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Thread: Oxygen (not DO) meter

  1. #1
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    Oxygen (not DO) meter

    I was wondering which oxygen meter everyone is using to verify that their tanks are properly intert with CO2. Are there any brands/models that people particularly love or hate?

  2. #2
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    Quote Originally Posted by anthonybaraff View Post
    I was wondering which oxygen meter everyone is using to verify that their tanks are properly intert with CO2. Are there any brands/models that people particularly love or hate?
    This can be done with a DO meter in most cases (Beverly, Cbox, Orbisphere, etc). You just run gas though instead of liquid and analyze results accordingly.

    Remember it is basically impossible to get 100% purge when using a gas to purge a gas. You will dilute the oxygen down but never remove all of it without a liquid/gas purge.

    Some use a slow trickle method, some use a pressurize and depressurize fast(er) method. I have seen an old write up somewhere on the effectiveness of the fast method, but it was years ago. I have found both methods sufficient for reducing O2 levels below acceptable thresholds. Most are not measuring a purged/emptied bright tank with instrumentation and are just relying on SOPs.

  3. #3
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    Quote Originally Posted by UnFermentable View Post
    This can be done with a DO meter in most cases (Beverly, Cbox, Orbisphere, etc). You just run gas though instead of liquid and analyze results accordingly.
    I had the Anton Paar salesman tell me point blank that their devices only worked on liquids, not on gas.

    What values do you typically get? The commercial CO2 must still have 5-30 ppm of oxygen straight out of the tank.

  4. #4
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    Dissolved oxygen meters are wonderful tools but........ they measure dissolved oxygen, not gas purity.
    To measure gas purity there are other methods. An old time method that works is to react a known quantity of gas with a caustic solution, the bubble of gas that is left is "air", a combination mainly of nitrogen and oxygen.
    We used to compress and collect fermenter gas for reuse in the first brewery I worked at. (Back before liquid CO2 tanks were common). We used a gas purity checker made by Zahm & Nagel to watch a fermenters gas output to see when the fermenter had purged all of it's air, and was putting out pure CO2 so that we knew when we could start collecting the gas.
    Low tech - but it works well and quickly. I believe they still sell the purity checkers but it wouldn't be overly hard to make one out of lab glassware.

  5. #5
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    Quote Originally Posted by anthonybaraff View Post
    I had the Anton Paar salesman tell me point blank that their devices only worked on liquids, not on gas.

    What values do you typically get? The commercial CO2 must still have 5-30 ppm of oxygen straight out of the tank.
    Quote Originally Posted by brewingpro View Post
    Dissolved oxygen meters are wonderful tools but........ they measure dissolved oxygen, not gas purity.
    To measure gas purity there are other methods. An old time method that works is to react a known quantity of gas with a caustic solution, the bubble of gas that is left is "air", a combination mainly of nitrogen and oxygen.
    We used to compress and collect fermenter gas for reuse in the first brewery I worked at. (Back before liquid CO2 tanks were common). We used a gas purity checker made by Zahm & Nagel to watch a fermenters gas output to see when the fermenter had purged all of it's air, and was putting out pure CO2 so that we knew when we could start collecting the gas.
    Low tech - but it works well and quickly. I believe they still sell the purity checkers but it wouldn't be overly hard to make one out of lab glassware.
    I'm by no means an expert on optochemical Oxygen sensors, so I can only go off what I've been told, but we had an Anton Paar tech tell us you can definitely use the Cbox for gas purity testing. The O2 zero-point is checked and calibrated by running the unit with high-purity Nitrogen, so I'm not sure why it'd be different when purging with CO2. We would periodically use the Cbox to check O2 readings on tanks post-purging to verify. But who knows, maybe we were incorrectly putting faith in the readings if it isn't actually built for that purpose. Like I said, I'm no expert. Could be worth reaching out to Anton Paar's website for an official answer on the issue.

    When using the Cbox on empty tanks, we'd look for readings down around 5ppb, which was definitely achievable given enough time and gentle purging.

    I'm not sure that I'd advocate purchasing a Cbox purely for the purpose of checking tank purging though. Those things don't come cheap.

  6. #6
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    Quote Originally Posted by Smelliot View Post
    I'm by no means an expert on optochemical Oxygen sensors, so I can only go off what I've been told, but we had an Anton Paar tech tell us you can definitely use the Cbox for gas purity testing. The O2 zero-point is checked and calibrated by running the unit with high-purity Nitrogen, so I'm not sure why it'd be different when purging with CO2. We would periodically use the Cbox to check O2 readings on tanks post-purging to verify. But who knows, maybe we were incorrectly putting faith in the readings if it isn't actually built for that purpose. Like I said, I'm no expert. Could be worth reaching out to Anton Paar's website for an official answer on the issue.

    When using the Cbox on empty tanks, we'd look for readings down around 5ppb, which was definitely achievable given enough time and gentle purging.

    I'm not sure that I'd advocate purchasing a Cbox purely for the purpose of checking tank purging though. Those things don't come cheap.
    Exactly. I’ve done it a number of times with The Beverly and the Orbisphere and they worked. We have a Cbox at the production plant, but I can’t verify first hand myself yet. I was pretty sure it would work based on my experience with the other two. I would purge and measure like above until readings began to plane out.

    I have used pliers to remove nails before, even though they aren’t designed specifically for it. Point being, yes a gas detector would be the “proper” tool, but there is no need for one when you can multi-purpose a very expensive piece of equipment that you already have. Even if measurements are not exactly accurate, it should be much more consistent over successive tank cycles. Sure beats blindly trusting SOPs (if you didn’t personally set and measure them). There is no reason gas should damage the equipment, so there is very little downside IMHO.

  7. #7
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    Quote Originally Posted by Smelliot View Post
    When using the Cbox on empty tanks, we'd look for readings down around 5ppb, which was definitely achievable given enough time and gentle purging.
    I don't doubt that the device is showing a reduction in oxygen over time as you purge the tank. The reading is probably proportional to the actual oxygen content in the tank, but the reading of 5ppb has to be garbage. It's my understanding that the amount of oxygen in coming out of CO2 tanks is measured in multiple ppm (5-100). It makes no sense to me that you could get a tank down to some number of ppb while purging with a gas with 1000x the oxygen content.

  8. #8
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    Using a DO2 meter to measure oxygen in gases, eg. tank purge, is simplicity itself!

    All you need do is connect up the meter, open its flow control fully then gently crack open the sample tap. The purpose of this is to have the gas flowing through the meter at close to atmospheric pressure.

    When the reading stabilises, convert the ppb to % as follows:

    Air, with ~20% O2, will read around 8ppm dissolved (=8000ppb), so a reading of 800ppb = 2%, 80ppb = 0.2%, etc.

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