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Thread: New DO meter user with questions!

  1. #1
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    New DO meter user with questions!

    Hi all, we recently bought a Hamilton Beverly portable DO meter. We've already noticed that the unit needs to be calibrated much more than every few months like Hamilton says.
    But the biggest question I'm having relates to my dissolved oxygen levels in pre fermented wort. We took a reading the other day and it read >27 ppm. baffled by the number I measured tap water directly afterwards and got 27 ppm again. Fermentation went fine like it always does. Then next batch we calibrated with compressed air before taking a reading and got 27 ppm again, then measured tap water at 24 ppm this time. Is this even possible?! I always understood the theoretical maximum solubility of water being less than 14 ppm?

    We oxygenate through a 8 inch carbonation stone with pure welding grade oxygen from prax air, at 2 LPM for a 30 minute transfer on a 10 bbl batch. The DO reading was taken directly after knockout was complete from my sample valve.

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    What sort is it? Optical or electrochemical?
    dick

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    Quote Originally Posted by dick murton View Post
    What sort is it? Optical or electrochemical?
    Optical cap. Also another tidbit, After high end calibration the compressed air sent through the unit was reading ~9.5 ppm

    Its been a PITA to calibrate the low end readings as well. We dont have a flowmeter inline yet and they say it needs .5 lpm flow to calibrate. How much does correct flow during calibration matter with these things? Our dedicatwd flowmeter and inline regulator to calibrate is on order.

  4. #4
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    Third attempt - damned internet keeps dropping out.

    Optical instruments come in two ranges - high for wort DO, e.g. ppm, and low for bright beer, e.g. ppb. Electrochemical sensors cover the whole range with one instrument, but are not so good to clean and calibrate, or quick to respond.

    So first question is - have you got the right range instrument? If not, afraid you will have to buy another of the correct range.

    I trialled 6 and subsequently used long term 2 makes of optical instrument, from Hach and Haffmanns. Both lasted months before needing any new sensors, and this was with them set on something like 2 second scans, but in big breweries where used almost continuously (wort) or for considerable time (bright beer - hours) per day. So unless you are leaving them switched on continuously you shouldn't need to replace yet.

    I suggest you go back to Hamilton and seek their advice.
    dick

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    From my understanding of the Hamilton instrument, there is only one range available (up to 25ppm) unlike Haffmans, Orbisphere, etc. who make low level (<2ppm) and high level (<20ppm) versions.

    If you are getting constantly high readings then my first advice would be to check the meter on a known low O2 medium like good quality CO2 or N2 gas. The meter should respond to this,with a low ppb result.

    Check also that all joints, connections, etc. are tight and leak-free as it is very easy for gas ingress to occur; however even a major leak us unlikely to result in the very high levels you are reporting.

  6. #6
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    TL is correct as the Bev has a selectable range of PPM and PPB and can indeed measure cold side O2 levels as well as hot side from 4 PPB to 25 PPM. I would agree with trying the N2 or CO2 approach to see if your levels drop to minimal readings.

    The Beverly may use two optical sensors considering what Dick said and the fact you have to select the range.

    Your readings are past the "range" of the device, so I suspect it is likely the calibration or fault with the sensors. Is this a brand new purchase from Hamilton or used? Have you tried a BBT reading to test suspected low end accuracy?

    If brand new I would ask them to send me a different unit, or a "loaner" to compare readings. If used, you probably need to replace the sensor(s). If N2 or CO2 reads extremely low (zeroed), it may not be the meter at all.

    It's been a while since I've worked with ole Bev, but it was one I preferred over the Orbisphere mainly due to the fact of the wide operating range (hot & cold side). Love the Anton Parr, but the cost is hard to swallow. Looking into the Haffmans for a new production expansion, but leaning towards the Bev. She tended to use more beer, but was very user (and budget) friendly. Tested the Bev and the AP on the same BBT and got very similar readings, so felt comfortable with its quality.

    To another point, your oxygen addition seems quite on the high side to me. It is possible to over oxygenate to the detriment of product, but that's a bit off topic.

  7. #7
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    The beverly is supposed to be accurate to 25 ppm.

    Today's batch we oxygenated at .5 LPM instead of 2 LPM, and still got a wort reading of >26ppm

    Think I have a faulty unit or am I misusing it?

