PID Quick Start - SoftPLC Internal PID - WEG CFW500 Variable Frequency Drive (vfd)

In this video, we’ll show you how to get  the Internal PID up and running quickly in   the CFW500 drive. Remember – that’s the one  that runs in the SoftPLC, not the drive.   You might be wondering, why would I use this  instead of the drive’s built-in PID? After all,   the drive’s PID is a good solid  basic PID implementation – right?   Well, there are a number of reasons why  you might want to use the SoftPLC version.   I find the SoftPLC version is easier to work with  because everything is in true engineering units.   It can use a second analog input that can be used  to bias your process – that’s really handy when   you want this process to track another one. The  SoftPLC version gives you more control over the   process variable, gives you control over the  sample time – something you can’t specify at   all in the drive's version - and has high  and low-level alarms. And I just like the   way the Remote HMI works better in the SoftPLC  version. You actually see the units spelled out.   There are a lot of subtle differences  between this SoftPLC PID implementation   and the one that’s in the drive so you  can’t just take the drive's version   and copy it over to the SoftPLC version - what  the manual calls the “Internal” PID version.   So, if you are thinking about  using the SoftPLC version of PID,   it’s really worthwhile to take a few  minutes to watch this video where I point   out all those differences and subtleties  – it will save you a lot of headaches.   Here we go. I’m using the EXACT   same hardware that we used in the PID Quick  Start video Part 1, which is interesting,   because the I/O card that comes with that drive  only has 1 analog input. That’s important, if you   aren’t going to use the 2nd analog input that  the Internal PID implementation has – which we   aren’t in this demo – then you don’t have to buy  an I/O card with two analog inputs! I like that.   This is my configuration worksheet for this Internal SoftPLC version of PID.   And while at a quick glance it looks a lot like  the drive’s version – once we have taken a closer   look you will realize it’s quite a bit different. This motor section is identical to the drive’s   version we used in the Quick Start videos  so I’m not going to spend any time on that.   If you don’t know what the state of your  SoftPLC is, then go ahead and reset it to   factory default by setting Parameter 204 to an 11.  That doesn’t affect the drive parameters at all.   I’ll do that just so you know  exactly where I am starting from.   The drive section has two differences.  In the built-in PID, the frequency   reference came from analog input 1 into the  drive – right? But, in the SoftPLC version,   the analog input feedback signal comes into the  SoftPLC, and then the SoftPLC sends the frequency   to the drive. So instead of a 1 here, we put a  12. That’s one of those subtleties I mentioned.   Same thing for the Auto-Manual switch. The  drive gets that from the SoftPLC’s internal   PID application. The PID application will see that  these I/Os have been allocated for those functions   and pass them to the drive. All the yellow  cells are gone, so that section is done.   We want that digital input to control  this switch, so we set P1015 to a 2.   This also sets the bumpless mode. It’s important  to note that the SoftPLC’s bumpless mode works in   both directions. When going from Manual to Auto  or from Auto to Manual. The drive's PID only does   it in one direction from Manual to Auto. Another  one of those subtle differences and yet another   reason to prefer this SoftPLC version of PID.  It gives you more control over the transition.   We’re going to leave it off for this video to  keep things simple. You can learn more about   Bumpless mode in this video which is on the WEG  CFW300 drive, but the same concepts apply.   And while we are here, let’s set the  manual setpoint to zero so we don’t get   any surprises when we turn this thing on. One of the things I like about the SoftPLC version is you can do everything in  native engineering units. You don’t have   to enter a 60 with the implied decimal  when you mean 6 for example. To do that,   you set up the units in Parameter 510 – we want  psi – and the decimal point in Parameter 511.   We’ll use the default single decimal place. So now if we want to enter the set point by   going to Parameter 1011, uh-oh, there  is no Parameter 1011. If I increment the   parameters, it skips from Parameter 1004  straight to Parameter 1. What’s going on?   if we go to Parameter 1000, we see it says No  Application because we haven’t created a PLC App.   And since we don’t have a custom user program,  there aren’t any parameters to go with it.   We want the built-in or Resident  SoftPLC PID application,   so we go to Parameter P1003 and change it to a 1.   Now if we go to Parameter 1000, we see  there is an application and it’s stopped.   It’s important to note that this is just like  any PLC, the PID application has to be stopped   before making any changes. To do that just go to  Parameter 1001 and change it from Run to Stop.   Also, the motor has to be stopped to  stop or make changes to the SoftPLC.   Now we can go to Parameter 1011  where we can change the set point.   Again, notice that the set point shows up in PSI! We want 6 psi so that’s what we enter.   We don’t have to remember to add that implied  decimal – the SoftPLC app does it for us.   For me, that’s a big advantage of the SoftPLC  version of PID because it makes my life easier.   All of the PLC configuration  stuff is in the upper left corner   to remind you to do that first before making  changes to the SoftPLC’s PID application.   You may remember that in the drive's PID  we had a filtering option here where we   could filter the analog input. The SoftPLC  version doesn’t have that. Why not? Well,   because it’s redundant. The analog input  already has filtering built-in. If you need   filtering on the analog input, just use that. Well, start with the same PID coefficients we   used in the Quick Start videos but notice that they  go to the SoftPLC parameters, not the   drive parameter numbers. You can tell because  the SoftPLC parameters are all greater than 1000.   