Have anyone worked with O2 analyser. (urgent! its for covid patients)

[Adhith]

Hello guys, I need you support on this one
As the conditions in our country, India is getting bad, me and few of my friends are planning to build an O2 concentrator. We have done our initial trial testing we are getting good results. Now we are moving towards the electronic part where, we need to analyse the O2 percent that we generated using the OOM202  oxygen sensor and display on a 7 segment display. This goes on to each system that we produce. could anyone guide me how to use this O2 sensor module with arduino ?

any help is appreciated, We will be pushing lots of these in this week, if we could figure out this electronic part. Thank you

[Manul]

Never used this, but here are my thoughts. From what I see, it is a passive sensor (without the need of power). It has voltage output proportional and quite linear to volume percentage of O2.

1. You can directly connect this sensor output to ADC input and take samples.
2. It seems it outputs a bit less then 1mV per 1% of O2, so lets say working range 0 - 100mV.
3. I would say you need at least 1mV ADC resolution. It means, that for example, Arduino UNO default configuration is not good enough (10bit ADC, 5V reference, resolution = ~4.9mV)
4. If you want to use UNO, your best bet is to configure it to use internal 1.1V reference, then the resolution is ~1mV. Might be good enough.
5. If you plan to use different MCU which has 12 or 16 bit ADC, that would be good. Just choose the lowest reference voltage possible.
6. When you connect sensor to MCU, use short and possibly shielded wire (shield connected to Arduino ground) to avoid noise, because sensor signal is quite small and high impedance, so it is easy for external electrical noises to mess up the readings.
7. If it is not possible to calibrate each sensor with known O2 concentrations, then just calculate the ADC raw value per O2 percentage based on reading at ambient air. For example, take raw ADC value at ambient. Let say it is 15. So it means 20/15 (~20% air O2 in most places) = 1.33% O2 per ADC step. If then your ADC reads value 25, you multiply by 1.33 and get 33.3% O2.
8. You can take multiple samples and average them - you will get more effective resolution.
9. Don't expect to get very accurate readings, but I guess 1-2% is good enough for this application.

Good luck

[daisizhou]

OOM202 oxygen battery, placed in normal air (oxygen concentration is 21%), output 13.9mV, placed under 100% pure oxygen, output 66.3mV, the actual error is much lower than 5%

The ideal oxygen sensor should be a paramagnetic oxygen sensor.The principle is that oxygen molecules are deflected by magnetic force in a magnetic field.This is a long-term effective sensor
OOM202 oxygen battery is only valid for half a year,Because the chemical reaction is going on all the time

[fcb]

Top of range: 21% O² is 16mV. 100% O² then something like: 76.2mV, so probably allow for 80mV FSD (full scale deflection).  Don't feed the sensor striaght into the Arduino - you'll struggle to get rid of ADC sampling pulses etc.. and your resolution will be really poor.

Just use a rail-to-rail opamp (like MCP6001 or MCP6002 or whatever you have to hand) in a non-inverting amplifier to scale your 80mV to 5V (for the Arduino, assuming Arduino is 5V).

You probably want to trim this in hardware rather than software then probably stick a 100K potentiometer on the front-end and tune your gain for say 50x.  If you can find an opamp with lower input offset then great, although any half-decent EE can design a circuit that would compensate for what parts you can get locally.

If you get stuck then I'm sure someone here can design you a circuit with what you can get locally.  Probably best just to list the bits you can get really fast.

[Manul]

Just use a rail-to-rail opamp (like MCP6001 or MCP6002 or whatever you have to hand) in a non-inverting amplifier to scale your 80mV to 5V (for the Arduino, assuming Arduino is 5V).

You probably want to trim this in hardware rather than software then probably stick a 100K potentiometer on the front-end and tune your gain for say 50x.  If you can find an opamp with lower input offset then great, although any half-decent EE can design a circuit that would compensate for what parts you can get locally.

I'm not sure, and main reason is that OP wants to produce it very quickly, maybe even without PCB. As you said, OpAmp will also add offset, so offset and scaling both need to be corrected. I would still vote for trying direct sampling. Small capacitor can be added, so ADC sees lower impedance for its sampling. Signal frequency is very low anyway. Also because it is so slow, huge averaging can be used, like 100 samples or more, possibly adding quite a few bits of extra resolution. What I'm saying is that for someone who is not an expert, adding frontend would probably cost some additional development effort and make production harder (especially if it is hand made devices).

Probably how I would do calibration is a hidden calibration button or jumper. With a system powered and stable (software timer might be included to not allow premature calibration), the button can be pushed and MCU saves the ambient (21%) reading to eeprom. Every time it boots, it reads and uses that value. So it is very easy to calibrate at production or any time later if it drifts.

