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Topic: recommedation for ultrasonic water level sensor? (Read 8 times) previous topic - next topic

Lavan

If you want to use only Ultrasonic, you can give a try replacing the existing sensors with water proof sensors.  Have a look at this link http://www.alibaba.com/product-gs/575210695/40KHz_waterproof_ultrasonic_transducer.html?s=p

gardner

For a cheap solution, I think I can do something with these:
http://www.sure-electronics.net/download/MB-SM19116_Manual.pdf
http://www.ebay.com/itm/Non-contact-Water-proof-Ultrasonic-Motion-Detector-Security-Sensor-Module-/120980811322?pt=LH_DefaultDomain_0&hash=item1c2b04ae3a

They are cheap at $13, but fussier to source than the $100 unit I mentioned first.

I can mount the board so the sensor peers through a hole and seal it up with RTV silicone.

retrolefty

Quote
I am very interested in trying a load cell to monitor the level of propane in a 300 lb cylinder, but that's a project for a different day.  I am curious though, if folks have real experience with a permanently installed load cell under a heavy load. Without the ability to zero it out once in a while, does it still provide usable, accurate weight readings month after month, year after year? In weather?


Commercial industrial load cells are very rugged and reliable unless subjected to large mechanical loads well above their maximum level. We used a lot of them in the refinery I worked at and rarely had problems with them. The best method to handle short term calibration factor is to have a 'software tare' factor in your sketch that you have the operator selects after placing a known empty cylinder on the scale. This will give your sketch a  'zero offset' factor you can subtract from the raw A/D measurement. Stability of your measurement over time will be more a factor of your external circuitry used to interface the load cell to the arduino. A load cell is a low level (millivolts) precision sensor and really should be used with an external A/D converter chip that has true differential input pins, internal voltage reference, and programmable gain, the added expense is justified in most cases and there are many such chips to choose from.

Lefty

gardner


For a load cell subjected to the elements


I'm not super worried about how to keep the thing dry and safe.

What I am worried about is extremes of temperature -- -30C .. +35C would be the range it has to deal with, and the fact that it would be installed permanently under an immovable load of 250Kg

When I use a strain-gauge load cell type scale, they always need to be zeroed out before they will give a useful readings.  In my application that would not be easy.  No one is going to go lift up a 1,000Kg water tank, or a 250Kg LPG tank, even every few days, just to zero out the load-cell.

Furthermore, when the mechanical linkages that transfer the weight of the tank onto the load cell are also subject to expansion and material property (elasticity) changes due to corrosion, temperature changes, fatigue, creep, age hardening and whatnot, the complexity of a permanent installation such as mine is rather high.

For measuring the water level in a 1,000L tank, it's not a winning approach for me.  For measuring the fuel level in an LPG tank, it's likely the best I can hope for.

gardner


This has a range of 0 to 1.45 PSI or 0 to 1019mm of water. Connect a tube to the port and anchor it to the bottom of the tank and it will have a 0 to 5V output based on the water level.


I wanted to follow up on this, because it is something I evaluated fairly carefully.  The problems are:

If you position the sensor at the bottom and have it reading the pressure of the water, it works great, but the sensor must be one that is able to work with a water medium, day after day, month after month, in continuous service.  The cheapie sensors are not suitable for this service.  I have an application where I do need to do this, and what I have in mind is to have the sensor read the pressure in a small balloon of dry air that is, in turn, submerged in the medium.

If you have the sensor at the top and have it read the pressure in a dip tube stuffed down into the water, you will have two problems: the air in the tube is not dry, and so it potentially runs up against the capabilities of the sensor, and worse, the air in the dip tube gradually dissolves in the water and effectively escapes over time.  So a few weeks down the road the water level appears to have dropped by 100mm.  There are workarounds, of course.  Like pumping air into the dip tube periodically to make up for lost air and stuff, but the complexity of the solution is greater.

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