Splash & spray experiment

Can somebody please point me in the right direction.

I'd like to do an experiment to measure the spray that comes off car tires traveling in the rain. I thought about rigging up a small system consisting of a laser, collimating lenses and a light sensor to measure the intensity of the laser through the water spray. Any suggestions as to what laser and light sensors (and vendors if you know any) would be appropriate for this type of application. The laser will travel the width of a car/truck tire ~ 200 mm max. I'm thinking to hook the light cells to a multimeter to check the drop in light intensity as the laser passes through the water spray/fog. I've never worked with this before and am on a very low budget. Any help is appreciated.

First off.... Welcome to the Forum...

We would need a bit more info.....
What is it used for....
What actually are you wanting to detect...
(Volume of spray.... density of spray....color of spray.... the existance of
spray... and so on....:-? :-? :-?)
And why specifically do you need a Laser... :-?

Jerry

Thanks for the welcome !

I considered using a laser as it (will?) give me better control over pointing direction. I also suspect that the beam from a flashlight may be too dispersed by the water fog/spray. I want to use the light intensity measurement as an indirect measurement of the "density" of spray. Some road surfaces are more porous than others and would not generate as much spray - I'm looking to quantify this effect. One way would be to collect the amount of water coming off the tire - I think using light measurements is a more practical approach.

Wouldn't a laser only give you a small cross section of the spray and therefore change value depending on the direction of spray and car speed?
Also laser light might act funny around the water droplets and as refraction through a large droplet or blocking by a stone could alter the results you'll need a way to store them and make an average.

sounds like a fun experiment though

Thanks for sharing your criteria...
Using light as a detection system would create a lot of variations...
(ambient light... road grime...etc)... but I suppose over the same stretch of
road on the same day at the same or near time stamp the reading variables
would be minimal..

Not to forget... your laser and sensor would be neat the spay and will themseves
be variable by the amount of water/dirt on the lenses.

Maybe directing the spray towards a container to be measured after or on
the the fly... That would get rid of a few variables...IMO..

Jerry

Viracocha said:

Wouldn't a laser only give you a small cross section of the spray

Click to expand...

Yep, I've considered this - hence the need for 2 collimating lenses - one to spread the beam and another to refocus it. I'm not sure how effective this will be though. Since I'll be doing the measurements in the vicinity of the tire, the direction of the spray should not be an issue (I'm guessing). Yes, testing will need to be done at a constant speed, say 60 mph. Another idea is to video a black & white image behind the spray and to determine the average RGB values from the video bitmaps as a measure of the spray volume. This requires more work though and an expensive waterproof camera beneath a tire traveling at 60 mph. I've googled and see one can pick up small lasers and light sensors for next to nothing, I'm just not sure what would be the right equipment for this type of system.

There are so many variables , even the color of the road will change the readings, maybe by just measuring the ammount of red light from a picture taken by a camera...

anyways I dont think thats a good method ;p

edit: the ammount of water in the road will change with every meter so how to put the same place with diferent roads but with the same ammount of water?

I'd forget about that

If you want to use light for this you might be better off using a difuse light source like a flourescent tube behind a bit of white perspex on one side of the rear of the wheel and a solar panel on the other side, then wrap the whole thing in a box so the only light is from the difuse source.
A couple of guides on ether side of the wheel to keep the spray off the light and solar panel, and you should get fairly constant readings. Although this may only work to indicate the amount of dirt that is sprayed by the wheels as the water could refract rather then block the light.

Lasers are very precise and this seems like a very unprecise requirement, the two just maybe uncompatable.