[fcb]

The offset is +/-4mV, the output of the sensor at 21% O² is 13-16mV.  If the OP want's do SW calibration, they could, but they have to write it.  Probably much easier to do a calibration in the analog domain. No point in spending time working out a schematic unless the OP states what parts we has available.

[daisizhou]

https://www.instructables.com/Easy-To-Build-Oxygen-Analyzer-Using-An-Arduino-Com/

[Zero999]

A cheap, widely available op-amp, with low offset is the OP07, but it isn't rail-to-rail, so you need to -3V and +8V rails, to get an output voltage range of 0V to 5V.

An even cheaper op-amp is the LM358, which doesn't need a negative rail, but it has a much worse offset, so will need calibration and will still need an 8V supply, if an output swing to 5V is required.

What power supply voltages are available? Is this being run off a mains transformer+rectifier+linear regulator? If so, it's easy to add voltage multipliers for the op-amp power supply rails.

If you have a spare spare of I/O pins to output a squarewave from, you can generate the higher +V and -V rails for the op-amp, with diode+capacitor voltage doubler circuits.

[CaptDon]

As others have stated, the oxygen battery sensor device has a finite lifetime based on the oxygen concentration mostly. The higher the content the faster the cell ages. Also it will age more quickly with large amounts of air moving across it. Limit the turbulence it sees. We changed ours yearly in the operating rooms and they were still accurate.

[CaptDon]

Also, you need an op amp with super high input impedance!!! A fet type front end. Just like any battery, the higher the load the faster it ages!!

[fcb]

Also, you need an op amp with super high input impedance!!! A fet type front end. Just like any battery, the higher the load the faster it ages!!

No you don't. The manufacturer specifies >10kOhms.

These have a finite life when you open the tin/bag they come in. So the OOM202 is quoted at >1,000,000% volume oxygen hours.  So essentially 10,000 hours (60 weeks) at 100% concentration, greater life at lower concentrations.

[Adhith]

Never used this, but here are my thoughts. From what I see, it is a passive sensor (without the need of power). It has voltage output proportional and quite linear to volume percentage of O2.

1. You can directly connect this sensor output to ADC input and take samples.
2. It seems it outputs a bit less then 1mV per 1% of O2, so lets say working range 0 - 100mV.
3. I would say you need at least 1mV ADC resolution. It means, that for example, Arduino UNO default configuration is not good enough (10bit ADC, 5V reference, resolution = ~4.9mV)
4. If you want to use UNO, your best bet is to configure it to use internal 1.1V reference, then the resolution is ~1mV. Might be good enough.
5. If you plan to use different MCU which has 12 or 16 bit ADC, that would be good. Just choose the lowest reference voltage possible.
6. When you connect sensor to MCU, use short and possibly shielded wire (shield connected to Arduino ground) to avoid noise, because sensor signal is quite small and high impedance, so it is easy for external electrical noises to mess up the readings.
7. If it is not possible to calibrate each sensor with known O2 concentrations, then just calculate the ADC raw value per O2 percentage based on reading at ambient air. For example, take raw ADC value at ambient. Let say it is 15. So it means 20/15 (~20% air O2 in most places) = 1.33% O2 per ADC step. If then your ADC reads value 25, you multiply by 1.33 and get 33.3% O2.
8. You can take multiple samples and average them - you will get more effective resolution.
9. Don't expect to get very accurate readings, but I guess 1-2% is good enough for this application.

Good luck

Thank you for your in depth explanation. That cleared a lot of things. I'm  planning use a dedicated ADC module for this purpose. Since we are running out of time, we are not planning to go for circuit design and all. we are looking for electronic kits that we could directly use for the purpose.

If I'm using a separate ADC module, How could I use in my application? any suggestions for ADC boards?

[Adhith]

OOM202 oxygen battery, placed in normal air (oxygen concentration is 21%), output 13.9mV, placed under 100% pure oxygen, output 66.3mV, the actual error is much lower than 5%

The ideal oxygen sensor should be a paramagnetic oxygen sensor.The principle is that oxygen molecules are deflected by magnetic force in a magnetic field.This is a long-term effective sensor
OOM202 oxygen battery is only valid for half a year,Because the chemical reaction is going on all the time

I'll take this into account, Thank you. Do you have any recommendations for paramagnetic oxygen sensor?  Actually I searched a lot for oxygen sensors. but results were pretty low. Thats why I planned to use OOM2O2 sensor

[Adhith]

Top of range: 21% O² is 16mV. 100% O² then something like: 76.2mV, so probably allow for 80mV FSD (full scale deflection).  Don't feed the sensor striaght into the Arduino - you'll struggle to get rid of ADC sampling pulses etc.. and your resolution will be really poor.

