You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old July 16th, 2017, 10:17 AM   #1
kkidd09
Member
United States

kkidd09 is offline
 
Join Date: Jul 2017
Location: Wisconsin
Posts: 2
Smile PID Process Control/PLC

I am currently trying to implement a process control of the temperature of water going down a drain after it has gone through 2 radiators. I have 5 RTDs and an electric actuator. I am trying to use a setpoint, the last RTD in the process as the Input(Process Variable), and the electric actuator as the output(Control Variable) which will inject cool water as needed to maintain setpoint. The actuactor works with an AC modulating 4-20mA input and 4-20mA output. Any tips on the best method of supplying the actuator with the 4-20mA input? Any tips on the best way to set up my PID in RSLogix500? Any help at all would be great!
  Reply With Quote
Old July 16th, 2017, 10:55 AM   #2
labeledas
Member
Canada

labeledas is offline
 
labeledas's Avatar
 
Join Date: Apr 2010
Location: Peace River Alberta
Posts: 524
post the model of the actuator but in general they get the 4-20mA DC signal from the PLC's analog output card the AC is normally only to power the unit and motorized parts the mA signals are isolated from the AC and almost always DC.

I say almost always as I have never seen a 4-20mA AC signal but they might exist for whatever reason.

What PLC are you using and do you have an Analog Output module?

You PLC analog output would tie to your actuators Analog input for "position setpoint" to tell the actuator where to go. the actuator analog output would normally be used for "position feedback" to tell you the current position, and tied into a PLC analog input module.

As for the PID setup, tuning wise, it will depend on a lot of things in your process.

Last edited by labeledas; July 16th, 2017 at 10:59 AM.
  Reply With Quote
Old July 16th, 2017, 11:13 AM   #3
kkidd09
Member
United States

kkidd09 is offline
 
Join Date: Jul 2017
Location: Wisconsin
Posts: 2
http://sharpevalves.com/images/Elect...%202-17-10.pdf

Above is the link to the model actuator. It is a SEA-3 model. According to the wiring I could do an AC or DC modulating setup. The PLC I am currently using is a SLC 5/05 CPU. I do have an analog output card but do not have any more free slots in the chassey, so I was hoping to be able to do this through the Point I/0 I have set-up through this PLC if possible? I understand your explanation of what would need to occur. Would this be possible through Point I/O?
  Reply With Quote
Old July 16th, 2017, 12:09 PM   #4
labeledas
Member
Canada

labeledas is offline
 
labeledas's Avatar
 
Join Date: Apr 2010
Location: Peace River Alberta
Posts: 524
Quote:
According to the wiring I could do an AC or DC modulating setup.
in terms of power supply it actually depends on the option you ordered it with, from what it looks like
SEA3-1 = 220VAC
SEA3-2 = 24VAC

SEA3-3 = 12VDC
SEA3-4 = 24VDC

I would double/triple check the nameplate for voltage ratings. Blue smoke is not cool.

The 4-20mA control signaling however will always be DC for these units. Are there any free channels on your SLC AOUT card.

I didn't think point I/O worked with the SLC line, but I don't real deal much in either of those products.
  Reply With Quote
Old July 16th, 2017, 06:29 PM   #5
danw
Member
United States

danw is offline
 
danw's Avatar
 
Join Date: Oct 2004
Location: midwest, USA
Posts: 2,636
These kinds of actuators are quite common in the HVAC world. That market typically uses a 115Vac/24Vac step-down transformer to step down 115Vac line voltage for the motor supply voltage.

As Labeledas says, the control signal is always DC.
  Reply With Quote
Old July 17th, 2017, 05:34 PM   #6
Plastic
Member
United States

Plastic is offline
 
Join Date: Feb 2009
Location: Michigan
Posts: 225
Red Flag - Soon to be obsolete

Kkid09,

You have been given a task to limit the discharge temperature, with economical effectiveness, by only using cool water when necessary.

I am not here to offer ideas to the simple task at hand, using the near obsolete control system.

My concern is the well being of your employers long term goals, as well as your awareness of long term goals.

The SLC 5/05 was developed when I was kidd88. I endorse that you first migrate your controller, and then take on the "tasks" of process and profit improvements.

http://www.rockwellautomation.com/gl...h/results.page

Regards
  Reply With Quote
Old July 17th, 2017, 06:11 PM   #7
sparkie
Supporting Member
United States

sparkie is offline
 
Join Date: Nov 2014
Location: KS
Posts: 579
Though some may consider my methods a bit unorthodox, I'm a get it done with what you have kind of guy when I feel it is feasible. Even if they are old, those 5/05's are some nice processors. There is no need to upgrade because you want to control a valve.

Take your control cabinet, put a 3" KO in the side and set yourself a small panel with a 2.5-3" nipple. In that panel add an old 4 slot rack you have lying around and pull you some power from your panel off one of the buses into that nipple. Run you a ribbon cable over, insert your analog out card (and the analog in card if you need one). Quick question here: Are you SURE there isn't a single spare analog output you can use instead of this? Is the RTD already in the program? Anywho, if you need some extra rack space this solves your problem providing you have enough room to mount a small panel. No need for point IO. You are trying to do this cost-effectively, not re-engineer the whole system that works just fine.

Now, I would need specifics on that transducer you have, but it likely takes a 4-20mA and outputs it to something like a 0-1A valve or such. Now you will need to do some fiddling to get it right, but you can just use an SCP instruction. Couple key questions to help you with this. What is the hottest the water from the radiator ever gets? What is the lowest temperature the water from the radiator ever gets? You can then scale that valve to open and close as needed to cool the water going into the drain.

You would be using a PID if you were trying to keep the water temperature constant, which you are not. You are just trying to keep it below a set point. This system would be a bit reactive, but I feel it would accomplish what you are trying to do, be much simpler than you think you need this to be and would be a LOT cheaper, especially if you have a small PSU and 4-slot rack laying around.

If you think this system would be expanded in the future, go ahead and wire the analog IO up to terminal blocks, put yourself a hot bus/24VDC bus depending on what kind of descrete IO you use, and a neutral/0VDC bus, once again depending on what kind of IO you use. Then as you add a card you can add/label the terminal blocks for future expansion.

Anywho, that is my two cents with the information you have provided. Good luck!

EDIT: Just checked your valve specs. You don't even need feedback from this. It is just something else to go wrong. Your RTD IS your feedback.

Last edited by sparkie; July 17th, 2017 at 06:15 PM.
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
PID block and out of range process parameter Ramon21 LIVE PLC Questions And Answers 4 June 10th, 2015 03:14 AM
Hobby project: Creating a batch process and seeking help in the design process! ignore-rant LIVE PLC Questions And Answers 11 September 19th, 2013 03:12 PM
PD vs PI tuning for a pid loop dawg67 LIVE PLC Questions And Answers 40 December 1st, 2010 05:57 PM
PID Tuning and Process Modeling kdcui LIVE PLC Questions And Answers 14 October 15th, 2009 12:27 PM
Siemens PID block, theoretical analysis Pandiani LIVE PLC Questions And Answers 3 July 11th, 2006 03:44 AM


All times are GMT -5. The time now is 01:47 PM.


.