Accelerometer Primer - Revision history

Patrick: /* Calculating tilt angle (roll and pitch) from acceleration */

2014-11-03T23:48:41Z

Calculating tilt angle (roll and pitch) from acceleration

← Older revision		Revision as of 23:48, 3 November 2014
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	==Calculating tilt angle (roll and pitch) from acceleration==		==Calculating tilt angle (roll and pitch) from acceleration==
	One thing people commonly want to determine with an accelerometer is the physical orientation of the object the device is mounted on. This can be done by calculating the tilt angle of the accelerometer board. This is possible due to gravity providing a constant acceleration which can be checked against, meaning we can break the total acceleration down into components and then perform a bit of math to obtain a tilt angle. Tilt angle can only be measured when the accelerometer is stationary. When in motion, the acceleration experienced by the accelerometer is a combination of the device’s physical orientation, and the device’s movement, and the tilt can therefore not be determined. The tilt is calculated as follows-		One thing people commonly want to determine with an accelerometer is the physical orientation of the object the device is mounted on. This can be done by calculating the tilt angle of the accelerometer board. This is possible due to gravity providing a constant acceleration which can be checked against, meaning we can break the total acceleration down into components and then perform a bit of math to obtain a tilt angle. Tilt angle can only be measured when the accelerometer is stationary. When in motion, the acceleration experienced by the accelerometer is a combination of the device’s physical orientation, and the device’s movement, and the tilt can therefore not be determined. The tilt is calculated as follows-

	~~:<math>T = arcsin(g_x)</math>~~

	:<math>Tilt = (arcsin(g_x))^\circ a_x + (arcsin(g_y))^\circ a_y</math>		:<math>Tilt = (arcsin(g_x))^\circ a_x + (arcsin(g_y))^\circ a_y</math>

Patrick: /* Calculating tilt angle (roll and pitch) from acceleration */

2014-11-03T23:31:36Z

Calculating tilt angle (roll and pitch) from acceleration

← Older revision		Revision as of 23:31, 3 November 2014
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	==Calculating tilt angle (roll and pitch) from acceleration==		==Calculating tilt angle (roll and pitch) from acceleration==
	One thing people commonly want to determine with an accelerometer is the physical orientation of the object the device is mounted on. This can be done by calculating the tilt angle of the accelerometer board. This is possible due to gravity providing a constant acceleration which can be checked against, meaning we can break the total acceleration down into components and then perform a bit of math to obtain a tilt angle. Tilt angle can only be measured when the accelerometer is stationary. When in motion, the acceleration experienced by the accelerometer is a combination of the device’s physical orientation, and the device’s movement, and the tilt can therefore not be determined. The tilt is calculated as follows-		One thing people commonly want to determine with an accelerometer is the physical orientation of the object the device is mounted on. This can be done by calculating the tilt angle of the accelerometer board. This is possible due to gravity providing a constant acceleration which can be checked against, meaning we can break the total acceleration down into components and then perform a bit of math to obtain a tilt angle. Tilt angle can only be measured when the accelerometer is stationary. When in motion, the acceleration experienced by the accelerometer is a combination of the device’s physical orientation, and the device’s movement, and the tilt can therefore not be determined. The tilt is calculated as follows-

			:<math>T = arcsin(g_x)</math>

	:<math>Tilt = (arcsin(g_x))^\circ a_x + (arcsin(g_y))^\circ a_y</math>		:<math>Tilt = (arcsin(g_x))^\circ a_x + (arcsin(g_y))^\circ a_y</math>