Just use a rail-to-rail opamp (like MCP6001 or MCP6002 or whatever you have to hand) in a non-inverting amplifier to scale your 80mV to 5V (for the Arduino, assuming Arduino is 5V).

You probably want to trim this in hardware rather than software then probably stick a 100K potentiometer on the front-end and tune your gain for say 50x.  If you can find an opamp with lower input offset then great, although any half-decent EE can design a circuit that would compensate for what parts you can get locally.

If you get stuck then I'm sure someone here can design you a circuit with what you can get locally.  Probably best just to list the bits you can get really fast.

What if I use a pre-made opamp circuit boards that is commercially available ?

[Zero999]

Never used this, but here are my thoughts. From what I see, it is a passive sensor (without the need of power). It has voltage output proportional and quite linear to volume percentage of O2.

1. You can directly connect this sensor output to ADC input and take samples.
2. It seems it outputs a bit less then 1mV per 1% of O2, so lets say working range 0 - 100mV.
3. I would say you need at least 1mV ADC resolution. It means, that for example, Arduino UNO default configuration is not good enough (10bit ADC, 5V reference, resolution = ~4.9mV)
4. If you want to use UNO, your best bet is to configure it to use internal 1.1V reference, then the resolution is ~1mV. Might be good enough.
5. If you plan to use different MCU which has 12 or 16 bit ADC, that would be good. Just choose the lowest reference voltage possible.
6. When you connect sensor to MCU, use short and possibly shielded wire (shield connected to Arduino ground) to avoid noise, because sensor signal is quite small and high impedance, so it is easy for external electrical noises to mess up the readings.
7. If it is not possible to calibrate each sensor with known O2 concentrations, then just calculate the ADC raw value per O2 percentage based on reading at ambient air. For example, take raw ADC value at ambient. Let say it is 15. So it means 20/15 (~20% air O2 in most places) = 1.33% O2 per ADC step. If then your ADC reads value 25, you multiply by 1.33 and get 33.3% O2.
8. You can take multiple samples and average them - you will get more effective resolution.
9. Don't expect to get very accurate readings, but I guess 1-2% is good enough for this application.

Good luck

Thank you for your in depth explanation. That cleared a lot of things. I'm  planning use a dedicated ADC module for this purpose. Since we are running out of time, we are not planning to go for circuit design and all. we are looking for electronic kits that we could directly use for the purpose.

I suppose it can be stored in an inert gas, such as nitrogen, when not in use.

It might be a good idea to record the date and log the runtime, so you know when it needs to be replaced. If the system has a realtime clock, it should be easy to store the date in flash memory and calculate when it needs to be replaced based on exposure to oxygen, both due to the background ambient level and whilst the machine is running.

Fortunately the sensor will fail safe, by underestimating the oxygen level.

If I'm using a separate ADC module, How could I use in my application? any suggestions for ADC boards?

I Googled for ADC PGA and found this module.
https://www.adafruit.com/product/1085

[Adhith]

I'm not sure, and main reason is that OP wants to produce it very quickly, maybe even without PCB. As you said, OpAmp will also add offset, so offset and scaling both need to be corrected. I would still vote for trying direct sampling. Small capacitor can be added, so ADC sees lower impedance for its sampling. Signal frequency is very low anyway. Also because it is so slow, huge averaging can be used, like 100 samples or more, possibly adding quite a few bits of extra resolution. What I'm saying is that for someone who is not an expert, adding frontend would probably cost some additional development effort and make production harder (especially if it is hand made devices).

Probably how I would do calibration is a hidden calibration button or jumper. With a system powered and stable (software timer might be included to not allow premature calibration), the button can be pushed and MCU saves the ambient (21%) reading to eeprom. Every time it boots, it reads and uses that value. So it is very easy to calibrate at production or any time later if it drifts.

Yes, indeed. without a PCB is what we are looking for. It could save lot of time and also custom PCB is tough to get it done at this pandemic time as well. I could buy an additional module and connect it between the sensor and UNO. So I guess an ADC module is the solution

[Manul]

Yes, indeed. without a PCB is what we are looking for. It could save lot of time and also custom PCB is tough to get it done at this pandemic time as well. I could buy an additional module and connect it between the sensor and UNO. So I guess an ADC module is the solution

You may first try the UNO ADC with analogReference(INTERNAL), so it uses 1.1V reference. It will not take a lot of time, maybe half hour to try. You may use 1-10nF capacitor in parallel with sensor. Use sample averaging and see what kind of results you get. If you need to build it fast, the minimum system which works good enough is good enough.

What is your target accuracy of O2 measurement?

