Scaling AB 5/02

Hi there. New to the site and hope someone can help. I have a scaling issue. I am using a flow meter for input and using a 4-20ma output for a positioner valve with I/P. Can't get the thing setup up right to scale. Please help

What are you doing now? Perhaps if you'd share what you have, we might be able to correct it...

I have AB 5/02 proc. with Panelview 350. Just started with company and they threw me in to a mess.
PID
control block N11:0
process variable I:4.1
control variable N7:15
control block length 23
SCL
source N7:15
rate 16762
offset 8929
dest o:8.1
MOV
source3278
dest O:8.1
hope that helps

What analog output card ( module) are you using.
Post your .RSS file if you can. ( zip it first then post)

I am using N041 module.

Please post your code so we can see what's going on. Help us help you!

do you want to "just get the job done" and get on with your life - or do you want to dig into the subject of scaling? ...

if you're looking for information to help you along the "learning curve" the information ("Scaling Part 1" and "Scaling Part 2") on my website should answer all of your questions ... look in the "Sample Lessons" area ...

of course regardless of what path you're trying to follow, you'll definitely need the "specifications" type material that my distinguished colleagues have already requested ... basic idea: different modules and different applications require different configurations ... (one size doesn't fit all) ...

going further:

process variable I:4.1

Click to expand...

that particular part of your PID setup looks highly suspicious ... most input modules don't have the capability of putting out a range of 0 to 16383 - and THAT is the ONLY input range that will allow your PID to give optimum control ...

reality check: in most SLC systems, you have to scale the signal coming from the input module before it goes to the PID ... you also usually need to scale the output also ... we'll be able to tell more about your system once you post your code ...

hope this helps ...

I am having to install zip on this computer will get the file as soon as its done. I am using RSLogix 500. The I:4.1 is coming straight from a flow meter and they are trying to scale the output to open and close the water valve.

pault said:

I am having to install zip on this computer will get the file as soon as its done. I am using RSLogix 500. The I:4.1 is coming straight from a flow meter and they are trying to scale the output to open and close the water valve.

Click to expand...

As an option to a real zip file. You can just change the extension of your .RSS file to "zip". But if you do that let the forum know.

thanks for the info. I have done changed the ext to zip. please let me know if it works.

First thing first -- you desperately need to add some documentation to that program!!!

Then, I think the major problem is that you need to scale your input. You're telling your PID in rung 76 that its setpoint is 120, which appears to be a scaled value. The PV is 4440, which is a raw value that is way out of the bounds that you have configured in your PID.

The reason the output is 6242 is because the SCL destination is being overridden in run 78 because the value is out of range.


All of your PIDs appear to have this same issue.

As others have pointed out you need to first rescale the raw flow meter input to something the PID instruction wants ( 0-16383 value for PV input)
See example PDF below for scaling values and PID setpoint setup.
This example is just for the one input you have questions about, I agree with OZEE the rest of the PID instructions all seem to have major issues along these same lines.
If you are close to Charleston,SC give Ron Beaufort a call. A short trip down there would be very valuable.

Thanks to all of you for the help. I will be working on this matter more tomorrow. I believe all the programs they have here are the same. It is taking me a little while to figure out what is what. I will let you know what I come up with.