infrared Liquid level detector-SharpGP2D12 - Page 2 - Electronic Circuits Projects Diagrams Free

fantabulous68 · 12th September 2009, 05:51 PM

Quote:

We are concerned about reflection from surfaces or interfaces other than the liquid's top surface.

In your case, you need to show that the reflective surface being measured is the air-liquid interface ("A" in the above example), not some other surface ("B" in the example).

Quote:

1)do you have a stable way to position the detector, like a ring stand and clamps, or is it just being hand held?

The sensor has holes, i fastened one side of it with a nut and bolt....its at the edge of my breadboard. Its fixed...

Quote:

2) What are the dimensions of your liquid container(s)? Is your detector situated over the center or near an edge? Do your results vary if you move the detector off center? I looked briefly at the datasheet and suspect you may be able to move one direction, but not the other, without an effect from the edge of the container.

Im using a glass tumbler...it has a bluish tint. I positioned the tumbler so that the detector is over the centre.....(i used a plumb bob to verify this)

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4) What was the "green" solution? Was it green-tinted water? Is it colored with a dye or a pigment?

Its hehe dish washing liquid...pretty thick

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It is great to see someone on these forums who is willing to put forth the effort and is not just an "I want the answer type."

Why thanks...

I'll answer the rest of your questions when i take new readings later....im half way done with my presentation for superconductivity..

fantabulous68 · 12th September 2009, 06:59 PM

MR RB

Quote:

Putting a 10uF cap right at the sensor power between +5v and ground is supposed to help, and also doing some low pass filtering of the analog voltage out would help especially if you have long wires between the sensor and the PIC.

What RC values would you recommend me using?

ericgibbs · 12th September 2009, 07:17 PM

hi Miss Fantabulous,

Its refreshing to see someone putting the time, effort and detail into their project as you are obviously doing.

I'm sure most of the older members of this Forum feel the same way as I do, well done, you deserve every success with the project.

Mr RB · 12th September 2009, 09:25 PM

Quote:

Originally Posted by jpanhalt

...
1) When you do these experiments, do you have a stable way to position the detector, like a ring stand and clamps, or is it just being hand held?
...

3) The experiment I suggested earlier was designed to detect secondary reflections that might influence your results. In other words, at a set distance from the liquid's surface, the value you get should be exactly the same (within experimental error) regardless of the depth of the liquid. A water depth of 1 to 2 cm was chosen, as that would allow a significant percentage of your IR light to penetrate to the wall.
...

I think 1) might be an issue especially up close if the sensor is at a different angle to the liquid surface the close readings will vary. There's still too much variation in the different charts for my liking, as IF the Sharp sensor is measuring the surface reflection properly then the weird rises/dips in the charts just won't happen. So it is either not reading the surface refection properly or there are errors in position and angle.

For 2) the problem with a liquid depth of 1 to 2 cm is that the sensor might just have been measuring the bottom of the container. That's why I said to the OP before it really needs some testing of the same surface distances, but with varying liquid depths, to test if there is any effect of change in depth and that it is always measuring the surface reflection only.

Fantabulous-
A 10uF cap right at the sensor between +5v and ground (tantalum is good). For the low pass filter it is not critical, the Sharp sensor takes one reading every 40mS so you can just put a large (0.1uF ?) cap on the ADC input pin and rely on the Sharp output circuit having some impedance so you don't need a series resistor. If this is eventually used for liquid measuring in a tank you could go for a much larger cap as the liquid level will never change that fast and the more filtering the better.

fantabulous68 · 12th September 2009, 09:47 PM

Quote:

Very nice. I love experimentation. Did you vary the depth of the liquid or just the distance from the liquid's surface? The experiment I would sugest is water in a deep bowl. Add about 3 to 4 cm of water and measure at 10 and 20 cm from the surface. Then increase depth of water 10 cm and repeat.

John

Edit: On reconsideration, make the initial water depth only 2 to 3 cm. Keep the rest the same.

Ok all the previous measurements were me varying the distance of the container to the sensor...........

But now i am varying the level of the liquid in the container...........................

I varied the level of water in a glass and plastic vessel......see the attached doc...
I will take more readings when i get time, will take readings at 2 10 20 ....80 for various liquids...got to finish up my presentation

Quote:

hi Miss Fantabulous

hehe Hi Mr Ericgibbs you got it right this time. Thanks

jpanhalt · 12th September 2009, 11:01 PM

I am assuming the x-axis is the depth of water in its container. Correct?

Did you keep the distance to the water surface constant? That value should be kept constant...actually, I suggest using 2 distances, like 10 cm and 20 to 30 cm, if it is not too hard to do that. Since your detector is fixed, just lower the vessel. Can you get a "lab jack" to do that?

