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.

New Here? Please read this important info!!!


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

Reply
 
Thread Tools Display Modes
Old August 29th, 2013, 07:29 PM   #1
tomizzo11
Member
United States

tomizzo11 is offline
 
Join Date: Jul 2013
Location: Michigan
Posts: 49
Ladder Units

Hello,

Iím having a difficult time grasping the idea of ladder units. Iíve been working in PicPro recently, and it keeps referencing the term ladder units. When I go and look up the term, it mentions a couple other units. So the three units are,

Ladder Units
Feedback Units
Axis Units


It says that ladder units are simply the units used in the ladderÖ What exactly does that mean? It then goes on to say feedback units are the units the Servo uses and axis units are the units of the systemÖ It then proceeds to talk about scaling between everything.

So besides the fact that Iím not confident with the real definitions of all of these ďunitsĒ, the scaling confuses me. Would it be correct to assume that feedback units are the smallest increments of positioning a servo? But then why would you have the ability to make ladder units smaller than feedback units? Isnít that just adding precision within your ladder that you have no control over? And I have no idea what axis units are. Could that be degrees or radians?
These terms seem to only be referenced by G&L manuals when I google them and canít find any other PLC developer talking about them.
  Reply With Quote
Old August 30th, 2013, 12:07 AM   #2
keithkyll
Member
United States

keithkyll is offline
 
Join Date: Jul 2005
Location: Heath, TX
Posts: 2,033
Ladder units. You can't use floating point math in this version of ladder software. Only whole numbers (integers). For example, you would use 1000 to represent 1 inch.

Feedback units. This is the pulses per inch from the encoder. The example in the manual shows 8000. That means if you tell the machine to move 1000 counts (Ladder Units), it will move 8000 counts (Feedback Units) on the encoder.

Axis units. This is the real world measurement. I used 1000 to represent 1 inch. It could be 1 millimeter, or 1 meter. It's whatever I choose.

The only fixed number is the encoder feedback (Feedback Units). The other units are your choice. You choose whether you want Inch or Metric, and resolution (precision).

Let's say I want Metric. The encoder is 8000 counts per inch, so 8000 per 25.4 mm. Let's round for this discussion. 100 mm would be 32000 counts. I decide I want .1 mm precision.

My Axis Unit is 100.0 mm, Ladder Unit 1000, and Feedback Unit 32000.

Last edited by keithkyll; August 30th, 2013 at 12:16 AM.
  Reply With Quote
Old August 30th, 2013, 10:06 AM   #3
tomizzo11
Member
United States

tomizzo11 is offline
 
Join Date: Jul 2013
Location: Michigan
Posts: 49
That actually makes a lot of sense. I think what confused me was the fact that a piece of code I was looking at had a ratio of ladder units to feedback units being greater than 1. That would make it so your program has more precision than the actual motor capabilities which made no sense to me.

Do you know if it is common practice to have more precision in ladder units than feedback units for future purposes, say for example if higher resolution encoders are released?
  Reply With Quote
Old August 30th, 2013, 11:18 AM   #4
keithkyll
Member
United States

keithkyll is offline
 
Join Date: Jul 2005
Location: Heath, TX
Posts: 2,033
Doesn't make sense to me either. I always want feedback to have at least 10x greater than ladder units.
Choice of resolution is based on the accuracy of your design. How much slop in bearings, etc.
  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
ControlLogix New Task and ladder Christoph LIVE PLC Questions And Answers 8 August 22nd, 2013 08:40 AM
Need help for drawing PLC ladder diagram mayank_04081989 LIVE PLC Questions And Answers 8 November 21st, 2012 12:18 AM
Contrologix IO Tree and HMI Units The Plc Kid LIVE PLC Questions And Answers 4 August 12th, 2011 05:45 PM
Make shift register with ladder solution sis LIVE PLC Questions And Answers 7 October 28th, 2005 08:36 PM
RSlogix500 + SCP = ??????? bikerdude LIVE PLC Questions And Answers 15 July 30th, 2003 11:00 AM


All times are GMT -4. The time now is 02:44 AM.


.