I have a project where I need to add a liquid level sensor to a steel tank with a plastic cap and the tank is pressurized (2bar). So I need a sensor that will have no wiring going into the tank since that will cause problems with proper sealing for pressurization.
Another big problem is that the vessel has a very small diameter of 4.8 cm so I can't fit very large sensors at level position.
The tank will most likely contain suspensions so the liquid might not be completely clear. The whole apparatus should fit in a 4.8cm dia x 10 cm height inside the tank. The accuracy needs to be less than 1cm.
Cost doesn’t really matter a lot
So, what do you think? What kind of sensors would you use?
I'm not kinda "tanks expert" but let me try to summarize what I can understand so far, from the description and the listed requirements:
You can't put anything inside the tank (or even through the plastic cap) because the tank is pressurized, and that's clear;
The tank is made of steel so detecion can therefore be just an "external" one, and no optical or some other solutions (like magnetic based) are possible;
We don't know what kind of liquid is inside the tank, so we can't make any speculations about its physical characteristics that could be used for detecion purposes;
We don't know if the tank is somehow fixed or if it could be subject to movements causing liquid sloshing (e.g. like a moving car gas tank);
You haven't specified if you just need a specific "boolean" level detection (full or empty) or a numerical level about level (or volume?);
Lastly, I can't get the difference between the tank and that "vessel", and therefore the physical constraints (e.g. what is the exact meaning of the space you described where the "apparatus" should be installed?). Could you please add here a drawing with dimensions?
Sorry about all those questions, but the problem is intriguing to me, even if I haven't any kinda practical solutions...
The DS1603L or similar might work. Attaches to the outside bottom of a tank. 50 mm blind distance. 1 mm resolution. Search the forum. @wvmarle has a library for it. Your tank could be too small. Try it and see.
I can tell you how I did it on tanks running 2,000 to 3,000 PSI (138 to 209 Bar). We used Rosemount (now Emerson) delta pressure gauges. Far from inexpensive at about $2,000 USD each and that was 10 years ago. We did have ports at the top and bottom of the tank. Our concern was Grade A water with a known specific gravity so you will need to know the specific gravity of whatever liquid is in the tank. The delta pressure gauges we used were rated for about 4,000 PSI so tank pressure was not an issue and if you want high accuracy and resolution it cost. You are only working with 2.0 Bar or about 30.0 PSI so relatively low pressure. Emmerson Delta Pressure Gauges. When I retired about 10 years ago those gauges were costing about $2,500.00 USD so accuracy did not come cheap but you are only looking at low tank pressure. The ones we used ran in a 24 VDC current loop of 4 to 20 mA out over their delta pressure range. Everything was 316 stainless steel. So if you can get a top and bottom port on the tank you may want to consider delta pressure to measure tank level. Here is an overview. You do need to know the specific gravity of whatever you have in the tank.
If it's a small tank, can it sit on some weight measurement device, or maybe suspended and similarly weighed. Could you infer volume from weight, and therefore level?
I would prefer to not put anything inside the tank since then I would have to redesign the cap and think of ways to seal wires. but inside is also possible.
2.The liquid is a suspension that is being filtered at the bottom of the tank
continuous measurement is required
4.The tank is stable and not moving
5.the whole dimensions of the tank are 4.8 cm in dia and 30 cm in height. the top 10 cm will not have liquid in it so sensor and other things can occupy that space
