Plc. V. Rtu

Hi folks ,In spite of the ease of use Remote Telemetry Units which are used in process automation appear to be playing second fiddle to programmable logic controllers plcs. The former has more channels and does not need elaborate ladder logic which can get very complicated. My question is, why Plc is more widespread?

Hi Don,
I would say that PLCs are more widespread b/c of the following reasons:

1. A lot of plant engineers/technicians are NOT as familiar with the concept of RTU.

2. PLCs are able to do everything RTU can do plus much more. Since most controls guys are already familiar with ladder logic it is not so "complicated"

3. In particular PLCs are have more communication capabilities as compared to RTUs and are also a lot more flexible in what you can do.

I feel when you are not trying to do "local control" and just get data from products like sensors, RTU is easier. Plus its "wireless communications" are a nice feature as well

Hope this helps

Price.
Availability of engineers that have 'cut their teeth' on less important machines.

I have worked with both RTUs and PLCs for the last 10 years. I've seen RTUs used when a PLC would have been more appropriate and vice versa. They are NOT the same beast, although the new SCADAPack 575 looks to be getting there in terms of blurring the lines.

I've only come across a handful of RTUs that allow online edits. Conversely very few PLCs could receive a program remotely over an unreliable 300 baud radio link.

It's horses for courses and anyone who doesn't recognize that will end up in hot water sooner or later. I've just completed a project of removing an RTU that was running a wastewater plant after it failed to operate a filter system correctly resulting in significant damage to the filters. Yes it was a programming issue but the logic in this particular RTU was not suited to continuous process control. Why make your life difficult by taking a knife to a gun fight?