level relative to what? what accuracy? why not just stick a yardstick in the middle of the pond?

If you have a decent rangefinder with tilt measurement, it can, or you can, calculate the angle, vertical run, and horizontal run.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

"1. the angle of the beam. We will mount the transmitter on the pond edge and aim it to the middle."

Why - does the pond surface slope? Are you making this measurement harder than it needs to be - the level at the edge wil be the same as at the centre.


An old technology but still applicable in some awkward cases, especially dirty ones with no means of mounting an overhead sensor: have you considered a bubbler-type instrument? An example from Google - no affiliation http://www.lesman.com/unleashd/catalog/level/level...

Generally I would use an ultrasonic level instrument mounted on a pole in the pond away from the edge. The reason for mounting in the pond is that as the level of the pond falls, the edge of the water will move toward the center of the pond. Ultrasonic level meters work great on liquid surfaces.

1) Laser
The laser has to penetrate any fog or steam both out and back.

The laser undoubtably has a lens. When the lens gets dirty or fogged the lens will inhibit the laser energy, and cause an issue with reliability. The lens will likely fog is the laser is suspended where its temperature is cooler than the dewpoint of the 'steam' arising from the water.

2) Submersible head pressure
It isn't clear how hot the water is, but submersible pressure transmitters are widely used for water level measurement.

As long as the transmitter body is below the level, you'll get quite accurate readings.

Operating temperature specs are all over the map:

Wike LS-10 is rated to 50°C (122°F)
GE 1830 to 60°C (140°F)
Siemens MPS to 80°C (176°F)
Ametek 575 is rated to 82°C (180°F)

Freezing will damage any of them.

Secure the transmitter to a stake/pole/strut driven into the bottom of the body of water.

The 'cable' includes an atmospheric vent tube that can condense humidity from the atmosphere if the vent tube is below the dewpoint of the ambient air. Collected condensation can appear as a offset resulting in an indicated level lower than expected. But in an elevated temperature environment, that's not likely to be a problem.

3) Ultrasonic
Ultrasonic is widely used for water level in open channel flow measurement.

Nice summation Dan!

Keith Cress
kcress - http://www.flaminsystems.com

Add radar to the list to Dan's list if you have the means to suspend a sensor above the pond. They generally work well in dirty environments which might upset optical solutions. That isn't clear from the original information.

Thank you for your replies.

djs has identified our problem. When the water level is low, the water is well away from the pond edge. building a structure out to the middle of the pond, to hold a transmitters, would be expensive. I have read that laser can be pointed at the water level from the side (angled).

In the past we have used ultrasonic transmitters with a stilling well next to the pond.

How much does sinking a telephone pole in the pond cost? probably less than what the instrument costs.

The pole is the cheap part. The walkway across the pond for access to the transmitter that the plant owner will want will cost.

Why not a low power wireless data link powered by battery charged by solar?
How often is data needed? Wake up, measure, transmit, sleep until next interval.
That's the mode of operation my wireless weather station uses. A 3.5V lithium with a small solar charging panel lasts 8-10 years.

Or just drain the pond, problem solved....

-AK2DM

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"It's the questions that drive us"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I've installed several transmitters that are powered by a Banner Engineering industrial radio which has configuration for sleep period (Like 20 minutes) after which it wakes up, powers the transmitter from its battery (configurable delay for power-up initialization, takes a reading, sends the reading via radio, goes back to sleep.

I don't play with laser, so making an angular shot at a distant point which is interpreted as elevation/level might well be doable, but it's outside my experience.

I'd throw a pressure transducer out in the middle and call it a day.

If you're worried about fouling then use the old trusted bubbler method.

Keith Cress
kcress - http://www.flaminsystems.com

The walkway is for servicing the unit. My experience with Ultrasonic units is that they rarely need servicing. Say once every 10 years. Get the owner a boat.

If going to put something out in the water, why not a traditional float sensor? Put a pipe around it, average the inputs to remove the wave action(minimal if mounted in pipe). I have used ultrasonic successfully too and they are very inexpensive (mounting issue too)