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Old January 10th, 2019, 11:29 AM   #1
rajy2r
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Boiloff Tank Level Measurement

I am looking at a Small Boil-off Tank (5' High) rectangular, and need to do some level measurement. The current tank has an opening at the top, so looking at options i could use with that unless i have to put some connections on the side.

It's some run-off water from wood drying so it foams quite a bit. I am hoping for a 4-20ma signal, so i can do a slow boil-off of rapid based on the water coming out.

Capactive and Radar are out as they won't eliminate foam. Any suggestions of something you might have used with some practical pricing.
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Old January 10th, 2019, 12:15 PM   #2
danw
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Submersible head pressure transmitter, if the temperature is within range because it goes in from the top. They come with an atmospheric vent tube that should be terminated in a dessicant to keep moisture out of the vent tube.

Or poke a hole at the bottom and run an impulse tube/pipe to a low pressure pressure transmitter. 5 feet is 60 inches of water column pressure, or 2.16 PSI. 2 PSI uses 40% of the available output of a 0-5PSI pressure transmitter, probably good enough for this application.

Head pressure is sooooo reliable for water level measurement, even the units inches or feet of water column are intrinisically the correct units.

Put ultrasonic on your list of technologies that can not handle foam.
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Old January 10th, 2019, 05:06 PM   #3
rajy2r
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Quote:
Originally Posted by danw View Post
Submersible head pressure transmitter, if the temperature is within range because it goes in from the top. They come with an atmospheric vent tube that should be terminated in a dessicant to keep moisture out of the vent tube.

Or poke a hole at the bottom and run an impulse tube/pipe to a low pressure pressure transmitter. 5 feet is 60 inches of water column pressure, or 2.16 PSI. 2 PSI uses 40% of the available output of a 0-5PSI pressure transmitter, probably good enough for this application.

Head pressure is sooooo reliable for water level measurement, even the units inches or feet of water column are intrinisically the correct units.

Put ultrasonic on your list of technologies that can not handle foam.
Thanks Dan. We are only trying to control 12~18". And i couldn't find a submersible unit with enough rating for the boiling water (Seems like they max out at 70C). My only concern with the side mount unit is the possibilty of gunk building up in the drain port we have.

Would a low pressure unit work well for 12~18" ?
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Old January 10th, 2019, 06:47 PM   #4
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RayJ2R - You could use a Guided wave Radar Level Probe. They are available in 4-20mA outputs and multiple probe lengths. Also highly recommended for foam environments. Not sure on cost though, but I doubt its cheap.
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Old January 10th, 2019, 07:00 PM   #5
danw
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Wika has a 0-50 inwc range for its S-1 cylindrical 2 wire gauge pressure transmitter (8367656) with a 1/2" NPT male process connection.

I assume the tank is an open tank, not under any pressure, where you can use a gauge pressure (atmospheric reference) transmitter, correct?

Using 18" of a 50" span is 18/50 or 36% of the range. I'd do it. That uses 4.0mA to 9.76 mA.

A 'smart' transmitter that can be ranged down to 18" but those transmitters are $2k.

Make a sludge trap by creating a U basin. Hydrostatic pressure is the same at all elevations, so it works OK. Put a cap on the bottom of the Tee and remove the cap to flush the sludge out.

The dashed line is at the elevation of the sensing diaphragm. If the diaphragm is too high, like in the drawing, you can't measure anything below the elevation of the dashed line. If the transmitter moves down (remove the reducer) then you might have a false amount of level because the sensing diaphragm ends up below the bottom of the tank.


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