Thanks a lot, your replay was very helpful.
Marina
Quoting mike healy <[email protected]>:
Hi Marina,
Curve fitting is used to do this conversation, employing a 4th order
polynomial. The polynomial coefficients used depends on the range resistor
selected on the gsr daughter card.
So with the polynomial being:
Resistance (in Ohms) = p1*x^4 + p2*x^3 + p3*x^2 + p4*x + p5
x corresponds to the raw adc value and the coefficients are as follows:
Internal Resistor: Polynomial coefficients
40k?: P1 = 6.5995e-09, P2 = -6.8950e-05, P3 = 0.2699, P4 = -476.9835, P5 =
340351.3341
270k?: P1 = 1.3569627e-08, P2 = -0.0001650399, P3 = 0.7541990, P4 =
-1572.6287856, P5 = 1367507.9270
1M?: P1 = 2.550036498e-08, P2 = -0.00033136, P3 = 1.6509426597, P4 =
-3833.348044, P5 = 3806317.6947
3.3M?: P1 = 3.7153627e-07, P2 = -0.004239437, P3 = 17.905709, P4 =
-33723.8657, P5 = 25368044.6279
And obviously the conductance (in Siemens) is the reciprocal of the
resistance.
Take a look at GspP.nc for an implementation of this, specifically the
Gsr.calcResistance() function:
http://code.google.com/p/tinyos-main/source/browse/trunk/tos/platforms/shimmer/chips/gsr/GsrP.nc
Mike
On Thu, Jun 30, 2011 at 7:06 PM,
<[email protected]>wrote:
Dear all,
I would appreciate a lot if someone could give me the conversion between
the output units of the GSR sensor module (Shimmer2r) and the standardized
microsiemens units for conductance.
Thanks in advance for your helpkind,
marina
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