Hi,
I don't have much experience with sensors and would like to measure the height of a pillow tank with an Arduino R3.
I was thinking of putting a sensor below the tank, and a piece of metal on top of it, but the distance between the two will be important. The height will vary between zero and 1.5 meter, so even though the tank will be filled with air, the distance is possibly too big for proximity sensors to work.
Also, the tank will be buried under the sand, so it's not possible to just put a sensor somewhere above it and measure its distance to the top of the tank.
Any ideas about the type of sensor that I could use?
Thanks in advance!
Olivier
The internal pressure depends on the weight of the sand above the tank, not necessarily the height
of the tank as the sand will simply rise with the tank's movements I reckon.
jremington: Sorry I was unclear. English is not my native language Pillow tanks have a fixed length and width, and their height varies when you inflate them. The height is zero when the tanks are empty and increases when the tanks are filled.
MarkT: The tanks are filled with air. They are buried under the sand and are actually used to lift the sand.
hammy & MarkT: The internal pressure depends indeed on the weight of the sand above the tank. It remains pretty much constant during inflation and only increases significantly when a tank is overinflated and about to burst, so we cannot use pressure as a proxy for the height of the tank.
We could use flow meters to measure how much air goes in and out of a tank, but they are expensive, and we expect some leakage, so after a while, we are likely to lose track of the real volume and height of a tank. This is why I am trying to figure out what type of sensors could help to estimate the height of a tank.
If we could place sensors inside the tank, that would be pretty easy, any sensor able to estimate a distance would work, but unfortunately, wiring them inside the tanks would be quite difficult, so we are looking for sensors that can be placed below and/or above the tanks.
arduarn:
Maybe (ultra)sound transmitter/receiver at the top/bottom of the pillow pointing inside?
Thank you for the idea. Maybe sound or ultra sounds could get through the tank lining. It's only a few millimetres thick, so it's probably worth trying! I could place one transmitter+receiver (with transmitter disabled) at the bottom + one at the top (with receiver eventually disabled) and see if that works.
Needing two devices and needing to modify them is not ideal, but at least it would be something!
Two layers of (probably) sound absorbing fabric plus the air gap will certainly make it challenging. Choice of transducers, their power and how they are mounted could be crucial. Don't expect it to "just work" - it might - but more likely it will need some careful experimentation.
If you enclose both TX and RX inside a sort of football of fabric then you should be able to test at the comfort of your desk.
EDIT: Another thing to try before investing in any hardware could be to put a portable radio inside a well sealed football of fabric. Can you hear it? Then add another football around it. Still hear it?
olivierbourdin:
Would you know if a big magnet or a big piece of metal could be detected from a distance of one meter ?
I know that both are technically possible. There are commercial metal detectors that could easily detect metal at that depth, more so since you have full control over the metal and its properties. I'm sure there are some metal detectorists on the forum here who will be better placed to advise on the simplest way to proceed than me.
Hi everybody,
I believe an ultrasonic distance sensor (TX and RX) at the bottom, catching a reflection from the top should be a nice fit. If the classic HC-SR04 is big for the job or might brake, take a look at those really really TINY ultrasonic range finders https://www.digikey.gr/product-detail/en/tdk-invensense/DK-CH201/1428-DK-CH201-ND/10445773
On the long run, if your company? develops a product based on those, you could have a very small and durable wireless device mounted internally, working on a battery for years, transmitting your wanted height....
Just throwing big-shot ideas...
If you want to go super cheap and dirty for a very few pieces only, an idea might be something like this:
(or a similar one) placed inverted on bottom, measuring the height of the "ceiling"
Hi Jim
Thank you very much for your suggestion. Unfortunately, I can't really install the sensors inside the tanks. They would need to work from the outside.
Pillow tanks have a fixed length and width, and their height varies when you inflate them. The height is zero when the tanks are empty and increases when the tanks are filled.