[Manul]

Does not matter what you use, op amp, sampling directly with external or internal ADC, you first need to worry about noise. If there will be a lot of external noise, long wires and bad layout, you will loose accuracy, because sensor signal is quite low and susceptible to interference. But if you keep signal clean, then 10bit ADC with 1.1V reference with oversampling should theoretically be enough to get 1% resolution or even less.

[ace1903]

Keeping sensor under inert gas is not recommended. This is called starvation mode and it will shorten sensor lifetime.
As I said here on the forum several times enriched air is dangerous stuff.
It is non conducting and produces static electricity in each component. Even invisible ESD event can result in disaster.
There were several hospitals that were engulfed in fire due to improper installation and/or equipment.
Instead of trying to make dangerous equipment is much better to organize purchase of certified equipment.
To many this looks as opportunity to show craftmanship and ingenuity but I look at this as planting bomb nearby innocent patients.
 Just search how many people died in fires in hospital recently.

[fcb]

Once opened the sensors can't be stored under inert atmosphere - it leads to premature failure.

[Adhith]

As others have stated, the oxygen battery sensor device has a finite lifetime based on the oxygen concentration mostly. The higher the content the faster the cell ages. Also it will age more quickly with large amounts of air moving across it. Limit the turbulence it sees. We changed ours yearly in the operating rooms and they were still accurate.

Yeah. I haven't thought about this. Now I'm planning to put the O2 sensor in a small chamber, with one end a micro solenoid valve. It will be only sampled when needed and will be kept air tight if not in use

[Adhith]

These have a finite life when you open the tin/bag they come in. So the OOM202 is quoted at >1,000,000% volume oxygen hours.  So essentially 10,000 hours (60 weeks) at 100% concentration, greater life at lower concentrations.

we are planning to put it in a sealed casing with a solenoid valve on one end. we only allows oxygen to contact if needed. So that could raise the life time right?

[Adhith]

You may first try the UNO ADC with analogReference(INTERNAL), so it uses 1.1V reference. It will not take a lot of time, maybe half hour to try. You may use 1-10nF capacitor in parallel with sensor. Use sample averaging and see what kind of results you get. If you need to build it fast, the minimum system which works good enough is good enough.

What is your target accuracy of O2 measurement?

Yes, I will try that and update here. I will only get the sensor in next two days. around 5% of deviation is acceptable

[Zero999]

These have a finite life when you open the tin/bag they come in. So the OOM202 is quoted at >1,000,000% volume oxygen hours.  So essentially 10,000 hours (60 weeks) at 100% concentration, greater life at lower concentrations.

we are planning to put it in a sealed casing with a solenoid valve on one end. we only allows oxygen to contact if needed. So that could raise the life time right?

It will need to be kept away from oxygen to last, longer than the specified life, but does it matter if it only lasts a year? It thought this was just to save lives during the current emergency situation, rather than as a permanent solution. Hopefully it won't be needed for that long.

If it's needed again, then the sensor can be replaced. It has a connector on the back. If you think it might be needed in the future, you should design the machine so it can be easily replaced. There's nothing wrong with having consumable parts. You change the tyres on your car, after driving a certain distance, or the rubber perishes and this is no different.

[Manul]

These have a finite life when you open the tin/bag they come in. So the OOM202 is quoted at >1,000,000% volume oxygen hours.  So essentially 10,000 hours (60 weeks) at 100% concentration, greater life at lower concentrations.

we are planning to put it in a sealed casing with a solenoid valve on one end. we only allows oxygen to contact if needed. So that could raise the life time right?

Not necessarily. Even if it adds 5% of lifetime, is it important? I would say - don't do it. Lets think, so it is more then 1 year in 100% oxygen. Probably could survive 2 years in normal conditions. Do you really care, what will happen after 2 years? Putting solenoid just for that and possibly degrading measurment response time is definetly not worth, at least in my opinion. Protect it from high air flow, just a little to maintain exchange and it will be fine. But don't put it into one end sealed pipe...

[Manul]

around 5% of deviation is acceptable

Then it is really easy. If you do not care about 20.5% vs 21.0%, then UNO ADC will be enough.

EDIT: I looked up some data from Atmel and it seems that oversampling works really well with internal reference. For a slow signal, even 15-16 bits of resolution is achievable, well below 0.1mV.

[fcb]

around 5% of deviation is acceptable

Then it is really easy. If you do not care about 20.5% vs 21.0%, then UNO ADC will be enough.

EDIT: I looked up some data from Atmel and it seems that oversampling works really well with internal reference. For a slow signal, even 15-16 bits of resolution is achievable, well below 0.1mV.

