hello all,
iam working on a project where i have to indicate the level of sand present in the tank.there will be only 2 indications..Full and empty.a bulb or LED will indicate the position of sand.
http://img177.imageshack.us/img177/9134/58274791zf8.gif
now the issues are.
1.if u look at the picture the empty and full levels formed by the sand will be concave and convex.so floating and magnetic sensors won't work.
2.the inside environment will be very dusty so i can't use opto method.

can u guys help with this issue?
my friend said ultra sonic stuff will work.but can i use them for such condition?

 

What is the vertical distance between empty and full?

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Ron

 

What about acoustic? Sand is a pretty decent conductor of sound and will give you almost as good a reflection at boundry changes as beteween rock and air. A simple acoustic transciever at near the low level area will give you very good feedback on when the sand gets that low. If you don't know what kind of signature or signal to look for you can start by simply using a 'ping' of medium frequency and immediatly switching to listen and recording what is heard, and viewing that to see how your signal changes as the level does.

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I would try capacitance with one electrode (or set of electrodes) at each level. I've never tried sand per se, but it should displace enough of the air to make a reproducible change. John

 

With electrodes on the side's of the container it might be more sensible than acoustical methods. It might be finacky though, the capacitance change isn't going to be great.

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The dielectric constant of SiO2 is about 4. The dielectric constant of air is, of course, 1. That should translate to a 4:1 capacitance change, assuming the sand is mostly SiO2, and there is no air in it. Of course, there will be air in the sand, but I don't think it would be too significant. Moisture might complicate things.

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Ron

 

the distance between the upper and lower level is 30cms.
all i have to do is indicating.A RED light when empty and a green when full.
i don't want it much precise.just rough estimation and lights shld glow.

i don't understand the capacitance method.how it works?

acoustic -can i use it for rough conditions?
if u guys have any rough circuit ideas pls do share.

 

Capacitative sensors are extremely common. They are used for fuel level measures, touchless switches, etc. They depend on the change in capacitance when a substance gets near one or between both plates of a capacitor.

The Zircon stud detector (but not metal detector) is a capacitative detector (See: US patent 6023159).

Search on capacitative detector, proximity detector, or capacitative sensor.

See also:

http://www.analogmicro.de/index.htm (provide pretty much a one-chip solution -- check out the CAV414)

John

 

I can't load the image, so I don't know the exact physical situation, but...

How about a sonic ranger pointing down into the container?

Do you know all the dimensions of the container? Will it always contain the exact same type of sand? How about calculating the full and empty weights of the container and measuring the weight as a signal?

 

what about a strain gauge or similar slipped under the container?

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can u guys help me with some rough circuit idea.
any sensor which u think best suitable for this purpose.

strain gauge and capacitance idea seems to be good.but i have no idea abt their circuit. i'll be regretful if u can help me with this issue.

thanks and regards

*the pic i posted is ok.i can open it.

 

Did you check any of the links? The CAV414 link has a full schematic with values. What is your level of experience in going from a schematic to a finished item? John