Cheap ultrasonic distance modules for measuring liquid level

[jmaja]

Can modules like US-100 http://www.e-gizmo.com/KIT/images/ultrasonicsonar/ultrasonic%20sonar%20module%201r0.pdf be used for measuring liquid level? Could they even work through a plastic tank wall? If not, are there modules that can?

[BillyD]

They're good as a cheap way of measuring liquid levels, I'm using one for this purpose myself, but they are very sensitive to any sort of obstruction and therefore can't work through the tank wall. I'd imagine that any ultrasonic sensor which could work through tank walls and distinguish the liquid from its container would be considerably more expensive and complex.

[kripton2035]

you need the same but waterproof ...
if you leave this module inside a water tank, it will soon rust.
something like this
http://www.ebay.com/sch/i.html?_sacat=0&_from=R40&_nkw=ultrasonic+module+waterproof&LH_PrefLoc=2&_arm=1&_armm=63

[jmaja]

I don't want to cut a hole to the tank nor to put anything inside the tank. I know that depth sounders in boats work OK through 10-20 mm glass fiber hull, thus I was hoping these might work through 1-2 mm plastic wall. Of course in boats the hull is in contact with water while in tank there is air. I guess I have to continue with the original approach using a capacitive sensor.

[128er]

How big is the tank? Are there any mechanical constructions inside the tank? The medium is only water?

In many cases it is necessary to penetrate the tank. Even with continuous capacitive level measurements.

A few weeks ago, I've buyed two of this cheap ultrasonic modules (HC-SRO4). Want to play around with it, and also install them in a tank. I've made some measurements at my bench, with a fixed range of 1,60m. I dont know if it depends on my construction. But from 100 measurements were almost 30, more than 20cm out of the target. I have to do it again with more repeatable conditions, to see if it was my failure.

Thats my own experiments ^^. At work i have some experiences with professional industrial level measurements. In one plant there are many 20m³ tanks with chemical waste water. Some tanks are equiped with ultrasonic, others with radar measurements. It showed, that the radar sensors are more reliable and less sensitive for any type of distortion (such as: deposits on the sensorhead, or condensation at the sensor, etc. )

Take a look at some manufacturer to get impressions:
-Contactless capacitive sensor (only up to 100mm  )
http://www.sensortechnics.com/en/products/liquid-level-sensors-and-switches/capacitive-level-sensors/clc/

-All sorts of level sensors
http://www.vega.com
http://www.endress.com/

[nowlan]

Expensive, but capacitive through side of tank.
industrial capacitive =
http://www.ifm.com/ifmus/web/pmain010_020_010_010.htm
$40 surplus?

Reasonable cheap.
milone etape =
http://www.milonetech.com/About_eTape.php
$40

My Tunze osmolator has a similar optical level detector.
prism liquid level =
http://www.digikey.com/catalog/en/partgroup/lle-series/11975
$80

Pressure sensor (use with tube) for washing machine fill.
http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=MPXx2010
$10

handheld capacitive level $90.
http://www.bayteccontainers.com/c-level-liquid-level-drum-guage.html

[Skimask]

"X" number of temperature sensors on the side of the tank, say 10 sensors for arguments sake.  Read all 10 sensors.  Where the reading changes appreciably, the liquid stops.

Built something similar for a guy awhile back for a 5000 gallon water tank.  8 LM35's spaced evenly along the north side, epoxied to the side of the tank.  Using a PIC18F2550 to read the LM35's directly.  Takes readings from the sensors every minute, averages them out over 10 minutes, looks for the largest change between two side-by-side sensors, if there isn't any, looks for the largest change between every other sensor, send the high/low readings via a simple 433Mhz serial link back to another PIC with an LCD up at the house.  For extra credit, got a solar panel charging the battery pack up too.
The theory being, and it happens to work in this case, that air and water heat up / cool down at different rates during the day and night.  Therefore, the air will heat up / cool down faster than the water, wherever that change is the greatest, that's where the water line is.  3 seasons in and it's still working.  This summer, the guy wants me to add in a water pump on/off switch to it to automatically fill the tank.
And didn't have to cut any holes in the tank.

[jmaja]

It's a 80 liter tank of waste water and no internal structure. I don't need much accuracy, more like 1/4, 1/2, 3/4 full, nor 100% reliability. The measurement method must be without penetration. I have already tested a DIY capacitive sensor for a bottle and it seems to work OK. Ultrasonic would have been easier to install, if it would have worked from outside.

[Niklas]

Is this just for a hobby project or something for volume production?

[jmaja]

Hobby, at least now.

[Niklas]

Will you be able to read a square wave with a frequency between 100 and 150 kHz? 150 kHz is empty and 100 kHz is sensor fully covered with fluid. 3.3 V supply, 5x5 cm and glue to the outside of a non-metallic tank.