Anyone have any experience with O2 analysers? - Page 1
Forum section: electronics / general

author: apelly
author_rank: Unknown
timestamp: April 11, 2017, 12:40:01 pm
content: Been on a bit of a buying spree. One of the things I bought was a fairly significant liquid nitrogen dewar. Obviously I need to fill it, freeze things and smash them, and make some LN2 ice-cream. After that I probably have no use for it. But I hear the ice-cream is amazing.But, it's a 60L dewar. That's a boat load of LN2. Or a house full. So it seems sensible to lock it up outside. But I don't need to be killing any wildlife or pets either, so I thought of getting an oxygen analyser to have a sniff around with and get a feel for potential problems.And so I end up here looking for advice. Again. If you've got something more constructive than "You're going to die! You don't know what you're doing. You should never be doing this." I'd love to hear from you.Cheers guys.

author: thm_w
author_rank: Super Contributor
timestamp: April 11, 2017, 09:15:05 pm
content: Are you looking at a full device or just the sensor?I haven't used them, but when looking for low cost devices I found:O2-A2 AlphasenseCost: $48Range: 0 – 20% O2Signal: 80 – 120 uAAccuracy: -Power: -Response: <15sSize: 20×17mmME2-O2 WinsenCost: $54Range: 0 – 25% O2Signal: 150 uA (0 - 15mV with 100load)Accuracy: <2% repeat, <2% stability/monthPower: -Response: <30sSize: 31×17mmSo they aren't terribly accurate, but if you cal it to outdoor air (21%) it should be fine for getting relative measurement.Shouldn't be hard to interface to a micro. A full product using one of these would probably be in the $1-2k range retail.

author: apelly
author_rank: Unknown
timestamp: April 11, 2017, 09:27:05 pm
content: Quote from: thm_w on April 11, 2017, 09:15:05 pmI was hoping to find something second hand on the cheap from ebay. As you say, they should be easy to cal outside, and test in zero O2But those devices are certainly something to go on. I'll look into them a bit later today. Thanks mate.

author: Someone
author_rank: Super Contributor
timestamp: April 11, 2017, 09:39:58 pm
content: Quote from: apelly on April 11, 2017, 09:27:05 pmDont do this! The typical sensors used for monitoring air for breathing have a limited lifespan:http://www.brandtinst.com/biosystems/appnotes/Downloads/25.%20Sensor_Life_Expectancy.pdfThe sensors used in automotive are another option with longer lifespans but they require a lot of energy to keep them at operating temperature.

author: metrologist
author_rank: Super Contributor
timestamp: April 11, 2017, 09:45:01 pm
content: Oh, yeah I was thinking automotive O2 sensor, but they have to be at high (exhaust) temp?I'd like one of those clip on your finger types so I could monitor myself over night...

author: Mr.B
author_rank: Unknown
timestamp: April 11, 2017, 10:34:47 pm
content: At work we use Industrial Scientific GasBadge Pro, part number 18100060-3.They are available from Entec here in NZ.Unfortunately they have a limited life - about 2,500 hours from memory.Thats not too bad if you only use it a couple of hours a week. My one at work is probably used for about 10 hours a week.They are a little on the expensive side but it is your life we are talking about here...http://www.gasdetectors.co.nz/portable-gas-detectors/gasbadge-pro/

author: apelly
author_rank: Unknown
timestamp: April 12, 2017, 02:10:07 am
content: Quote from: Mr.B on April 11, 2017, 10:34:47 pmThanks for the tip mate.Care to elaborate on "little expensive?" Like $200 or $2k?

author: Mr.B
author_rank: Unknown
timestamp: April 12, 2017, 02:18:58 am
content: I just asked accounts.4 months ago they were NZD 525 plus the Grab Snatch and Take.

author: apelly
author_rank: Unknown
timestamp: April 12, 2017, 02:38:46 am
content: Well, you are right; it could be life or death without due care.But that does sound like a corporate price. I wouldn't rule it out at this stage, but it doesn't seem too likely.Thanks for checking for me though. I appreciate the effort.

author: Mr.B
author_rank: Unknown
timestamp: April 12, 2017, 02:50:01 am
content: Additional...Having them serviced (new sensor element after 2,500hrs) is NZD 140 +GST.

