Precise Continuous Pulse Output Control

by | Jul 20, 2010 | Technologies

Jim Cahill

Chief Blogger, Editor

TweetDeck Screen Capture
I like to use the application TweetDeck first thing in the morning to quickly scan Twitter posts from the trade press and trade analysts, #PAuto (the established hashtag for “Process Automation”), Emerson folks and brands, and specialized searches on DeltaV, Emerson, and me. This helps me quickly spot news and trends going on in our world of process automation. TweetDeck is nice since it has a multi-column format for each of these tweet filters.

By using this mechanism, I discovered the Process Control Musings blog post, Roadrunner Fast. I discovered this post in the DeltaV search column from this tweet:

New blog post at http://bit.ly/JMPSA – Exploiting the new capabilities of Electronic Marshalling and Discrete CHARMS in #DeltaV V11.3

The blog’s author, Bruce Greenwald, has done a number of posts about the version 11 release of the DeltaV system. What I like about his posts is his hands on approach to testing and documenting different aspects from the release. In this post, he sets up a test with Continuous Pulse Outputs in the discrete output (DO) CHARMs. He describes an example of how these pulsed outputs might be used:

So for instance, if the duty cycle was set to 5 seconds and the output of the loop was 80%, the DO would turn on for 4 seconds, then go off for 1 second. So this was great for applications that used electric heat – you could create a PID loop for temperature control with a final control element of a pulsed heater.

He describes the duty cycle specs for the DO CHARM:

The Pulse Period (duty cycle) for a DO CHARM can be set anywhere between 2 ms and 130 seconds. That wasn’t a mistype – 2 milliseconds… If my duty cycle can be as fast as 2 ms, how fast can an output from DO CHARM be turned on, then off? Turns out it’s 1 ms.

He shows a Fluke meter screen capture of this 1ms performance. This granularity provides an opportunity for very exact control. Bruce closes the post with how to configure a very precise digital output pulse width of 57msec.

If you have a DeltaV system in your facility, you may want to subscribe to the Process Control Musings RSS feed to be notified when tomorrow’s post on counting those pulses with a DI CHARM is published.

GreenPodcast.gif MP3

Update: As promised, Bruce comes through with a post today on the DeltaV digital input (DI) CHARM, A Lot Less Blood, Sweat, and Tears for the Spinning Wheel.

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The opinions expressed here are the personal opinions of the authors. Content published here is not read or approved by Emerson before it is posted and does not necessarily represent the views and opinions of Emerson.