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Author Topic: Sensors to measure volume change, weight and distance  (Read 1119 times)
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Hi,

I have a research project whereby i need to determine the change in mass and volume of soil with time. Basically, as the soil dries it shrinks, and this rate of shrinkage is something I'm trying to measure in the laboratory. Arduino can log on an hourly basis the change in these measurements.

I have considered using a load cell sensor for the weight change......should be simple enough.
The volume change i could measure with a ultrasonic/laser sensor (ideally i need 0.1 mm accuracy) in the vertical plane, but the horizontal shrinkage i have no idea how i can measure this. 

The soils are placed in glass beakers.

Any ideas would be very helpful. I've been banging my head on the wall for a long time with this. Its an interesting and very practical arduino project that would help me get lots of nice data.  smiley-grin

Thanks...
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Quote
I have considered using a load cell sensor for the weight change......should be simple enough.
Sorry but not simple.
A load cell permanently under a load will distort and the reading will drift. That is why scales ask you first to turn them on and then put the load on them. This is so they can take a reading without to load on and use that as a zero reference.

Unfortunately in this day and age people expect that there is a sensor to measure anything, this is not always the case.
You will not get 0.1mm from ultrasonics.
Sorry to be not more constructive but nothing obvious springs to mind.
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Thanks Mike for the honesty.

The loads are typically 300 g, so not too high, but equally noted, if there was distortion could i not lift the beaker off the load cell for a few seconds then replace it (or even have a on/off switch while raised)? This should reset the system daily or allow me to see the zeroed data in the logged information that i can as calibration daily?

What distance sensor is best at the moment regarding precision? My sample height change is around 50 mm in the beaker, but the sensor can be mounted at any distance over the beaker to get the best precision. Note that the sample initially has water, then this eventually evaporates to show the dried soil surface.

I did think of a LVDT sensor, but this will have to be in contact with the water surface and slowly drop until in contact with the wet soil and then further drop with the drying of the soil. I saw this which could work:

http://www.lvdts.cn/lvdt_macro_sensors/lvdt_applications/h20_level_measurement.pdf

However, having a sensor in contact with the sample surface is not preferable due to affecting the evaporation rate.

 
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you could probably rig a little servo to lift your sample before every mass mesurement. this would allow you to set "zero point" automatically every time.
as for distance, i think optical reflection sensor would be your best bet. i have those installed in my digital wah-wah pedal (15 milimeters movement with 1024 steps) smiley-wink.
but this sollution would prolly still require you to put little reflector on top of the sample. it might me small piece of tin foil so hopefuly it won't affect your experiment
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Patryk,

Thanks for the comments. The optical reflection sensor could work very well. What accuracy are you getting in your 15 mm movement? Any suggestions on suitable sensor for this to try?

Perhaps, its an idea, but could an optical sensor measure the horizontal movement through the glass wall of the beaker? As the distance increases the reflection quality reduces. I guess it would require calibration.
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i honestly don't know how acurate is this thing. all i know it has 1024 step resolution, because that's the reading i get after hooking it up to the computer (and that's not sensor's accuracy, but A/D converter's resolution) smiley-wink

a quick google search gave me this: https://www.mysick.com/ecat.aspx?go=FinderSearch&Cat=Row&At=Fa&Cult=English&FamilyID=380&Category=Produktfinder&Selections=77544 it suppose to be acurate to 1µm.
it's a red laser so if your container is made with clean glass and it has flat walls, then the reading shouldn't be much affected. you might want to look for something a bit cheaper on ebay though smiley-wink
« Last Edit: September 13, 2013, 07:28:22 pm by patryk » Logged

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Patryk,
any indication of the price?
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I looked at the SICK sensors (DT50 and DT35), but the resolution is stated as +-10 mm. However, another research student reported they could consistently get 2 - 3 mm accuracy with this laser. However, after reading another post i'm not sure the SICK sensors can be connected to an Arduino.

Not sure which output is best compatible with the Arduino, PNP output or NPN output?

Regarding price, i was quoted almost US$500 for a DT50 (sensor only) where i'm located. In the states or Europe, it would be cheaper.
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I'm not making any promises here and cannot comment on the suitability of these sensors, but let's just say am kind of familiar with that SICK company. They were among the top European employers in 2012 and are, for over ten consecutive years, among the highest rated employers in Germany. 
IF you have an affiliation with an educational institution like e.g. a college or university (or pretend you are a grad student) and ask them nicely and offer a short descriptive abstract of your research in return, or mentioning their name in a paper you intend to publish, I am pretty sure they will "make things become possible". From personal experience I can assure you that having access to a university email address (or one from any other recognized research or educational institution, or convincingly bullshitting them) stuff will literally materialize out of thin air if you know what I mean. Politely asking never hurts! Most of these businesses will send free samples in small quantities IF you manage to sound like a legitimate, honest and eager person involved in legitimate research. Even materials that are pretty much unobtainable to the general population (due to their potential uses, e.g. defense related stuff) can be easily obtained via that route unless you happen to live in Iran, Sudan or North Korea... At least that's my experience here in Europe. Delivered to your doorstep by special courier service in the shortest possible time, for free.

If everything else fails, private message me and I might talk to my former neighbor who happens to be working for them (not exactly on the assembly line, but rather upper management).
« Last Edit: September 14, 2013, 08:02:18 pm by SMArd » Logged

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check this one out: http://www.ebay.com/itm/Balluff-BOD-26K-LA01-S4-C-Laser-Distance-sensor-NEW-/231041331307?pt=LH_DefaultDomain_0&hash=item35cb22f06b&_uhb=1

advertised 0.08mm reesolution
spect here: http://www.murri.fi/documents/balluff/BOD/BOD26K_LA01_S4_C_en.pdf
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Thanks for the comments. I'll get in touch with SICK and see if they can help. I'm intending to write a conference paper if i manage to get this thing working, so it would be in their interest.

Patryk, am i missing something. Is the beam width actually the accuracy of the sensor? If so i think this type of laser would work very well.
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This is an old thread, but for posterity sake, SICK UM30 and UM18 ultrasonic sensors should be able to get to the repeatability and resolution you are looking for. Their OD series of laser measurement sensors can also look thru the glass tube and give distances to the dirt. Two sensors looking at each other with the tube of dirt in the middle can be used to get diameter at that point. Sensor A - Sensor B - K (constant distance between sensor heads) = Diameter.

The DT35 mentioned is also under $400 USD.

The other poster is also correct about asking for a sample in exchange for info about the application, pictures, etc so they can learn about the application (successful or not) and maybe use it for write-ups, marketing, training, etc.
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Interesting discussion.   Air temp?  Turbulence? (movment doors/people/ventlitation) Air humidity?
Are theese factors to be included in the total equation.?
..this is what I call a real challenge!
I wish you luck.
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Ny

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