Included raw differential pressure field

This commit is contained in:
Andrew Tridgell 2014-02-13 14:25:52 +11:00 committed by Lorenz Meier
parent 9719af623d
commit cdec5e1d05
2 changed files with 43 additions and 15 deletions

View File

@ -206,20 +206,46 @@ MEASAirspeed::collect()
dT_raw = (0xFFE0 & dT_raw) >> 5;
float temperature = ((200.0f * dT_raw) / 2047) - 50;
/* calculate differential pressure. As its centered around 8000
* and can go positive or negative, enforce absolute value
*/
// Calculate differential pressure. As its centered around 8000
// and can go positive or negative
const float P_min = -1.0f;
const float P_max = 1.0f;
float diff_press_pa = fabsf((((float)dp_raw - 0.1f * 16383.0f) * (P_max - P_min) / (0.8f * 16383.0f) + P_min) * 6894.8f) - _diff_pres_offset;
const float PSI_to_Pa = 6894.757f;
/*
this equation is an inversion of the equation in the
pressure transfer function figure on page 4 of the datasheet
if (diff_press_pa < 0.0f) {
diff_press_pa = 0.0f;
}
We negate the result so that positive differential pressures
are generated when the bottom port is used as the static
port on the pitot and top port is used as the dynamic port
*/
float diff_press_PSI = -((dp_raw - 0.1f*16383) * (P_max-P_min)/(0.8f*16383) + P_min);
float diff_press_pa_raw = diff_press_PSI * PSI_to_Pa;
// correct for 5V rail voltage if possible
voltage_correction(diff_press_pa, temperature);
voltage_correction(diff_press_pa_raw, temperature);
float diff_press_pa = fabsf(diff_press_pa_raw - _diff_pres_offset);
/*
note that we return both the absolute value with offset
applied and a raw value without the offset applied. This
makes it possible for higher level code to detect if the
user has the tubes connected backwards, and also makes it
possible to correctly use offsets calculated by a higher
level airspeed driver.
With the above calculation the MS4525 sensor will produce a
positive number when the top port is used as a dynamic port
and bottom port is used as the static port
Also note that the _diff_pres_offset is applied before the
fabsf() not afterwards. It needs to be done this way to
prevent a bias at low speeds, but this also means that when
setting a offset you must set it based on the raw value, not
the offset value
*/
struct differential_pressure_s report;
/* track maximum differential pressure measured (so we can work out top speed). */
@ -232,6 +258,7 @@ MEASAirspeed::collect()
report.temperature = temperature;
report.differential_pressure_pa = diff_press_pa;
report.differential_pressure_filtered_pa = _filter.apply(diff_press_pa);
report.differential_pressure_raw_pa = diff_press_pa_raw;
report.voltage = 0;
report.max_differential_pressure_pa = _max_differential_pressure_pa;
@ -328,7 +355,7 @@ MEASAirspeed::voltage_correction(float &diff_press_pa, float &temperature)
return;
}
const float slope = 70.0f;
const float slope = 65.0f;
/*
apply a piecewise linear correction, flattening at 0.5V from 5V
*/
@ -478,7 +505,7 @@ test()
}
warnx("single read");
warnx("diff pressure: %8.4f pa", (double)report.differential_pressure_pa);
warnx("diff pressure: %d pa", (int)report.differential_pressure_pa);
/* start the sensor polling at 2Hz */
if (OK != ioctl(fd, SENSORIOCSPOLLRATE, 2)) {
@ -506,7 +533,7 @@ test()
}
warnx("periodic read %u", i);
warnx("diff pressure: %8.4f pa", (double)report.differential_pressure_pa);
warnx("diff pressure: %d pa", (int)report.differential_pressure_pa);
warnx("temperature: %d C (0x%02x)", (int)report.temperature, (unsigned) report.temperature);
}

View File

@ -52,13 +52,14 @@
* Differential pressure.
*/
struct differential_pressure_s {
uint64_t timestamp; /**< microseconds since system boot, needed to integrate */
uint64_t error_count;
uint64_t timestamp; /**< Microseconds since system boot, needed to integrate */
uint64_t error_count; /**< Number of errors detected by driver */
float differential_pressure_pa; /**< Differential pressure reading */
float differential_pressure_raw_pa; /**< Raw differential pressure reading (may be negative) */
float differential_pressure_filtered_pa; /**< Low pass filtered differential pressure reading */
float max_differential_pressure_pa; /**< Maximum differential pressure reading */
float voltage; /**< Voltage from analog airspeed sensors (voltage divider already compensated) */
float temperature; /**< Temperature provided by sensor, -1000.0f if unknown */
float voltage; /**< Voltage from analog airspeed sensors (voltage divider already compensated) */
float temperature; /**< Temperature provided by sensor, -1000.0f if unknown */
};