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PICList Thread
'acceleration sensor'
1999\10\15@112753 by Peter Keller

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Hi
I am looking for a lowcost acceleration sensor for capturing the
acceleration of a 3ft long pendulum.
Peter

1999\10\15@115659 by Wagner Lipnharski

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Very low cost? Glue a magnet at the bottom of the pendulum, and below
that install a coil, or a series of coils, or a long curved shape coil
to "pick-up" the magnetic induction. Any low cost op-amp can amplify the
picked up voltage, that will be proportional to the pendulum speed, the
delta-voltage along the time will tells you the acceleration.

Wagner

Peter Keller wrote:
>
> Hi
> I am looking for a lowcost acceleration sensor for capturing the
> acceleration of a 3ft long pendulum.
> Peter

1999\10\15@170056 by Peter Keller

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good idea, but i am looking for something small, fixed to the pendulum.
Peter

Wagner Lipnharski schrieb:

{Quote hidden}

1999\10\15@175313 by Dave Johnson

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Peter Keller wrote:

>good idea, but i am looking for something small, fixed to the pendulum.
I don't know what your definition of "low cost" is, but Analog Devices
makes several single chip accelerometers.

Dave Johnson

1999\10\15@175526 by Wagner Lipnharski

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Ok, now I got curious...

What is the accuracy, resolution and maximum cost you expect from this
sensor?

Wagner

1999\10\16@022822 by Peter Keller

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No idea for the moment. It was only a thought how to recognize an obstacle
on a moving device by looking at the acceleration. I found some
interesting parts from analog devices. Costs are about $20. That's ok for
an experiment. More infos and results later.
Peter

Wagner Lipnharski schrieb:

> Ok, now I got curious...
>
> What is the accuracy, resolution and maximum cost you expect from this
> sensor?
>
> Wagner

1999\10\16@022831 by Peter Keller

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Thanks
Peter

Dave Johnson schrieb:

> Peter Keller wrote:
>
> >good idea, but i am looking for something small, fixed to the pendulum.
> I don't know what your definition of "low cost" is, but Analog Devices
> makes several single chip accelerometers.
>
> Dave Johnson

1999\10\16@125124 by Wagner Lipnharski

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Sure, the ADXL05 and ADXL50 are very good and easy to interface, but by
the common "low cost" expression at this list I thought you were talking
about cents... :)

Peter Keller wrote:
{Quote hidden}

1999\10\17@181808 by William K. Borsum

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Hi All--just had to add some seasoning to the soup....

ADXLxx devices are NOT "very good" except in being cheap.  Look at their
signal to noise ratio--the 05's used to be 10:1! probably improved some by
now--but still not suitable for much past airbag sensing--definitely not
adequate for seismic work or accurate tilt sensors. (Sorry Wagner--I got
bit hard by these things a few years ago)

The ICsensors (now EG&G) can go for <$100, and I've got one going on the
space station with a gain of 1.9 Million to one--giving 200 micro-G's full
scale.  Thats good and cheap.  Had some real problems getting there,
though.  A lot of 60 cycle stuff kept showing up--tried shielding and
all--no effect.  Finally stuck the sensor in a foam lined box, and noise
went away--was acoustically coupling off the air conditioner motors on the
roof.

For pure cheap--look at the piezo film devices AMP Connectors are selling.
You can get a free kit to play with even.  Basically just a film with a
piezo coating applied--flex it, and you get a voltage out--NO current, but
hi voltage, so it needs a very hi impedance amp (commonly referred to as a
charge amp) as the first stage.  Might be perfect for sensing pendulum
impacts.  A couple of companies are actually selling multi-axis acell's
based on this stuff.  NOT suitable for DC though.

Kelly




At 12:51 PM 10/16/99 -0400, you wrote:
{Quote hidden}

William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<spam_OUTborsumTakeThisOuTspamdascor.com> & <http://www.dascor.com>San Diego, California, USA

1999\10\17@182634 by Sean H. Breheny

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At 03:17 PM 10/17/99 -0700, you wrote:
>The ICsensors (now EG&G) can go for <$100, and I've got one going on the
>space station with a gain of 1.9 Million to one--giving 200 micro-G's full
>scale.  Thats good and cheap.  Had some real problems getting there,
>though.  A lot of 60 cycle stuff kept showing up--tried shielding and
>all--no effect.  Finally stuck the sensor in a foam lined box, and noise
>went away--was acoustically coupling off the air conditioner motors on the
>roof.
>

Kelly,

That sounds exactly like what I need for the helicopter project. What is
the URL please?

