Max Lynn wrote:
| As an exercise, consider how you would perform your suggested computation
in
| an orbiting spacecraft(i.e., zero g).

Do you understand the concept of how the ADXL202 works? They are designed to
work in a one g environment. The gravitational force is exerted on a solid
state (silicon) beam and the beam deflection produces the output which is a
function of the sensed gravitational field which is essentially 1g when the
beam is perpindicular to the gravity field and 0g when the beam is parallel
to the field. Read the data sheets and the application notes that you can
easily find at the AMD site ( http://www.amd.com/us-en/ ). I urge you to do
so.

Very few boats will ever find temselves in a zero g environment. My comments
are directed to a query about a pitch/roll sensor for a sailboat. Just
trying to stay on topic.

HTH

Vic

--
__________________________________________________ ______

Victor Fraenckel - The Windman
vfraenc1 ATSIGN nycap DOT rr DOTcom
KC2GUI

Home of the WindReader Electronic Theodolite
Read the WIND

"Victory at all costs, victory in spite of all terror, victory however long
and hard the road may be; for without victory there is no survival."
- Winston [Leonard Spencer] Churchill (1874 - 1965)

Dost thou not know, my son, with how little wisdom the world is governed?
-Count Oxenstierna (ca 1620) to the young King Gustavus Adolphus

Vic:
I was also trying to stay on topic. And I completely understand the
function of the accelerometer which you reference, as well as a number of
other similar instruments. I would similarly invite you to reconsider my
question regarding a zero-g environment for such an instrument. You state
that the accelerometer is built to function in a one-g environment. I
submit to you that the instrument is built to function in a +/- 2 g
environment. If you place this instrument's two sensitive axes in a local
horizzontal plane in your laboratory, neither axis will see a gravitational
input, and therefore will provide no output. Now, rotate the instriment
about one axis. The opposite axis will begin to sense a component of
gravity as a function of the angle which you have rotated about the other
axis. Vic will say AHA, I have sensed a rotation. But now, let me simply
slide the accelerometer across the table, moving along that same axis which
just provided the output previously, but not rotating the instrument about
either axis. As you can see, the indication from the instrument is the same
in either case. In both cases, all you have "sensed" is linear
acceleration, in one case, the amount proportional to the component of
gravity, and in the other case, the amount proportional to the force exerted
on the case to provide the linear motion.

Picture the accelerometer on a boat in turbulent conditions with the input
axes similarly aligned(both horizontal), and consider how you would remove
the component of acceleration due to a wave passing under a boat and lifting
the boat several feet and then allowing it to sink several feet,
simultaneously causing both roll and pitch motion. Consider, please, that
the wave may cause vertical and horizontal displacement of the boat, as well
as rotational motion about the pitch and roll axes. Then please explain to
me how you plan to discriminate on an instantaneous basis between the two
totally independent types of motion using only the two outputs from your
accelerometer. I really wish you would stop and consider my original post
where I pointed out that an accelerometer, and particularly the Analog
Devices ADXL 202(not made by AMD as your URL directed us) is an instrument
built to sense LINEAR acceleration along an axis, NOT ROTATION about an
axis. Gyros are used to sense rotational motion, not accelerometers.
Pendulums(sometimes also called inclinometers) are also used for limited
rotational sensors, provided the motion is not too large and/or the
frequency of the rotational motion is not too high. I did not mean to get
so wrapped up, so please excuse my fervor.(rant??)

"Vic Fraenckel" wrote in message
...
Max Lynn wrote:
| As an exercise, consider how you would perform your suggested
computation
in
| an orbiting spacecraft(i.e., zero g).

Do you understand the concept of how the ADXL202 works? They are designed
to
work in a one g environment. The gravitational force is exerted on a solid
state (silicon) beam and the beam deflection produces the output which is
a
function of the sensed gravitational field which is essentially 1g when
the
beam is perpindicular to the gravity field and 0g when the beam is
parallel
to the field. Read the data sheets and the application notes that you can
easily find at the AMD site ( http://www.amd.com/us-en/ ). I urge you to
do
so.

Very few boats will ever find temselves in a zero g environment. My
comments
are directed to a query about a pitch/roll sensor for a sailboat. Just
trying to stay on topic.

HTH

Vic

--
__________________________________________________ ______

Victor Fraenckel - The Windman
vfraenc1 ATSIGN nycap DOT rr DOTcom
KC2GUI

Home of the WindReader Electronic Theodolite
Read the WIND

"Victory at all costs, victory in spite of all terror, victory however
long
and hard the road may be; for without victory there is no survival."
- Winston [Leonard Spencer] Churchill (1874 - 1965)

Dost thou not know, my son, with how little wisdom the world is governed?
-Count Oxenstierna (ca 1620) to the young King Gustavus Adolphus

"maxlynn" wrote in message
news:9tXKb.103004$pY.50340@fed1read04...
What you say is true in a fixed one-g environment. You can derive a crude
measurement of angular rotation in any fixed, uni-directional acceleration
environment in the manner that you suggest. But as I understand the
proposed application, the accelerometer(s)/instruments are to be mounted
in
a dynamic environment. The accelerometers mentioned are designed to
measure
linear acceleration. That is what the manufacturer designed them to do.
They are NOT designed to measure rotation or rotational rates. That is
generally a domain reserved for gyroscopes and related insruments or
systems.