  8. #8
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    No idea about a faulty unit as I have no experience of Hamilton, but the others I trialled simply went to the top of the range, or showed out of range.

    Re wort oxygenation - just giving a gas flow rate is meaningless. You need to know what pressure the oxygen is going in at, and what the wort flow rate and temperature is, and to a lesser extent the gravity, just for starters. Then you have to ensure it is fully dissolved, which raises a whole load of other issues. You may have all of it dissolved or virtually none of it dissolved, in which case you are wasting money if your meter reading is vaguely correct. Maximum DO2 from pure oxygen is approx. 30 ppm, but wort gravity and temperature affect this value.

    Chances are you don't need anything like that amount of oxygen dissolved anyway. I know of one brewery producing high gravity worts and they used 27 ppm, but more typical values are 8 to 15 ppm - lots of discussions on this site about suitable values. And if you are using fresh dried yeast every time, normally you don't need to oxygenate / aerate at all.

    According to the Hamilton site, they do two ranges, one for wort, one for BBT type levels, which are not easily interchangeable - at least with all the units I tried out. So my guess is you have the wort range - but worth checking.
    dick

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    Quote Originally Posted by dick murton View Post
    According to the Hamilton site, they do two ranges, one for wort, one for BBT type levels, which are not easily interchangeable - at least with all the units I tried out. So my guess is you have the wort range - but worth checking.
    It’s one machine with both ranges. You have to select the range on the interface. They are not separate instruments.

    Probably a bad sensor(s) but could be faulty calibration. Highly doubtful you are misusing it. You may have to close the valve on the instrument half way or so to prevent foaming, but that still shouldn’t raise your o2 reading to the levels you are seeing.

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    As far as I could see, according to the User Manual on Hamilton's website, the units preferred for DO2 measurement can be selected from ppb, ppm, vol% and mg/l. However it has a single sensor and there is only one type of replaceable opticap.

    Calibration is performed in air (for the upper end) and oxygen-free gas (for the lower/zero point). Essentially this is exactly the same as the calibration process for all EC sensors. This would suggest the sensor has to have a wide range; other instruments that have the option of low-level optical sensors (Hach, Haffmans, etc.) will typically use a known-O2 gas standard of around 1-2% oxygen for the upper end of the response as the level of O2 in air is higher than the 'saturation' value for the low-level units.

    The tech spec in the manual confirms there is only one measurement range, of 4ppb to 25ppm.

    I would certainly carry out the CO2/N2 checks advised previously and ensure the two calibrations are being performed/accepted. Something that concerns me - and I am happy to be corrected on this - is the use of COMPRESSED air for calibration; whilst air at any pressure will still contain ~20% O2, the number of oxygen molecules in a given space will increase as the pressure increases. Now, since optical sensors respond to the amount of oxygen present in a sample, with higher levels causing a faster fluorescence decay, would flowing compressed air through the unit cause incorrect calibration?

    eg. If the air flowing through the unit was at 3 bar (absolute) as opposed to atmospheric pressure (ie. 1 bar absolute) would the resultant calibration be around 3x higher?

    Optical (fluorescence) sensors are effectively measuring the partial pressure of the oxygen present, so surely the partial pressure of oxygen in air at 3 bar (abs) will be three times higher than the partial pressure in air at 1 bar (abs)...
    Last edited by TL Services; 01-10-2018 at 12:17 PM.

  11. #11
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    Quote Originally Posted by TL Services View Post
    As far as I could see, according to the User Manual on Hamilton's website, the units preferred for DO2 measurement can be selected from ppb, ppm, vol% and mg/l. However it has a single sensor and there is only one type of replaceable opticap.

    Calibration is performed in air (for the upper end) and oxygen-free gas (for the lower/zero point). Essentially this is exactly the same as the calibration process for all EC sensors. This would suggest the sensor has to have a wide range; other instruments that have the option of low-level optical sensors (Hach, Haffmans, etc.) will typically use a known-O2 gas standard of around 1-2% oxygen for the upper end of the response as the level of O2 in air is higher than the 'saturation' value for the low-level units.

    The tech spec in the manual confirms there is only one measurement range, of 4ppb to 25ppm.