Mparadis: /* Gravity vs. Acceleration */

2012-08-21T15:43:08Z

Gravity vs. Acceleration

← Older revision		Revision as of 15:43, 21 August 2012
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	An accelerometer at rest relative to the Earth's surface will indicate approximately 1 g upwards (Because in order to remain at rest, it is experiencing a force opposite to the earth's gravity- this is called the normal force). To obtain the acceleration due to motion with respect to the Earth, this "gravity offset" must be subtracted. The effects of this acceleration are indistinguishable from any other acceleration experienced by the instrument, so an accelerometer cannot detect the difference between sitting in a rocket on the launch pad, and being in the same rocket in deep space while it uses its engines to accelerate at 1 g. For similar reasons, an accelerometer will read zero during any type of free fall in a vacuum. When free falling through air, the air resistance produces drag forces that reduce the acceleration, until constant terminal velocity is reached. At terminal velocity the accelerometer will indicate 1 g acceleration upwards. For the same reason a skydiver, upon reaching terminal velocity, does not feel as though he or she were in "free-fall", but rather experiences a feeling similar to being supported (at 1 g) on a "bed" of uprushing air.		An accelerometer at rest relative to the Earth's surface will indicate approximately 1 g upwards (Because in order to remain at rest, it is experiencing a force opposite to the earth's gravity- this is called the normal force). To obtain the acceleration due to motion with respect to the Earth, this "gravity offset" must be subtracted. The effects of this acceleration are indistinguishable from any other acceleration experienced by the instrument, so an accelerometer cannot detect the difference between sitting in a rocket on the launch pad, and being in the same rocket in deep space while it uses its engines to accelerate at 1 g. For similar reasons, an accelerometer will read zero during any type of free fall in a vacuum. When free falling through air, the air resistance produces drag forces that reduce the acceleration, until constant terminal velocity is reached. At terminal velocity the accelerometer will indicate 1 g acceleration upwards. For the same reason a skydiver, upon reaching terminal velocity, does not feel as though he or she were in "free-fall", but rather experiences a feeling similar to being supported (at 1 g) on a "bed" of uprushing air.

	In order to correct for gravity you will need to [[Accelerometer Primer#Calculating tilt angle from acceleration\|determine the tilt angle]] and subtract 1g in that axis. This means that if you want to measure dynamic acceleration, you can only be sure that you'll be able to measure 1g less than your accelerometer's rated range, since gravity can contribute up to 1g to the measurement and cause the accelerometer to reach its saturation value at a lower acceleration. When the accelerometer saturates, an error will be generated in your program telling you that the value is out of range. For some applications this isn't a big deal, for instance in a remotely controlled vehicle whose accelerometer saturates at a value that can only be reached when the vehicle crashes.		In order to correct for gravity you will need to [[Accelerometer Primer#Calculating tilt angle (roll and pitch) from acceleration\|determine the tilt angle]] and subtract 1g in that axis. This means that if you want to measure dynamic acceleration, you can only be sure that you'll be able to measure 1g less than your accelerometer's rated range, since gravity can contribute up to 1g to the measurement and cause the accelerometer to reach its saturation value at a lower acceleration. When the accelerometer saturates, an error will be generated in your program telling you that the value is out of range. For some applications this isn't a big deal, for instance in a remotely controlled vehicle whose accelerometer saturates at a value that can only be reached when the vehicle crashes.

	==Orientation==		==Orientation==

Burley: /* Products that fall under this category */

2012-08-10T16:40:00Z

Products that fall under this category

← Older revision		Revision as of 16:40, 10 August 2012
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	If you're using the accelerometer as part of a navigation system, you may benefit from adding a gyroscope and compass to aid in calculations. You can keep things simple by getting all three components on one board, such as the [http://www.phidgets.com/products.php?product_id=1056 1056 - PhidgetSpatial 3/3/3].		If you're using the accelerometer as part of a navigation system, you may benefit from adding a gyroscope and compass to aid in calculations. You can keep things simple by getting all three components on one board, such as the [http://www.phidgets.com/products.php?product_id=1056 1056 - PhidgetSpatial 3/3/3].

	~~==Products that fall under this category==~~
	*[http://www.phidgets.com/products.php?product_id=1049 1049 - PhidgetSpatial 0/0/3]
	*[http://www.phidgets.com/products.php?product_id=1056 1056 - PhidgetSpatial 3/3/3]

Mparadis: /* Products that fall under this category */

2012-08-01T21:26:02Z

Products that fall under this category

← Older revision		Revision as of 21:26, 1 August 2012
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	==Products that fall under this category==		==Products that fall under this category==
	*[[1049 - PhidgetSpatial 0/0/3]]		*[http://www.phidgets.com/products.php?product_id=1049 1049 - PhidgetSpatial 0/0/3]
	*[[1056 - PhidgetSpatial 3/3/3]]		*[http://www.phidgets.com/products.php?product_id=1056 1056 - PhidgetSpatial 3/3/3]

Mparadis: /* Orientation */

2012-08-01T15:11:44Z

Orientation

← Older revision		Revision as of 15:11, 1 August 2012
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	==Orientation==		==Orientation==
	[[File:1041 0 Axis Diagram.jpg\|400px\|thumb\|Positive and negative directions on all axes for the [http://www.phidgets.com/products.php?product_id=1043 1043 - PhidgetSpatial 0/0/3].<br />[[Media:1041 0 Axis Diagram.jpg\|Full-size Image]]]]		[[File:1041 0 Axis Diagram.jpg\|400px\|link=\|thumb\|Positive and negative directions on all axes for the [http://www.phidgets.com/products.php?product_id=1043 1043 - PhidgetSpatial 0/0/3].<br />[[Media:1041 0 Axis Diagram.jpg\|Full-size Image]]]]

	When working with an accelerometer it is important to know which is the +/- direction on each of the axes. This can be determined by orienting the accelerometer along each axis and checking the output. For example, in the image on the right we can see the orientation for the [http://www.phidgets.com/products.php?product_id=1043 1043 - PhidgetSpatial 0/0/3] accelerometer. Since the measurement limit is given on a per-axis basis, you could theoretically measure more than the maximum acceleration per axis if the accelerometer was tilted and held in place so that the acceleration being measured is aligned half way between two axes.		When working with an accelerometer it is important to know which is the +/- direction on each of the axes. This can be determined by orienting the accelerometer along each axis and checking the output. For example, in the image on the right we can see the orientation for the [http://www.phidgets.com/products.php?product_id=1043 1043 - PhidgetSpatial 0/0/3] accelerometer. Since the measurement limit is given on a per-axis basis, you could theoretically measure more than the maximum acceleration per axis if the accelerometer was tilted and held in place so that the acceleration being measured is aligned half way between two axes.

Mparadis: /* Choosing an Accelerometer */

2012-08-01T14:58:18Z

Choosing an Accelerometer

← Older revision		Revision as of 14:58, 1 August 2012
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	If you're using the accelerometer to measure high-frequency vibrations, you want to pay attention to the bandwidth of your device. Accelerometers will measure up to a particular frequency of acceleration (easiest to understand as a vibration). Bandwidth specifies the maximum frequency at which the accelerometer will only 'see' 50% of the acceleration. To achieve a particular bandwidth in your application - say you want to measure a vibration or motion with acceleration up to 100Hz, your accelerometer should be rated for at least 150Hz bandwidth (>50% higher), and have a sampling rate of at least 400 samples per second (4x higher).		If you're using the accelerometer to measure high-frequency vibrations, you want to pay attention to the bandwidth of your device. Accelerometers will measure up to a particular frequency of acceleration (easiest to understand as a vibration). Bandwidth specifies the maximum frequency at which the accelerometer will only 'see' 50% of the acceleration. To achieve a particular bandwidth in your application - say you want to measure a vibration or motion with acceleration up to 100Hz, your accelerometer should be rated for at least 150Hz bandwidth (>50% higher), and have a sampling rate of at least 400 samples per second (4x higher).

