PLC State Machines / Sequences

[Bobbias]

I'd forgotten about the integer-as-state-identifier method. That works, but not always as well as you'd like. It works wonders in systems where each state is mutually exlusive. And of course, you can represent a system with various non-exclusive states by expanding the number of exclusive ones to involve all possible combinations, but that can get very messy and complex if your dealing with a number of states that can go on and off independant of a certain process (such as say, a washing machine that has to control the water temp by a simple "if too cold, heat up, if too hot, turn heater off" scenario, along with various the usual sequence of events). Of course, you could go for a hybred approach and have the heater control and wash cycle control have their own independant process controlling variables as well.

This is a good example of how there are plenty of different ways to go about this sort of thing, davidd31415.

 

[PLCRookie]

O.K. Still too big.
How about a link.

http://www.dmcinfo.com/Knowledge/Wh...tion-Chart-to-Ladder-Diagram-Translation.aspx

 

[Bill Wheeler]

AB Phase State Manager

For Allen Bradley take a look at these 2 manuals. They offer quite a bit of help in understanding SFC and Phase State programming. They can be found at the Allen Bradley site without a tech-connect contract.

SFC 1756-PM006B-en-p
Phase State LOGIX-um001A-en-p

I have only run into SFC a couple of times on a Direct Logic PLC. I was amazed how quickly I could understand how the equipment was programmed to operate.

I have not had the pleasure of using the AB Phase State programming, but had planned to use this method on a project that has since been cancelled. I really think that there is a lot of power in this method because it forces one to think in terms equipment in terms of normal states; stopped, running, idle, or faulted and the transitional actions needed to move from one state to the next. I see too many pure ladder logic routines that are poorly organized where it is difficult to key in on an equipment state and what leads to a state transition. At the very least this method looks like it forces a logical organization.

Even if you decide not to use Phase State programming, I believe using the phase state model is an excellent tool to use when developing a new project. Most processes and tools fall very neatly into this model.

 

[Bobbias]

I'll have to look into those myself. Phase State does sound very interesting.

 

[Archie]

A few years ago I did a short video on how to design a state diagram/SFC and represent it in ladder logic. You can find it here:

http://www.youtube.com/watch?v=rCa_U6YATTA

 

[powereng]

If we want to design this problem using state diagrams OR Flip-Flops, How can we do that: