Simple question

[danesh]

Dear all,​

I have a question, could experts answer?​

What is different between a PLC and a RTU? ​

​

Thanks in advance,​

Danesh​

 

[danw]

I use the control/non-control distinction.

An RTU collects data, analogs and/or discretes (sometimes via digital protocols like Modbus to local devices) and communicates those analog values and status conditions via a link to a SCADA or DCS. The link was traditionally termed 'telemetry' and can be wired, or wireless.
An RTU can also provide outputs, which are driven by instructions from the SCADA or DCS. An RTU doesn't make control decisions on its own, the mother SCADA or DCS or PLC makes the decisions.

A remote PLC that controls some process and is connected to other devices or a SCADA is not an RTU in my mind, it's a remote PLC, because the PLC's been programmed for control.

A remote rack of AI's kconnected back to a mother PLC is an RTU in my mind.

Of course, if my customer wants to call his remote PLC an RTU, he wins, as long as his check doesn't bounce.

Dan

 

[bernie_carlton]

I basically agree with danw's answer. No logic = RTU. (Well mayby minimal logic such as - if communications fail then either turn off outputs or leave in the last state.)

 

[danesh]

Very Thanks,

But nowadays RTUs have ladder logic capability and can control (of course not complicated control), and please help me if I have some PLC in my sites, can I use PLC for RTU in addition to PLC function?



Regards,

Danesh

​

 

[Tark]

I think time and advancements in technology have expanded (or blurred) the definition of an RTU. I am of the opinion that RTUs were first designed to act as remote alarm notification units. They took discrete inputs and were used to dial preprogrammed phone numbers to notify someone of an alarm. Then came the ability to dial into an RTU to obtain status. Then adding in the ability to datalog and to be able to retrieve this data through the telephone. And now they have the ability (be it limited) to perform logic.

RTUs were originally designed to operate over a standard telephone line. Once cellular became common place, you started seeing RTUs which functioned over cellular. You can throw in radio in there someplace as well. RTUs were considered Remote Telemetry Units, now I have seen them referred to as Remote Terminal Units.

I think Dan pretty much covers the difference between today’s RTUs and PLCs.

Can you use a PLC in place of an RTU? Depends on what functionally you are trying to accomplish.

 

[RussB]

Very simple,we don't need so much verbage.
PLC = Programmable Logic Controller
RTU = Remote Terminal Unit

 

[jedft]

Very Thanks,

But nowadays RTUs have ladder logic capability and can control (of course not complicated control), and please help me if I have some PLC in my sites, can I use PLC for RTU in addition to PLC function?



Regards,

Danesh

We use the PLC as the RTU all the time. I guess it depends on the application. I just keep the control logic seperate from the RTU stuff in the program to make it easy to understand/troubleshoot. We use wireless radios to communicate over Ethernet with SCADA and everything SCADA is looking for is a word in the program. If you are going to use the control PLC as the RTU, you are probably going to want to put the PLC and communications gear on a UPS so you know when there is power loss. Most "simple questions" aren't, really.

 

[danesh]

WOW simple!!​

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Really we use some PLCs in automation rule and I think to use PLCs in rule of RTU additionally.​

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Can we do this?​

 

[jedft]

WOW simple!!​

Really we use some PLCs in automation rule and I think to use PLCs in rule of RTU additionally.​

Can we do this?

Hmmm, Yes?

 

[basharath]

Dear can we develop the PLC functionality in RTU.so that a device can work with both plc and rtu features.OR can we use them in combination.

 

[tragically1969]

A PLC can be whatever you want it to be, there is no rules, its up to you.