sorry my mistake... confused the magnetometer with accelerometer :$ On 9/19/07, Giri Baleri <[EMAIL PROTECTED]> wrote: > > Hmm... I am not sure if this calibration approach would work for > magnetometer. This works for accelerometer since Earth's gravitational > acceleration is constant (1g) as long as you don't accelerate/decelerate. > > Although, earth's total magnetic field is constant at a given location on > the earth, your magnetometer can be easily affected other ferrous materials > in the neighborhood and it is very difficult to factor them out from just > Earth's magnetic field. > The correct approach to calibrating magnetometer involves placing it > inside a mu-metal shield to measure the bias voltage (output at zero input > field) and then placing it inside a Helmoltz's coil in different > orientations while given a known input (eg. 0.5 gauss) to calculate scale > factor (output for incremental change to the input). > > Regards, > Giri > > ------------------------------ > *From:* [EMAIL PROTECTED] [mailto: > [EMAIL PROTECTED] *On Behalf Of *sougata sen > *Sent:* Wednesday, September 19, 2007 5:47 AM > *To:* Urs Hunkeler > *Cc:* Tan Simin Jeremy; [email protected] > *Subject:* Re: [Tinyos-help] 2-axis Magnetometer MTS310CA > > hi jeremy > adding to Urs' comments to caliberate, u should get a +1/-1 mGauss when > the +ve/-ve X/Y axis is facing towards the earth or vice versa. if that is > different, u have to caliberate the values to get this reading. > > > On 9/19/07, Urs Hunkeler <[EMAIL PROTECTED]> wrote: > > > > Hi Jeremy, > > > > I see you have been posting this message several times and apparently > > have not received a reply. So here is my unqualified reply. Maybe this > > gets somebody so annoyed that they just want to correct me :-) > > > > 1. I think the sensors need to be calibrated. For instance this could be > > done by turning the mote slowly around while simultaneously sampling the > > magentic field. That way you'll get a maximum and a minimum value > > corresponding to perfect (mis)alignment to the earth's magnetic field. > > How you do this exactly I don't know (but would like to learn as well). > > > > 2. Based on the calibration you need to adjust the on-chip amplifier. > > There is are some functions in the Mag interface that seem to allow > > exactly this: gainAdjustX and gainAdjustY. > > > > 3. It should. But I seem to vaguely remember that the magnetic sensors > > on the MTS310 sensor board only measure differences in the magnetic > > field, so you could not measure a static field. > > > > I hope this helps a bit. Please let me know if you find out more about > > it. Maybe you could contribute these findings then also to the TinyOS > > wiki? > > http://www.eecs.harvard.edu/~mdw/tinyosdocs/index.php/Main_Page<http://www.eecs.harvard.edu/%7Emdw/tinyosdocs/index.php/Main_Page> > > > > Cheers, > > Urs > > > > > > Tan Simin Jeremy schrieb: > > > Hello ppl, > > > > > > I'm currently working on the Honeywell HMC1002 Magnetometer which is > > located on > > > the MTS310CA sensor board. However I'm facing a few problems and hope > > that you > > > will be able to assist me. > > > > > > 1. Why is it that my readings for the x and y-axis are different when > > I use > > > different sensor boards (MTS310CA) on the mote? > > > > > > 2. My readings for the x-axis is changing but the readings for the > > y-axis does > > > not change in the room. WHy is this so? The y-axis only changes when I > > bring a > > > magnet near the magnetometer. > > > > > > 3. Will the magnetometer still give us a reading if we do not bring a > > magnet > > > near it? I'm sure there is still the earth's magnetic field present in > > the room. > > > > > > Thank you for your help. Have a blessed week ahead! > > > > > > Cheers, > > > Jeremy > > _______________________________________________ > > Tinyos-help mailing list > > [email protected] > > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help > > > > > > -- > Sougata Sen > Bangalore >
-- Sougata Sen Bangalore
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