I am new to automation. I am trying to understand the FBD logic in concept. The function blocks are not placed in order and are located as clusters in a single page. I understood the execution order in that page is listed in parentheses on top of the function block. It will be very helpful and time saving if some one can tell me a short cut key or similar which allows me jump to the next executable block with out manually looking out for it in a big cluster.

 

If timing is such an issue, why not separate the blocks onto separate pages and remove all doubt?

Cheers

Gerald Beaudoin

 

You are not understanding a fundamental principle of machine control software. It does not matter what order the function blocks, or ladders rungs are executed in. If you are used to programming for batch or event driven applications, this might come as a shock.

A PLC is a state machine. As such, it executes the same logic over and over again, in a circle with no beginning or end.

There are important exceptions to this, but you won't be ready to understand them until you grok the basic algorithm.

 

Hello,

> It does not matter what order the function blocks, or ladders rungs are executed in.

Now that is far from the truth.

Just talking ladders, with a set and reset instruction. Or if you like a latch and unlatch, same thing different names.

First rung set, second rung reset.

That makes it a reset over set.

Reverse the order and you have set over reset.

That very simple principle means the order is very important.

If you think it is not important, you will one day.

I could go on and on about the order of math instructions or copy instructions or compare instructions...and the wrong execution order will be trouble.

My2c.

Good luck,

Mark
http://www.peakhmi.com/