Looking for Water Level measurement Options

P

Thread Starter

Pavan

Hello

I am looking for suggestions for measuring continuously water level of range 10 meters to 100 meters range in hydro power plant such as surge tank and water well and river.

I had though of Ultrasonic type but those are available up to 40 to max 60 meters only. Other than that a simple pipe, float based coupled with multi-turn potentiometer can also be worked out.

What could be the easy, reliable and accurate solution.

Any suggestion are welcome.

Thanks in advance.

Regards
Pavan
 
There are commercial submersible head pressure level transmitters. They are frequently used in wells. It's dropped down, suspended on its own electrical/vent cable with the transmitter at the bottom.

The cable assembly includes some form of flexible breather vent tube so the pressure cell can get an atmospheric reference pressure. Sone are available with a sturdy stainsless steel cage around it to protect the sensor from debris.

I know I've used one for a 100' well. I assume that longer length cables and slightly higher range pressure trransmitters should be available.

The water temperature can easily be colder than the dewpoint of the atmospheric reference air in most climates, causing condensation.

It is important that the vent tube not collect condensed moisture, which can drip to the bottom, apply its own head pressure on the reference side and make the transmitter give a false low signal.

There are dessicant drying cartridges that are used to dehumidify the open end of the vent tube.

Wika, Siemens, Ametek are brands that carry submersibles.

David
 
Thanks David for your suggestion.

I have one more question, that if I want to use WIKA LH-10 submersible pressure transmitter, it has vent tube to give me differential pressure that is equivalent to water level above the sensor point.

Now if I do not use the vent tube and close it permanently, in that case LH-10 should give me absolute pressure as sensed by it. I can have another pressure sensor on ground exposed to atmospheric pressure, and both these output i.e. submersible pressure and atmospheric pressure is given to electronics to get the differential pressure. Will this arrangement be OK? This will avoid any maintenance requirement of vent tube. I am OK with sensors and electronics, so I can easily interface the arrangement.

Regards
Pavan
 
W
Unless Mr. Anonymous is a SAAB-Rosemount rep, the use of radar in water level measurement as compared to a downhole pressure sensor from Wika, PSI, or a buncha other people is downright silly. The huge cost differential alone would make radar an irresponsible choice for this application.

I have used "cigar-style" downhole level sensors for this application for over twenty years, from a variety of vendors, and even, in one employment, manufactured my own. They are accurate, repeatable, difficult to injure, and
are essentially as maintenance-free as a sensor I've ever used can be.

I recommend you use the vent tubing, and cover it with insect screen, and locate it where it cannot be flooded.

Walt Boyes
Editor in Chief
Control magazine
www.controlglobal.com
blog:Sound OFF!! http://waltboyes.livejournal.com
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Putman Media Inc.
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Pavan wrote:
> Now if I do not use the vent tube and close it permanently, in that case LH-10 should give me absolute pressure as sensed by it.>

The transmitter is designed for gauge pressure output with a reference to atmospheric pressure.

The transmitter pressure output will only be absolute pressure if you can evacuate the reference side with hard vacuum to absolute zero (which is what is done for absolute pressure transmitters), then seal the reference side off and maintain the integrity of the seal.

Just closing off the reference side in a breathing atmosphere will leave some given pressure on the reference side (and depending on the temperature that might be involved in the sealing, for instance brazing or welding).

The construction of the transmitter would determine how well the reference chamber would hold its pressure under conditions where it's submersed and external pressure is applied to the body.

Whether the reference side can be effectively sealed off is really a question for Wika, or any manufacturer.

Pavan wrote:
>I can have another pressure sensor on ground exposed to atmospheric pressure, and both these output i.e. submersible pressure and atmospheric pressure is given to electronics to get the differential pressure. Will this arrangement be OK? >

No. You are assuming the submersible is absolute, and it isn't. The correction for an absolute submersible would be to add to the absolute level value the atmospheric (barometric) correction value, but that barometric value would require another absolute pressure transmitter. Absolute pressure transmitters are the most expensive kind of transmitters and you do not need an absolute for this kind of application.

If the relatively minor changes in atmospheric pressure are not of concern (because those changes do contribute to an error), then ideally having a transmitter with its reference side fixed at sea level atmoshpheric pressure (or whatever your average barometric pressure is) would be useable. The output would be gauge pressure, just like the vent tube is.

David
 
I concur with Walt,

The "cigar-style" probe is well (no pun intended) established in the industry.

The problems that I have seen include:

-Lightning destruction of the transmitter or secondary equipment

-Condensation in the vent tube

-Poor grounding

These can be mitigated by proper choice of manufacturer and following their instructions for installation and maintenance.

Having an insect screen and desiccant will help reduce the condensation and debris. Most manufacturers have a kit to do this.

Try Druck for their resistance to lightning (they claim to have a transmitter which will operate after the strike -- I have yet to witness a transmitter failure, I have seen secondary instruments destroyed -- I suppose that if I were in Florida I could see a transmitter having problems).

Grounding is site and contractor specific (use your own caution there).

Dennis
 
Hi Pavan-

See my comments below.

> I am looking for suggestions for measuring continuously water level of range 10 meters to 100 meters range in hydro power plant such as surge tank and water well and river. <

There are many options. The most accurate is
laser which would work very well with quick changing levels and accurate.

The economical option would be a submersible unit that would work up to 200 meters. See link:
http://www.hitechtech.com/submersible_pressure_transmitter.htm

> I had though of Ultrasonic type but those are available up to 40 to max 60 meters only. Other than that a simple pipe, float based coupled with multi-turn potentiometer can also be worked out. <

Ultrasonics also have high wind and noise issues. If there are gusts, you could lose your echo as the wind would move the sound out of range, away from the transmitter.

> What could be the easy, reliable and accurate solution. <

1. A submersible aka "Cigar style" sic. :)
2. Laser more accurate and fast response but very expensive.
3. Radar but that would also be expensive.

HTH
-Steve
 
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