Well, read the datasheets. AD says specifically in their datasheets that the
ADXL's can be used as an inclinometer. Apart from that, a boat seems an
'almost fixed' one-g environmet to me.

Meindert

"maxlynn" wrote in message
news:j90Lb.103199$pY.54961@fed1read04...
Vic:
I was also trying to stay on topic. And I completely understand the
function of the accelerometer which you reference, as well as a number of
other similar instruments. I would similarly invite you to reconsider my
question regarding a zero-g environment for such an instrument. You state
that the accelerometer is built to function in a one-g environment. I
submit to you that the instrument is built to function in a +/- 2 g
environment. If you place this instrument's two sensitive axes in a local
horizzontal plane in your laboratory, neither axis will see a
gravitational
input, and therefore will provide no output. Now, rotate the instriment
about one axis. The opposite axis will begin to sense a component of
gravity as a function of the angle which you have rotated about the other
axis. Vic will say AHA, I have sensed a rotation. But now, let me simply
slide the accelerometer across the table, moving along that same axis
which
just provided the output previously, but not rotating the instrument about
either axis. As you can see, the indication from the instrument is the
same
in either case. In both cases, all you have "sensed" is linear
acceleration, in one case, the amount proportional to the component of
gravity, and in the other case, the amount proportional to the force
exerted
on the case to provide the linear motion.

Picture the accelerometer on a boat in turbulent conditions with the input
axes similarly aligned(both horizontal), and consider how you would remove
the component of acceleration due to a wave passing under a boat and
lifting
the boat several feet and then allowing it to sink several feet,
simultaneously causing both roll and pitch motion. Consider, please, that
the wave may cause vertical and horizontal displacement of the boat, as
well
as rotational motion about the pitch and roll axes. Then please explain
to
me how you plan to discriminate on an instantaneous basis between the two
totally independent types of motion using only the two outputs from your
accelerometer. I really wish you would stop and consider my original post
where I pointed out that an accelerometer, and particularly the Analog
Devices ADXL 202(not made by AMD as your URL directed us) is an instrument
built to sense LINEAR acceleration along an axis, NOT ROTATION about an
axis. Gyros are used to sense rotational motion, not accelerometers.
Pendulums(sometimes also called inclinometers) are also used for limited
rotational sensors, provided the motion is not too large and/or the
frequency of the rotational motion is not too high. I did not mean to get
so wrapped up, so please excuse my fervor.(rant??)

"Vic Fraenckel" wrote in message
...
Max Lynn wrote:
| As an exercise, consider how you would perform your suggested
computation
in
| an orbiting spacecraft(i.e., zero g).

Do you understand the concept of how the ADXL202 works? They are
designed
to
work in a one g environment. The gravitational force is exerted on a
solid
state (silicon) beam and the beam deflection produces the output which
is
a
function of the sensed gravitational field which is essentially 1g when
the
beam is perpindicular to the gravity field and 0g when the beam is
parallel
to the field. Read the data sheets and the application notes that you
can
easily find at the AMD site ( http://www.amd.com/us-en/ ). I urge you to
do
so.

Very few boats will ever find temselves in a zero g environment. My
comments
are directed to a query about a pitch/roll sensor for a sailboat. Just
trying to stay on topic.

HTH

Vic


Excellent explanation of the problem, and thats why we used two dirty great
big Datawell Hippi's filled with glycerin or some such thick fluid.

garry

I've read a lot of data sheets, Meindert, and so have you, I'm sure. Under
the right conditions, and applying a lot of knowledge of its limitations,
the device could be used as an inclinometer. But that's another topic. If
you constrain the boat to always be anchored, we get closer to an
application in which it could be used as an inclinometer, but again, that
seems to me to be another topic. I have, in fact, used similar(single axis)
accelerometers, but usually as vibration pickups. That particular
instrument is not a high-grade device, in spite of what you think you might
read from the data sheet. This class of device typically has a bias output
which, while capable of being calibrated, is often unstable and/or
temperature dependent, and/or g-sensitive. So when you say it is usable in
an application, you always must specify to what level of accuracy, etc.
And to use it as a generalized rotational sensor is a total misapplication.

And we weren't discussing horeshoes, so I do not consider "almost 1 g" to be
close enough.

Max Lynn

"Meindert Sprang" wrote in message
...
"maxlynn" wrote in message
news:9tXKb.103004$pY.50340@fed1read04...
What you say is true in a fixed one-g environment. You can derive a
crude
measurement of angular rotation in any fixed, uni-directional
acceleration
environment in the manner that you suggest. But as I understand the
proposed application, the accelerometer(s)/instruments are to be mounted
in
a dynamic environment. The accelerometers mentioned are designed to
measure
linear acceleration. That is what the manufacturer designed them to do.
They are NOT designed to measure rotation or rotational rates. That is
generally a domain reserved for gyroscopes and related insruments or
systems.

