CynertiaDoug

I agree, it's pretty nonsense.  Especially because the backlash only happens when it changes directions.  We've been back and forth with the manufacturer MANY times about this.  Eventually, by reading through the manual for the positioner we found out that the "Local Mode" where the actuator responds to "open" or "close" button presses, which also has contacts for PLC open/close control; and it can apparently also ignore any deadband (meaning I'll have to program some in so the actuator doesn't chatter).  In fact, the manual mentions "This function is effective in remote automatic control mode", i.e. external PLC control.  Lol, the nuggets of wisdom that get lost in the casual comments in the manuals... Right now our solution is to watch the setpoint and if its increasing, let it do so, if it changes directions and begins to decrease we're adding in an additional -5% to the sp to get it to move right away.  Then if it begins increasing, we just use the setpoint as posted and hopefully this will help us "zoom" the setpoint past the mechanical backlash so the actuator will actually move when we want it to.

Thank you very much for this insight.  If we continue to have problems this gives me some options to work with! The actuator does have a positioner, and this is where our deadband ~0.3% and an added mechanical backlash when reversing directions of ~5% comes from.  We have been back and forth quite a bit with the valve manufacturer and this is how we found out the Valve is made by the company we're dealing with, and the positioner is made by a separate company. We have a plan to overcome the shortcomings with coding...I'm a little skeptical as "just fix it in the code" never works very well; but who knows until you try right? Thanks again!

Not sure what you mean by positioner...the actuator is what changes the position of the valve isn't it? The valve assembly is a valve by Mascott with an actuator by Heli.  The valve seems to be good for the application, except that it is controlling in the bottom 10 percent of it's movement which drastically reduces resolution, but that does let the slowly moving actuator have more of an effect on the system as a small change in position has a noticeable effect on the output. Another issue I've found; an electrician I'm working with was running tests with a manual PID controller that the customer brought in to see if it could do better than the CCW PID block.  In manual you can get a steady state pressure, for example say  2500psi, when the valve is at 10.0%.  Then if we manually open the valve to 15% the pressure will drop to 2000psi.  Then, when we put the valve back to 10% (and 10% shows on both the PID controller and the Actuator signal display [the one nice thing about this actuator is it comes with an LCD display that shows the control signal value and the position feedback]), the pressure will only build to ~2250 psi.  So I'll keep closing the actuator to 5% and then we achieve 2500psi again.  It's like the actuator will not move until you get a change of ~5%, but then it only moves a little bit, not the whole 5% because we end up at the same steady state, but with different actuator positions depending on if we approach it from above or below.

Hello everyone, Not sure if I have the right forum, so please forgive me; but... I have a control loop to tune, and it's the first one that I've ever been in charge of.  My question is about tuning PID.  The loop I have to tune is controlling a pressure reactor to setpoints ~3000psi with a safety valve that blows around 4500 psi.  My question is what procedure you might go through to tune it safely.  I'm quite honestly a bit afraid of the high pressures and I really don't want to make anything "pop".  What also makes it tricky is that the reactor has to heat up to get to full pressure.  Without heat, the reactor will reach ~1000 psi, then it sits there for a long time and eventually the heat kicks in and the pressure can rises up very quickly. I currently have a very small gain value, something like 0.009 and an integral time of ~7sec.  I'm getting pretty good results in that the PID controller will bring the reactor up to pressure without major overshoot, but it oscillates at ~ +-100psi, which seems excessive to me. [The situation is further complicated by the material in the reactor, a slurry, which has variable density often causing pressure spikes and drops as thicker sediments blob through.  Then, valves that we are using to control appear to be only opening ~10% to maintain setpoint, meaning I only get 1/10th the resolution I would be hoping for.  Also, the valve responds quite slowly to command signal changes.  The controller will be attempting to open the valve in 0.1% increments, but it only responds at minimum to 0.4% changes in the control signal, and when it reverses directions it seems to only respond after a ~5% change in control signal.  This alone appears to cause oscillations that I don't know if a PID loop could ever get ahold of.] Anyways, aside from the obvious valve issues, is there any tips for tuning a system with this high pressure?  I need fast response, but slow buildup... (Oh yeah, I'm also having to use connected components workbench for control software.  At least the newest version of CCW seems to have a nice iPID control block; but man, I have never had to ctrl-alt-delete a program more times due to freezing while building or downloading...so frustrating...).

Thanks Bob, that sounds about right on all counts and at least gives me an idea of what's going on under the hood.  It's always such a discovery process when you find a new customer!

Thanks, BobLfoot. The more I dig in, the more I realise I need to learn.  I've got a "programming philosophy" question you might be able to help me with.  For some context, this customer has two HMIs, one main floor, one mezzanine, that run the same program so changes on one are to be applied and logged on the other.  For some reason, instead of having one PC that is a server with another PC as client, Both PCs are running servers that are then connected to each other and the PLC via RSLinx (This is FTView Network SE V 8, I think they evolved to FTLinx after version 9...but I digress) however, the program is also running a VBA program to export the data to an excel sheet...I think.  As far as I can tell this is so both Servers can read and serve data to the Excel sheet which then serves the changes to the PLC...but this is where the setup confuses me: is it doing this?  Do you know at all why two HMIs would be both running servers and how they would interconnect?

