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Old February 14th, 2011, 10:11 AM   #1
Rob735
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RSLogix 500 4~20ma output signal

Hey guys, I feel a little embarrassed asking this as I am sure it is pretty simple and I am just overlooking something but,
What is the best/easiest output command to use to write a 4~20ma signal out to a VFD and a modulating valve?
I've used 4~20ma inputs before temp sensors and pressure sensors but never had to control with 4~20ma signal yet so I have tryed to look through old posts, but, not much has come up in the searches I have entered. Could be how I am searching but any help would be greatly appriciated.
Thanks for your time and understanding
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Old February 14th, 2011, 10:32 AM   #2
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With so little information about the only thing we can say is, just as the measurement of a 4-20ma input shows up as a number in the module's input table then sending a number to the 4-20 ma output module's output table will cause it to control the current output.

For more precise help you will have to specify the exact system and ouput module.
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Last edited by bernie_carlton; February 14th, 2011 at 10:38 AM.
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Old February 14th, 2011, 10:35 AM   #3
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Sorry was typing this post while trying to take care of some other stuff as well.

I am using a ML1400 with a 1762sc-OF8 expansion card.
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Old February 14th, 2011, 10:47 AM   #4
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The user manual, available at Spectrum Controls, seems to have an example program for module setup.
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Old February 14th, 2011, 10:32 PM   #5
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For RSLogix500 I like to use the SCP (Scale with Parameters) command for analog inputs and outputs. I believe the Spectrum card lets you select the data format (percentage, raw, scaled for PID, etc) but my preference is to set it to raw/proportional and perform my own scaling in the SCP command.
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Old February 15th, 2011, 08:50 AM   #6
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Hey Guys I really feel like I am lost right now, could somebody please point me in the right direction or tell me if I am as lost as I feel.

I am having no luck with getting my Analog output card to work I have read the user's manual and have tryed to follow everything I read but to be honest I am not sure that i really understood all of what I read.

I want a 4~20ma signal out of my ML1400 using my 1762sc-OF8.

I have zipped my project and attached for review.

I greatly appriciate the help thus far but still feel lost so anymore input you guys have, I would be very greatful for.

I have my 1762sc-IF8U working great now reading my sensors bang on! So Thank you for the help on those.
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Old February 15th, 2011, 10:49 AM   #7
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The file you posted cannot be a working program, for one thing none of the subroutines are being called. And no configuration for any of the analog cards. Can you post the working program?
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Old February 15th, 2011, 11:08 AM   #8
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Sorry Guys we have recently done server upgrades stuff is saved in to many places right now and not sinking the way it should be.

anyway here is the actual file I have been working with.
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Old February 15th, 2011, 11:17 AM   #9
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Quote:
Originally Posted by Rob735 View Post
Sorry Guys we have recently done server upgrades stuff is saved in to many places right now and not sinking the way it should be.

anyway here is the actual file I have been working with.

Try again Rob, no file.
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Old February 15th, 2011, 12:06 PM   #10
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Sorry and Thanks
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Old February 15th, 2011, 12:29 PM   #11
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It appears that you have copied the example in the manual. At this point if you ran the program you should have 4ma from channel 0 ( first channel of the output card). If you want all channels to do the same you need to change the length value in the "FLL" instruction to 8. You also need to finish the edit on your "JSR" instruction in ladder 2.

Now what is it that you want to control the analog output with ? ( the PID instruction?)
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Old February 15th, 2011, 12:33 PM   #12
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Yes i did copie the example, will this work ok?

and Yes??? I am not really sure how i want to control the output i think with the PID instruction. like I said earlier in this thread I don't have any experience with analog outputs so not sure what is the best and perferably easiest way to do it.
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Old February 15th, 2011, 12:41 PM   #13
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Rob,

This is slightly off topic, but something I noticed right off the bat is that you are nesting parallel branches. This is generally not a good programming practice for parallel branches. You can nest branches only four levels. I suggest you extend branches instead of nesting branches. While nesting is limited to four levels, you can extend a branch to as many levels as you want.

See the following thread for more information.
http://www.plctalk.net/qanda/showthr...ht=nest+branch

To extend a branch position your mouse pointer on the left corner of the branch and right click. Choose extend up or extend down from the context menu.
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Last edited by TConnolly; February 15th, 2011 at 12:47 PM.
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Old February 15th, 2011, 12:48 PM   #14
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Alaric, Thank you, Changed and Noted!
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Old February 15th, 2011, 12:56 PM   #15
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See sample below for using the PID's output to control channel 0's output.

Let us know how it works out.

Note I have not used your Spectrum card but the manual seems to explain it well after reading it several times of course.

Also when I verified the program it recommended using a larger power supply.
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