Low cost sealed liquid level sensor - Stock or Custom solution - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: January 24, 2022, 11:09:28 pm
content: Hi,I am looking for a low-cost liquid level sensor for sensing the level of extremely mild caustic soda. It is so mild and diluted that you can even wash you can keep your hands in it for long time without any issues.It is for a production product, so I did quite a bit of research but they are either not for a sealed container or very expensive.I have also come across some thermistor level sensor which I am not sure how reliable or accurate they are... I can understand on-off (using a second one as reference) but level..?I simple to make I can also consider designing the float and use stock components for the rest (but the sealing still remains an issue unless it can be detected through the metal enclosure.In summary- the liquid to be measured is inside a sealed (air tight) tank.- the tank containing the liquid is stainless steel- the displacement is 130mm to 150mm- precision does not nee to be high at all, even 5mm "granularity/accuracy" (+/-2.5mm) in reading is acceptableDoes anybody have any suggestion on either some stock parts or ways to make a custom one?Many thanks

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 24, 2022, 11:46:50 pm
content: If it was a plastic container, a simple foil stick-on capacitive sensor could work.You could also use a loadcell, or repurpose a small scale for DIY, and measure the change in weight from empty to full.

author: ledtester
author_rank: Super Contributor
timestamp: January 25, 2022, 04:20:50 pm
content: QuoteQuote from: Kim Christensen on January 24, 2022, 11:46:50 pmHow about a stick-on capacitive sensor attached to a dipstick inserted vertically into the container?

author: ricko_uk
author_rank: Super Contributor
timestamp: January 25, 2022, 04:34:52 pm
content: Thank you both.@ledtester,what kind of capacitive sensor are you thinking of?Thank you

author: ledtester
author_rank: Super Contributor
timestamp: January 25, 2022, 04:38:17 pm
content: Have a look at this video:How to make a Capacitive Water Level Sensor - Heilman Hackatronicshttps://youtu.be/nO_GJJ6HfTIAlternatively you could etch an interlocking comb pattern on a single copper PCB strip to form the capacitor.

author: ricko_uk
author_rank: Super Contributor
timestamp: January 25, 2022, 05:09:25 pm
content: @ledtesterahaha, thank you, that is the same video I was watching soon after replying. The only thing that might not be reliable enough is the sealing.I was wondering is some reliable sealed ultrasonic ranging solution can be implemented at low cost?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 25, 2022, 05:28:48 pm
content: Ultrasonic sensing (sensor firing down form top of tank) would avoid/reduce the whole waterproofing problem.

author: ricko_uk
author_rank: Super Contributor
timestamp: January 25, 2022, 05:39:42 pm
content: Thank you @mikeselectricstuff,the tank is small and can be tilted accidentally so I was looking for some sealed ultrasonic sensor which is also relatively low cost excluding the electronics. Maybe 20-30USD at most in quantities of few 100s.But couldn't find any around that price range, I assume also because it includes the electronics.Does anybody know of any without the integrated electronics so they might be a lot cheaper?Thank you

author: ledtester
author_rank: Super Contributor
timestamp: January 25, 2022, 05:44:50 pm
content: You might find this guy's experience with a hobbyist ultrasonic senor helpful:Ultrasonic distance sensor as an oil level gauge - Matthias random stuffhttps://youtu.be/c0SpsUMR2fU

author: max_torque
author_rank: Super Contributor
timestamp: January 25, 2022, 07:38:44 pm
content: How quickly does the level of the tank change? You can use a basic sensor, and ignore tilting or other effects perhaps if you simply average lots of readings if the level only changes slowly?

author: ricko_uk
author_rank: Super Contributor
timestamp: January 25, 2022, 11:43:50 pm
content: Thank you both.@max_torque,the level changes extremely slowly, maybe a mm every 30 minutes.What do you mean "You can use a basic sensor"? What basic sensor? That's what I am asking.Thank you

author: ledtester
author_rank: Super Contributor
timestamp: January 26, 2022, 12:01:50 am
content: Quote from: ricko_uk on January 25, 2022, 11:43:50 pmTo find the one used in the video just search Amazon/Ebay/Aliexpress for "arduino ultrasonic sensor".

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: January 26, 2022, 01:15:42 am
content: How about tapping a pressure sensor into the bottom of the tank. I did this for a caustic tank at a textile mill once. Also did it for a fuel oil tank at the same plant.

author: nctnico
author_rank: Super Contributor
timestamp: January 26, 2022, 01:33:30 am
content: Quote from: ricko_uk on January 25, 2022, 05:39:42 pmYou can buy these. They are called ultrasonic transducers. You'll have to build the electronics yourself though. The distance they can measure depends on the shape. A relatively simple microcontroller circuit can be used to process the output of the transducer (reading the echo of a pulse sent out). If the sensors are close to eachoter (say up to 20 meters) you can build a central unit that deals with a whole bunch of sensors.

author: BMK
author_rank: Regular Contributor
timestamp: January 26, 2022, 01:43:49 am
content: Ultrasonic has a lot of problems in tanks, in industry ultrasonic is often avoided.Fine if you have consistent temperature, humidity and pressure in the vessel. These effects of course inter-play with each other, especially in a closed vessel. Most industrial US sensors for liquid level are temp compensated and use algoritmic magic to avoid effects of air currents etc. In my experience you are better with anything but ultrasonic. Main industrial methods are Microwave(radar type) Microwave(proximity type) Capacitive, differential pressure, load cells...