Thanks,

Sean

|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
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1999\10\17@183258 by Sean H. Breheny

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At 03:17 PM 10/17/99 -0700, you wrote:
>The ICsensors (now EG&G) can go for <$100, and I've got one going on the
>space station with a gain of 1.9 Million to one--giving 200 micro-G's full
>scale.  Thats good and cheap.  Had some real problems getting there,
>though.  A lot of 60 cycle stuff kept showing up--tried shielding and
>all--no effect.  Finally stuck the sensor in a foam lined box, and noise
>went away--was acoustically coupling off the air conditioner motors on the
>roof.
>

Just found it! Which one did you use to get 200uG full scale? We are
looking to make an INS that has no greater error than 0.5mG,but less would
be great!

Thanks,

Sean


|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
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1999\10\18@005624 by Peter Keller

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Thanks Kelly
what means EG&G ? Do you have a web-address ?
Peter

"William K. Borsum" schrieb:

{Quote hidden}

1999\10\18@014933 by Sean H. Breheny

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Hi Peter,

http://www.egginc.com

Go to their optoelectronics section, you'll see the ICsensors.

http://www.egginc.com/egg/view_division.cgi/Divisions/Opto|112

Sean

At 06:58 AM 10/18/99 +0100, you wrote:
>Thanks Kelly
>what means EG&G ? Do you have a web-address ?
>Peter
>

|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
EraseMEshb7spam_OUTspamTakeThisOuTcornell.edu ICQ #: 3329174

1999\10\18@100219 by Wagner Lipnharski

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"William K. Borsum" wrote:

> ADXLxx devices are NOT "very good" except in being cheap.  Look at their
> signal to noise ratio--the 05's used to be 10:1! probably improved some by
> now--but still not suitable for much past airbag sensing--definitely not
> adequate for seismic work or accurate tilt sensors. (Sorry Wagner--I got
> bit hard by these things a few years ago)
>
> The ICsensors (now EG&G) can go for <$100, and I've got one going on the
> space station with a gain of 1.9 Million to one--giving 200 micro-G's full
> scale.  Thats good and cheap.  Had some real problems getting there,
> though.  A lot of 60 cycle stuff kept showing up--tried shielding and
> all--no effect.  Finally stuck the sensor in a foam lined box, and noise
> went away--was acoustically coupling off the air conditioner motors on the
> roof.

EG&G Still out of the $20 suggested by Peter.  We always considered
silicon acceleration sensors as high sensible microphones, they really
capture any vibration from air, mechanical coupled, whatever.  The
exception goes to the mechanical sensors (linear bearings), mostly
recommended for high impact application.  For the price, the ADXL units
worked pretty well at the application used, since the unit was always
vaporized at the impact, never misfired. Of course better units are
available and cost should always be a consideration of application.

1999\10\18@102510 by eplus1

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See:
http://204.210.50.240/techref/default.asp?url=io\sensor\posdd.htm

All credit to Annie.

James Newton jamesnewtonspamspam_OUTgeocities.com phone:1-619-652-0593
http://techref.homepage.com NOW OPEN (R/O) TO NON-MEMBERS!
Members can add private/public comments/pages ($0 TANSTAAFL web hosting)
PICLIST guide: http://204.210.50.240/techref/default.asp?url=piclist.htm


-----Original Message-----
From: pic microcontroller discussion list
[@spam@PICLISTKILLspamspamMITVMA.MIT.EDU]On Behalf Of Peter Keller
Sent: Friday, October 15, 1999 9:30 AM
To: KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU
Subject: acceleration sensor


Hi
I am looking for a lowcost acceleration sensor for capturing the
acceleration of a 3ft long pendulum.
Peter

1999\10\18@132814 by William K. Borsum

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At 06:25 PM 10/17/99 -0400, you wrote:
>At 03:17 PM 10/17/99 -0700, you wrote:
>>The ICsensors (now EG&G) can go for <$100, and I've got one going on the
>>space station with a gain of 1.9 Million to one--giving 200 micro-G's full
>>scale.  Thats good and cheap.  Had some real problems getting there,
>>though.  A lot of 60 cycle stuff kept showing up--tried shielding and
>>all--no effect.  Finally stuck the sensor in a foam lined box, and noise
>>went away--was acoustically coupling off the air conditioner motors on the
>>roof.
>>

Sorry but I don't know the URL for AMP--do a search for AMP and
Connectors--should turn it up.

