PID problem

Hi, everybody.

It is a question about RSLogix5000 PID.

Can I set a PID instruction to Manual mode and write a value directly to PID.Out?

Thanks:beer:

If using PID, write to PIDTag.SO (set output)

If using PIDE, write to PIDETag.CVInit and set PIDETag.CVInitReq

Greetings yfcarer ...



my distinguished colleague, Alaric, has already answered your question ... but here’s a little bit more detail that might be helpful ...

Can I set a PID instruction to Manual mode and write a value directly to PID.Out?

Click to expand...

sorry ... it’s not quite that easy ... first of all there are TWO different types of “manual” mode operation ... we usually refer to the first one as “MANUAL MODE” ... the other is usually referred to as the “SOFTWARE MANUAL MODE” ... (incidentally Alaric based his answer on the “software manual mode” which is the more common approach) ...



first let’s cover the “MANUAL MODE” ...



suppose that your PID tag is named “My_PID” ... to use the MANUAL MODE, enter a tagname for the “Tieback” on the PID instruction when you program the rung ... for example: set up “TB” as a REAL tag ... on the PID “Scaling” tab, set the scaling for the Tieback ... for example: Max = 100 ... Min = 0 ... now put a 1 into the BOOL at My_PID.MO ... this step will put the PID into the “MANUAL MODE” ... now enter a value into TB ... for example: 16.0 ... the value from TB (16.0) will be sent to the PID’s output ...



now let’s cover the “SOFTWARE MANUAL MODE” ...



again suppose that your PID tag is named “My_PID” ... to use the SOFTWARE MANUAL MODE, we use the built-in tagname “My_PID.SO” (instead of the “Tieback” tag) ... put a 1 into the BOOL at My_PID.SWM ... this step will put the PID into the “SOFTWARE MANUAL MODE” ... now enter a value into My_PID.SO ... for example: 31.0 ... the value from My_PID.SO (31.0) will be sent to the PID’s output ...



note that if BOTH of the BOOLs (My_PID.MO and My_PID.SWM) are set to 1 conditions, then the “Tieback” value will prevail and will be sent to the PID’s output ... normally a well-written program will prevent this “both-manual-modes-at-the-same-time” situation from happening ...



this is just a quick rundown on the basic ideas – but hopefully it will be enough to get you started ... the best way to learn more about this particular subject is to experiment (using a safe system of course) ...



you can manually set most of the values mentioned above right from the PID configuration screen using RSLogix5000 software ... (major exception: you won’t be able to enter the “Tieback” value from the PID screen) ...








I hope this helps ... good luck with your project ...

Ron,

Could you elaborate on the difference between the two modes, manual and software manual?

Greetings rohan,

yes, I'll be glad to but it's probably going to be at least a week or two before I'll have time to do it ... in the meantime, some of our other members will probably step in and take care of the job for you ... do you have a specific need? - or just looking for general knowledge? ...

yfcarer is lucky to have the reply .
actually Ron has described detail how to using of the two muanual mode

i get much from here

BR

Ron Beaufort said:

Greetings yfcarer ...



my distinguished colleague, Alaric, has already answered your question ... but here’s a little bit more detail that might be helpful ...

....................................................

I hope this helps ... good luck with your project ...

Click to expand...

Hi, greetings Ron Beaufort.
Thanks for your perfect answer and I have done it as you and Alaric mentioned in your reply.

By now, the Sofeware Manual Mode fits my project well but I got another question: What is a loop update time and how should I set it?

Thanks in advance!
BR/Yang

Let me start by explaining how I use the PID:

My PID is placed in a periodic task set to be processed every 1000 msek. Then I set my Loop update time to 1 sek.

Ron Beaufort said:

Greetings rohan,

yes, I'll be glad to but it's probably going to be at least a week or two before I'll have time to do it ... in the meantime, some of our other members will probably step in and take care of the job for you ... do you have a specific need? - or just looking for general knowledge? ...

Click to expand...

I am just looking for general knowledge, i understand the difference in functionality of the two modes. In PID manual the Tie back value is sent as PID out when pid.mo bit is set, whereas in software manual mode when the pid.swm bit is set, value of pid.so is sent to the pid out.

I am not very clear how and why to choose between the two. I see that the Tie Back can be scaled. Is that the point of difference between the two? I dont have a 'safe system' to test so i am bugging you with so many questions...