Monitor CO2 Useage

  1. I have a project that I have been thinking about and need to us CO2 for it. What ways are there to measure the amount of CO2 left in a cylinder if its mounted to a moving object? I thought about the normal scale method but with bumps it wouldn't be accurate. You cant really measure pressure since it self regulates in a way and will change with temperature. The only other thing I have been able to come up with is measure the flow and come up with a calculation that a certain volume weighs so much but that seems like that would leave a pretty high margin of error. The only way I see to get close using that method is to fill your own tank that you know the weight on with a known weight of liquid co2 using a scale.
  2. jcsd
  3. Baluncore

    Baluncore 3,217
    Science Advisor

    You have not specified the rate of CO2 use, is it kg per minute or ug per hour.

    (1). Weigh the tank on load-cells but have another load-cell, with a smaller reference mass, to identify when there is no bump, or to generate a mass ratio. For times when there are too many bumps you measure the P, V and T of the CO2 being used. Subtract that from the last known good weight. A thermal mass-flow meter would be able to estimate usage.

    (2). Use a load cell, but record the data continuously. The long term average represents the mass. By picking an optimum time period for the running average, the major component of vibration could be reduced.

    (3). Weigh the tank on an asymmetric beam balance. A movable fulcrum mounted on a rubber block.

    (4). Sense the presence of liquid level in the cylinder by looking at the reflectance of an ultrasonic pulse from outside the cylinder wall. A similar technique as is used for measuring the thickness of steel plate.

    (5). Measure the level in a cylinder by momentarily heating the CO2 cylinder wall. The wall will cool more rapidly adjacent to the liquid, more slowly where there is gas. Campers pour a little hot water down the side of their gas cylinders. The resulting pattern quickly identifies the level of the gas-liquid boundary.
  4. I dont have any useage info yet. Those are some good ideas and starting points. Ill do some more research on them and see what would be the good and bad points of the methods. That may steer me in a more focused direction. 1,2 and 3 would work well in a horizontal position too where as 4 would be better in a vertical position to keep sloshing of the liquid to a minimum. Short of a custom tank I don't think they make baffled tanks since there really wouldn't be any use for them other than a very special application.
  5. Baluncore

    Baluncore 3,217
    Science Advisor

    You could put something like an open cell foam or activated charcoal into your tank to stop sloshing.
  6. I have been working on measuring volume for a while and perhaps you can build something similar. You can release part of the gas (if that's possible) by opening a valve through a flow restrictor and measure the time it takes for the Pr to drop certain amount (1% for instance). With that info you can reconstruct the exponential equation and find the gas volume in the tank. In this case (contrary to mine) temp will not be a problem, I think. The time required for the Pr to drop certain amount is independent of the temp and only depends on the volume of gas and the flow restrictor.
    Problem is, you will be loosing part of the gas and being CO2, I don't know if you can do that legally and/or safely. You need to find out that first or use another gas. There are serious difficulties though in making the system work and measure time accurately.

    Hope it helps.

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