Dl06 Scan Order - Help

I'm writing a program that determines the first outage in a series of limits.

E-stop - Hi Limit - LGPS - HGPS - Exhaust Input

Are all physically wired in series. So if i open the E-stop contact, all others down the row will open as well.



This logic (supposedly) should handle this, but for some reason, HGPS keeps energizing the HGPS FAIL contact, and it shouldn't be.
I've been working on this all day yesterday and it has me perplexed.

The DL06 scans from the first rung to the last rung, correct? Anyone have an idea why the HGPs would be energizing at the same time or before the E-stop when only the e-stop has been opened?

you're not going to like this answer - but I think that it's the one you're looking for ...

http://www.plctalk.net/qanda/showthread.php?p=246883&postcount=25

PS EDIT ...

post #49 in that same thread offers a wiring approach that might work better for your purposes - IF (that's a big IF) you can come up with ISOLATED inputs ...

That explains a lot. Thank you.
I was thinking about putting an on-delay timer for each one of those contacts - so they would have to be powered for a certain amount of time (hopefully allowing the plc to run through a few more scans) before energizing the alarm coil.
Would that work or am i missing something?

Usually no matter which switch i open upstream of the HGPS, the HGPS almost ALWAYS opens first.
In fact, when it didn't ONCE, i thought i had solved the problem and proceeded to celebrate.

Only to find out i tried it again and it did not work.

Without knowing how your system is wired I can't say for sure, but consider the possibility that your logic is working as intended and that when you hit the big red E-Stop button the HGPS signal at the X4 terminal is actually dropping out before the E-Stop signal at the X0 terminal.

How could that happen? If a contact on the E-Stop button simultaneously kills power to the HGPS device and an E-Stop relay and a contact from the E-Stop relay is wired in the circuit and a contact from the high gas pressure switch is wired in the circuit, it's possible the HGPS device reacts faster than the E-Stop relay.

Do you work where I think you work? That is, your company President's name is Tom.

I agree that your HPGS signal may be dropping before your Estop is. A timer on that input to slow it down a bit might help.

Steve;
Yes, i do work there - I'm the new guy, and all the others can't figure this one out either.

And right now the system is on a test-bench with 5 toggle switches going into terminal blocks.
The E-stop is wired to line, and into x0, then the high limit is wired from x0 to x1.. ect ect all the way down the line.

So there are no relays. Just toggle switches and internal coils.

Check your wiring connections. X0 through X3 reference the C0 terminal. X4 through X7 reference the C1 terminal. Presumably both C0 and C1 are connected to a common reference.

Wiring is good so far as i can tell. Ran a quick continuity test and it all checks out. Plus all the wires leading from the plc to the terminals are numbered, and all the wires leading from the switches to the terminals are numbered pairs. - I checked them anyway, but they're good.

I'm playing with timers right now - i'm determined to get this to work.