Home Made Oxygen Meter - Page 1
Forum section: electronics / projects

author: German_EE
author_rank: Super Contributor
timestamp: December 23, 2016, 10:04:48 am
content: Given the current insane price of oxygen sensors at places like Mouser and Farnell would it be possible to use the O2 sensor from a car to measure (approximately) the amount of oxygen in the air? I have no idea how either of the sensors work and I was hoping for some insight.

author: cs.dk
author_rank: Unknown
timestamp: December 23, 2016, 10:14:32 am
content: I've got wideband O2 sensor from Innovate Motorsport, it'll directly tell you the amount of O2 in the surrounding air. Either as a %-value or lambda-value. But it was quite expensive;http://www.innovatemotorsports.com/products.phpThe sensor it self is a standard Bosch sensor.It's probably more difficult to drive a wideband sensor, but they are more precise. A regular narrowband O2 sensor is more an "hot or cold" type.http://forum.diyefi.org/viewtopic.php?f=16&t=1882Would not use it for checking for O2 levels in a tank prior to enter it. Better use properly tested life saving equipment. They are insanely expensive though.http://www.bw-gasmonitors.com/

author: max_torque
author_rank: Super Contributor
timestamp: December 23, 2016, 11:47:29 am
content: Exhaust oxygen sensors or "lambda sensors" are very good at telling you oxygen concentration, at least when there is a lot of oxygen around! The downside is that they must be HOT to work, and this requires the internal heater to be operated. Narrow band (switching) and wide band (ratiometric output current vs reference cell O2 content) are very different, although they work on similar principals.Easiest to use will be a narrow band sensor, but all of them will requires some form or calibration before you can use the reading. For automotive use, they are of course calibrated at relatively low oxygen concentrations, but they will happily read normal atmospheric concentration (~21%) and often this is used as one of the calibration points.Plenty of explanations on how they work, and how to interface to them on google!

author: BradC
author_rank: Super Contributor
timestamp: December 23, 2016, 12:18:04 pm
content: Fuel cell oxygen sensors (of the type used in medical applications) are accurate with periodic calibration, much easier to use than automotive sensors and run in the $70-100 buck mark retail. How accurate do you need to be?

author: LaserSteve
author_rank: Super Contributor
timestamp: December 23, 2016, 01:23:33 pm
content: Co2meter.com makes what we use at work.Steve

author: pyroesp
author_rank: Regular Contributor
timestamp: December 23, 2016, 02:09:21 pm
content: Quote from: max_torque on December 23, 2016, 11:47:29 amWe have a few O2-meters where I work at with Zirconia cells. These have to be heated to around 700 to 750°C for it to work properly.Also, the price for a cell is ridiculously high.

author: German_EE
author_rank: Super Contributor
timestamp: December 23, 2016, 04:04:42 pm
content: OK, this is not a life and death situation and the sensor does not need to be accurate. Someone I know works in a room where there are two large CO2 cylinders and he's worried about them leaking whilst he's in there. He wants to build a simple oxygen sensor so that if the amount of oxygen in the air falls below a preset amount an alarm will sound. Wikipedia shows that air is about 21% oxygen so an alarm set at (say) 15% would probably be enough to avoid false alarms due to work activity. It looks as if we will be spending about a hundred Euro for a sensor unless someone knows any different.I initially suggested a canary

author: dmills
author_rank: Super Contributor
timestamp: December 23, 2016, 04:20:09 pm
content: An O2 sensor is the totally wrong approach for CO2 leak detection....CO2 becomes dangerous at a few percent concentration, which will not significantly change the O2 level, for a gas that is actively toxic at relatively low levels (<10% within 5 minutes) you need to sense that gas not the reduction in concentration of something else (CO would be even worse of course).Normal O2 partial pressure is ~0.21 bar, replace 10% or the air with CO2 and that drops to 0.19 bar, but 10% CO2 will kill in minutes, going for an alarm at 1% would need a very stable O2 sensor as the change would be just 0.002 bar ppO2.Using a CO2 sensor instead would be a change of over 100% between ~400ppm and 1000pm for a 1% alarm threshold.Now if you were worrying about an N2 leak, then sensing O2 partial pressure may make sense, because the danger there is reduced oxygen concentration, but this is not the risk for CO2.73 Dan.

author: DaJMasta
author_rank: Super Contributor
timestamp: December 23, 2016, 10:42:33 pm
content: It may not be practical, but what about weighing the air? CO2 is heavier than the normal air mix, so a collector of some sort and a sensitive weight sensor would do the job.I think in the vein of keeping it simple, you have two good options (which are not mutually exclusive):Weighing your CO2 cylinders and watching for a changeHaving a small circulation fanIf there's a leak, those cylinders will be getting notably lighter. If there's extra CO2 around, it likely won't take much mixing to make even high concentrations fairly safe, a continuous running fan would be plenty, but you could probably even have one that turns on when someone enters the room or trips a motion sensor or something.If you (or he) is really concerned about getting too much CO2 in their work environment, then shelling out 100 euro is really not much to ask... and if the risk is significant in any way, having that sort of monitoring equipment is probably mandated by your local OSHA equivalent.

author: LaserSteve
author_rank: Super Contributor
timestamp: December 23, 2016, 11:33:08 pm
content: Really you should buy a workplace gas monitor. That said, a Cozir usb NDIR sensor from Co2meter.com has been remarkably effective in a lab I Maintain. We of course are not using it for safety of life purposes.However, It's cost effective, too. 100-155$, reasonable cost. While you want one with an alarm or voltage output, the usb version with the Gaslab software is amazing.Steve

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 24, 2016, 01:24:22 am
content: Quote from: German_EE on December 23, 2016, 04:04:42 pmEither there is no reason to look for a monitor, or it IS a life and death situation. If there is not enough fresh air ventilation to make the room safe in spite of leaks it is worth whatever the most you, your friend, the employer, the insurer and the government think a life is worth to provide the protection. And if a leak is a real possibility and the fresh air ventilation is adequate, an alarm to warn of failure of the ventilation system.