Oversampling doesn't work like that.  If you've got a 10 bit ADC and you sample it 64 times, you'll end up with a 16bit result, but with 10bit resolution - divide the result by 64 and you'll still be at 10bit resolution but have averaged out some noise by virtue of the software low-noise filter.  If you add dither (noise) then you can increase resolution, but not otherwise.

Much better to scale the sensor voltage to match the ADC or use a higher resolution external ADC.  Someone else pointed out that the Atmel 328P (the proc on the UNO) has an 1.1V scale mode.

1.1V/1023=1.07mV per bit, and 1% O² change is roughly 0.65mV to 0.8mV, and if the sensor is +/-2%........whir...whir...... you'd probably get within +/-5% accuracy.

If you just use an opamp and two resistors (gain of say 14) to scale it, you should easily get with +/-2.5% overall accuracy, better still, make one of those resistors variable and you'll be able to easily calibrate the unit with simple maths and a known calibration gas (100% O²).

[Manul]

around 5% of deviation is acceptable

Then it is really easy. If you do not care about 20.5% vs 21.0%, then UNO ADC will be enough.

EDIT: I looked up some data from Atmel and it seems that oversampling works really well with internal reference. For a slow signal, even 15-16 bits of resolution is achievable, well below 0.1mV.

Oversampling doesn't work like that.  If you've got a 10 bit ADC and you sample it 64 times, you'll end up with a 16bit result, but with 10bit resolution - divide the result by 64 and you'll still be at 10bit resolution but have averaged out some noise by virtue of the software low-noise filter.  If you add dither (noise) then you can increase resolution, but not otherwise.

Much better to scale the sensor voltage to match the ADC or use a higher resolution external ADC.  Someone else pointed out that the Atmel 328P (the proc on the UNO) has an 1.1V scale mode.

1.1V/1023=1.07mV per bit, and 1% O² change is roughly 0.65mV to 0.8mV, and if the sensor is +/-2%........whir...whir...... you'd probably get within +/-5% accuracy.

If you just use an opamp and two resistors (gain of say 14) to scale it, you should easily get with +/-2.5% overall accuracy, better still, make one of those resistors variable and you'll be able to easily calibrate the unit with simple maths and a known calibration gas (100% O²).

This is not correct. Divide by number of samples is ok, but it is floating point operation, usually the decimation is done. For 64 samples, you sum them and divide by 8. And this is extra 3 bits (theoretical, but sometimes very near in practice too). What I mean about it working well with internal reference is that the internal reference + other things in the 328p ADC gives near optimal amount of noise to naturally dither from itself. A lot of ADCs react quite well to oversampling with just the internal noise, no external dither. Some better, some worse. Atmel 328p is quite good, I checked some data.

Also, yes, I wrote on the second post in this thread, that UNO (328p) has 1.1V reference.

[Adhith]

These have a finite life when you open the tin/bag they come in. So the OOM202 is quoted at >1,000,000% volume oxygen hours.  So essentially 10,000 hours (60 weeks) at 100% concentration, greater life at lower concentrations.

I was planning to use a solenoid valve to isolated the sensor from oxygen and use when needed by powering the solenoid valve. Seems like the sensor will run itself more than a year even if its exposed to 100% oxygen concentrations. So i guess I could simply skip all these solenoid valve setup right?

[Manul]

I was planning to use a solenoid valve to isolated the sensor from oxygen and use when needed by powering the solenoid valve. Seems like the sensor will run itself more than a year even if its exposed to 100% oxygen concentrations. So i guess I could simply skip all these solenoid valve setup right?

Even if it is isolated by the valve, there is still oxygen left inside the sensor from the last time valve was open, right? It could be, that there is no benefit at all. I don't know how fast the oxygen is consumed by such a sensor. I presume that it would consume some. So theoretically, if it is sealed, the concentration would drop. But probably very slowly. Not worth to think about it. They have quite good lifetime anyway.

[Adhith]

It will need to be kept away from oxygen to last, longer than the specified life, but does it matter if it only lasts a year? It thought this was just to save lives during the current emergency situation, rather than as a permanent solution. Hopefully it won't be needed for that long.

If it's needed again, then the sensor can be replaced. It has a connector on the back. If you think it might be needed in the future, you should design the machine so it can be easily replaced. There's nothing wrong with having consumable parts. You change the tyres on your car, after driving a certain distance, or the rubber perishes and this is no different.

Yeah ,you are right. on a second thought, I have made my mind to keep things simple and use the sensor full time in contact with oxygen

[Adhith]

Not necessarily. Even if it adds 5% of lifetime, is it important? I would say - don't do it. Lets think, so it is more then 1 year in 100% oxygen. Probably could survive 2 years in normal conditions. Do you really care, what will happen after 2 years? Putting solenoid just for that and possibly degrading measurment response time is definetly not worth, at least in my opinion. Protect it from high air flow, just a little to maintain exchange and it will be fine. But don't put it into one end sealed pipe...

