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Re: [Paparazzi-devel] airspeed_ets calibration

From: Prof. Dr.-Ing. Heinrich Warmers
Subject: Re: [Paparazzi-devel] airspeed_ets calibration
Date: Tue, 27 Aug 2013 09:34:37 +0200
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; de-DE; rv:1.4) Gecko/20030619 Netscape/7.1 (ax)

can you fly with a special flight  plane at different speed  over ground  with wind  and again the wind  and the calculate the TAS with the true speed over ground from the GPS?
Martin was calculating the wind speed by flying circles with constant throttle and pitch.
I found a temperature dependence for the accelerometer of the MPU60x0 and the bmp085 to.
The MPU60x0 has a temperature sensor on the chip as the bmp085. The BMP085 is heating up for 3-5°C over the air temperature.
I found that the temperature from the autopilot pcb was vary strong  (about 20°C).
There are other pressure difference sensors   working inside by difference temperature flow. This sensors have no temperature  drift but are expensive about 80 Euros.
The interface is i2c.


alonso acuña schrieb:

Hi. I have one of these sensors but my plane is not flying yet so I can't test at this time. I think you should try to discuss this with the manufacturer as it seems that if you had to calibrate for temperature they should have included a thermometer directly in the sensor. Otherwise it would be useless as sold. Perhaps there is another explanation.

On Aug 26, 2013 6:48 AM, "Refik Sever" <address@hidden> wrote:

I tried to disable the airspeed_ets offset calculation in initialization. However, it did not work because I think that sensor offset strictly depends on temperature. When I first power on, sensor gives values around 1500. It worked for 15-20, and it came to its actual offset value of 1550. It was in room so the temperature was constant. I think that the sensor's own temperature has increased because of working.

Considering the temperature variation during long flights, I think that we must calibrate the sensor for temperature variation.

Best regards,

>In the airspeed_ets.c file, I saw that the offset value ("airspeed_ets_offset", not "AIRSPEED_ETS_OFFSET") is >calculated for once when we power on the autopilot. Therefore, the offset changes in every time we open it >in different wind conditions. That explains why we couldn't calibrate it.

>I think that calculating and fixing the airspeed_ets_offset for once will be better then to change it in every >power on.

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