Nice touch using both a plastic and a glass container. The glass has a very high refractive index, so will reflect differently than the plastic will at the liquid-container interface.

John

fantabulous68 · 13th September 2009, 09:40 AM

Quote:

I am assuming the x-axis is the depth of water in its container. Correct?

Yes it is........uhmmmm no lab jack at my disposal...(use shoe boxes and text books to stack up

)

Tonight i am going to take readings for all those liquids i did b4(its 10:40 now)....but by varying the depth of the liquid...and keeping the distance to the surface fixed.....

i got to practice my presentation and my exams start next month

....
I need to make a study time table...time management!very important

jpanhalt · 13th September 2009, 12:20 PM

Just looked at the datasheet and some other information about the GP2D12 sensor. Based on that, I recommend increasing your minimal fixed distance from 10 cm to 12 to 14 cm. Then, pick a longer distance that is 10 to 13 cm more than your minimum distance for your second point (if you do the experiment as suggested awhile back). The reasons to avoid 10 cm exactly are: 1) it is the minimum distance; 2) there is rapid drop off at shorter distances; and 3) there is variation between devices (devices are characterized for quality control at about 24 cm). So, going to a slightly greater minimal distance will reduce unknown variability due to working at the device's extreme lower limit. You don't want to go too far, because the response curve flattens, which will increase your imprecision, and band spread of the IR beam will make edge effects more prominent. That is, you will have to use a larger diameter container for the liquid. Beam diameter vs. distance is shown in some of the technical sheets.

John

fantabulous68 · 13th September 2009, 09:28 PM

the glass vessel and sensor were at a fixed distance apart, took readings of the depth of the water which I varied...I did not move the sensor or the vessel once i started taking readings-the sensor was positioned over the center of the glass vessel.....see attached document...only problem is....the longest glass vessel i got is 21.5cm----so i took 3 readings for each case:

10cm fixed

12cm fixed

14cm fixed

jpanhalt · 13th September 2009, 09:50 PM

I am very confused by that chart. You say, "10 cm fixed" but show 3 readings at different distances. Distance to what? You did triplicate readings. Does each point represent the average?

What does this mean:

Quote:

1. Graph of Sensor @ fixed distance of 10cm away from glass vessel
2. Graph of Sensor @ fixed distance of 10cm away from glass vessel
3. Graph of Sensor @ fixed distance of 10cm away from glass vessel

Are you measuring from the top of the glass container, the top of the liquid, or the bottom of the glass container? All three "variations" are identical. Is that a typo?

John

fantabulous68 · 13th September 2009, 10:21 PM

thats a typo coz i cut and paste......its 10cm, 12cm and 14cm................let me change that on the document....

The graphs are correctly labled

fantabulous68 · 13th September 2009, 10:26 PM

sensor<-------10cm--------->top of glass This was the fixed distance
Then i took 3 readings from the sensor to the surface of the water at THAT fixed distance and plotted a graph

and i repeated this at 12cm.......................then again for 14cm

fantabulous68 · 13th September 2009, 10:35 PM

WATER 10*away
[

Code:

distance   output V
30	       0.509
20	       0.724
13	       0.725

Eg.
sensor<-------10cm--------->top of glass This was the fixed distance

Then i took 3 readings from the sensor to the surface of the water at THAT fixed distance and plotted a graph

and i repeated this at 12cm.......................then again for 14cm

fantabulous68 · 13th September 2009, 10:56 PM

Oh i have to be going now...its 23:55 and i wake @5:00 to get ready for uni and leave home at 6:15...Take care Jpanhalt....i will see your response at uni tomorrow....thanks for all your input....

jpanhalt · 13th September 2009, 11:15 PM

Can you find a light-gray or white piece of cardboard? Get as big a piece as practical, at least 20 cm X 20 cm. Flat, stiff, card stock would be best.

Take multiple measurements at 12, 20, 30 cm from your detector. let's see what your best-case reproducibility is. I suspect it is pretty good. If not, then you need to look for problems in the basic sensor setup.

Assuming that reproducibility with the cardboard is good, then lets return to your liquid surface. Off hand, those results do not look too good, but don't despair. I think it is the set up you are using, which is why reproducibility seems so poor.

Let's focus only on water for now -- wine is later

Do you have a cooking pot or aquarium -- anything -- that is much bigger in diameter than the drinking glass you are using. If you can get something about 20 cm or more in diameter, use it. Hopefully, it will be at least 10 cm high. Place your sensor 20 to 25 cm form the bottom of that container. Take a blank measurement of the empty pot. Then add 2 cm of water, take 3 measurements and average them, if they are relatively close to each other. Otherwise, report what the 3 values are. Then add 5 MORE cm of water and repeat. Keep adding water and taking measurements until the water is at the top of the pot.

