Ladder Logic vs. Function Block

S

Thread Starter

Sugar Lips

I'm looking to new technology and a move to more integration of control and logic. Does it make sense and will it save me money (increased productivity, maintenance, end user simplicity) to move from my multi instrument solution of PLC for logic, loop controllers and indicators to a small unit control system? One caveat I see is that these control systems support function blocks, thus transition is needed of my ladder logic to function block. Don't know if this conversion is difficult, and is this truly the way to go for the future (increased productivity)?

Any guidance from gurus that have implemented or faced into this?
 
It really depends on your comfort factor for configuration. There are programmers who love PLC ladder logic, and others who love the function blocks.

I don't think the type of configuration will save you time or money - still depends on the programmer. Increased productivity? No. End User Simplicity? If your refering to the Operator, the programming is 'behind the scenes': If your refering to the plant personel performing maintenance - again, it's their comfort factor of ladder vs function. If they have not seen function blocks - it's a steep learning curve.

The conversion of logic to function blocks will cost you more than just keeping logic.

Also, if you have a fast process, PLCs are the way to go. The typical Function Block DCS's are very slow compared to PLC.
 
Your objective is noble, but not very practical at this juncture. Rockwell and Siemens have this same objective, but support it in very different ways. Rockwell has deep function block support. Siemens depends less on function blocks but more on STEP7 programming. I personally like a hybrid approach that depends on Sequential Function Charts like Grafcet from Schneider.

The process control companies do not support this concept well, but the "best" hybrid solutions for batch still come from the DCS
suppliers, although there are lots of disagreements on this.

I think its still too early to make the kind of break with tradition you are seeking.

Dick Caro
===========================================
Richard H. Caro, CEO
CMC Associates
2 Beth Circle, Acton, MA 01720
Tel: +1.978.635.9449 Mobile: +.978.764.4728
Fax: +1.978.246.1270
E-mail: [email protected] <mailto:[email protected]>
Web: http://www.CMC.us
Buy my books: Automation Network Selection
Wireless Networks for Industrial Automation
http://www.isa.org/books
===========================================
 
I agree it depends on what type of control you are doing.

If you have loop type applications I dont think you will be disappointed in function block programming. The transition is very easy and once you use it most wouldnt go back the other way.

If your system is all discrete then function block programming doesnt buy you a whole lot.

[email protected]

John
 
Top