best way to measure lpg level on a cilinder, HELP
Miguel Hiciano wrote 03/14/2019 at 19:25 • 1 pointIm trying to measure the lpg level on a lpg cilinder, the issue, what kind of sensor can i use for that?
im going to try it with a gas pressure sensor but im open to suggestions
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The gas pressure should remain relatively steady as there is always more liquid to vaporize and pressurize the tank. The pressure will only change with temperature and depending on where you place the pressure sensor with flow rate. In industry they would probably use an ultrasonic sensor because the liquid will transmit the sound faster than the gas will.
Alternatively temperature could be used if you placed several temperature sensors along the side, as you used fuel the temperature of the liquid will decrease, by looking at the temperature difference between the "empty" top portion and "full" bottom portion you can find out where the level is. For example the temperature readings from the top to the bottom might look like this. 75,75,73,70,70,70. from this you could assume that the level was at or near the first 70 degree reading.
This would have the disadvantage that the instrument would not know where the level was initially because there would be no temperature difference.
any hoo, good luck and let us know what you are working on! (if you want to)
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Hola, la opción más simple y precisa es la del peso, para utilizar grandes pesos y celdas de carga chicas que son más económicas se puede mediante el diseño de una balanza con un brazo palanca que te permita pesar 150kg con una celda de 2kg, sería la combinación de un sistema mecánico y electrónica. Te recuerdo que los envases se miden por peso motivos de seguridad, saludos y suerte con el proyecto!
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You can measure the temperature of the tank at multiple hight. You can get these magnetic color changing temperature thingies (https://www.aliexpress.com/item/Propane-Butane-LPG-Fuel-Gas-Tank-Level-Indicator-Magnetic-Gauge-Caravan-Bottle-Temperature-Measuring-Stick/32725187341.html). The only downside is that they only work when you are using gas, as using gas will make some of the liquid turn to gas, which requires energy to fase-change, and thus cool down the liquid (I think).
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yep you got it :)
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Another option may be measuring the actual level of the liquid gas with an ultrasonic sensor from below. Basically trying to catch the echo from the surface of the the liquid that is reflected back down. This should be easier than measuring from above - but I don't have any real expertise with ultrasonic devices.
This has the benefit of being able to measure without modifying the gas system. You just need to press the Piezo actuator against the bottom of the cylinder.
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I like this idea. Not sure how well it will work through steel, but they are commonly used with other liquids, through the container, with great effect.
And just to be perfectly clear, a gas pressure sensor isn't going to work. Until you run out of liquid, the vast majority of any shift you see in pressure is just related to the temperature of the tank.
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It's a good option, but, i'm like you, i don't know which sensor can i use.
btw thank you for the idea!
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Well, quick search shows that those sensors are easy to come by: https://www.aliexpress.com/item/Non-Contact-Ultrasonic-Liquid-Level-Sensor-Ultrasonic-Level-Gauge-Analog-Output/32946725874.html
Just search for ultrasonic and liquid.
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I think the easiest way is to weigh the cylinder by placing a strain gauge under the cylinder. It requires simple and inexpensive material you can easily order online for a few $.
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That's probably the easiest option assuming you can get the load cells in between the cylinder and the mounting brackets.
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I thought of that option, but the kind of cilinders that i want to measure are too bigger to make it in that way
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Weight? Good luck making it portable.
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Why? Just average over a few seconds. Most applications can't sustain acceleration to one direction for a longer time.
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It could get bigger than OP wants it. It's quite effective though.
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OP said nothing about whether the cylinder is stationary or portable. Maybe OP wants to monitor a cylinder installed in a cage. If it's allowed to move up and down slightly, then it can rest on a load cell.
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That's true. It would work very well like that.
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https://en.wikipedia.org/wiki/Liquefied_petroleum_gas
"... As its boiling point is below room temperature, LPG will evaporate quickly at normal temperatures and pressures and is usually supplied in pressurised steel vessels. They are typically filled to 80–85% of their capacity to allow for thermal expansion of the contained liquid. The ratio between the volumes of the vaporized gas and the liquefied gas varies depending on composition, pressure, and temperature, but is typically around 250:1. ..."
Given such a high ratio of gas to liquid, is there any point to measuring the "level" of the liquid? What is it you are trying to measure? Whether you have run out of LPG?
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Well, the high ratio makes measuring the level (as in level of the liquid) relevant as most of the content of the cylinder is in the liquid.
But this makes it impossible to measure the amount of stored gas by measuring the pressure. The pressure will only be determined by the temperature as long as there is still liquid gas left.
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No, it's the other way around if that Wiki sentence is correct, most of the volume is gas. It also makes sense, they wouldn't allow only 0.4% space for expansion. But I think the OP was using "level" loosely, just wanted to know how much LPG is left. Weighing would be my choice.
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I believe you are reading this sentence wrong. The ratio of 1:250 is for the volume of the same amount of gas. If it is liquid it only uses up one 250th of the space. This is independent of the ratio of liquid to gas in the tank. So the bulk of the gas is store in liquid form (which is unsurprising giving the name)
The ratio of liquid to gas in the (full) tank is given in the sentence before (80–85% of their capacity). The remaining 15-20% acts as a buffer as it can liquify and then use 250 times less space to accommodate any thermal changes.
Having only 4 percent of the content of the cylinder in liquid form would not make much sense anyway.
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This all moot anyway, why would you measure the level of the liquid. If you want to know how much is left, I'd weigh the tank. BTW, 1:250 is 0.4%, not 4%.
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