I would like to get ideas on how to measure the thickness of ice forming on a backyard ice skating rink. The rink is basically a big, shallow swimming pool. The ice forms over several days and weeks, and my usual method of checking thickness is to drill a hole. I would like to fashion some kind of sensor and use an Arduino to report ice thickness.
I could measure either from the top or the bottom, but measuing from the bottom would require the sensor to be waterproof.
I can think of three options: ultrasonic, pressure and mechanical.
If you placed an ultrasonic sensor on the bottom facing up at the underside of the ice, you could figure out how far away it is and calculate the thickness. However, I'm not sure how well the signal would travel in water.
For pressure, I thought about some kind of sealed tube oriented vertically with a transducer at the end, and as the forming ice expanded around the tube it would change the pressure. You would have to do some calibration.
Mechanical would just be some kind of float and positional sensor under the ice.
I've never tried doing anything like this. However, I might research whether there
is a noticeable interface between ice and water that can be picked up by sonar.
Secondly, I might simply attach a ruler vertically to a board and weight it down in
the bottom of the pool, and let the ice form around it.
Thirdly, I might tie a small sheet of white plastic to the side of the pool, and let it
float on top of the water uner the ice, and then use a Sharp IR ranger through the
ice from above,
The commercial systems I've seen use ultrasonic. I would suggest searching using that hint as part of your search criteria. Apparently the interface between liquid and solid water provides enough of a change in whatever the equivalent of refractive index is for sound to reflect the ultrasound.
I suppose the thickness will vary depending where you measure - are you trying to find the minimum thickness over an area, or do you think you will be able to choose a representative place to measure?
As a starting point, I'd just put a metal post in the water, with a flat base on it so that it will stand upright and resist being pulled through the ice, and a handle on top. To measure the thickness, just pull up on the post and see how far it will come up. It's low-tech, but quite a lot easier than drilling holes and so on.
Thanks for the suggestions. There are any number of 'manual' ways to measure the thickness. I was really looking for something elegant that could log some data at pretty regular intervals (say every 15 minutes). Ultimately I would measure air temperature as well and maybe even wind speed.
I have an HC-SR04 ultrasonic sensor that seems to work pretty well sensing solid objects, but also does a good job detecting the surface of a tank of water so not sure how I would work this underwater (besides keeping it dry).
I also thought about a magnet at the bottom with a Hall effect sensor above the ice but I have no experience with these so don't know if you could get a field strong enough to measure.
rwiens:
I have an HC-SR04 ultrasonic sensor that seems to work pretty well sensing solid objects, but also does a good job detecting the surface of a tank of water so not sure how I would work this underwater (besides keeping it dry).
The commercial units just press the US transceiver down on the surface of the ice. If you did it from the surface, you'd have less to worry about waterproofing it.
I also thought about a magnet at the bottom with a Hall effect sensor above the ice but I have no experience with these so don't know if you could get a field strong enough to measure.
The neodymium magnets you can get now are VERY powerful.
Reminds me of an ultrasound machine in hospitals. You may need a good contact between the sonic ranger and the top ice. You can experiment with ice you make in your fridge see if you can pick up the weak reflection at the interface. It would be a fun project. You need a large ice sheet and your bathtub
I was thinking that the interface would only be detectable if you were going from water to ice...of course now it occurs to me that ice is actually less dense than water. So analagous (sort of) to going from air to a solid object like a wall.
Would US reflect from and interface (change in density) or just going from lower to higher density?
rwiens:
I also thought about a magnet at the bottom with a Hall effect sensor above the ice but I have no experience with these so don't know if you could get a field strong enough to measure.
Given that neither the magnet nor the sensor would be at the water/ice boundary, I can't think of any way to use that to measure the ice thickness.
I have no experience of ultrasonic sensing but it seems like the most promising approach to try.
I also wonder whether there are any easily measurable properties of water and ice that differ significantly - conductivity, dielectric constant and so on. If so, I suppose it might be possible to get an indication of the relative proportion of ice and water in contact with a sensor that went through the ice layer and extended into the water.
rwiens:
I was thinking that the interface would only be detectable if you were going from water to ice...of course now it occurs to me that ice is actually less dense than water. So analagous (sort of) to going from air to a solid object like a wall.
Would US reflect from and interface (change in density) or just going from lower to higher density?
US reflects from any discontinuity of density. The reflectivity of UL from water to ice and from ice to water should be the same in theory (Stokes relations). I don't know what happens in practice.
In practice you should measure from the water side to the ice. This is because you will get very little energy into the ice to reflect off the water / ice boundary so going upwards is the only option. However the range you are talking about here is very small and I don;t think you can use ultrasonics at such short distances.
The resistivity of ice and water however are very different, I would use that.
In the case where the US pulse travels through the ice and is reflected off the ice/water boundary, the travel time of the reflected wave will depend on the speed of sound in ice (~3400 m-sec-1) and the transmitted wave will depend on the speed of sound in water(about half the speed in ice). So, the measured travel time in a few inches of ice will be a few microseconds. This will require some work to time with the Arduino board. Also, the transceiver will need to be a higher frequency than the normal hobby-style transceiver, around 5 MHz. Unfortunately, cost starts to rear its ugly head when you are talking about that sort of transducer.
I would consider one of the less high-tech methods mentioned here if it were me.
The commercial ice thickness gauges use a transceiver that looks exactly like this one, viewed from the surface that touches the ice. I found it by Googling "5 MHz ultrasonic transducer".
Wow, those 5 Mhz transducers probably cost more than the skating rink. One thing
about using sonar is, you'd no doubt have to build the electronics yourself, and do
measurements along the lines of regular submarine-type measurements - ie, analyze
signals on an oscilloscope and look for transition blips at ice-water and ice-air
boundaries. Not nearly as easy as simply reading a Ping sonar.
My latest idea involves using a clear plexiglass cylinder, place vertically in the pool, so
you can look inside and see the ice boundaries. Or for more "elegance", read the
boundaries using some electronics means.
oric_dan(333):
Wow, those 5 Mhz transducers probably cost more than the skating rink. One thing
about using sonar is, you'd no doubt have to build the electronics yourself, and do
measurements along the lines of regular submarine-type measurements - ie, analyze
signals on an oscilloscope and look for transition blips at ice-water and ice-air
boundaries. Not nearly as easy as simply reading a Ping sonar.
My latest idea involves using a clear plexiglass cylinder, place vertically in the pool, so
you can look inside and see the ice boundaries. Or for more "elegance", read the
boundaries using some electronics means.
They're $100 on ebay. Maybe too much for OP's project, not to mention the hardware needed to use them.
Can you think of a way to read the boundary electronically?
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.
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.
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.
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.
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).
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.
