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# shock detection

M

#### Michael

Jan 1, 1970
0
I need to find a way to detect whether our hand held instrument ($25k-$40k) was abused (dropped, bumped, etc).
It means free fall and shock detection (detect, timestamp, go back to
sleep). First one is relatively simple. "Relatively" because this
shock_detection_system needs to rely on it's own battery - the
instrument may be dropped when main battery is out and this "battery
out" state may be as long as two months. And occupy no (ok, very low)
volume.
Shock detection is what I need help with. I found out (http://
www.isthq.com/main.asp?a=2&b=0&pageid=86&view=active) that 25G is
"small" shock. This gives some clues - shock detector will not
necessarily be able to see free fall - two different devices - ???
"...You have a tough job ahead of you. I know of no technology that
will get you the kind of low power performance you want without a lot
of pain. We do not offer anything like that...." - response from the
accelerometer manufacturer tech support.
I have EE background and my knowledge of physics is limited.
To add insult to the injury: we do not know how much shock our
instrument can sustain without losing performance.
Can anybody point me in the right direction?

Thanks!!

J

#### Jim Thompson

Jan 1, 1970
0
I need to find a way to detect whether our hand held instrument ($25k-$40k) was abused (dropped, bumped, etc).
It means free fall and shock detection (detect, timestamp, go back to
sleep). First one is relatively simple. "Relatively" because this
shock_detection_system needs to rely on it's own battery - the
instrument may be dropped when main battery is out and this "battery
out" state may be as long as two months. And occupy no (ok, very low)
volume.
Shock detection is what I need help with. I found out (http://
www.isthq.com/main.asp?a=2&b=0&pageid=86&view=active) that 25G is
"small" shock. This gives some clues - shock detector will not
necessarily be able to see free fall - two different devices - ???
"...You have a tough job ahead of you. I know of no technology that
will get you the kind of low power performance you want without a lot
of pain. We do not offer anything like that...." - response from the
accelerometer manufacturer tech support.
I have EE background and my knowledge of physics is limited.
To add insult to the injury: we do not know how much shock our
instrument can sustain without losing performance.
Can anybody point me in the right direction?

Thanks!!

Just measure the deformation of the case ?

...Jim Thompson

S

#### Spehro Pefhany

Jan 1, 1970
0
I need to find a way to detect whether our hand held instrument ($25k-$40k) was abused (dropped, bumped, etc).
It means free fall and shock detection (detect, timestamp, go back to
sleep). First one is relatively simple. "Relatively" because this
shock_detection_system needs to rely on it's own battery - the
instrument may be dropped when main battery is out and this "battery
out" state may be as long as two months. And occupy no (ok, very low)
volume.
Shock detection is what I need help with. I found out (http://
www.isthq.com/main.asp?a=2&b=0&pageid=86&view=active) that 25G is
"small" shock. This gives some clues - shock detector will not
necessarily be able to see free fall - two different devices - ???

Why would you care about free fall? It's not the fall that kills your
instrument, it's the sudden stop at the end.
"...You have a tough job ahead of you. I know of no technology that
will get you the kind of low power performance you want without a lot
of pain. We do not offer anything like that...." - response from the
accelerometer manufacturer tech support.
I have EE background and my knowledge of physics is limited.
To add insult to the injury: we do not know how much shock our
instrument can sustain without losing performance.
Can anybody point me in the right direction?

Thanks!!

It's not necessarily an appropriate job for electronics.

Cheap zero-power technology:
http://www.uline.com/Browse_Listing_1051.asp?desc=Drop+(N)+Tell

Best regards,
Spehro Pefhany

J

#### Jon Slaughter

Jan 1, 1970
0
Michael said:
I need to find a way to detect whether our hand held instrument ($25k-$40k) was abused (dropped, bumped, etc).
It means free fall and shock detection (detect, timestamp, go back to
sleep). First one is relatively simple. "Relatively" because this
shock_detection_system needs to rely on it's own battery - the
instrument may be dropped when main battery is out and this "battery
out" state may be as long as two months. And occupy no (ok, very low)
volume.
Shock detection is what I need help with. I found out (http://
www.isthq.com/main.asp?a=2&b=0&pageid=86&view=active) that 25G is
"small" shock. This gives some clues - shock detector will not
necessarily be able to see free fall - two different devices - ???
"...You have a tough job ahead of you. I know of no technology that
will get you the kind of low power performance you want without a lot
of pain. We do not offer anything like that...." - response from the
accelerometer manufacturer tech support.
I have EE background and my knowledge of physics is limited.
To add insult to the injury: we do not know how much shock our
instrument can sustain without losing performance.
Can anybody point me in the right direction?

