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
On Memorial Day, Americans remember the sacrifices the US armed forces have made, and continue to make, in service to the country. All of us should also consider the developments in technological capabilities and equipment over the years that contribute to the success of our military operations.
Imagine if you could train it from San Francisco to New York faster than flying?
In order to keep in line with safety protocols, industrial networks need to be filtered in a semantic way so that only information related to diagnostics is flowing back to the vendor and that any communications that could be used for remote machine operations are suppressed.
Siemens PLM has launched an online store to help customers search for, compare, and purchase partner-developed apps for its Solid Edge software.
Advanced visualization can depict an entire plant in motion, while also detailing an individual workstation. Individual products can be rendered different for each discipline involved — marketing, engineering, or suppliers.
More:Blogs|News
Design News Webinar Series
5/21/2015 11:00 a.m. California / 2:00 p.m. New York
5/7/2015 11:00 a.m. California / 2:00 p.m. New York
3/31/2015 11:00 a.m. California / 2:00 p.m. New York
6/11/2015 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.
Jun 8 - 12, Everything You Ever Wanted to Know about Filters
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  6 |  7


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.
Next Course June 2nd-4th:
Sponsored by Proto Labs
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