Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Analog Lagging Techniques

Analog Lagging Techniques

Analog Lagging Techniques

I am programming a system that will have a 4-20mA linear position sensor that will go from 4-20mA then 20-4mA in one full cycle. This cycle will continuously repeat itself at a set speed. Next, I have an identical hardware setup that I need to lag behind or follow the first cycle at roughly 30% of the cycle. It will be controlled by an analog output signal. I have had several ideas of how to do this that would work as the leading value is increasing from 4-20mA but I am running into a roadblock of how to get the second value to continue to increase to 20mA and then follow the leading value back to 4mA. I am programming in RSLogix 5000. Any help or ideas would be greatly appreciated!

RE: Analog Lagging Techniques

You say "set speed". That's the key. Both ramp/cycles should execute temporally accurately and identically. That means the second one should NOT need to track the leading one at all. What you need to have is a single sync point. The first cycle should provide a trigger pulse at the moment it starts that the second cycle accepts then delays initiation of its cycle start until the appropriate time period has passed providing the 30% lag you desire. This method also allows easy tuning by simply altering that delay period. Both cycles do their own up and down so it's not an issue with the second cycle having to carry thru and return to the start. Both cycles should be written identically with only the second using the initial delay.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Analog Lagging Techniques

You can just do a compare in the plc.

There are scaling on inputs and other features on the analog cards that are kind of nice. Like rail limits, scaling inputs, and all that other nice features.

20mA = 100
4ma = 1

Once the first one gets to 30 then latch a bit till the 2nd one gets to desired output then reset bit and disable function. There are a hundred ways to program, but if you are with a company just try to follow whatever standards they have established.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close