URL for ICsensors is <http://www.egginc.com/icsensors>

Enjoy

William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<RemoveMEborsumTakeThisOuTspamdascor.com> & <http://www.dascor.com>San Diego, California, USA

1999\10\18@132819 by William K. Borsum

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At 06:31 PM 10/17/99 -0400, you wrote:
>At 03:17 PM 10/17/99 -0700, you wrote:
>>The ICsensors (now EG&G) can go for <$100, and I've got one going on the
>>space station with a gain of 1.9 Million to one--giving 200 micro-G's full
>>scale.  Thats good and cheap.  Had some real problems getting there,
>>though.  A lot of 60 cycle stuff kept showing up--tried shielding and
>>all--no effect.  Finally stuck the sensor in a foam lined box, and noise
>>went away--was acoustically coupling off the air conditioner motors on the
>>roof.
>>
>
>Just found it! Which one did you use to get 200uG full scale? We are
>looking to make an INS that has no greater error than 0.5mG,but less would
>be great!

They really only have one device that would be applicable--it is a 2-G
sensor in a package roughly 5/8" square by 3/16" thick.
Model is 3022 and 3028 for uncompensated, and 3052 for compensated.

Uncompensated have lowest noise, BUT--and this is a BIG BUT--about 0.3% per
degree gain and zero drift!
Ideal solution is to put the accelerometers in a thermally controlled
block--just need a 1-2 watt resistor as a heater element, and a power
op-amp and thermistor to control the temperature to 30-50 degrees above
ambient. 3058 has internal compensation and reduces the error down to a few
percent over the full temperature range--but at the expense of noise.
Specs are on their web page.

Alternate method is to provide a integrating feedback on the
instrumentation amp so it serves as a hi pass filter with a time constant
for 100 seconds or so (See burr brown's web page for their app-notes on how
to do this)--this will take care of zero drift rather nicely, but leaves
the larger gain drift.  Math in the pic can deal with that--as long as you
have a temperature sensor near the accelerometers too.  We do this with our
earthquake alarms in a PIC711--plus a lot of other signal conditioning.

ALSO do not trust the calibrations from ICS if you require high accuracy!
They are Ok for a few percent--but have proven to be very unreliable.  A
2-G sensor is easy to calibrate yourself at DC levels--just remember the
earth has a 1 G field--just rotate the device through 180 degrees and you
have +/- 1 G available.  Cosine of the angle in between.

Enjoy
Kelly

William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<spamBeGoneborsumspamBeGonespamdascor.com> & <http://www.dascor.com>San Diego, California, USA

1999\10\18@134528 by Marcelo Yamamoto

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You wrote:

>Sorry but I don't know the URL for AMP--do a search for AMP and
>Connectors--should turn it up.


It's http://www.amp.com
If you are looking for connectors, take a look at Molex http://www.molex.com and
Autosplice http://www.autosplice.com too.

Marcelo

1999\10\18@140825 by Sean Breheny

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Hi Kelly,

Thanks for the VERY valuable info. What is the price for the ones you
mention,if you don't mind my asking? I asked for a quote,but I don't know
how long it will be until I get an answer,and I didn't know which ones to
ask about until now.

Thanks,

Sean


On Mon, 18 Oct 1999, William K. Borsum wrote
{Quote hidden}

1999\10\18@174734 by Don Hyde

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Your problem with the 60Hz is basically that there really WAS 60Hz
acceleration, and your sensor was sensing it.  If your sensor has 1KHz or
more bandwidth (as I recall the cheapie ones from Analog Devices have), and
you're sampling at 2 Hz, say, then all that sensor bandwidth from 1Hz up is
just noise that's getting folded into your signal by good old Mr. Nyquist.
What you need is an anti-aliasing filter that has lots of attenuation by
60Hz (I figure that's what your foam box is doing).

App. note 699 by Bonnie Baker (download from Microchip website) is a
wonderful clear explanation of the problem.

> {Original Message removed}

1999\10\18@221235 by William K. Borsum

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Close--but the client also wanted a 200 HZ or there-abouts frequency
response, and was sampling at several thousand per second--so the
anti-alias filter was set up accordingly--about 90 dB down at 1/2 the
sample rate.  And yes it was measuring 60 Hz. acceleration--caused by
acoustic noise.