Well, read the datasheets. AD says specifically in their datasheets that
the
ADXL's can be used as an inclinometer. Apart from that, a boat seems an
'almost fixed' one-g environmet to me.

Meindert

On Wed, 07 Jan 2004 18:32:24 GMT, Rick wrote:

Try this for a start. There are several manufacturers of electrolytic
sensors and I am sure you can get what you need in just about any output
configuration.

http://www.microstrain.com/FAS-E.htm

The FAS-E looks slightly interesting, though they have a FAS-G which looks a
lot better. In fact the PDF manual for the FAS-G has some useful information
which might help in the lively debate going on regarding suitability of
accelerometers for this task! :-)

"What makes FAS-G unique is not only its ability to measure static angles,
but also dynamic, fast angular movements. Through the use of the two
accelerometers and one piezo-ceramic gyro coupled with the requisite digital
filtering and embedded software tracking algorithms, FAS-G provides dynamic
response while maintaining the DC (static) measurement accuracy. As a result,
during rapid angular movements, both static and the dynamic components of
movement can be measured. This is not possible with conventional
inclinometers based on fluidic electrolytes or DC response accelerometers."

Ooh - just spotted the 3DM-G on the same site - seems to be exactly what I
need, for about US$1500. This looks good. 3 weeks lead time is about the only
worry.

Thanks,

Dave

You are on to a possibility. You should know that there is a lot more than
meets the eye in what you are buying. These devices require high
computational capabilities. Hopefully there are canned algorithms available
to provide the outputs that you require. But they have the potential to
provide proper pitch and roll outputs AND simultaneous acceleration outputs
Max Lynn

"Dave Baker" wrote in message
...
On Wed, 07 Jan 2004 18:32:24 GMT, Rick wrote:

Try this for a start. There are several manufacturers of electrolytic
sensors and I am sure you can get what you need in just about any output
configuration.

http://www.microstrain.com/FAS-E.htm

The FAS-E looks slightly interesting, though they have a FAS-G which looks
a
lot better. In fact the PDF manual for the FAS-G has some useful
information
which might help in the lively debate going on regarding suitability of
accelerometers for this task! :-)

"What makes FAS-G unique is not only its ability to measure static angles,
but also dynamic, fast angular movements. Through the use of the two
accelerometers and one piezo-ceramic gyro coupled with the requisite
digital
filtering and embedded software tracking algorithms, FAS-G provides
dynamic
response while maintaining the DC (static) measurement accuracy. As a
result,
during rapid angular movements, both static and the dynamic components of
movement can be measured. This is not possible with conventional
inclinometers based on fluidic electrolytes or DC response
accelerometers."

Ooh - just spotted the 3DM-G on the same site - seems to be exactly what I
need, for about US$1500. This looks good. 3 weeks lead time is about the
only
worry.

Thanks,

Dave

On Wed, 7 Jan 2004 21:02:09 -0800, "maxlynn" wrote:

You are on to a possibility. You should know that there is a lot more than
meets the eye in what you are buying. These devices require high
computational capabilities. Hopefully there are canned algorithms available
to provide the outputs that you require. But they have the potential to
provide proper pitch and roll outputs AND simultaneous acceleration outputs

I'll just log all the data - my boss has the degrees in Maths & Surveying, so
he can be the one that has to make sense of it all! :-)

Dave

Hello Dave,

My company has been marketing a system for ship-motions measurement for
some time. It is called ship-motion-controller (SMC) and consists of an
electrolytic sensor and accompanying sotware for logging and analysis.
The sensor measures accelerations and angles on all three axis and is
connected to a PC via USB. The angular accuracy is better than 0.01
degree. The system has been extensively tested, and can easily log three
months of data. It is a commercial-of-the-shelf-system and we have a
system available for rent if required.

Maybe this could be helpfull to your project.

Willem Amels


Dave Baker wrote in
:

On Wed, 7 Jan 2004 21:02:09 -0800, "maxlynn" wrote:

You are on to a possibility. You should know that there is a lot more
than meets the eye in what you are buying. These devices require high
computational capabilities. Hopefully there are canned algorithms
available to provide the outputs that you require. But they have the
potential to provide proper pitch and roll outputs AND simultaneous
acceleration outputs

I'll just log all the data - my boss has the degrees in Maths &
Surveying, so he can be the one that has to make sense of it all! :-)

Dave

On 08 Jan 2004 18:51:11 GMT, Willem Amels wrote:

The sensor measures accelerations and angles on all three axis and is
connected to a PC via USB. The angular accuracy is better than 0.01
degree. The system has been extensively tested, and can easily log three
months of data.

If it can output in real time (so I can correlate it with Inmarsat
transceiver signal strength) then it sounds interesting. I'll email you to
get more info (if I can guess your real email address correctly)

Dave