How do you plan on measuring free fall? This is probably impossible for
you. Netwon and Einstein say that free fall is an inertial frame of
reference so there is no method that can measure it directly. Any method
doing so must use something about the surroundings(which almost surely = air
resistance).

In any case if your handhelds cost $25k+ then I'm sure you make enough money so that you can hire someone to try and solve the problem. As far as impact, which seems to be what you actually need, take a look at http://en.wikipedia.org/wiki/G-force http://en.wikipedia.org/wiki/Shock_(mechanics) http://en.wikipedia.org/wiki/Impact_force But again, if your selling a "handheld" for$25k+(what, is it made of solid
gold?) then you can afford to hire a real scientist to do the work(or are
you that "scientist" that was hired?).

J

#### John Larkin

Jan 1, 1970
0
How do you plan on measuring free fall? This is probably impossible for
you. Netwon and Einstein say that free fall is an inertial frame of
reference so there is no method that can measure it directly. Any method
doing so must use something about the surroundings(which almost surely = air
resistance).

The Brat dropped her Dell laptop yesterday, and lunched the hard
drive, including a powerpoint presentation that took 8 hours to do and
is due today. She called for help. I told her to head for Wal-Mart,
get a new pc, and start over. They had DElls and a Sony Vaio
available, and called me from the Wal-Mart and asked me which to buy.
The Sony of course. It has mems accelerometers inside that detect
zero-G and retract the disk heads before impact.

1G = not falling

0G = falling

John

F

#### Frithiof Andreas Jensen

Jan 1, 1970
0
Michael said:
I need to find a way to detect whether our hand held instrument ($25k-$40k) was abused (dropped, bumped, etc).
"...You have a tough job ahead of you. I know of no technology that
will get you the kind of low power performance you want without a lot
of pain. We do not offer anything like that...." - response from the
accelerometer manufacturer tech support.

Calibrated glass tubes are often used - if they break, there was a shock of
at least X g.
I have EE background and my knowledge of physics is limited.
To add insult to the injury: we do not know how much shock our
instrument can sustain without losing performance.

Either measure it - or don't worry about it because then it is not
important.

M

#### Michael

Jan 1, 1970
0
Calibrated glass tubes are often used - if they break, there was ashockof
at least X g.

Either measure it - or don't worry about it because then it is not
important.

We need to have a time stamp (to be able to properly assign
blame ;o) ) - glass tubes won't do.
I do not know:
a. "how much is too much?"
b. How to keep this system running for, say, two months between
recharges on whatever tiny volume available for the battery. The
minimum I will need (I have found so far is) ~1..1.5Amp-hour cell.
It's not tiny... (

J

#### John Larkin

Jan 1, 1970
0
I need to find a way to detect whether our hand held instrument ($25k-$40k) was abused (dropped, bumped, etc).
It means free fall and shock detection (detect, timestamp, go back to
sleep). First one is relatively simple. "Relatively" because this
shock_detection_system needs to rely on it's own battery - the
instrument may be dropped when main battery is out and this "battery
out" state may be as long as two months. And occupy no (ok, very low)
volume.
Shock detection is what I need help with. I found out (http://
www.isthq.com/main.asp?a=2&b=0&pageid=86&view=active) that 25G is
"small" shock. This gives some clues - shock detector will not
necessarily be able to see free fall - two different devices - ???
"...You have a tough job ahead of you. I know of no technology that
will get you the kind of low power performance you want without a lot
of pain. We do not offer anything like that...." - response from the
accelerometer manufacturer tech support.
I have EE background and my knowledge of physics is limited.
To add insult to the injury: we do not know how much shock our
instrument can sustain without losing performance.
Can anybody point me in the right direction?

