HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
William K.
User Rank
Platinum
Unexpected interactions
William K.   9/19/2011 6:50:23 PM
NO RATINGS
In years past we needed to do similar things with PLC input modules that were driven by solid-state proximity-type limit switches. The fault was that the off-state current draw of the switch was enough to convince the sensitive input module that it had a valid input. 7500 ohm, 5-watt resistors across each input solved the problem.

But it was good detective work that found the problem with the transmitter shutoffs.

Thinking_J
User Rank
Platinum
similar problem
Thinking_J   9/20/2011 5:54:39 PM
NO RATINGS
I have resolved several situations with same root cause.. inputs with not enough protection from RF sources.

First...

A CPLD IC (22v10) on a failsaft circuit. It's inputs would pick up enough RF energy from relay contacts (equ. spark gap transmitter) loaded with inductive load. Actually erased the device!.. required 1000pf caps across all inputs for this environment (couldn't put a snubber across the contacts - leaked enough to hold the smart magnetic contactor load "on" , even when contacts opened).. and we couldn't move the relay farther away from the electronics.

Always keep mechical relays / large inductive loads away from the rest of the electronics (if possible)... just asking for trouble when close to each other.

Second...

Battery powered device with GSM transceiver/processor monitoring an external device via a simple contact closure. Reduced the pull up on the contact closure in effort to reduce battery drain (resistor array - 100K) , contact was normally closed drawing current across the pullup. The external circuit - no problem. However, the other three inputs (membrane push buttons with flex cable) would normally be "open". These inputs would close when the GSM transciever transmitted. The RF energy (not that much) would be rectified by the silicon junction on the processor input and pull the input low (randomly).... net result: it "pushed" it's own buttons when transmitting (occasionally)!

Next time , will use ferrite beads on these inputs. This time , changed pull up resistor array to 10K.



Partner Zone
Latest Analysis
National Instruments sees 5G WiFi and software-enhanced test equipment as advances that will change technology and business.
The new $120,000 Model S P85D boasts a 221-horsepower front motor and a 470-horsepower rear motor that packs a punch. The car is able to go from 0-60 MPH in just 3.1 seconds … quietly.
The new composites manufacturing innovation center is intended to be a source of grand challenges for industry, like the kind that got us to the moon under JFK. These aren't the words its new CEO Craig Blue used, but that's the idea and the vision behind the Institute for Advanced Composites Manufacturing Innovation (IACMI).
The ideal gas law, first stated in 1834, has suddenly become big news.
Bill Gates took to Reddit for an AMA (Ask Me Anything) and fielded fielded questions on everything from his outlook on the future of technology to who he's rooting for in the Super Bowl.
More:Blogs|News
Design News Webinar Series
12/11/2014 8:00 a.m. California / 11:00 a.m. New York
12/10/2014 8:00 a.m. California / 11:00 a.m. New York
11/19/2014 11:00 a.m. California / 2:00 p.m. New York
2/25/2015 11:00 a.m. California / 2:00 p.m. New York
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Feb 9 - 13, Embedded Development Using Microchip Microcontrollers and the CCS C Compiler
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  67


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Last Archived Class
Sponsored by Stratasys
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2015 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service