And look at this! The SoftPLC version gives  you control over the sample time. Which for some   applications can be real important. Knowing the  sample time is critical when optimizing PID using   some of the techniques we outline in other videos.  That’s yet another benefit of using the SoftPLC   version. Most of the time, the blue default  value is fine. So that’s what we’ll use here.   The process variable is in Parameter 1013  and again, it’s in true engineering units.   Forward and reverse acting is a little  different. Another subtle difference.   In the drive’s version, you simply chose  forward or reverse. In the SoftPLC version,   this is where you disable PID or choose forward  or reverse. We want forward or direct-acting.   This is where you specify how the second  analog input reacts with the system.   You can add the two analog inputs,  take the difference or take an   average. This is great for those  times when you want to inject an   offset or even track another process. Another  advantage of using the SoftPLC version of PID.   We aren’t using a 2nd analog input in this demo,  so we just leave this at the default value.   We have two new parameters that the drive  PID didn’t have – PV Min and PV Max. In the   Quick Start videos, we made a big deal out of  figuring out what the min and max speeds were   that generate the min and max sensor  outputs. These guys over here.   That assumed 0 to 100% for this horizontal  axis. In the SoftPLC version, you specify   these numbers in engineering units. This is where  the SoftPLC PID algorithm gets its scaling from.   Which is cool because maybe you have a minus  15 to plus 15 psi sensor. You just enter   those numbers in here and you are done. No fancy  manipulation of the analog input to worry about.   Another subtle advantage of using the SoftPLC version of PID. We are using a zero to   15 psi sensor, so I’ll enter those values here.  Again, in true engineering units without having   to worry about the implied decimal. So nice. Configuring the analog channel is almost   identical to the drive version except we need  to tell Input 1 it is being used for the PID   feedback signal to the SoftPLC, not the drive. In  the drive version that was done in Parameter 203.   And I’ll add a little filtering  on the analog input. Again,   keep that small. Large values will reduce  the responsiveness of the PID algorithm.   We are not using sleep mode in this demo, so let’s  go to Parameter 1028 and set it to a zero to turn   it off so it doesn’t surprise us. You can learn  how to use sleep mode in the sleep mode video.   Finally, we need to configure the display.  It’s the same as the Quick Start video except   the set point comes from the SoftPLC setpoint,  and the process variable comes from the Soft PLC process variable. Remember that  we set the SoftPLC units back here.   Great! All the yellow cells are gone, and we  are left with white values and blue defaults.   Which tells us we have a  complete PID configuration.   I went ahead and entered all of these into the  drive. In Parameter 1000 we see the SoftPLC   is still stopped so we go to Parameter 1001 and  set it to a 1 to enable the SoftPLC and get it   running. Parameter 1000 tells us the SoftPLC is  now running. Perfect. In Parameter 1002 we can   also see the scan time in milliseconds. Another  thing you can’t do with the drive version.   Back up the display to main level. I love  that the SoftPLC version of PID shows   clearly on the display exactly what the units are. Let’s start in manual mode which is this way.   Yeah, the SoftPLC uses the opposite contact  definition relative to the drive’s built-in PID.   I’m going to overwrite the labels in the video to  serve as an obvious reminder they are different.   Ok, we are in manual mode, and  the manual set point in Parameter   1012 is at 0 percent of the motor speed. Switch to Run and the drive takes the motor   to the minimum speed we put in Parameter 133 which  corresponds to this many RPMs. I’ll change it to   50%. Once I get past the min speed the motor  responds as I scroll. Manual mode is a great   way to test out your system. In particular,  you can use this to make sure the motor is   spinning in the right direction. Our pressure  is increasing as the motor RPMs increase so we   are operating in the forward direction. Perfect.  Save that and escape back to the main display.   We see the RPMs up here and  the motor's current down here.   I’ll switch to auto mode and sure enough, PID  automatically adjusts the motor’s speed to get   the system pressure to the 6 psi we asked for. But it’s taking a long time. Apparently, the   SoftPLC scales the PID coefficients differently  than the drive’s PID does. If you’ve watched any   of the videos on how to tune a PID loop, then  you will know I typically just double the P   coefficient until things oscillate then back off.  If I go to Parameter 1017 I can adjust the gain in   real-time. Oops! Went too far and my system  started to oscillate. Let’s try again of 3.   Open and close some valves. Yeah, that’s a lot  more responsive. We can play with this all day,   but you get the idea. Watch this video  to learn how to tune a PID loop.   If we change the system pressure to 5 psi,   PID automatically adjusts the motor  speed to accommodate it. Perfect.   How about 7 psi. Yep, the drive tracks the new  setting almost as fast as I can change it. Cool.   That ought to be enough to help you get up and  running. I’ll put a link to the spreadsheet   configuration tool in the description  below the video. Please just use that   as a guideline – I can’t guarantee everything  in it is perfectly correct. Any questions? See   the manual. If you find an error please leave  us a comment below so we can get it updated!   Click here to learn more about the  WEG CFW500 variable frequency drive.   Click here to learn about AutomationDirect’s free  award-winning support options and click here to   subscribe to our YouTube channel so you will be  notified when we publish videos like this one.