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Posted by B1ackwater on January 9, 2006, 11:33 am
Please log in for more thread options wrote:
>B1ackwater wrote:
>> 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.
>>
>
>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.
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 ...
>Certain important optically-based sensors have been known to mount a
>miniature mechanical wiper on the front glass for these types of situations.
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* :-(
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> 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.
>