GE LM90 gurus, why would a programmer do this?

TConnolly

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GE 90-30, Logic Master 90 DOS software.

Why would a programmer put all these instances of %S0007, always on, in a rung? There are lots of cases of this in this program.

I've also encountered many instances where the exact same rung is pasted six to eight times in a row in the program where each rung has -] [-%S0008 (always off) programmed as the first instruction, so the rungs do absolutely nothing but they are duplicated.

Is there some quirk about LM90 that a programmer would to this, say maybe to make online editing easier or something?

Or was this maybe a programmer who billed by rungs of code padding his bill?

This is a 290 rung program for a task that I think is worth maybe 50-60 rungs tops.

tc101713.jpg
 
My guess -

They have multiple versions of essentially the same program. The %S0007's are placeholders for what would be additional conditions in other versions. (Though, if that were the case, I would keep the conditional contacts and just parallel them with the %S0007 contact.

I'm guessing a similar thing about the redundant but disabled rungs.
 
I would agree with Bernie. LM90 and formatting rungs to look "nice" is a hassle, heck it still might be for GE!!

Would you consider this an "OEM" machine?
 
I agree. This is merely an individual programmer's quirk. It is not peculiar to GE PLCs and I doubt that anyone would be foolish enough to attempt to charge a customer for these redundant references in their ladder logic. They are merely placeholders for a generic scheme that is modified for specific applications. Personally, I would have deleted them. I don't like useless junk in my programs.
 
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Not an OEM machine. Its from a machine custom built circa 1994.

The HMI kicked the bucket and is 16 years out of manufacture. After spending a futile day trying to find a replacement, not to mention the unlikelyhood of finding software to reprogram it, I'm now picking through the program to extract the information I need to program a RedLion HMI to take over the task. I just hope this print out is accurate. I do have LM90, I could set up a dosbox and run it if I absolutely had to.

I'm seriously tempted to rip out the 90-30 PLC and put in a L32E CompactLogix, its only 25in/18out, and with a more capable HMI I can reduce that to 19in/14 out. A CompactLogix because except for the 1769 power supply I've already got all the hardware.
 
FYI, LM90 does run on XP SP3, if you want a more modern system to run the program. Personally I would import the project into Proficy Machine Edition to get some better editing tools.

As for replacing the 90-30, I'd let it run until failure unless this is a mission critical machine. A VersaMax Micro could be used for replacement, or the 90-30 baseplate/power supply/CPU (if separate) might be able to be traded in an RX3i.
 
GE 90-30, Logic Master 90 DOS software.

Why would a programmer put all these instances of %S0007, always on, in a rung? There are lots of cases of this in this program.

I've also encountered many instances where the exact same rung is pasted six to eight times in a row in the program where each rung has -] [-%S0008 (always off) programmed as the first instruction, so the rungs do absolutely nothing but they are duplicated.

Is there some quirk about LM90 that a programmer would to this, say maybe to make online editing easier or something?

Or was this maybe a programmer who billed by rungs of code padding his bill?

This is a 290 rung program for a task that I think is worth maybe 50-60 rungs tops.
Most likely an AB programmer doing his first GE system and can't figure out why it don't work just like the SLC 5/00 did?

I see that sort of thing a lot. :D
 
Considering each rung starts with a "SEQ STEP ##" it looks like maybe the original "hard wired relay controlled system" was using a "step sequencer" relay and when the system was converted to plc logic these were unused contacts for each "step" to "sequence" the switch to the next "step".

Also....he could have done some extensive editing and used the 7S to remove the old logic. For example...maybe 2 devices were being controlled and one is removed. He used 7S to remove the other device from the logic and left the 7S so he would know where to go to re-add device...
 
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