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Author Topic: Measuring ice thickness  (Read 2706 times)
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Dallas, TX
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Can you think of a way to read the boundary electronically?

I'm still working on that. So far, I have a [virtual] robot that runs up and down vertically
in the tube, but not sure what sensor it will use [TIC!]. It depends a lot upon the
properties of the ice in the pool. Eg, a lot of ice cubes are perfectly clear, but the
ones made by my refrigerator ice maker are full of air bubbles, and therefore appear
white, which should be easy to detect from clear ice or water, by light scattering.

Yeah, it's a puzzler.

Grumpy_Mike pointed out that the conductivity of ice is very different than water, by about an order of magnitude, so maybe a transducer could be made that exploited that fact. The resolution would be dependent on the spacing between the electrodes but in this application I don't think that would be a problem.
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Great info and ideas here.  What I have surmised is that I would have to spend a bunch of time learning a whole lot more about US than I currently know, spend some big money and write sophisticated code.  I might rather be skating.

Latest idea: pingpong ball (or something else that floats) on a string, wound around a spool attached to a motor/potentiometer.  Release a catch of some sort and let the ball float to the underside of the ice, then measure the position of the potentiometer.  Wind it back up and wait for the next measurement.
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the land of sun+snow
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I might rather be skating.
Best idea yet.

One problem I think most of the schemes mentioned haven't really dealt with is the fact that
you have to measure both top and bottom edges of the ice layer to get a proper thickness
value. All in all, I think, if the ice is fairly transparent, possibly the best scheme is the one
using Sharp IR rangers mentioned in post #2.
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The ice may or may not be transparent.  At the moment it has a 2cm layer of slush on top so it is anything but clear.

I know where the top of the ice is relative to the bottom of the 'pool', so all I need is a measurement of the distance from the bottom of the pool to the underside of the ice.

I like the graduated electrode idea.  I would probably be happy with resolution of a couple of mm (1 mm would be better).
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the land of sun+snow
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Offhand I would think any kind of electrical conductivity measurement would be too
variable and difficult to calibrate. Possibly only a visual measurement will work robustly.
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Dallas, TX
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Offhand I would think any kind of electrical conductivity measurement would be too
variable and difficult to calibrate. Possibly only a visual measurement will work robustly.
Since the difference in conductivity is so great you would be sensing the delta rather than being concerned with absolute values.
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So if we went with the conductivity concept, how would one implement that?  I'm imagining a non-conductive strip with leads coming off every Xmm.  Apply a voltage at one end, ground the other and essentially you have a voltage divider.  Two practical considerations, however: for a high resolution, you would have lots of leads and might have do some kind of switching to measure them in succession.  Also, would resolution of the ADC be good enough or would I need some kind of op amp?
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Hard to say without trying it, but as a starting point I'd try making a water depth detector out of a couple of stainless spikes parallel and close together, apply an AC signal and use a voltage divider to measure the resistance. Compare ice and water to see whether the concept gives you any significant difference between them. If it does, then experiment with the dimensions/spacing, resistance etc and see whether you can get a reading that varies when you keep the total depth constant but vary the proportion of the length immerse in ice and water. The hope is that the properties of ice/water are sufficiently different that you can determine the relative proportions of ice/water from the single overall reading.
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Why AC?
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To minimise corrosion and ionisation effects.
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Thanks.  I would only be measuring for a few weeks at most (the time it takes my rink to freeze solid) so corrosion is not likely an issue, but I assume that ionisation effects might have an impact on measurements.
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If you have any contaminants in the water then electrolytic effects can speed up corrosion and/or surface deposits dramatically. (Ionisation effects also skew the readings.) Although these effects might not be enough to stop the system working in that sort of time scale, they could easily have enough effect to alter the calibration.
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Forgive me my ignorance on this, but water gets bigger when it turns to ice.
So the top of the ice flow isn't static correct? wouldn't it "push up"? Even ice cubes in a tray are significantly higher once frozen than they are when just water.

So measuring just the bottom of the ice flow to the bottom of the pool isn't a true representation of the thickness of the ice is it?
Or am I overstating how much push up the ice is going to have over the unfrozen surface of the poll?
I live in the desert so the only ice I see is in my drink   smiley-lol
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You are absolutely correct.  I think somebody else mentioned this earlier on in the thread but it didn't click.  So theoretically you would have to measure the position of the bottom of the slab relative to the top, or both relative to the bottom of the pool.  Frankly, I don't need anything super-accurate so just measuring the bottom would likely be OK.
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9% is how much water expands when it becomes ice.

I just use the Canadian method. Walk out onto the ice (or ride your snowmobile) if you get wet it wasn't thick enough.
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