Positive differential contacts only work after coil

[apmcs1]

Positive differential contacts (oneshots) are supposed to work for one complete scan.
When a coil energizes any oneshot contacts with that coil # should energize for one scan, that scan starts at the rung that coil is in and ends back at that coil the next scan.
BUT that is not the way the Koyo works, PD contacts only work the rest of the scan! so if you have a PD contact in a rung before the coil it will not energize!
If you use a PD coil it will work but I don't want to have to add a PD coil in parallel to every coil I want to use a PD contact from it.

[marksji]

This behaviour has been in Koyo/Directsoft on the 205 series PLC's for a long time. Move your one-shots to the stop of your stage/program or set a bit then at the top of your program have that bit fire a one-shot, course then you need logic to reset the bit.

[clasentech]

http://forum1.automationdirect.com/b...ML/001077.html

[marksji]

Well I can't find my 250 CPU right now, but I did try this on the following and it works exactly as I would expect (PD stays true for one full scan).

D250-1 v4.10
D250-1 v4.00
D250-1 v3.90
D2-240 v2.2
D2-230 v1.4

I did a simple test program on each of the 5 CPU's, in each case both Y0 and Y1 came on.

C0
| |-------------------------------SET(Y1)

X1                               
| |-------------------------------PD(C0)

C0
| |-------------------------------SET(Y0)

----------------------------------END

[This message has been edited by marksji (edited 01-27-2005).]

[clasentech]

And I did the same test on a DL06 yesterday and it worked as it should. I also did it with PD contacts instead of PD outputs (to regular contacts) and it worked as well.

[marksji]

Wish I could find my 250 CPU, I could swear it didn't work that way back then...

[RHanrahan]

Have you tried just using the Pos/Neg differential contact? It looks like this:

|  _|
|_| |
|   |

|_  |
| |_|
|   |

The only rub is that these are not available for the 105 and I think the 05 plcs.

These contacts are on for one scan when rising/falling.

Bob

[This message has been edited by RHanrahan (edited 01-29-2005).]

[apmcs1]

marksji
Your first answer was correct it doesnt work and yes I could add other coils to make it work but why do I have to!! All other PLC's I've worked with use oneshots like they should be and AD should fix theirs (though that might screw with previous programs but so they don't update the cpu's on those).

The rest of the answers yes if I use a PD coil it works but if I use a PD contact (example: strPD or orpd)off of a regular Out coil it doesnt fire any of the contacts above the coil.

0 strpd C1
1 OR C2
2 OUT C2
3 STR C0
4 OUT C1
5 STRPD C1
6 OR C3
7 OUT C3

...C1
---|z|----OUT (C2)
.|.....|
.|.C2..|
---| |--

...C0
--| |----OUT (C1)

....C1
---|z|----OUT (C3)
.|.....|
.|.C3..|
---| |--

|z| stands for Positive Differential contact

control C0 from directsoft or use X1 or something else you can control but it's important that you don't control C1 directly or it messes with when it is set in the scan


Everyone please use this program to test, I don't dispute that if instead of using the OUT (C1), I use PD (C1) that it works, that just proves my point that using PD contacts from an OUT coil should work the same way!!

clasentech, I read the other message on this and I have some exceptions to it. real world I/O is updated physically at the end of the scan but internally is updated any time something is written to the memory table for the I/O. So if I set Y1 with an output coil and then use a normally open Y1 contact in a rung below it, it's on! even though the real world output will not turn on until the end (or start) of the scan

Thanks to all who looked at this, sorry I didnt include the program before for clarity.

Dave Welch


[This message has been edited by apmcs1 (edited 01-29-2005).]

[This message has been edited by apmcs1 (edited 01-29-2005).]

[apmcs1]

So why does the PD coil work for one full scan (one scan being starting at the rung its in, to the rung its in on the next scan)
but a PD contact off of a regular coil only work for the rest of the scan.

I'm using a DL 450 processor

[This message has been edited by apmcs1 (edited 01-29-2005).]

[RHanrahan]

apmcs1,

I just checked what you are saying and am seeing the same results. It is not wrapping around for a full scan like it says in the manual. According the the book, this is supposed to be on for one full scan. The way I had it explained to me a while ago was that they were supposed to be on for the rest of the scan and one full scan afterwards. I never checked...

All my testing was done with a 250-1 with CPU Version 3.9 installed.

Maybe someone from AD can chime in and give us some direction. I agree with you that something is not right here. I am really surprised that I had not noticed it before since I use the STRPD(N)and ORPD(N) all the time.

Bob

[marksji]

apmcs1, sorry about the confusion. I went back and used STRPD and your code and found the following:

D250-1 v4.10 works as it should
D250-1 v4.00 works as is should
D250-1 v3.90 doesn't work right
D250-1 v3.50 doesn't work right

Looks like ADC fixed it, but didn't bother to let any of us know. Try upgrading your firmware to the latest and see if it makes things work.

[apmcs1]

RHanrahan and marksji
Thanks for your investigations again, I am using the latest firmware version for the 450 which is version 2.00, I havent tried any earlier versions. AD do you have any answers??
update:
I've talked to tech support and they acknowledge that its a problem on at least the 450 latest firmware but not some of the other processors like you found marksji.
They have passed to their programmers to fix.

Thanks everyone for all the help
Dave Welch


[This message has been edited by apmcs1 (edited 01-31-2005).]

[Andy]

Actually there was a mention of it in the firmware history of the 250-1. I had to check the history myself.
http://support.automationdirect.com/...ail.php?pid=41

Andy

[RHanrahan]

Originally posted by marksji:
apmcs1, sorry about the confusion. I went back and used STRPD and your code and found the following:

D250-1 v4.10 works as it should
D250-1 v4.00 works as is should
D250-1 v3.90 doesn't work right
D250-1 v3.50 doesn't work right

Looks like ADC fixed it, but didn't bother to let any of us know. Try upgrading your firmware to the latest and see if it makes things work.

Thanks for the tip on the firmware change. I have an older PLC that I have sitting in my office for checking out code before putting in the field. It looks like I am going to have to DL the latest firmware. (again)

This is not the first time that I have been bitten by a firmware change.



[This message has been edited by RHanrahan (edited 01-31-2005).]

[marksji]

Originally posted by Andy:
Actually there was a mention of it in the firmware history of the 250-1. I had to check the history myself.
http://support.automationdirect.com/...ail.php?pid=41

Andy

How right you are, I guess I skipped that line while reading, my apologies ADC!