Thanks!!

Hobo:

http://www.microdaq.com/data-logger/shock.php

John

D

#### D from BC

Jan 1, 1970
0
I need to find a way to detect whether our hand held instrument ($25k-$40k) was abused (dropped, bumped, etc).
It means free fall and shock detection (detect, timestamp, go back to
sleep). First one is relatively simple. "Relatively" because this
shock_detection_system needs to rely on it's own battery - the
instrument may be dropped when main battery is out and this "battery
out" state may be as long as two months. And occupy no (ok, very low)
volume.
Shock detection is what I need help with. I found out (http://
www.isthq.com/main.asp?a=2&b=0&pageid=86&view=active) that 25G is
"small" shock. This gives some clues - shock detector will not
necessarily be able to see free fall - two different devices - ???
"...You have a tough job ahead of you. I know of no technology that
will get you the kind of low power performance you want without a lot
of pain. We do not offer anything like that...." - response from the
accelerometer manufacturer tech support.
I have EE background and my knowledge of physics is limited.
To add insult to the injury: we do not know how much shock our
instrument can sustain without losing performance.
Can anybody point me in the right direction?

Thanks!!

You just need a loose wire.

The Fonz would punch the side of a jukebox and it would start working.

D from BC

A

#### [email protected]

Jan 1, 1970
0
How do you plan on measuring free fall? This is probably impossible for
you. Netwon and Einstein say that free fall is an inertial frame of
reference so there is no method that can measure it directly. Any method
doing so must use something about the surroundings(which almost surely = air
resistance).

<rolls eyes> You are quite serious when you say that?

T

#### Tim Wescott

Jan 1, 1970
0
Michael said:
I need to find a way to detect whether our hand held instrument ($25k-$40k) was abused (dropped, bumped, etc).
It means free fall and shock detection (detect, timestamp, go back to
sleep). First one is relatively simple. "Relatively" because this
shock_detection_system needs to rely on it's own battery - the
instrument may be dropped when main battery is out and this "battery
out" state may be as long as two months. And occupy no (ok, very low)
volume.
Shock detection is what I need help with. I found out (http://
www.isthq.com/main.asp?a=2&b=0&pageid=86&view=active) that 25G is
"small" shock. This gives some clues - shock detector will not
necessarily be able to see free fall - two different devices - ???
"...You have a tough job ahead of you. I know of no technology that
will get you the kind of low power performance you want without a lot
of pain. We do not offer anything like that...." - response from the
accelerometer manufacturer tech support.
I have EE background and my knowledge of physics is limited.
To add insult to the injury: we do not know how much shock our
instrument can sustain without losing performance.
Can anybody point me in the right direction?

Thanks!!
There are some large-format piezo accelerometers out there that appear
to produce a big enough signal to turn on some electronics -- I did some
preliminary work on this for a prospective customer. That takes care of
the "big shock" case.

For free-fall, perhaps some self-centering tilt switches?

Instead of consuming power all the time, you can get this down to
consuming power for each event -- but I'll bet a hand-held instrument
sees a lot of free fall without seeing consequent shock; you may run out
the battery from all the "whee!" events then miss the "thump!" that you
wanted to capture.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

S

#### Spehro Pefhany

Jan 1, 1970
0
<rolls eyes> You are quite serious when you say that?

Sure-- you've failed to consider that the end user may be attempting
to use the product in, say, a space station, so the 0g state is
indistiguishable from normal operation.

Best regards,
Spehro Pefhany

T

#### Tim Williams

Jan 1, 1970
0
Michael said:
We need to have a time stamp (to be able to properly assign
blame ;o) ) - glass tubes won't do.
I do not know:
a. "how much is too much?"
b. How to keep this system running for, say, two months between
recharges on whatever tiny volume available for the battery. The
minimum I will need (I have found so far is) ~1..1.5Amp-hour cell.
It's not tiny... (

Alright, so use an opto detector of some sort that watches the glass! Or a
contact (metallize the glass tube?), or who knows what else... ;-)

Tim

J

#### John Larkin

Jan 1, 1970
0
Sure-- you've failed to consider that the end user may be attempting
to use the product in, say, a space station, so the 0g state is
indistiguishable from normal operation.

