High accurate liquid level measurement

Smikac writes:

Can you guys help me about high accurate, less than 0,5 mm, liquid level measurement

Hello, Smikac, and welcome. More details would help here - what sort of liquid, what height range, what temperature range. And, out of curiosity, why the need for such a precise measurement?

Lapinbleu,

Not sure if he has the same problem but I encountered one customer once who wanted very accurate level indication.

They had a large, 50 meter diameter, 10 meter high water tank that they wanted to measure the level from. They neglected to tell us the accuracy that they wanted but they chose our quote over the others. We installed a pressure gauge that was calibrated in meters of water. When they learned that the accuracy was about +/-50 centimeters, their eyebrows shot up (it's amazing how high some of them can go). They said they wanted the accuracy in millimeters. I asked why and they said, 50 centimeters of error means almost a thousand cubic meters of water. Back in those days (about 20 years ago), there wasn't much you could do with the available technology.

Smikac,

I believe the new laser level transmitters can give you accuracy in millimeters as well as the radar types. I'm not sure if they can give you 0.5 mm accuracy but it would be best if you looked at the manufacturer's literature. You can try googling for the following instrument manufacturer's websites:

Foxboro, Endress+Hauser, Emerson, Honeywell, Yokogawa, to name a few. You could also google "level transmitter" and you'd get a couple million hits.

Good luck.

We use radar level transmitters to do the job in most case since they are not affected by vapors from the measured fluid. Check out www.nagllc.com

See this link http://www.enraf.com/default.aspx?topic=Servo&app=Content&sub=&cpID=296&miID=351

Question: is your fluid level stable enough? No wave, ripple from vibration?

It's very well to suggest laser measuring systems, no doubt fragile and expensive, but might I suggest the good old-fashioned float, pulley, string and scale method. Perhaps this seems too low-tech to be true... An open-ended tube inside the tank to guide and carry the float should solve problems caused by waves, and you could always make a Vernier scale to achieve the necessary 0.5mm accuracy. A-a-a-and no electricity! Just a thought from an old bog-trotting engineer, who has too often seen overly-sophisticated equipment eaten by the elements...

Yup, I was talking about water. If your liquid is corrosive or has vapors, then laser might not not be a good idea.

I don't think you can achieve +/-0.5mm accuracy with a float level though. If the temperature changes in the tank, the water density will also change and affect the buoyancy.

It's a little too late to say this, since I've already posted a suggestion, but +/-0.5mm seems too much. I've never encountered a level measuring requirement that needs this much accuracy. Back in my previous post, I asked the owners of that huge tank if they were planning to use the level to bill their customers. Of course, the answer was no so I told them that this much accuracy was totally unnecessary.

There's a company called Mohr and Associates that has a guided ultrawideband radar level sensor that could probably do it -- their electronics have 0.7 ps timing resolution, which works out to about 0.2 mm resolution in air.

http://www.mohr-engineering.com/efp-guided-radar-liquid-level.php