RSLogix 500 4~20ma output signal

Rob735

Member
Join Date
Jan 2011
Location
Mississauga
Posts
38
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
 
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.
 
Last edited:
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.
 
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.
 
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.
 
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?
 
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.
 
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?)
 
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.
 
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/showthread.php?t=43027&highlight=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.
 
Last edited:
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.

sampleoutput.jpg
 

Similar Topics

Hello, Haven't been on in a while. I need to generate a bit level pdf of the I/O for RSLogix 500. I can generate a report but it just shows the...
Replies
1
Views
110
I would like to copy register N61:131 thru N61:147 into ST252:0 I keep failing What happens is I copy into ST252:0,1, 2 etc. What am i missing...
Replies
18
Views
482
I'm trying to fix a mess of code on an older machine that's running a Micrologix 1400 and an RS232 ASCII barcode scanner. The previous guy had...
Replies
3
Views
304
I'm not super familiar with the Micrologix line of processors, but I am pretty familiar with RSLogix 500. I'm trying to simply copy a string to...
Replies
4
Views
258
I have been using RSLogix 500 version 9 for a long time now. I am about to need to move to something else Rockwell related to cover the...
Replies
8
Views
907
Back
Top Bottom