For now, be sure to let any ripples in the water settle. If you get an unusual reading, check for ripples, and record your data.

It is getting late for you now, I understand. But, I will check in tomorrow several times.

John

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12th September 2009, 07:17 PM	#18
ericgibbs	hi Miss Fantabulous, Its refreshing to see someone putting the time, effort and detail into their project as you are obviously doing. I'm sure most of the older members of this Forum feel the same way as I do, well done, you deserve every success with the project. __________________ Eric " Good enough is Perfect " I will NOT answer PM's requesting technical help, please use the Forum PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/

12th September 2009, 11:01 PM	#21
jpanhalt	I am assuming the x-axis is the depth of water in its container. Correct? Did you keep the distance to the water surface constant? That value should be kept constant...actually, I suggest using 2 distances, like 10 cm and 20 to 30 cm, if it is not too hard to do that. Since your detector is fixed, just lower the vessel. Can you get a "lab jack" to do that? Nice touch using both a plastic and a glass container. The glass has a very high refractive index, so will reflect differently than the plastic will at the liquid-container interface. John

13th September 2009, 12:20 PM	#23
jpanhalt	Just looked at the datasheet and some other information about the GP2D12 sensor. Based on that, I recommend increasing your minimal fixed distance from 10 cm to 12 to 14 cm. Then, pick a longer distance that is 10 to 13 cm more than your minimum distance for your second point (if you do the experiment as suggested awhile back). The reasons to avoid 10 cm exactly are: 1) it is the minimum distance; 2) there is rapid drop off at shorter distances; and 3) there is variation between devices (devices are characterized for quality control at about 24 cm). So, going to a slightly greater minimal distance will reduce unknown variability due to working at the device's extreme lower limit. You don't want to go too far, because the response curve flattens, which will increase your imprecision, and band spread of the IR beam will make edge effects more prominent. That is, you will have to use a larger diameter container for the liquid. Beam diameter vs. distance is shown in some of the technical sheets. John

13th September 2009, 10:21 PM	#26
fantabulous68	thats a typo coz i cut and paste......its 10cm, 12cm and 14cm................let me change that on the document.... The graphs are correctly labled __________________ Learn without thinking begets ignorance. Think without learning is dangerous.

13th September 2009, 10:26 PM	#27
fantabulous68	sensor<-------10cm--------->top of glass This was the fixed distance Then i took 3 readings from the sensor to the surface of the water at THAT fixed distance and plotted a graph and i repeated this at 12cm.......................then again for 14cm __________________ Learn without thinking begets ignorance. Think without learning is dangerous. Last edited by fantabulous68; 13th September 2009 at 10:28 PM.

13th September 2009, 10:35 PM	#28
fantabulous68	WATER 10away [ Code: distance output V 30 0.509 20 0.724 13 0.725 Eg. sensor<-------10cm--------->top of glass This was the fixed distance* Then i took 3 readings from the sensor to the surface of the water at THAT fixed distance and plotted a graph and i repeated this at 12cm.......................then again for 14cm __________________ Learn without thinking begets ignorance. Think without learning is dangerous. Last edited by fantabulous68; 13th September 2009 at 10:36 PM.

13th September 2009, 10:56 PM	#29
fantabulous68	Oh i have to be going now...its 23:55 and i wake @5:00 to get ready for uni and leave home at 6:15...Take care Jpanhalt....i will see your response at uni tomorrow....thanks for all your input.... __________________ Learn without thinking begets ignorance. Think without learning is dangerous.

13th September 2009, 11:15 PM	#30
jpanhalt	Can you find a light-gray or white piece of cardboard? Get as big a piece as practical, at least 20 cm X 20 cm. Flat, stiff, card stock would be best. Take multiple measurements at 12, 20, 30 cm from your detector. let's see what your best-case reproducibility is. I suspect it is pretty good. If not, then you need to look for problems in the basic sensor setup. Assuming that reproducibility with the cardboard is good, then lets return to your liquid surface. Off hand, those results do not look too good, but don't despair. I think it is the set up you are using, which is why reproducibility seems so poor. Let's focus only on water for now -- wine is later Do you have a cooking pot or aquarium -- anything -- that is much bigger in diameter than the drinking glass you are using. If you can get something about 20 cm or more in diameter, use it. Hopefully, it will be at least 10 cm high. Place your sensor 20 to 25 cm form the bottom of that container. Take a blank measurement of the empty pot. Then add 2 cm of water, take 3 measurements and average them, if they are relatively close to each other. Otherwise, report what the 3 values are. Then add 5 MORE cm of water and repeat. Keep adding water and taking measurements until the water is at the top of the pot. For now, be sure to let any ripples in the water settle. If you get an unusual reading, check for ripples, and record your data. It is getting late for you now, I understand. But, I will check in tomorrow several times. John