Whelp, since no one seems to have any insight; I did have a session with the customer and was able to finally get in and get a copy of the program and here's how it went: 1. I was able to finally migrate a copy of the HMI program to my PC; it might not be very useful in the end, but I'll get to that later.  To get a copy of the program you first need to log into Factory Talk View (FTV) Station ON THE COMPUTER THAT IS RUNNING THE SCADA HMI.  I say this because FTV is , rightfully, very security focused and the program will not log you in, even if you are on their network and using your own licensed copy of FactoryTalk View.  This is because FTV keeps a list of the computer names that are allowed to access its files.  If you log in from a different computer it is no-go.  You can also get individual user accounts linked to individual computers so even if one person who uses a computer has access, another user might not.  But I digress... - Once you are logged into the HMI Scada pc go to the Windows Start menu and navigate to Rockwell Software.  Depending on your Windows version you will find the "HMI Server Backup and Restore" utility either listed in the first dropdown (windows 10) or possibly inside an embeded "Tools" folder.  Alternatively just search for "HMI Server Backup and Restore".  This program has a very simple front-end, it asks you if you are trying to backup or restore a server; pick Backup.  Then it asks where the backup server is stored, click the three dots next to the Select Source input; typical folder is "All Users>Documents>RSView Enterprise>SE>HMI Projects", you are looking for the *.sed file inside the program folder.  Once you've selected the.sed file, then choose a destination folder and hit "Start Backup".  Once this is done you've got it!  There will be a new folder with the archive name in the location you specified, and inside said folder will be many new folders, and most importantly, a ".sed" file with the archive name that you will use to import your copied program into your computer. So... 2. Take your new archive folder and copy it to your other computer, in my case it is a virtual machine that I do all my Rockwell stuff with.   3. Open your FTV studio and create a new program, I used the same name as the archive to keep it simple (Plus if you intend to make changes to the program and load them later it might help to have everything named the same, but this is also a very complicated procedure as I'll explain later). 4. In your new program, there will be another computer with gear icon.  Right Click it and select "Add New Server",  a pop-up will appear asking you which type of server you want to add and in our case it's an HMI Server; you can also choose, File->New->Add New Server->HMI Server.   5. Yet another pop-up.  This time it asks if you want to create new, copy, import, or attach to an existing server.  In this procedure it will be "Import a project". 6. New popup, what type of project is this, click the Project Type dropdown and select "Factory Talk View Site Edition Project".  Click the "..." next to "Project File", navigate to your archive file from before and select your ".sed" file. 7. Click next and get the option to give it a new name (I kept the name of the original project).  Name it and click Finish. 8.Boom, FTV Studio will now import the project and you should have a "Complete" (I'll explain later) copy of the HMI server.   - Now comes the "I'll explain this later" portions.  Doing all of this is a good exercise, but in the end might not accomplish much for the following reasons.  A Network SE Project is set up this way because it is most likely networking several different systems together.  This means tags from a PLC are coming up to your HMI server, but that server is likely then turning around and "serving" those points to other computers and systems and might in turn also be getting served info and data from those systems.  In the list of servers on the program there are very likely going to be other servers like "OPC DA servers, Tag and alarm servers, and OPC UA servers"  These all contain important data for your program and when you open up your faceplates to learn about the program it will likely give you a message about missing a file and having to create a new one.  You will see the graphics but everything will be question marks and blank strings because the data is coming from elsewhere.  You can also make copies of the other servers in the program, but to get it all to work, you will have to edit the data inside and re-link all of the data points to the copied program.  Remember up top where I said that only computers with names that have been added to the FTV safe list will be allowed to log on, well all of the links in the servers will include the name of the computer that the data is supposed to go to, and your personal computer has a different name, so you need to change all the links...    Needless to say this is a very time consuming process and it can be quite difficult to get a "Compete" version of the program copied to your computer. All of this is to say that if you do have to make changes to a customer's program that is set up like this, it is most likely going to be safest and easiest (and least time consuming) to actually visit the customer and make the changes directly on their system (*Groan* Site visits, am I right?  ) As I say in my profile, I am new to a lot of this and I've may have made some mistakes in describing this.  Feel free to let me know and I'll edit them accordingly!  Hope this helps in any matter... <Edits as I had the procedure wrong>

Hello, I'm a little experienced, a little new with (I hope) a fairly beginner question. I've got a customer that has a pre-existing HMI running a Factorytalk View SE - Network program.  The customer would like to make some changes to the HMI, and I feel pretty confident that I could do this; the only problem is I'm having difficulty connecting to their system and downloading a version of the program that I can edit. Almost every How to video and instructional PDF that I can find appears to start from the premise that I created the program and have an existing copy on my computer or am starting from scratch, but that is not the case.  I know the IP address of the Networked PC that is running the HMI and can ping it etc, but I do not know how to connect to it.  I even have a copy of almost all of the files that the PC is running from the customer, but do not have a file that I can open in FTView to edit or change then download; I think I'm missing the .cli file or somesuch? Do I have to be directly logged on to the PC or can I be on my programming laptop and connect via Ethernet->switch->PC (I think I need FactoryTalk Linx for that, which I have a licensed copy of)?  I know that Machine Edition requires a .mer file to be able to open and edit an HMI program, is the network edition the same? Any help would be greatly appreciated!