Yes. agree with you. I'm using the sensor as it is.

[fcb]

around 5% of deviation is acceptable

Then it is really easy. If you do not care about 20.5% vs 21.0%, then UNO ADC will be enough.

EDIT: I looked up some data from Atmel and it seems that oversampling works really well with internal reference. For a slow signal, even 15-16 bits of resolution is achievable, well below 0.1mV.

Oversampling doesn't work like that.  If you've got a 10 bit ADC and you sample it 64 times, you'll end up with a 16bit result, but with 10bit resolution - divide the result by 64 and you'll still be at 10bit resolution but have averaged out some noise by virtue of the software low-noise filter.  If you add dither (noise) then you can increase resolution, but not otherwise.

Much better to scale the sensor voltage to match the ADC or use a higher resolution external ADC.  Someone else pointed out that the Atmel 328P (the proc on the UNO) has an 1.1V scale mode.

1.1V/1023=1.07mV per bit, and 1% O² change is roughly 0.65mV to 0.8mV, and if the sensor is +/-2%........whir...whir...... you'd probably get within +/-5% accuracy.

If you just use an opamp and two resistors (gain of say 14) to scale it, you should easily get with +/-2.5% overall accuracy, better still, make one of those resistors variable and you'll be able to easily calibrate the unit with simple maths and a known calibration gas (100% O²).

This is not correct. For 64 samples, you sum them and divide by 8. And this is extra 3 bits (theoretical, but sometimes very near in practice too). What I mean about it working well with internal reference is that the internal reference + other things in the 328p ADC gives near optimal amount of noise to naturally dither from itself. A lot of ADCs react quite well to oversampling with just the internal noise, no external dither. Some better, some worse. Atmel 328p is quite good, I checked some data.

Also, yes, I wrote on the second post in this thread, that UNO (328p) has 1.1V reference.

I agree that if you get some noise then you can increase the effective resolution, however this is not a guaranteed or tested behaviour - linearity/ and 'no-missing-codes' would be questionable.  I would balk at anyone suggesting you can get 15-16bit out of a 10bit converter. It might look like it if you squint hard enough, but it will suck.  Pretty much a moot point in this application as the OP is happy with +/-5% (unless the really mean +/-2.5%).

As for isolating the sensor with a solenoid valve to extend the life.  I wouldn't bother, the extra headache, complexity and delay for a marginal increase in sensor life isn't worth it, not to mention that you are pressed for time I guess??

Perhaps the OP can describe how they are using the O² percentage in their control system/loop? Or is it just to give confidence to the operator??

[Manul]

I agree that if you get some noise then you can increase the effective resolution, however this is not a guaranteed or tested behaviour - linearity/ and 'no-missing-codes' would be questionable.  I would balk at anyone suggesting you can get 15-16bit out of a 10bit converter. It might look like it if you squint hard enough, but it will suck.  Pretty much a moot point in this application as the OP is happy with +/-5% (unless the really mean +/-2.5%).

Yes, I totally agree that it is inferior to a proper high resolution ADC, but from a practical standpoint it could be a solution. And could work surprisingly well if the amount of noise happens to be optimal. For the OP application, I bet that the external noise coupling to the signal could easily be the limiting factor. I mean, it is very easy to get millivots of mains or switching noise interfering with something connected on wires. Averaging will of course solve some of that, but still. Extra resolution or op amp front end becomes irrelevant in that case.

[Adhith]

Great! Thank you all for your support. Reading from all your suggestions, I'm planning to first directly connect the sensor to the UNO and use the internal ADC function.

The thing is that, the O2 generator system itself is a pretty solid system. It could deliver more than 90% oxygen for at least a year without any attention. The sensor and controls are for safety and medical regulations approval. We are following all the guideline for the system.
We have a three led lights which shows '90-100%, 80-90%, 70-80%. So I think a bit of resolution difference is not a problem.

Since my expertise is in mechanical engg. domain and being a beginner in electronics, I need to finalize on this with you guys.

could someone help me in what to do step wise?

[Manul]

Since my expertise is in mechanical engg. domain and being a beginner in electronics, I need to finalize on this with you guys.

could someone help me in what to do step wise?

To do what? Steps for what? Anyway, as you see, quite a lot of people got involved here in the discussion, so I'm sure you will have support if some problems arise.

[Zero999]

As I said here on the forum several times enriched air is dangerous stuff.
It is non conducting and produces static electricity in each component. Even invisible ESD event can result in disaster.
There were several hospitals that were engulfed in fire due to improper installation and/or equipment.
Instead of trying to make dangerous equipment is much better to organize purchase of certified equipment.
To many this looks as opportunity to show craftmanship and ingenuity but I look at this as planting bomb nearby innocent patients.
 Just search how many people died in fires in hospital recently.

