Can an Ultrasonic wave penetrate a LPG cylinder

[sophiecentaur]

The HCSR04 transmitter/receiver device is low power and only works for non contact detection in air .

Try to find devices with separate transmitter and receiver and which are designed for direct contact applications .

Matching the power in and out is very important and it's important to use the appropriate devices.

Temperature sensing shouldn't be too much of a problem because it's pretty easy to use your hands to establish where the level is by the temperature variations over the surface. A number of fixed sensors (say 10) would give you an accuracy of 10% in level. You could perhaps do better than that with some clever interpolation between readings.

 

[NascentOxygen]

I vaguely recall there used to be a liquid-crystal strip that you could buy to glue down the side of your gas cylinder----as propane was drawn off latent heat loss cooled the liquid's surface, and the strip (basically a liquid crystal thermometer) would show a colour change at the boundary. I'm not sure how it worked to accommodate wide-ranging ambient temperatures; perhaps it comprised multiple thermometer strips in parallel?

Amazon will enlighten you: here are two such gauges. https://www.amazon.com/dp/B0010P3OU2/?tag=pfamazon01-20

The customer comments teach you how each can be used successfully.

 

[sophiecentaur]

Amazon will enlighten you: here are two such gauges. https://www.amazon.com/dp/B0010P3OU2/?tag=pfamazon01-20

The customer comments teach you how each can be used successfully.

That device is very convenient to use when all you need is a visual inspection (plus you have to actually get to the site of the bottle). It could be the basis of a system, perhaps based on the change in reflectivity of the whole strip as the coloured portion changes length. That could produce an electrical signal etc. etc.

 

[meBigGuy]

Post 24 was a link to an LCD strip.

I wonder how the electrical characteristics of the LCD might change when the color changes. Putting them at intervals and measuring XXX (whatever it might be) would provide what you are looking for. Anyone have the materials science background to comment of the electrical characteristics of LCD strips with temperature?

 

[sophiecentaur]

If you want to go electronic then there's no reason why you couldn't use an array of thermistors (ten, twenty or whatever) in series, stuck to the side and measure the total resistance. The scale would be a bit non-linear but it would at least be monotonic and the signal out could be read and recorded easily. An identical control chain, mounted near (or perhaps around the top of the bottle) could compensate for overall temperature changes.

 

[Baluncore]

The external temperature difference sensed is driven either by the internal evaporation of gas as gas is used or by externally applied hot water when gas is not being used.
A system to measure liquid level when gas is not being used will need to apply external heat. The challenge will be to apply the external heat evenly and then sense the temperature profile as it returns to ambient conditions.

 

[sophiecentaur]

The external temperature difference sensed is driven either by the internal evaporation of gas as gas is used or by externally applied hot water when gas is not being used.
A system to measure liquid level when gas is not being used will need to apply external heat. The challenge will be to apply the external heat evenly and then sense the temperature profile as it returns to ambient conditions.

You are right. Would it be easier to have a few seconds venting of the gas?

When we get down to it, there's a lot to be said for just weighing the bottle continuously. The installation for that would be pretty cheap and robust and could even work (low pass filtered) when the bottle was in a moving vehicle.