.”  The interface between objects and SCADA takes place by using supervisory system messages to control all the objects connected and by transmitting to the system all the telemetry data.
The RTU does not support control loops and control algorithms. The functionality of RTUs and PLCs has started overlapping because of cheaper hardware, and thus the industry standardized the language for programs on which RTUs run. IEC 61131-3 has been standardized.
It is different from a PLC because it is considered more suitable as it uses wireless communication and is suited to a wider geographical telemetry whereas PLCs are better with local controls, for example, production lines or plants, etc. In plants and production lines, the system is more based on physical media. IEC 61131-3 is used more by PLCs, and RTUs use other proprietary tools.


PLC                                                                                      


“PLC” stands for “programmable logic controller.” PLCs are digital computers. They are used mainly for automating the electromechanical processes, for example, assembly lines in factories, light fixtures, amusement rides, etc. They are specially designed for output arrangements and multiple inputs. They have electrical noise immunity, vibration and impact resistance, varied temperature ranges, etc.
Some of the functions of PLCs are; process control, relay control, motion control, networking, etc. They have started matching the desktop computers in storing, processing, communicating, and handling data.


IED                                                                                        



Intelligent End Device Similar to a PLC, an intelligent end device (IED) can establish communication between remote
sensors and controllers and the communications network. An IED differs from a PLC in that a
single IED can control several different aspects of a piece of equipment, so that the entire piece of equipment works in harmony with the rest of the needs of the system and within established design parameters. IED is a relatively new term and has come about in part because of confusion between remote telemetry units, with the acronym (RTU) and remote terminal unit, also with the acronym RTU. To help solve this issue, the industry has begun to call these more sophisticated interface and controller units, IEDs.
A key difference between the remote terminal unit (RTU) and the IED, is the same as that of the RTU and PLC, and it is illustrated in the figure below. In this figure, note that the machine
language, and hence the data, moves in both directions, thus allowing for not only data
acquisition, but also control.

Simplified Illustration of PLC or IED Function in a SCADA System

It is important to note that specific instructions for equipment automation are stored locally, in the PLC or the IED. This is usually due to the fact that over most Communication Networks,
there is a limited bandwidth, thus limiting the actual control to that which is “pre-programed”
into the PLC or IED. As communication networks and the technology that SCADA is based on
continues to improve, there will no doubt be a day when unlimited control can be exerted from
the SCADA Master to the desired equipment.

Summary:

  1. “RTU” stands for “Remote Terminal Units.” It is also referred to as “Remote Telemetry Unit”; “PLC” stands for “programmable logic controller, & “IED” stands for Intelligent End Device.
  2. RTUs are considered more suitable for wider geographical telemetry, the reason being that RTUs  use wireless communication; PLCs are more suitable for local control, for example, for assembly lines in factories, light fixtures, amusement rides, etc. PLCs are specially designed for output arrangements and multiple inputs. They have electrical noise immunity, vibration and impact resistance, varied temperature ranges, etc. An IED differs from a PLC in that a single IED can control several different aspects of a piece of equipment, so that the entire piece of equipment works in harmony
  3. IEC 61131-3 is used more by PLCs, and RTUs use other alternative proprietary tools.

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