Do you really think he would be doing this if it wasn't absolutely necessary? This isn't someone's fun, hobby project, but their response to a medical emergency. You have no idea how bad the situation is in India. SARS-Cov-2 is on the rampage. More people are dying, than in developed countries because of a shortage of oxygen, hospital beds and general poor health due a large disease burden of malnutrition and diabetes.  If it was that easy to just go and buy an oxygen concentrator, I'm sure they would do it.

You're right about being cautious. Keep the room well ventilated, which should be the case anyway, as it cuts the risk of transmission of respiratory viruses and don't leave large amounts of highly flammable materials around.

Great! Thank you all for your support. Reading from all your suggestions, I'm planning to first directly connect the sensor to the UNO and use the internal ADC function.

The thing is that, the O2 generator system itself is a pretty solid system. It could deliver more than 90% oxygen for at least a year without any attention. The sensor and controls are for safety and medical regulations approval. We are following all the guideline for the system.
We have a three led lights which shows '90-100%, 80-90%, 70-80%. So I think a bit of resolution difference is not a problem.

Since my expertise is in mechanical engg. domain and being a beginner in electronics, I need to finalize on this with you guys.

could someone help me in what to do step wise?

If you do need an op-amp, there's this module which has a gain of 100.
https://www.sparkfun.com/products/9816

[Robert Smith Eco Warrior]

My brother and his work collegues made a ventilator.

It is based around a gas fuel injection system and uses the ECU to inject oxygen in a massively flexible way... Constant volume/constant pressure etc and also can do what's called CPAP (constant positive airway pressure)

I don't know if that is of any use?

I could put you in touch with them.

[daisizhou]

The theoretical effective time of the OOM2O2 sensor is about 1 year.But the actual use time is shorter,Effective measurement on ICU ventilator takes only 6 months
Because there are still interference effects of water vapor (H20) and other gases in actual use,If you use a lot, you need to replace the oxygen sensor frequently,Or buy a high-quality oxygen sensor, but the price is expensive

Therefore, OOM2O2 sensor is not the best solution,If you use a small amount temporarily,Just a temporary solution

[fcb]

If you can, you should try and involve a local electronics engineer, or group of engineers.  They will know what is available locally as well.

Whilst EEVBLOG members can design your electronics etc.., debugging it will have to be done locally - and the devil will be in the details!  You really do need to find local electronic expertise.

My understanding is that getting components/PCB's etc.. into India is difficult/slow/expensive at the best of times - so you're likely to only be able to use the parts in local subcontractors, colleges, radio stores, etc...  Out of my depth here.

[Zero999]

My brother and his work collegues made a ventilator.

It is based around a gas fuel injection system and uses the ECU to inject oxygen in a massively flexible way... Constant volume/constant pressure etc and also can do what's called CPAP (constant positive airway pressure)

I don't know if that is of any use?

I could put you in touch with them.

At the start of the pandemic, a lot of time and money was invested in ventilators, but it turned out it wasn't needed. Ventilators are only any good if clinicians are available to operate them. All the ventilators in the world are no good, without doctors and nurses.

The problem in India is lack of pure oxygen, rather than ventilators. Many COVID-19 patients just need oxygen. It is also required for anesthesia and without it, other life saving surgical procedures can't take place, causing many more excess deaths.

The theoretical effective time of the OOM2O2 sensor is about 1 year.But the actual use time is shorter,Effective measurement on ICU ventilator takes only 6 months
Because there are still interference effects of water vapor (H20) and other gases in actual use,If you use a lot, you need to replace the oxygen sensor frequently,Or buy a high-quality oxygen sensor, but the price is expensive

I repeat: does it really matter? Hopefully it won't be needed in six months time. Hopefully COVID-19 cases will have fallen by then and if not, they will have approved medical grade, oxygen concentrators.

Therefore, OOM2O2 sensor is not the best solution,If you use a small amount temporarily,Just a temporary solution

Exactly. It's not supposed to be a permanent solution, but a temporary fix, to get them out the current crisis. A life of even three months will hopefully be more than enough.

Engineering is about finding the most suitable solution to a problem, which depends on the requirements. In this case, if the OOMO2 is cheaper and more widely available, than more expensive oxygen sensors, then is the best solution to this problem.

