Strange looking signal

jsr745 · Post by **jsr745** » Thu Apr 29, 2010 2:55 pm

Hi,

I've had a slightly strange looking signal recently. Thought it was a one off but its happened twice now on different subjects. It's difficult to describe but the link below should show you what I mean...

http://www.psychologyparticipants.co.uk ... roblem.htm

In the screen shot I've included you can see vertical deflections that appear on all channels. This was happening on a fairly regular basis and I can't work out what might be causing it.

Any help would be much appreciated.

Post by **Coen** » Tue May 04, 2010 1:06 pm

The interference pulse is a Common Mode signal (same signal on all channels). Your picture shows the unreferenced signals. After referencing, there will be an extra 40-60 dB Common Mode Rejection Ratio, which should decrease the interference below noise level.

The origin of this particular Common Mode interference may be on/off switching of a high power electric device (construction work in the building ?).

Best regards, Coen (BioSemi)