HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
Thinking_J
User Rank
Gold
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.

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.



Partner Zone
Latest Analysis
We shared our list, now Design News readers tell us which artificial intelligence movies they watch again and again.
Researchers have been working on a number of alternative chemistries to lithium-ion for next-gen batteries, silicon-air among them. However, while the technology has been viewed as promising and cost-effective, to date researchers haven’t managed to develop a battery of this chemistry with a viable running time -- until now.
Norway-based additive manufacturing company Norsk Titanium is building what it says is the first industrial-scale 3D printing plant in the world for making aerospace-grade metal components. The New York state plant will produce 400 metric tons each year of aerospace-grade, structural titanium parts.
Researchers have simplified the fabrication of the geometric requirements for fluid motion in microrobots for in vivo medical applications.
The National Aeronautics and Space Administration’s recently announced plan to put an electric airplane in the air by 2018 is forward-looking, but hardly unique.
More:Blogs|News
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Jul 11 - 15, Embedded System Design Techniques™ - Debugging Real-time Embedded Software – Hands on
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  6 |  7 | 8 | 9 | 10


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.
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Technology Marketplace

Copyright © 2016 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service