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 November 28th, 2017, 04:52 PM   #1
d.dinh
Member
Australia

d.dinh is offline
 
Join Date: Mar 2011
Location: Brisbane, QLD, Australia
Posts: 15
RSLogix 5000 PIDE Cascade

Hi all,

Having some issues setting up a PIDE Cascade control loop.
Have been trying to go through the Wp008 doc but there's probably something easy/small that I'm missing.

I have a tank with an oil jacket which is directly heated up using resistive heaters (SSR). The oil jacket in turn heat transfers to the tank product (wax).

The application is heat only, as the client generally turns on the oil jacket heaters and leaves overnight for the wax to melt.

Am I correct in assuming that this calls for a PIDE Cascade Loop?
Primary Loop - Wax Temperature - 4-20mA - 0-200C with SP cutoff at 150.
Secondary Loop - Oil Jacket Temperature - as above.
Secondary Loop output goes to SRTP for the SSR output.

Thanks ahead for any help.
d.dinh
Attached Images
File Type: jpg PIDE_Error.jpg (58.8 KB, 24 views)
Attached Files
File Type: zip PIDE_Loops.zip (6.8 KB, 8 views)
  Reply With Quote
Old November 29th, 2017, 12:23 PM   #2
rankhornjp
Member
United States

rankhornjp is offline
 
Join Date: Dec 2008
Location: Georgia
Posts: 156
right click on all your "wires" that go from the PID on the right to the PID on the left, and click "Assume data available"
  Reply With Quote
Old November 30th, 2017, 05:40 PM   #3
d.dinh
Member
Australia

d.dinh is offline
 
Join Date: Mar 2011
Location: Brisbane, QLD, Australia
Posts: 15
Quote:
Originally Posted by rankhornjp View Post
right click on all your "wires" that go from the PID on the right to the PID on the left, and click "Assume data available"
Thanks mate. Did work it out in the end. But was a quite frustrating process trying to figure what I had done wrong.

Does anyone know whether "assuming data available" is in the white papers/manuals anywhere?
  Reply With Quote
Old November 30th, 2017, 05:50 PM   #4
raffles
Member
Canada

raffles is offline
 
Join Date: Dec 2013
Location: Vernon, BC
Posts: 65
It's in the FB programming manual, page 14

http://literature.rockwellautomation...m009_-en-p.pdf
  Reply With Quote
Old December 1st, 2017, 03:30 AM   #5
rdrast
Lifetime Supporting Member
United States

rdrast is offline
 
rdrast's Avatar
 
Join Date: Apr 2003
Location: South Carolina Lowcountry
Posts: 5,184
I'm not seeing where you need cascaded loops here...Honestly, I'm not seeing where you even need two, perhaps a diagram?
__________________
------------------------------------
How to ask questions the SMART Way!

Look First, Ask Second!

  Reply With Quote
Old December 3rd, 2017, 05:14 PM   #6
d.dinh
Member
Australia

d.dinh is offline
 
Join Date: Mar 2011
Location: Brisbane, QLD, Australia
Posts: 15
Quote:
Originally Posted by rdrast View Post
I'm not seeing where you need cascaded loops here...Honestly, I'm not seeing where you even need two, perhaps a diagram?
Here's a quick sketch.

I am not exactly sure whether the client/operators control the wax temperature as the setpoint, or the oil jacket temperature as the setpoint.

But essentially, they heat up the oil using a pair resistive heaters that are turned on using solid state relays(on/off only).
As the oil heats up, the wax product heats up.

They generally leave this on overnight at the set temp so the wax melts overnight without supervision (apart from PLC).
Attached Files
File Type: pdf Oil Jacket Wax Sketch.pdf (162.7 KB, 15 views)
  Reply With Quote
Old December 4th, 2017, 04:42 AM   #7
rdrast
Lifetime Supporting Member
United States

rdrast is offline
 
rdrast's Avatar
 
Join Date: Apr 2003
Location: South Carolina Lowcountry
Posts: 5,184
I really don't see any need for cascaded loops there.
Run one PID for the oil temp, and one for the wax temp. Done.
__________________
------------------------------------
How to ask questions the SMART Way!

Look First, Ask Second!

  Reply With Quote
Old December 4th, 2017, 06:18 AM   #8
jamesau
Lifetime Supporting Member
United States

jamesau is offline
 
Join Date: Mar 2004
Posts: 163
Quote:
Originally Posted by d.dinh View Post
I am not exactly sure whether the client/operators control the wax temperature as the setpoint, or the oil jacket temperature as the setpoint.
I'd try to find out more from them about their process/product.

I'd like to think the melting wax behaves as any other melting-solid process. Specifically, the solid temperature rises until it reaches a solid/liquid transition temperature (or temperature range). The temperature of the melting product remains relatively constant until all is melted and then the all-liquid product temperature begins to rise. As an analogy, think of heating a block of ice; the ice block temperature will rise until it reaches 0C/32F and stay at that temperature until it is completely melted. The water temperature will then rise towards the temperature of its surroundings.

For a process as described above, I would simply control oil temperature at some high level, wait for the wax temperature to indicate all has melted, and then set the oil temperature to some melt-maintenance temperature. (And note different temperature schedules/recipes might be necessary for different wax products).
  Reply With Quote
Old December 4th, 2017, 07:01 AM   #9
d.dinh
Member
Australia

d.dinh is offline
 
Join Date: Mar 2011
Location: Brisbane, QLD, Australia
Posts: 15
Quote:
Originally Posted by rdrast View Post
I really don't see any need for cascaded loops there.
Run one PID for the oil temp, and one for the wax temp. Done.
Sorry. You have me a little confused (and probably my limited understanding).
If I were to use two separate PIDs, would the output of the Wax temp PID control? I only have the one SSR to control the heaters that heats up the oil only.
  Reply With Quote
Old December 4th, 2017, 09:58 PM   #10
d.dinh
Member
Australia

d.dinh is offline
 
Join Date: Mar 2011
Location: Brisbane, QLD, Australia
Posts: 15
Quote:
Originally Posted by jamesau View Post
I'd try to find out more from them about their process/product.
I will have to double check at the client's old site and with the previous OEM they used for the PID loop controllers.

But how it was explained to from an operator's PoV:

When they start the heating process:
- the heaters will turn on and get the oil jacket temp up to 145C
- the wax product temp SP will be something like 120/130
- as the wax temp PV gets towards the SP, the heaters back off so the oil temp PV also backs off to keep the Wax temp at its SP.
- main reason for the over temp of the oil vs the wax is so the wax melts faster to reduce waiting time
- heaters turn on/off as required to maintain wax temp PV at the SP.

Hopefully that makes sense. Anyone have further thoughts on this?
Cascade PIDE control or not? Similar applications done in the past?

Many thanks,
d.dinh
  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
How to access other ASIC registers in Rslogix 5000? csjokerd1123 LIVE PLC Questions And Answers 0 August 18th, 2017 01:48 AM
RSLogix v20 - PIDE Cascade setup. KristienP LIVE PLC Questions And Answers 2 January 27th, 2016 11:55 AM
RSLogix 5000 Read Only Access? chrisj91 LIVE PLC Questions And Answers 5 September 19th, 2014 11:23 AM
Pid Cascade Loops Rslogix 5000 learner LIVE PLC Questions And Answers 5 November 23rd, 2008 06:36 PM
RSLogix 5000 V15 Features Samneggs LIVE PLC Questions And Answers 18 April 20th, 2006 05:45 PM


All times are GMT -5. The time now is 03:42 PM.


.