    I would certainly carry out the CO2/N2 checks advised previously and ensure the two calibrations are being performed/accepted. Something that concerns me - and I am happy to be corrected on this - is the use of COMPRESSED air for calibration; whilst air at any pressure will still contain ~20% O2, the number of oxygen molecules in a given space will increase as the pressure increases. Now, since optical sensors respond to the amount of oxygen present in a sample, with higher levels causing a faster fluorescence decay, would flowing compressed air through the unit cause incorrect calibration?

    eg. If the air flowing through the unit was at 3 bar (absolute) as opposed to atmospheric pressure (ie. 1 bar absolute) would the resultant calibration be around 3x higher?

    Optical (fluorescence) sensors are effectively measuring the partial pressure of the oxygen present, so surely the partial pressure of oxygen in air at 3 bar (abs) will be three times higher than the partial pressure in air at 1 bar (abs)...
    I did notice that when the flow of compressed air into the unit fluctuated- so did the readings. I suppose due to varying partial pressures of oxygen. I'm thinking this is why the manufacturer requires high end calibration to be taken place with a regulated very slow flow of compressed air (.5 LPM)

  12. #12
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    heres the email I got back from the Rep after I told him we were having issues with their meter. My flowmeter and regulator arrived today, so I'm going to do some calibrations exactly the way the factory wants and see if anything improves. I don't think I have ultra high pure co2 or n2 (just welding grade n2). I have heard it may not be a bad idea to calibrate (or at least verify calibration) with cans of an industrial lager (thoughts?.

    First off, I’m wondering why you needed to calibrate so quickly. You should only calibrate every 2-3 months. Second, what is the purity of your CO2? We use 99.999% N2 when we calibrate in the lab before we ship. If you are not using 99.999% CO2 to calibrate, then yes, something that should be low DO’s might drop to 0 since you raise the bottom of the low limit calibration. 99.999% is expensive and hard to come by, that’s why we use 99.999% N2. Do you have a 500ml/min gas regulator? This is important when performing both the high and the low end calibration. You should always perform both high and low end calibrations consecutively, but it doesn’t matter which you start with. You should always do a thorough hot water flush before you calibrate and allow ample time for the temperature of the unit to come down. Always make sure the internal chamber of the unit is completely dry before you calibrate. You can blow plant CO2 through it to dry it out. Never put any sanitizers or chlorinated cleaners through the unit. You can perform a low temp, low caustic concentration, low pressure cleaning on it every now and again, but make sure you thoroughly flush it out with hot water afterwards.

    Give me a call if you want to discuss further.

    Best regards,

  13. #13
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    You can't calibrate with cans of industrial lager, but you can check your calibration somewhat with them. Although Hamilton uses "zero gas" N2, you should be able to use a welding/industrial grade without issue. Grades usually come down to moisture content more than gas molecules.

    I find it interesting he didn't mention exactly what they use for high end calibration. We are left to assume its the compressed air you talked about. Not exactly a quantified number of oxygen molecules. We have to assume our compressed air would contain the roughly 21% of standard expectancy (hope your compressor isn't next to a de-gassing tank).

    I would think if they were to specify a 99.999% pure N2, that they would use pure O2 on the high end, or a calibrated mixed gas.

  14. #14
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    As per my earlier post, the key here is to calibrate at atmospheric pressure as I am pretty certain elevated pressure will cause errors.

    Ordinary air, flow-regulated before going into the meter, is the way to get a correct upper end calibration.

    This is the way electrochemical sensors have been calibrated and I see no reason why optical sensors should be any different.

  15. #15
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    Our compressor is in the same room as a furnace in a well ventilated utility room. Im not sure what effect this would have but considering tap water was reading 27 ppm before we recalibrated from the factory i have to imagine the effect is nil?

    We got our flow meter hooked up yesterday and recalibrated exactly as our rep instructed us. (Rinse then dry, .5LPM constant flow to cal). We are using grade 2 co2 99.9% to calibrate currently. We then measured a dry Hopped IPA at 0 PPB. And measured tap water alongside an inexpensive milwaukee membrane DO meter (the milwaukee read 13.5 ppm, the beverly read 26 ppm.

    We then went back to the same co2 source we calibrated with and it measured 26 ppb. (Is this an acceptable error range?)
    Do i ask the manufacturer to take it back?

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