Don't recall the AD accelerometers being good much above 30-50 HZ, however.
ICS units are good to several hundred Hz depending on full scale rating.
My main--and only--complaint with most of the internally conditioned units
such as AD, CSEM, and others is a very poor signal to noise ratio.

kelly



At 04:42 PM 10/18/99 -0500, you wrote:
{Quote hidden}

>> {Original Message removed}

1999\10\21@063458 by Cser Laszlo

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> >Just found it! Which one did you use to get 200uG full scale? We are
> >looking to make an INS that has no greater error than 0.5mG,but less
would
> >be great!
>
> They really only have one device that would be applicable--it is a 2-G
> sensor in a package roughly 5/8" square by 3/16" thick.
> Model is 3022 and 3028 for uncompensated, and 3052 for compensated.

How do you get rid of the transverse sensitivity error? In such low 200uG
applications +-3%span is quite a lot. (By the was what do they mean by
span.)

I have found the 3022 and the 3028 butI could not find the datasheet of the
3052. Is it available on the web site? I could'n download the application
notes which goes for accelerometers. It is on FTP but anonymous logon was
not accepted. Could you help?

Did you get your samples through a distributor?

Looking forward to your answer,
Laszlo Cser
RemoveMEs7222csespamTakeThisOuTural2.hszk.bme.hu
Budapest University of Technology

1999\10\21@165132 by William K. Borsum

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Serbus Elvtars Ur!
Lived on Klauzal Ter in Pest for a while--prior lifetime--early 70's.
LOTS of good memories!

Transverse error is a tough one.  It comes from not mounting the die
exactly square on the substrate--do the math and you will see that even a
degree can make a real difference!  Most people I know that are really
concerned spend the time with a multi-axis table and calibrate under all
possible conditions, then set up their data correction algorithms to take
out the cross axis stuff.

Alternative is to buy the die and mount them yourselves--but that
introduces other problems best not dealt with at the hobby level.
I have heard that Crossbow (the company, no url, etc) takes three of the
ICS sensors, mounts them in a triax configuration with a PIC, and an ADC
and DAC, and actually outputs a corrected analog signal--all for around
$500.  THIS IS RUMOR--I have not confirmed with crossbow yet.  If so, it is
on good deal!

3052 is a new product--I was faxed a copy of the pre-release data sheet.
Try calling ICS directly.  Cliff Kirk at 1-800-767-1888.
Ditto for the app notes--I never have used their web page successfully.
Cliff can help you with samples--but remember you are asking for $100+ each
parts.

Kelly




At 12:34 PM 10/21/99 +0200, you wrote:
{Quote hidden}

William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<EraseMEborsumspamdascor.com> & <http://www.dascor.com>San Diego, California, USA

1999\10\22@002549 by Russell McMahon

picon face
>Serbus Elvtars Ur!
>Lived on Klauzal Ter in Pest for a while--prior lifetime--early 70's.
>LOTS of good memories!


Sounds interesting.
What / where is this?
On?

>Transverse error is a tough one.  It comes from not mounting the die
>exactly square on the substrate--do the math and you will see that even a
>degree can make a real difference!  Most people I know that are really
>concerned spend the time with a multi-axis table and calibrate under all
>possible conditions, then set up their data correction algorithms to take
>out the cross axis stuff.


Presumably one could remove this mechnically with vernier alignment of the
sensor module relative to the host product. This may be an abomination
depending on the application.


RM

1999\10\22@005915 by Sean H. Breheny

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If one has a three axis setup, then it seems to me that you could combine
the outputs of all of the sensors in a weighted sum to get the actual X,Y,Z
acceleration values.

Sean

At 04:58 PM 10/22/99 +1300, you wrote:
>Presumably one could remove this mechnically with vernier alignment of the
>sensor module relative to the host product. This may be an abomination
>depending on the application.
>
>
>RM
>
|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
RemoveMEshb7EraseMEspamEraseMEcornell.edu ICQ #: 3329174

1999\10\22@160244 by William K. Borsum

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I think this is what the analysis software does--but the cross-axis errors
(sensitivity) must be known (Calibrated) in order to weight the components
of the sum correctly.  Also the object would be to come up with a
directional vector in 3D.  Like I said--I just collect the data and let the
PhD types do the math.

Don't know many (any!) people with six axis calibration tables (surge,
heave, sway, roll, pitch, and yaw) that can do much over a Hz or two with
any kind of accuracy.  Usually just settle for doing two axes at a time
using roll and pitch in the earth's 1 G field.

Kelly



At 12:57 AM 10/22/99 -0400, you wrote:
{Quote hidden}

William K. Borsum, P.E. -- OEM Dataloggers and Instrumentation Systems
<RemoveMEborsumTakeThisOuTspamspamdascor.com> & <http://www.dascor.com>San Diego, California, USA

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