Opaqueness of Water Measurment

Hi all,

I have a question that I hope some of you vastly experienced people might be able to give some advice on . Has anyone ever come across a sensor that measures the opaqueness of water?? Or a better term might be a sensor to measure how "dirty" the water is??? I guess I am trying to relate dirtiness of water to a colour. I have done a google search, and have not found too much. I found something to what I am looking for, they use it in a Maytag dishwasher. I couldnt find it in an industrial form. This is not a pressing issue for me, but it is just something that has me curious. Any idea's would be great.

Thanks

Andrew

Google on "turbidity sensor" ... see what pops up ...

In the water and wastewater industry this kind of instrument is called a "nephelometer" and the unit of measurement is the NTU (Nephelometric Turbidity Unit).

And I have no idea why.

I can't remember exactly what it is called (not even inexactly) but we are using a radioactive sensor that measures the density of the water that is flowing by the sensor port. Using the density of clean, deionized water as a reference point we make a "relative" reading of the density of the "dirty" water.

It's a spendy little device with all of the "You gonna die!" warnings attached.

From what I've read, the Nephelometric Turbidity Sensor mention by Tom and Ron uses the light-scattering effect to make a "relative" measurement. I see that those devices are a bit spendy as well.

Speaking of "relative dirt" makes me wonder if there is such a thing as an "Absolute Dirt Sensor". Those of us that have been married for more then a month or two (Honeymoon is over, don' cha know?) have undoubtedly sensed that there is such a thing as an "Absolute Dirt Sensor".

Anyway... it occurs to me that you might be able to roll-yer-own. After all, somebody "rolled" the first commercial one.

This is all off the top of my head...

It seems you would need a light-source that has the ability to weave its way through any particles - if it can - to an analog light detector.

Infra-RED has a very long wave length. Ultra-VIOLET has a very short wave length.

There are plenty of RED and Infra-RED LED's available on the market as a light source. Recently BLUE (Near Ultra-VIOLET) LED's have been developed.

I suspect that the BLUE LED's would have the better chance of passing through the particulates to the detector.

BTW, have you noticed how the headlights in the newer cars are all shifted toward the BLUE-end of the spectrum? Might be fine for the driver, but it sure is a killer for the oncoming drivers.

I wonder if the general detectors are sensitive to the BLUE-end. They should be. But what kind of resolution... I wonder.

hmmmm....

comments?

If you can apply it, there is a less expensive way.

I work on 2 processing lines with Baume (Specific Gravity) Meters.

Since pure water has a S.G of 1.0, any contaminates (other than lighter than water oils) will increase the solutions weight.

You may be able to use something like this, say when S.G. rises to 1.25 the metal band on the meter activates a proxy switch.

Another possibility I work on is a Light Cell, available from a few vendors, that contains a light and photocell that can detect clarity, bubbles and specific compounds in the water (copper, nickel, tin, acids, alkalines, etc.)

Greg

Opacity Meter

There are brands of Opacity meters available in the market that can provide analog and digital outputs.

In the past I have across an Opacity Meter with digital output. The application is on Opacity measurement of Steam condensate return and energizes a solenoid valve on detection of dirty water.

Try few links below for your reference:

http://www.bestobell.com/products/bca/4/default.asp
http://www.directindustry.com/cat/optical_measurement_instruments_I_312_61.html

Regards,

Vic Jasareno

In the Water/Wastewater industry we use Turbidity meters. To put it into simple terms, they measure the "clarity" of water. You can get benchtop or on-line instruments.

Check out www.hack.com they are probably the best in the industry.

Hello !
Here is one brouchure of that kind of gauges.
Check out www.endress.com or metsoendress.com (finnish)

Could GuestPat stop putting those kind of links that open pop up´s and
tries to make it my home page !!


No attachment to big sorry!
download from:
https://easy.endress.com/apps/downl_pilot/downl_req.cfm?downl_id=4406

We use a turbidimeter, Surface Scatter 6, made by Hach (pronounced hawk). It works by shining light into a running sample of water and reading the amount of light that is reflected (scattered) back out of it. The fewer particulates in the sample, the more light is absorbed down the sample tube. The more "stuff" in the sample, the more light hits the particles and is scattered back out to the sensor. This scattered light is then converted to a 4 to 20 mA signal. I don't really recommend these units since they require lots of maintenance. In warm weather algae grows on the walls of the sample tube quickly and throws the reading way off but they work ok for us.

Thanks!!!!

Gentlemen,

Thank you very much for the responses. I think this is exactly what we might be looking for. I am not the one engineering the project, but will certainly pass this on to the ones who are.

A little quick and dirty background on the project( I have left out details):

What we are installing is a Fume Scrubber. What it does is sucks in dirty contaminated air from our process tanks. The scrubber has a basin at the bottom of it filled with water. Recirc. pumps continually recirculate the water upward into spray nozzles, and the water falls back down into the basin. Hence the cycle continues. The dirty air is drawn into the scrubber, upwards through the sprays and out a stack outside. When the dirty air hits the water sprays, the dirt particles are knocked down into the water basin. Eventually the recirc water get dirty, and they add more water to help desolve the particles. Orignally the people enginnering the project wanted to use a density meter to determine if the water was dirty, but they are mega bucks. So they settled on a conductivity analyzer.

This might be a better solution to the conductivity analyzer in my mind. I will have to see if the powers to be agree.

Again, thanks very much for your help and suggestions.

Andrew Evenson

It's called a turbidity meter.
Take a look at apv.com

Turbidimeters are not cheap.

Most fume scrubbers also add caustic or hypochlorite to chemically react with odor causing materials. In these cases it is fairly standard to use pH and/or conductivity to trip a blowdown cycle.

If you are mostly concerned about suspended contaminants, Royce metering (now a division of ITT Industries) and others make what is called a sludge blanket detector, some of which are optically based. Do a search on this site for wastewater instrumentation:

http://ww.pennnet.com/home.cfm

You can probably roll your own pretty cheap with a rectangular sight glass with two windows and a through beam photo switch. By adjusting the sensitivity or position of the switch you can make it trip an input when the transmitted light falls below a setting. That is essentially how nephelometers work. Make sure you have a convenient way to clean the inside of the sight glass - fouling will be an ongoing problem.

You probalby also want to have a timed blowdown as well as a precaution, based on scrubber run times.

Tom,

Just a wild idea.....

Have you ever played around with a Devicenet photo cell and used the diagnostic word (the one that measures signal strength to flag a dirty sensor or reflector) instead of the on-off signal? Kinda like a poor man's light meter or something to that effect.

Actually, Greg, I've never done wet scrubber controls - only dry gas scrubbers. I do keep my eyes open when I wander around these plants, though, to see what else is out there. I think your idea has a lot of merit.

Tom. If you check this site I am sure they give a description of what a Nephelometric Turbidity Unit is compared to the older style scattered light unit.
Regards Alan Case

http://www.wtw.de/