	If you're using the accelerometer as part of a navigation system, you may benefit from adding a gyroscope and compass to aid in calculations. You can keep things simple by getting all three components on one board, such as the [[PhidgetSpatial 3/3/3]].		If you're using the accelerometer as part of a navigation system, you may benefit from adding a gyroscope and compass to aid in calculations. You can keep things simple by getting all three components on one board, such as the [http://www.phidgets.com/products.php?product_id=1056 1056 - PhidgetSpatial 3/3/3].

	==Products that fall under this category==		==Products that fall under this category==
	*[[1049 - PhidgetSpatial 0/0/3]]		*[[1049 - PhidgetSpatial 0/0/3]]
	*[[1056 - PhidgetSpatial 3/3/3]]		*[[1056 - PhidgetSpatial 3/3/3]]

Mparadis: /* Orientation */

2012-08-01T14:57:21Z

Orientation

← Older revision		Revision as of 14:57, 1 August 2012
Line 37:		Line 37:

	When working with an accelerometer it is important to know which is the +/- direction on each of the axes. This can be determined by orienting the accelerometer along each axis and checking the output. For example, in the image on the right we can see the orientation for the [http://www.phidgets.com/products.php?product_id=1043 1043 - PhidgetSpatial 0/0/3] accelerometer. Since the measurement limit is given on a per-axis basis, you could theoretically measure more than the maximum acceleration per axis if the accelerometer was tilted and held in place so that the acceleration being measured is aligned half way between two axes.		When working with an accelerometer it is important to know which is the +/- direction on each of the axes. This can be determined by orienting the accelerometer along each axis and checking the output. For example, in the image on the right we can see the orientation for the [http://www.phidgets.com/products.php?product_id=1043 1043 - PhidgetSpatial 0/0/3] accelerometer. Since the measurement limit is given on a per-axis basis, you could theoretically measure more than the maximum acceleration per axis if the accelerometer was tilted and held in place so that the acceleration being measured is aligned half way between two axes.

			<br clear = all>

	==Noise==		==Noise==

Mparadis: /* Orientation */

2012-08-01T14:55:25Z

Orientation

← Older revision		Revision as of 14:55, 1 August 2012
Line 34:		Line 34:

	==Orientation==		==Orientation==
	[[~~image~~:~~orientationz~~.jpg\|400px\|thumb\|Positive and negative directions on all axes for the [[1043 - PhidgetSpatial 0/0/3\|~~1049~~]].]]		[[File:1041 0 Axis Diagram.jpg\|400px\|thumb\|Positive and negative directions on all axes for the [http://www.phidgets.com/products.php?product_id=1043 1043 - PhidgetSpatial 0/0/3].<br />[[Media:1041 0 Axis Diagram.jpg\|Full-size Image]]]]

	When working with an accelerometer it is important to know which is the +/- direction on each of the axes. This can be determined by orienting the accelerometer along each axis and checking the output. For example, in the image on the right we can see the orientation for the [[1043 - PhidgetSpatial 0/0/3]] accelerometer. Since the measurement limit is given on a per-axis basis, you could theoretically measure more than the maximum acceleration per axis if the accelerometer was tilted and held in place so that the acceleration being measured is aligned half way between two axes.		When working with an accelerometer it is important to know which is the +/- direction on each of the axes. This can be determined by orienting the accelerometer along each axis and checking the output. For example, in the image on the right we can see the orientation for the [http://www.phidgets.com/products.php?product_id=1043 1043 - PhidgetSpatial 0/0/3] accelerometer. Since the measurement limit is given on a per-axis basis, you could theoretically measure more than the maximum acceleration per axis if the accelerometer was tilted and held in place so that the acceleration being measured is aligned half way between two axes.

	==Noise==		==Noise==

Mparadis at 14:50, 1 August 2012

2012-08-01T14:50:35Z

← Older revision		Revision as of 14:50, 1 August 2012
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	\|- valign=middle		\|- valign=middle
	\| align=center width=300px\| __TOC__		\| align=center width=300px\| __TOC__
	\| [[Image:1056.jpg\|400px]]		\| [[Image:1056.jpg\|link=\|400px]]
	\|}		\|}