Accelerometer

[john]

Hi,

I am planing to use an analog accelerometer ( ADXL330KCPZ) in a
project. And i have following questions

1. The accelerometer will place flat on the table. How can I get or
calculate the angle information from the three outputs of the
accelerometer? I will read the outputs via 12 bit analog to digital
converter. So, there will be three numbers of 12 bit data.

2. How can I calbriate the readings? For example, the accelerometer
is no longer on the flat table but installed on the wall, the
reference has changed.


Please advice!

Thanks
John

 

[Sjouke Burry]

john wrote:

Hi,

I am planing to use an analog accelerometer ( ADXL330KCPZ) in a
project. And i have following questions

1. The accelerometer will place flat on the table. How can I get or
calculate the angle information from the three outputs of the
accelerometer? I will read the outputs via 12 bit analog to digital
converter. So, there will be three numbers of 12 bit data.

2. How can I calbriate the readings? For example, the accelerometer
is no longer on the flat table but installed on the wall, the
reference has changed.


Please advice!

Thanks
John
You have to integrate 3 signals twice, and end up with a highly

unstable signal drifting all over the place.
Also you have to add 2 gyros, and integrate those once.
Airplanes use this, and those platforms cost ~ 100.000 dollars,
to get the needed accuracy/stability.

 

[Bob Masta]

On Thu, 11 Dec 2008 09:57:27 -0800 (PST), john
<conphiloso@hotmail.com> wrote:

Hi,

I am planing to use an analog accelerometer ( ADXL330KCPZ) in a
project. And i have following questions

1. The accelerometer will place flat on the table. How can I get or
calculate the angle information from the three outputs of the
accelerometer? I will read the outputs via 12 bit analog to digital
converter. So, there will be three numbers of 12 bit data.

2. How can I calbriate the readings? For example, the accelerometer
is no longer on the flat table but installed on the wall, the
reference has changed.

2) Assuming this accelerometer responds down to
DC, you can calibrate simply by turning it in 90
degree steps: When its axis is vertical you have
+1g, horzontal is 0g, inverted is -1g. Repeat for
all 3 accelerometer axes.

Best regards,


Bob Masta

DAQARTA v4.51
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[John O'Flaherty]

On Fri, 12 Dec 2008 13:39:46 GMT, N0Spam@daqarta.com (Bob Masta)
wrote:

On Thu, 11 Dec 2008 09:57:27 -0800 (PST), john
conphiloso@hotmail.com> wrote:

Hi,

I am planing to use an analog accelerometer ( ADXL330KCPZ) in a
project. And i have following questions

1. The accelerometer will place flat on the table. How can I get or
calculate the angle information from the three outputs of the
accelerometer? I will read the outputs via 12 bit analog to digital
converter. So, there will be three numbers of 12 bit data.

2. How can I calbriate the readings? For example, the accelerometer
is no longer on the flat table but installed on the wall, the
reference has changed.


2) Assuming this accelerometer responds down to
DC, you can calibrate simply by turning it in 90
degree steps: When its axis is vertical you have
+1g, horzontal is 0g, inverted is -1g. Repeat for
all 3 accelerometer axes.

Expanding for question 1.,
1) The sensed acceleration varies from 0g to 1g according to the angle
of the device's sensitive axis to the horizontal, from 0g when
parallel to 1g when perpendicular. The angle with the horizontal will
be the arcsin of the g value, or the arccos if referenced to a
vertical line.
--
John