author: thm_w
author_rank: Super Contributor
timestamp: April 12, 2017, 07:34:51 pm
content: Quote from: Someone on April 11, 2017, 09:39:58 pmWhy would you not use a sensor because it has a limited lifespan? As long as you are aware its not an issue.The Alphasense I mentioned has a 2 year spec until output reaches 85%. So cal once per year should be reasonable.If you want long life, the Luminox is ideal (uses optical method, >5 year life), but I cannot find any pricing information,LOX-O2:http://www.gassensor.ru/data/files/oxygen/LuminOx_O2_optical.pdfThis is ~2.3 year:http://www.sensore-electronic.com/wp-content/uploads/2016/04/SO002e-3_Data-sheet-sensor.pdfedit: I asked for quote for LOX-O2 will update if I receive info.

author: Someone
author_rank: Super Contributor
timestamp: April 12, 2017, 11:47:06 pm
content: Quote from: thm_w on April 12, 2017, 07:34:51 pmRead the whole quote, I'll add emphasis to make it clear:Quote from: Someone on April 11, 2017, 09:39:58 pmBuying a short lifespan product second hand through a grey channel is foolish.

author: thm_w
author_rank: Super Contributor
timestamp: April 12, 2017, 11:53:11 pm
content: Quote from: Someone on April 12, 2017, 11:47:06 pmSorry should have read more carefully, you are right, would not buy a used product.

author: apelly
author_rank: Unknown
timestamp: April 13, 2017, 12:01:59 am
content: Quote from: Someone on April 12, 2017, 11:47:06 pmI agree.Before I asked here I didn't realise the sensors were essentially consumables. Now I think about it though, I do remember Dave tearing down some gas sensor or another. I recall the discussion of electro chemistry.But now I know. EEVBlog forum FTW! Thanks for the help guys.

author: mtdoc
author_rank: Super Contributor
timestamp: April 13, 2017, 12:04:38 am
content: I don't understand why you think you need an O2 sensor.Large volumes of liquid N2 are stored in cryogenic dewars in medical offices all over the world without need for any for O2 sensors.As long as it is not kept in an air tight space with animals you don't have to worry about oxygen being displaced to any dangerous degree.Other than the risk of localized frostbite with improper handling, liquid N2 is really relatively safe stuff.

author: MarkS
author_rank: Unknown
timestamp: April 13, 2017, 12:28:54 am
content: I don't know how enclosed your "outside" is, but mine is open enough for this not to be is an issue.

author: mtdoc
author_rank: Super Contributor
timestamp: April 13, 2017, 12:42:12 am
content: Quote from: MarkS on April 13, 2017, 12:28:54 amAnd it's not an issue for an indoor space either unless it is a completely sealed, airtight space.Right now I'm sitting next door to a 8 x 10 foot room with a 10 liter cryogenic storage dewar full or liquid N2. Not an O2 sensor anywhere to be found.

author: Someone
author_rank: Super Contributor
timestamp: April 13, 2017, 12:58:48 am
content: Quote from: mtdoc on April 13, 2017, 12:04:38 amAnd in other parts of the world it wouldn't be considered safe without a calibrated sensor, differing levels of risk are accepted by different people/communities/governments

author: mtdoc
author_rank: Super Contributor
timestamp: April 13, 2017, 01:11:54 am
content: Quote from: Someone on April 13, 2017, 12:58:48 amWell the regulations governing medical facilities in the US are crazy strict and conservative so I have a hard time imagining that they would not require it if there was any reasonable risk. We do have regulations about it's use and storage but none of them involve O2 sensors.I doubt there's ever been an accidental asphyxiation from liquid N2 while it's being stored inside a proper container.Looking atthis Wikipedia articleseems to confirm this. Of the 80 deaths by accidental nitrogen asphyxiation between 1992 none were from that scenario. They where either industrial accidents, spills, "recreational inhalation" or similar Darwin award incidents (pouring liquid N2 into a pool).

author: MarkS
author_rank: Unknown
timestamp: April 13, 2017, 01:31:41 am
content: LN2 is remarkably safe. Your greatest danger is from frostbite. It dissipates quickly, so you would have to pour a large amount in a sealed room to suffocate. If you are storing it outdoors or in a shed or garage, the chances of suffocation are slim. Not zero, but very low.That fog you see pouring off experiments with LN2, if you don't know better, appears concerning. That's not nitrogen gas, but rather water vapor in the air having been frozen by the cold. The nitrogen had dissipated by the time the water vapor froze.

author: apelly
author_rank: Unknown
timestamp: April 13, 2017, 12:45:14 pm
content: Quote from: mtdoc on April 13, 2017, 12:04:38 am100 litres of liquid nitrogen, in a dewar with unknown performance, warrants respect.And so I'm good to accept (entertain?) advice from the breadth of the community over here.I will remove no warts!

