PLC-5/30 PID Control Block/Analog Input Card Numeric Values

I am new to this analog stuff and am having problems understanding the value or scaling or ?? when passing data between an analog input card and the PID control block. We have a pressure transmitter scaled from 50-150 deg F (4-20ma) to a 1771-IFE/C analog input card (channel 3) on an AB PLC-5/30 . The raw data is 0-4095 in the input card.

When the data shows up at the PID control block it looks like its in different units (decimal?). I would like to be able to enter my set point in degrees F. and have the process variable show up as 50 - 150 degrees.
PID Configure Screen

PID Status Screen


I have read a ton of stuff on this site and it has gotten us to the point where the steam valve that this PID is controlling actually works. I just don't think I should have to figure out that 10,340 set point = 120 degrees. Any help is appeciated.

Greetings myrd03 ...



and welcome to the forum ...



first of all, the Data Format should USUALLY be set for Two’s Complement Binary ... BCD is USUALLY only appropriate for older PLC-2 systems ...



NOTE: are all of the rest of your field inputs working OK with the present BCD setting? ... if so, then do NOT change the setting to Two’s Complement Binary - or you’ll mess up all of your IFE inputs ... my best guess from what you’ve posted so far: someone in the past left the IFE module set for BCD and then “compensated” for that numbering system by using “unusual” scaling for the input signals ... suggestion: post your .RSP program file ...



also, when using PID, we USUALLY set the Raw Min for 0 and the Raw Max for 4095 ... specifically, we keep the module running “wide open” and do the scaling in the ladder logic ... either the PID does it for us - or we use ladder logic math functions ...








next ... the numbers that I’ve circled below are USUALLY only appropriate for PID based on RSLogix500 ... but ... the BCD setting mentioned above (as opposed to the more common Two’s Complement Binary setting) is probably causing these unusual settings (0 to 16533) to work ... this is an unusual configuration ... suggestion: post your .RSP program file ...







in a NORMAL PLC-5 system, these settings would be used instead:



Engineering Unit Maximum: 150

Engineering Unit Maximum: 50

Input Range Maximum: 4095

Input Range Minimum: 0



if that doesn’t work, then we’ll need to know more about the range and setup for your field transmitter ... it would also be very helpful if you could post your entire .RSP program file ...



once again, that BCD setting is not normally used for this type of system ...

Hi Ron - Thanks for your response

NOTE: are all of the rest of your field inputs working OK with the present BCD setting?

Click to expand...

This is the first input (its channel 3, not channel 1 - I can see I screwed up channel 1) we have wired and working - the others are future upgrades.

the Data Format should USUALLY be set for Two’s Complement Binary

Click to expand...

I will switch it and see what happens - the process can be shut down and I can play with it without much trouble.

I have attempted to attach the .rsp file

I've only had time to QUICKLY GLANCE at your file ... nothing serious jumps out at me except for the setup stuff that I've already mentioned ... if you can easily make those changes, I recommend that you start there ...

and you probably already know about this next item, but I feel compelled to at least mention it ... there are jumpers inside the IFE cards that must be set correctly ... if you didn't know about those, you need to take care of that possible issue before doing anything else ...

please keep us posted on your progress ...

this won’t change anything - but I just noticed an error that I made in my post #2 ... I’d like to clear that up - hopefully before someone else notices it too ...



I mentioned that the values 16533 were USUALLY associated with PID in the RSLogix500 systems ... oops! ... the actual values which are commonly used there are 16383 instead ...



the value 16533 is the decimal equivalent for 4095 hex ... and so yes I was probably correct in assuming (gosh, I hate that word) that the values the original poster had entered were “compensation” for the unusual BCD setting of the IFE module ...



sorry if I confused anyone ... that’s what I get for trying to do two (or more) things at one time ...


party on ...

Thanks Ron. I made the changes you suggested in post 2 and everything looks like I expected it to look and it works great. Thanks for your help!

Dan

glad we were able to help ...

Hi,

When we set the PID configure screen and status screen, is it should be saved or no need?Because after i set, i closed the window, then when i open it back, all parameter that i set, had lost.