hello everybody,
i have some questions about the accelerometer usage, i'm wondering if there is any specific hight for using it "i mean i'll be using it on an airplane to measure it's acceleration so is it going to work no matter the airplane hight off the ground was?
and what does 2g accelerometer means?
and my last question is :does the "g" unit have anything to do with the sensor being off the ground by a specific hight???
if anyone has an answer for any of my questions plz tell me, coz i need some help...
thanx in advanc.

 

Check this link. Good info

http://www2.usfirst.org/2005comp/Manuals/Acceler1.pdf

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Height doesn't matter. But using an accelerometer to measure the acceleration of a plane doesn't work too well most of the time because gravity is always superimposed into the acceleration of the airplane. So unless you know where the ground is at all times it's not going to work well. And if you are integrating to get velocity or distance it adds a very severe error onto an already horrible integration error. And the methods to keep track of where gravity is at all times are quite expensive and computationally intensive (3-axis gyroscopes which also suffer from the same integration error). GPS is far better in this case because an error of 10m doesn't usually mean much for a plane and since it's a plane there probably isn't going to be anything obstructing it's view of the sky.

2g means the accelerometer can measure a maximum acceleration of 2x earth's gravity (g). So a max acceleration of 2*9.81m/s^2 can be measured.

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The accelerometer will not be effected much by altitude, but it is severely effected by the flight dynamics of an airplane... As I said before in the other thread, you need to combine it with at least a gyro and filter (IE: Kalman filter) to have a usable system....
Will the thermopiles not work for what you want to do?

My system I am working on use:
GPS
Gyro's
Thermopiles
Sonar

and that is about the easiest DIY way available.

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Boomslang, seeing as how thermopile is a very generic term for a thermocouple array and about 90% of their uses have nothing whatsoever to do with measuring attitude or acceleration, can you tell us what device you're using? I've heard of Mems devices that use thermopiles to measure acceleration, is this what you're referring to?

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THermopiles are used to measure the blackbody temperature of the earth relative to the sky to figure out where the ground is.
http://www.uavs.net/horizon_sensing_autopilot.pdf

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hi,
thanx mike for the website u sent
thanx dk for ur wonderful explaination
thanx boomslang for ur advice
and thanx for all of ur replies.
but i have one more question which is for u boomslang, i want to ask u about the GPS and thermopile , is there any good websites that explain how do they work or connected??
i mean if u have some free time plz remember me and send them here..
wish u all the good luck

 

wow it'f a beautifull fill that u sent dk thanx for that

 

Yes, dknguyen that's what I am talking about... I did post some links in the previous thread to the ones I use.

HSM1968: I use the thermopiles to keep the plane level, and the gps for navigation.

Paparazzi make use of the thermopiles. They code in C and use AVR or some other processors which I don't know anything about... but all their work is open-source.
Paparazzi Site

To buy some of the hardware pre manufactured: Paparazzi Sales

Another site I frequent: DIYDrones

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hi boomslang i want ask u one question plz , where can i find the thermopile sensor??i mean in whitch device does it found?
sorry for my many questions.
and thanx in advance

 

I don't kno in which devices, but the cheapest I found was to buy the sensor from www.fmadirect.com. The complete sensor unit with op-amps built-in cost the same from them as buying 4 of these sensors loose.

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The individual sensors themselves (which I prefer to use) are the Melexis MLX90247 (regular thermopile with tiny voltage analog output) or the MLX90614 (which is I2C interface). I prefer the 90247 mainly because I like building things myself and I am not sure how well matched and accurate the regular analog 90614 thermopiles are (I can't figure this out from looking at the datasheet). The MLX90247 are serial and they come with a calibrated accuracy so I can ensure their readout is matched within a certain tolerance they but they cost money. You can get both from Digikey but they cost money. Thermopiles are not cheap.

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thank u boomslang and dk for ur answers,
but u see my real problem is not money really!! it's that things such as (accelerometer/gyroscope/thermopile) is not available here in my country!!!
that's why i asked for the possible devices that uses the thermopiles, cause i already sent for the accelerometer and gyro sensor from UAE but i didn't send for thermopile?
and now that i liked that sensor, i don't know any other company that can import them for me..
so if anyone have any information about the devices that have thermopile inside plz tell me???
i mean i think that mike once said something about devices he took thermopiles from! so if u can help me i'll be thankfull..
thanx in advance

 

Can't you order from an online shop?

On the Melexis site they say the sensors are used in cars... but you would need to buy t least 4 cars to get the sensors.

These devices might contain similar sensors.
http://www3.towerhobbies.com/cgi-bin...&I=LXEMG5&P=ML
http://www3.towerhobbies.com/cgi-bin...&I=LXLXW8&P=ML

You can also buy the sensors from Paparazzi

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hi,thanks for the hint.
boomslang u told me to buy the sensor online, and my question is : how are they going to send me my orders???
and are they going to send it through airlines??
and how am i going to receive the goods??
i know those r too many questions, so i want to tell u that it's ok if u don't want to answer coz u helped me alot already..
so if there's anyone who has time and can answer my above questions i'll be thankfull