But then, if he drops it, nothing breaks!

John

A

#### [email protected]

Jan 1, 1970
0
But then, if he drops it, nothing breaks!

John

Argh, beat me to it! But there's really no "dropping" on a space
station, is there???

E

#### Ecnerwal

Jan 1, 1970
0
Michael said:
I need to find a way to detect whether our hand held instrument ($25k-$40k) was abused (dropped, bumped, etc).
It means free fall and shock detection (detect, timestamp, go back to
sleep).

Well, the disgustingly easy method won't do timestamps. It is however
small, cheap enough to stick on a cardboard box, and reliable - with no
batteries at all.

http://www.drypak.com/SWLabelSelectionGuide.pdf

This will monitor, but could miss an event depending on logging
interval, which trades off with battery life. Could probably arrange to
OEM the guts to cut the size down (take out of waterproof package). Also
rather low-range for you, I guess (+-3G)

http://www.onsetcomp.com/solutions/products/loggers/_showloggerfamily.php
5?lf=37&view=2

A bit large for you, but otherwise seems to do what you want:

J

#### Jon Slaughter

Jan 1, 1970
0
Tim Williams said:
Alright, so use an opto detector of some sort that watches the glass! Or
a
contact (metallize the glass tube?), or who knows what else... ;-)

Tim

How bout springs? F = kx, mount two opposite springs(actually 6) on a ball
then any accelleration will compress one and extent the other... the amount
of acceleration being proportional to the acceleration... i.e., F = ma = kx.
(with 3 axis you'll need a better algorith as it would depend on the
orientation(in this case it does too but I'm assuming lateral motion)).

I'm sure there are a bazillion ways... In fact somehow they do it with very
small chips using ingenious methods. I'm sure it can be done for a few
dollars?

Knowing the minimum high at which the device could potentially break would
help. If its in free fall(and not thrown) from 1 feet then it will take
about 0.35 s to hit the ground so one does not actually have to sample at a
high rate(well, depends on what this guy wants to do).

But seriously, I don't see what real damage could come from a handheld made
of solid gold. What if it is dropped? Why does it matter? Does the gold
really know its in free fall?

J

#### Jon Slaughter

Jan 1, 1970
0
Jon Slaughter said:
How bout springs? F = kx, mount two opposite springs(actually 6) on a
ball then any accelleration will compress one and extent the other... the
amount of acceleration being proportional to the acceleration... i.e., F =
ma = kx. (with 3 axis you'll need a better algorith as it would depend on
the orientation(in this case it does too but I'm assuming lateral
motion)).

(I'm not actually saying this is a good method... I imagine it would work on
a large scale with precision components but I'm sure it probably doesn't
beat your standard accelerometers in cost, size, and accuracy)

J

#### Jon Slaughter

Jan 1, 1970
0
Ecnerwal said:
Well, the disgustingly easy method won't do timestamps. It is however
small, cheap enough to stick on a cardboard box, and reliable - with no
batteries at all.

http://www.drypak.com/SWLabelSelectionGuide.pdf

This will monitor, but could miss an event depending on logging
interval, which trades off with battery life. Could probably arrange to
OEM the guts to cut the size down (take out of waterproof package). Also
rather low-range for you, I guess (+-3G)

http://www.onsetcomp.com/solutions/products/loggers/_showloggerfamily.php
5?lf=37&view=2

A bit large for you, but otherwise seems to do what you want:

Eggs are a good source of accelerometers too... although they don't actually
test acceleration ;/

S

#### Spehro Pefhany

Jan 1, 1970
0
Argh, beat me to it! But there's really no "dropping" on a space
station, is there???

It's sort of in free-fall continuously.

Best regards,
Spehro Pefhany

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