xtal_01 (Customer) asked a question.
Long story but someone asked if i could replaced a "dead" PLC in a small roof bending machine. They don't care how I do it ... simpler the better. They even asked it I could replace the PLC with relays (that way their in house electrician can repair it) ... maybe but it would take about 10 relays and still would not do everything the PLC is doing right now.
OK ... the unit is a DL105 ... now obsolete.
The company does not even have the program (DirectSOFT) to read the ladder logic.
A few weeks ago, I asked if on this forum is someone could open the file and print it out for me (it was too large for the free version).
Got that!
There was not documentation but since then I was able to get a wiring diagram!
So, now I am thinking I want to move this into a BRX PLC ... nice part about this is the software if free!
Now, I am not an "expert" in PLC programing .. self taught ... and I have never used a Direct Logic PLC ( have used several BRX units) ... but this should be simple and I am perplexed.
Maybe explaining just one of my issues will explain them all.
In the program (attached) ... rung 7 ... the third line .... X2 and X3 are NO contacts ... in series (they are in parallel in the first two lines ... that makes sense to me).
X2 and X3 are contacts on an HOA switch (I have included the wiring diagram). They are on opposite sides of the switch. They could never be on at the same time so why even have this line?
Now, that said, I do see down in the data, under X2, it is listed in rung 7 three times ... once with STR ... once with STRN and once with AND.
I have no idea what this means.
I looked all through the manual ... tried google searches ... I is probably something very simple that I will hate myself for not recognizing.
I just "assumed" (hate that word) that an Normally Open contact is always a Normally Open contact.
Did they do something I have never seen making it work differently?
I don't mind directly (well just changing the addresses) using the same program ... it has worked for more that 20 years ... but I want to understand exactly what it does.
Thanks so very much!
Adobe PDF Schem_Page26Adobe PDF ZIM
People do sometimes make mistakes, code that does something wrong will tend to get fixed, but code that does nothing at all doesn't really call attention to itself and may not get cleaned up
Also the hardware design might have been changed at some point. You say:
"X2 and X3 are contacts on an HOA switch (I have included the wiring diagram). They are on opposite sides of the switch. They could never be on at the same time so why even have this line?"
But on rung 9 there is another X2 AND X3 and also NO X2 AND NC X3 and vice versa, either the original programmer was a "belt and suspenders" guy or there was a possibility of X2 and X3 being on at the same time in some iteration of the pendant station.
First I would put Nicknames to all those addresses, and then the logic might make better sense. As Tinker said, sometimes you have additional logic 'just in case'. Unless you know for certain it's a bug, you're probably best to straight duplicate it. It might be in there to fix a bug they had on the very rare occasion.
Btw, I find the Click has a bit lower learning curve for straight ladder than Domore.
I agree with @ssweber (Customer) , with nicknames to all your I/O, replicating what is was done in the old PLC will make sense AND later you may find you can make the code clearer/better. Finally, ignore the statement list of the logic with terms you don't understand; "STR," "STRN," etc., just copy the ladder.
You write: "... I do see down in the data, under X2, it is listed in rung 7 three times ... once with STR ... once with STRN and once with AND. I have no idea what this means."
The "STR", "STRN", "AND", "ORN", etc. are a throw back to when the hand-held programmer (Part Number D2-HPP) was used to program the PLC. Interestingly I see they are still available from Automation Direct! This listing of logic code words and elements is not helpful at understanding the program logic. It appears your program only has 17 rungs, so that is a plus. You don't have hundreds of rungs to analyze. Having a clear, detailed sequence-of-operation document (including IO names) would help analyze the existing PLC program, as well as develop a new program to be used on another PLC, Click for example, as was mentioned.
You guys are awesome!
I have done a few PLC programs but always from scratch.
I was just shaking my head trying to figure out what was going on with this program ... if there was something I was missing.
I remember someone telling me loading K2060 into V7633 simply puts the unit into run mode. Otherwise, I think it is a straight forward program.
Thanks again so much for the help !!!!!
Mike
See the image for the value in V7633 - from the manual available at Automation Direct