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Meisei: Add comments to T calculation

pull/45/head
Rolf Meeser 2022-06-30 19:59:01 +02:00
rodzic 16193a3200
commit 40675e4322
1 zmienionych plików z 18 dodań i 7 usunięć
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25
demod/mod/meisei100mod.c
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@ -913,16 +913,27 @@ int main(int argc, char **argv) {
ui16_t t_raw = bits2val(subframe_bits+HEADLEN+2*46+17, 16);
float f = ((float)t_raw / (float)gpx.f_ref) * 4.0f;
if (f > 1.0f) {
// Use config coefficients to transform measured frequency to absolute resistance (kOhms)
f = 1.0f / (f - 1.0f);
f = gpx.cfg[53] + gpx.cfg[54]*f + gpx.cfg[55]*f*f + gpx.cfg[56]*f*f*f;
if (f <= gpx.cfg[33]) {
gpx.T = gpx.cfg[17];
} else if (f >= gpx.cfg[44]) {
gpx.T = gpx.cfg[28];
float R = gpx.cfg[53] + gpx.cfg[54]*f + gpx.cfg[55]*f*f + gpx.cfg[56]*f*f*f;
// iMS-100 sends known resistance (cfg[44:33]) for 12 temperature sampling points
// (cfg[28:17]). Actual temperature is found by interpolating in one of these
// 11 intervals.
if (R <= gpx.cfg[33]) { // R below min value?
gpx.T = gpx.cfg[17]; // --> Set T = highest temperature
} else if (R >= gpx.cfg[44]) { // R above max value?
gpx.T = gpx.cfg[28]; // --> Set T = lowest temperature
} else {
// We now know that R is inside the interpolation range. Sampling points are
// ordered by increasing resistance (decreasing temperature).
// Search for the interval that contains R, then interpolate linearly
// (using log(R)).
// NOTE: This assumes that the sonde sends the sampling points as described
// above. Shall we do a sanity check to confirm?
// For the time being, T=NAN in case the search doesn't find an interval.
for (j = 0; j < 11; j++) {
if (f < gpx.cfg[34+j]) {
f = (logf(f) - logf(gpx.cfg[33+j])) / (logf(gpx.cfg[34+j]) - logf(gpx.cfg[33+j]));
if (R < gpx.cfg[34+j]) {
f = (logf(R) - logf(gpx.cfg[33+j])) / (logf(gpx.cfg[34+j]) - logf(gpx.cfg[33+j]));
gpx.T = gpx.cfg[17+j] - f*(gpx.cfg[17+j] - gpx.cfg[18+j]);
break;
}