author: LaserSteve
author_rank: Super Contributor
timestamp: April 13, 2017, 02:37:54 pm
content: If you just want piece of mind, I use a self calibrating USB Oxygen sensor from CO2METER.COm at work and love it.Our loading dock, with the main LN2 tank, has an oxygen alarm. One that is type approved. That LN2 tank is the size of a compact car, and merits respect.Most other Dewers vent at such a low rate into confined spaces that we do not monitor them. We do however check the sanity and training of the bulk users fairly often.Steve

author: mtdoc
author_rank: Super Contributor
timestamp: April 13, 2017, 03:16:10 pm
content: Quote from: apelly on April 13, 2017, 12:45:14 pmI agree. But I don't understand how an O2 sensor will help. Are you concerned about a leak from your storage container? Any non-visible leak would be small enough to not be a danger unless it is being stored in a small, airtight space (which would be a bad idea!). The real risk is from a large spill, in which case an O2 sensor will be of no use since the risk will be immediate and readily apparent. Attention to secure storage in a proper cryogenic storage dewar and safe handling is important. But there's no benefit from an O2 sensor that I can imagine. If there's a scenario where it would help, I'd be happy to hear about it.

author: CM800
author_rank: Frequent Contributor
timestamp: April 13, 2017, 03:51:31 pm
content: Heres a situation:a small leak over a weekend or holiday, all the doors are closed up... then a lone janator comes in to do some cleaning before people return, or a manager comes to picks some stuff up from his desk....then passes out.

author: thm_w
author_rank: Super Contributor
timestamp: April 13, 2017, 05:18:48 pm
content: Quote from: LaserSteve on April 13, 2017, 02:37:54 pmI see they sell the LUX-O2 sensor I mentioned for $99 which is not bad for a >5 year life O2 sensor:https://www.co2meter.com/collections/co2-sensors/products/25-percent-oxygen-sensorThen to add usb/board is not much more.Thats quite reasonable.

author: mtdoc
author_rank: Super Contributor
timestamp: April 13, 2017, 06:17:52 pm
content: Quote from: CM800 on April 13, 2017, 03:51:31 pmRight, but unless the room is actually completely airtight it would not happen. But even then it wouldn't since as soon as the door was opened - almost immediately, the air in the room would equalize with the atmosphere.I've worked with liquid N2 for decades. In medical offices it is always stored in a cryogenic dewar that has a loose, non sealed top - by design. These are kept in small rooms. The last office I worked in, it was kept in a very small locked med room maybe 4 x 5 feet. Every time someone went in that room the door had to be closed. If that person was then filling up a "cryogun" with liquid N2' the process would inevitably result in spilling of some N2 and some boiling off of N2 from the cryogun before it was sealed. Even in a very small room this caused no issues.

author: ebclr
author_rank: Super Contributor
timestamp: April 13, 2017, 08:57:17 pm
content: http://www.lutron.com.tw/ugC_ShowroomItem_Detail.asp?hidKindID=&hidTypeID=&hidCatID=&hidShowID=1102&hidPrdType=S&txtSrhData=o2

author: Someone
author_rank: Super Contributor
timestamp: April 13, 2017, 10:47:14 pm
content: Quote from: mtdoc on April 13, 2017, 06:17:52 pmThere is not enough mixing from an open door to purge a room. The opposite extreme is a freezer or cool room which will have an extremely low rate of air change, but even it won't be sealed to allow a pressure differential.Yes, most commercial buildings have a HVAC system which sets an air change rate of 5-10 volumes per hour but if the HVAC fails...Is the user informed of the failure? Even so do they know the consequences?Small rooms in residential properties can have extremely low rates of air change:https://en.wikipedia.org/wiki/Passive_houseWhen pushing for less than 0.6 volumes per hour overall there will be rooms and spaces with much lower air change rates. A failed LN2 storage could leave a dangerous atmosphere in a small room for hours.The maths are not complicated:https://intranet.birmingham.ac.uk/hr/documents/public/hsu/information/hazardoussubstances/Appendix3Oxygendepletioncalculations.pdfAnd while most large spaces would have no problems when there is adequate air circulation, in still air local pockets of dangerous atmospheres can be created. Given HVAC systems don't provide continuous assurance of their correct operation, its left to well designed and installed oxygen depletion monitoring systems to provide adequate safety.