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electromagnetic distortion - communication killed

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#1 dabreaka

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Posted 25 April 2013 - 01:45 AM

Hi folks, I use a labjack UE9 to measure signals coming out of a DB25 signal monitor plug (DC signals 0-10V and 1 counter signal, counter pulses 5V hig for serveral ms) of a high voltage power supply. The acquisition location is inside a switching cabinet and the system is a high voltage pulser - so high voltage (several kilovolts) is switched with frequencies from some hundred Hz to over 2000 Hz. The labjack measurement takes place outside the machine room with labview and for most of the time it works. But sometimes the acquistion stops and I have no more ethernet connection to the labjack. Unplug the 5V DC supply and replug helps. The acquisition again works. When I try to measure the AIN ports with a scope for this trigger point I can't find the reason. The analog voltages look noisy, the 5V supply voltage looks good over time. The environment is rough and full of electromagnetic distortion and noise due to the high voltage switching. Earlier I used a labjack U12 and with USB this problem occured much more often. With the ethernet based communication the problem occurs not that often. What do you think is the port where the labjack is attacked - is it the 5V input, the ethernet cable, the digital IO ports, the AIN ports ? Any idea how I can protect the jack from enviromental noise? Best regards and many thanks in advance for any ideas and help on this topics. Cheers dabreaka

#2 LabJack Support

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Posted 26 April 2013 - 04:07 PM

How often does the problem occur? Can you make it occur quickly on purpose?

I suggest you disconnect all connections from the UE9, except for Ethernet and power, and see if the problem goes away. If it does, start adding back connections one at a time to see if a particular wire causes the problem. It could be a wire connected to an I/O terminal, or could be a wire connected to a VS or GND terminal.

To recover without you having to intervene, consider using the watchdog to reset the Comm and Control processors automatically if the UE9 does not get any communication for some time (e.g. 60 seconds):


You can set this up to be always enabled using "Config Defaults" in LJControlPanel, or you can have your software enable the watchdog when it starts and disable the watchdog when it is closed.

#3 dabreaka

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Posted 29 April 2013 - 10:14 AM

Hi Labjack Support, thanks a lot for your first suggestions - it is not that easy to provoke the behaviour - but I will do the tests as you mentioned and report on my analysis - thanks a lot for the hint to use the watchdog - I wasn't aware of this feature and I will try and come later back to report on my progress Best regards dabreaka

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