[FieldTrip] Polhemus Patriot

Julian Keil julian.keil at gmail.com
Wed Jun 5 18:02:55 CEST 2013

Dear all,

thank you very much for your input.
I'll have to experiment a bit more with the distance to the walls (which probably contain metal) and the chair.
Thank you also for the idea with the second sensor, I hadn't tried this before.



Am 05.06.2013 um 17:53 schrieb Elizabeth Anne Bock, Ms:

> Hi Julian,
> We have experienced this problem as well.  We solved it using the following guidelines:
> No metal near the polhemus or any of the receivers/transmitters - you will need to move the setup around the room to find the perfect spot.
> Use a wooden or plastic chair
> Use plastic or cloth glasses/holder to attach the receiver to the subject
> My system is sensitive to the proximity of the transmitter and the receiver.  I use two receivers, #1 is the stylus and #2 is secured to plastic glasses that the subject wears.  The transmitter is taped to the back of the chair.  If #2 and the transmitter are too close to each other (i.e. a short person or child), then the measurement are inaccurate.  You would have to experiment with different distances that give good results.
> Hope this helps!
> Beth
> ------------------------------------------------------------------------------------------
> Elizabeth Bock / MEG System Engineer
> McConnell Brain Imaging Centre / Montreal Neurological Institute
> McGill University / 3801 University St. / Montreal, QC H3A 2B4
> Office: 514.398.3706 
> MEG Lab: 514.398.6056
> Mobile: 514.718.6342
> From: fieldtrip-bounces at science.ru.nl [fieldtrip-bounces at science.ru.nl] on behalf of Julian Keil [julian.keil at gmail.com]
> Sent: Monday, June 03, 2013 11:14 AM
> To: FieldTrip discussion list
> Subject: [FieldTrip] Polhemus Patriot
> Dear FieldTrip-Users,
> I have a not really FieldTrip-related question, but maybe one of you can help me anyways.
> In our lab, we have a Polhemus Patriot 3D tracking system to acquire electrode positions.
> Unfortunately, the recordings are severely distorted in the Z-axis (up-down).
> After contacting the Polhemus Support, I got the information, that this is due to metal in the surroundings of the source which distorts the magnetic field.
> I tried to get as far away from any metal as possible in our lab (~1.5 m to the walls and floor) but to no avail.
> Now to my question: Has anyone any experience dealing with this? I'm quite puzzled by this as I know plenty of labs use Polhemus trackers, and I'm not sure if our lab is especially metal prone or if I'm missing something.
> Thanks a lot for any help.
> Julian
> ********************
> Dr. Julian Keil
> AG Multisensorische Integration
> Psychiatrische Universitätsklinik
> der Charité im St. Hedwig-Krankenhaus
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> 10115 Berlin
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