EQ tank temperature & level sensor recommendation

I was wondering if any of you folks with waste water experience could help me out. We are adding an Equalization tank at our plant's WWTP. The tank is made of concrete, is about 30' tall and sits mostly below ground.

We need to measure level and temperature inside the tank. Access to these devices will be through a 4' square hatch on top of the tank. Temperature inside the tank will be maintained between 90 - 110°F.

We'd prefer not to install an RTD 30' below grade as I'm sure troubleshooting & replacing would be a huge ordeal. We've used ultrasonic level sensors elsewhere but I wasn't sure if they are the best type for this application. If anybody's worked with EQ tank controls before, could you clue me in as to what type of devices can be used here?

Thanks in advance & Happy New Year!!!

I've had success with ultrasonic level transmitters. I usually prefer using submersible pressure transmitters, as they are less expensive and more robust. I've had luck with this type: http://www.keller-druck.com/home_e/paprod_e/36xky_e.asp

There are submersible temp transmitters like this: http://www.astsensors.com/submersible_level_sensors/AST45PT

I'mnot sure why you don't want to put an RTD below grade - use a thermowell, of course, but I don't see an issue, or a better alternate for that matter.

Does the tank have top access? If so, drop the RTD down on a cable. Easy to access, remove/replace.

Here's a sample of one vendor that has a watertight assembly (the transition to the lead wire needs to be watertight.

Tom Jenkins said:

I'mnot sure why you don't want to put an RTD below grade - use a thermowell, of course, but I don't see an issue, or a better alternate for that matter.

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The issue is that the tank is already in the ground and there's no easy access to the bottom from outside. Just so happened I was in a meeting today and someone asked how we could do this.

I'm up to my armpits in alligators presently, so I'll check out the links next year. Thanks again.

+1 on the AST sensors. They work well!!
AST does make an integrated temperature and pressure sensor, but I don't know if they make that as a submersible version. It might be worth a phone call to them.

How about guided radar for your level measurement?
http://www.us.endress.com/en/Tailor...evel-measurement/Guided-Radar-Levelflex-FMP51

The tank is 30 feet tall? Will the temperature be uniformly distributed in the tank?

I'd say go with the hydrostatic level sensor option as Tom suggested. Super easy for setting up your min and max % full readings... Just lower into into the tank until it hits the bottom then mark the cable at 100%. Pull out and measure distance from sensor to the mark. Very useful if it's an existing tank and you're not sure on accurate dimensions.

If the tank is fully sealed and you are somewhere with high humidity then ultrasonics can suffer from condensate build up on the sensor face.

If the tank is turbulent then you may need to install a stilling well to stabilize your reading and prevent damage to the sensor. A length of 2" or 4" PVC pipe with a 45 deg cut end and holes drilled along it's length works well. I only add the holes for equalization if there's a chance of sludge build up on the tank floor.

Saffa said:

If the tank is fully sealed and you are somewhere with high humidity then ultrasonics can suffer from condensate build up on the sensor face.

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Thanks Saffa, we were concerned this would be the case.

Saffa said:

If the tank is turbulent then you may need to install a stilling well to stabilize your reading and prevent damage to the sensor. A length of 2" or 4" PVC pipe with a 45 deg cut end and holes drilled along it's length works well. I only add the holes for equalization if there's a chance of sludge build up on the tank floor.

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GREAT IDEA!!

mendonsy said:

AST does make an integrated temperature and pressure sensor, but I don't know if they make that as a submersible version.

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I called and the AST45PT is submersible. I think we're going to try this one out.

Thanks again!!!