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B1ackwater posted on January 9, 2006, 9:08 am
I need to accurately measure distances of up to one. maybe
1.5 meters in an outdoor environment. Accuracy to 1/2" at
the outside of the detection envelope is required.
I've looked at the Sharp IR distance sensors and they're
usable - but I'm worried about condensation building up in
humid environments. I've found a number of ultrasonic sensors
that are accurate, versatile and weatherproof - but they cost
a bleedin' fortune (usually > $250US) and I need two of them
for each project.
So - two questions ...
First, does anyone know what that plastic is that they make
those condensation-resistant bathroom mirrors out of ? If
I put the Sharp sensors behind a thin sheet of that ... no
more condensation problems. (power-consumption IS an issue
here so heated optical windows are out of the question)
Second, has anyone come across an AFFORDABLE ultrasonic
distance sensor roughly fitting my accuracy needs ? 1/2"
at 1 meter is adequate but the thing MUST be capable of
withstanding 100% humidity pretty much forever.
Any help appreciated. Reply to group.
1.5 meters in an outdoor environment. Accuracy to 1/2" at
the outside of the detection envelope is required.
I've looked at the Sharp IR distance sensors and they're
usable - but I'm worried about condensation building up in
humid environments. I've found a number of ultrasonic sensors
that are accurate, versatile and weatherproof - but they cost
a bleedin' fortune (usually > $250US) and I need two of them
for each project.
So - two questions ...
First, does anyone know what that plastic is that they make
those condensation-resistant bathroom mirrors out of ? If
I put the Sharp sensors behind a thin sheet of that ... no
more condensation problems. (power-consumption IS an issue
here so heated optical windows are out of the question)
Second, has anyone come across an AFFORDABLE ultrasonic
distance sensor roughly fitting my accuracy needs ? 1/2"
at 1 meter is adequate but the thing MUST be capable of
withstanding 100% humidity pretty much forever.
Any help appreciated. Reply to group.
cbm5 posted on
Re: Weatherproof Distance Sensors ?
Anti-fog plastic just contains a form of detergent that keeps the water
from beading up. Not a 100% reliable solution, and it'll wear out
quickly in constant humidity. The same result can be obtained from a
spray-on surface treatment, which needs to be applied often.
Certain important optically-based sensors have been known to mount a
miniature mechanical wiper on the front glass for these types of situations.
Re: Weatherproof Distance Sensors ?
Hmmm ... I used to own one of those fog-proof mirrors.
The effect didn't disappear over time, no treatments
were necessary. Likely the stuff was dosed with a
halogen or something to alter the surface chemistry
and/or charge. Maybe I could buy one and eat the
aluminum backing off with HCL ...
Yea, I've considered it - but I also believe in
the KISS principle and moving parts are just
something else to break down (and consume power).
Besides, it might *smear* instead of clean - yuk !
Ultrasonic would be perfect ... but the *cost* :-(
Re: Weatherproof Distance Sensors ?
But where is that mirror now? How long did you have it? By quickly I
meant something like a year, in almost constant humidity...a shower is
going to be dry 23 hours out of 24.
And as far as ultrasonic goes, you could always glance a few threads
back. ;) www.maxbotix.com $30.
Mitch Berkson posted on
Re: Weatherproof Distance Sensors ?
Maybe this stuff is ready. From http://web.mit.edu/newsoffice/2005/fog.html
"Foggy windows and lenses are a nuisance, and in the case of automobile
windows, can pose a driving hazard. Now, MIT scientists may have found a
permanent solution to the problem. The team has developed a unique polymer
coating--made of silica nanoparticles--that they say can create surfaces
that never fog.
The transparent coating can be applied to eyeglasses, camera lenses, ski
goggles ?K even bathroom mirrors, they say. The new coating was described
Aug. 29 at the national meeting of the American Chemical Society."
Mitch
Re: Weatherproof Distance Sensors ?
I'd heard about that ... but they don't exactly have
tubes of the stuff down at K-Mart yet.
There was another approach, I believe using flourine
gas applied to the surface of the plastic. Not really
a do-it-yourself kind of thing however. Both techiques
creat a hydrophobic nano-roughened surface that H2O
doesn't properly 'fit' into.
They were *supposed* to have diamond coatings by now
also for eyeglasses and such - created by decomposing
methane and H2 at certain temperatures and pressures.
Deposited thin, flat diamond 'flakes' on any surface.
Might not work on plastic lenses though because the
underlying substrate is STILL soft and subject to
macroscopic gouges by sand and such. Kinda like
putting tinfoil over jello - yea, the metal is a lot
harder than the jello but you can still scoop out a
chunk of the rasperry/lime right through the foil
using a spoon.
Larry posted on
Re: Weatherproof Distance Sensors ?
Please check out PSR-1 at www.eutectos.com. and let me know what you
think.
As in most Sonars, there is a dead zone, which in this case (gain and
pulse width dependent) can be as low as 8 inches. Current
implementation provides 1" resolution, which could be reduced to
perhaps 1/4 inch. Hardware supports it, but firmware would need to be
changed. Can you tell me more about your requirement both technically,
application wise and what the potential volume may be? We might be able
to help, and would like too.
Regards,
Larry
Re: Weatherproof Distance Sensors ?
From the title and his original post, isn't it clear that he wants a
WEATHERPROOF sensor? Yours isn't and neither are other offerings in the
<$100 price range. I think there would be many people thrilled to know
about a WEATHERPROOF distance sensor for less than $100. For starters, this
would mean that it would work when wet.
Also, the Devantech or the new (see other thread) MaxSonar-EZ1 are about
half the price of the PSR-1. Is there an advantage of yours over those
offerings?
Mitch
Re: Weatherproof Distance Sensors ?
cost, size and flexibility. Putting the sensor in a plastic or metal
box that fits your specific platform is the best bet. Put a couple of
o-rings around the transducer and mount the sensor through a close
fitting hole in the box. Then ...
Have you tried putting a latex finger-cott over the sensor head? The
thin membrane will be acoustically transparent. One way I've used to
protect the transducers is as follows:
1) partially inflate a balloon. 2) apply a thin film of super-glue,
silicone RTV or epoxy around the side of the transducer. 3) press the
balloon against the face of the transducer so that the balloon deforms
over the sides of the transducer. 4) hold until adhesive cures. 5) cut
away excess balloon material.
Stay dry,
Larry
Stef Mientki posted on
Re: Weatherproof Distance Sensors ?
There are a lot of good hermetic sealed US transducers, between $5 ..
$10, see e.g. Farnell, look for "ultrasonic" or "400ET" or "400EP"
Stef Mientki
Re: Weatherproof Distance Sensors ?
Let's just say my project needs to visit drainpipes ...
Anyway, I wasn't expecting SUB-$100 weatherproof ultrasonics, but
$149.99 would have been bearable. Are you aware of anyone who has
put an ultrasonic behind a very thin rubber/plastic membrane and
got it to halfway work ? If it had a lot of xmit power ...
I think his offer an 'echogram' in addition to a simple
distance measurement - so faster offboard hardware can
do fancy stuff with the signal. Might be interesting,
especially if you used a binocular sensor arrangement
and some way to scan the beams around. A low-rez 3-d
'image' with exact distance easily availible ... but
you'd need to be better than me with the math because
it would be kinda like processing an MRI or CAT scan.
An echogram would also be cool for a robot sub - if
the sensor could be seriously waterproofed that is ...
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