[daisizhou]

I am a biomedical engineer,Engaged in clinical medical engineering for more than 20 years
I just combined my work experience and actual use of the effect description

When testing a sample may not find the problem,For example, 100, 1,000, 10,000, these problems will be big problems,This will directly cause the program to fail to implement and eventually fail

[Adhith]

Keeping sensor under inert gas is not recommended. This is called starvation mode and it will shorten sensor lifetime.
As I said here on the forum several times enriched air is dangerous stuff.
It is non conducting and produces static electricity in each component. Even invisible ESD event can result in disaster.
There were several hospitals that were engulfed in fire due to improper installation and/or equipment.
Instead of trying to make dangerous equipment is much better to organize purchase of certified equipment.
To many this looks as opportunity to show craftmanship and ingenuity but I look at this as planting bomb nearby innocent patients.
 Just search how many people died in fires in hospital recently.

As a personnel working in aerospace combustion, I would definitely agree with your statement. However totally disagree with your point on craftsmanship and showoff. The situation in India is so tough now, people are dying due to lack of oxygen than covid. We have the machines and fabrication stuff within our reach, so that's why we have planned to do this. Hope nothing is wrong in that considering the situation that we have.

[Zero999]

I am a biomedical engineer,Engaged in clinical medical engineering for more than 20 years
I just combined my work experience and actual use of the effect description

When testing a sample may not find the problem,For example, 100, 1,000, 10,000, these problems will be big problems,This will directly cause the program to fail to implement and eventually fail

He needs a oxygen concentrator, which is cheap and easy to build from widely available parts. It doesn't need to last for long, just a few months, until the epidemic is either over, or oxygen concentrators which meet all the relevant regulations to become available. What would you recommend?

[Adhith]

To do what? Steps for what? Anyway, as you see, quite a lot of people got involved here in the discussion, so I'm sure you will have support if some problems arise.

mainly the code for the arduino. Say, I need to turn on three different leds on the output which one ofor 95-90% rangem one for 90-95% and one for 85-90%,. So how should I setup the code?

[Adhith]

Guys, we are planning to roll out the thing next week. All stuffs are done expect the coding part. Final testing is going to happen in 2 days. Thank you all for your feed backs and suggestions.

Few people have raised some concerns over this and I just wanted to let you know, We are not doctors or expert people in this. This is just for emergency situation prevailing in the country. This is supposed to be used under the supervision of doctors till the medical oxygen demand is met by hospitals. Also, as a safety precaution for the third wave.

[Adhith]

If you do need an op-amp, there's this module which has a gain of 100.
https://www.sparkfun.com/products/9816

Great! Thank you. I will be moving to a LCD screen display eventually. So I would use this one for high accuracy.

[Manul]

Do you already have sensor? I might be able to help with some code, so do others. Have you ever done something with Arduino? Do you have people on your team with at least some coding experience?

[Adhith]

My brother and his work collegues made a ventilator.

It is based around a gas fuel injection system and uses the ECU to inject oxygen in a massively flexible way... Constant volume/constant pressure etc and also can do what's called CPAP (constant positive airway pressure)

I don't know if that is of any use?

I could put you in touch with them.

Great! best wises to him. We are not into ventilators at the moment, but definitely would keep this in mind if we need his assistance. Thank you very much

[Adhith]

quote author=Manul link=topic=282235.msg3569610#msg3569610 date=1621018086]
Do you already have sensor? I might be able to help with some code, so do others. Have you ever done something with Arduino? Do you have people on your team with at least some coding experience?
[/quote]
Yes I got the sensor a day ago. I know electronics but, not good at arduino. Have built few project around it as well but I'll take way more time to understand the terms & attributes on IDE which in this case I'm planning to accelerate.

This is my attempt on the codes. I don't kow if it works or not. Plus I dont know how I could calibrate with ambient air sensing.

[Manul]

This is my attempt on the codes. I don't kow if it works or not. Plus I dont know how I could calibrate with ambient air sensing.

I can offer help with calibration, but you need to add a push button inside your device. Can you do that?

[fcb]

How are you proceeding - do you need more help/advice etc..??

[StuartA]

Some of the oxygen concentrators on the commercial market use an ultrasound method of measuring the nitrogen / oxygen ratio, which I think is what you actually want to do if you are using molecular sieve to achieve concentration. It's actually sensing gas density.

These ultrasound sensors were available on ali express last year, but I no longer have a link to them. However, these are the notes I made about their technical function;

Detection principle：Principle of ultrasonic measurement
Detection range：20.9%~100%
precision：±1.8%FS@ (10-45
Distinguishing rate：0.1%
The response time：30s
The working conditions：- 10% - 50 ° c, 0-95% RH (condensation)
Storage conditions： - 20% - below 60 ° c, 0-95% RH in T (condensation)
Working voltage：DC 5.0 V to 12.0 V
Working current：Average operating current <40mA
Signal output：UART_TTL (3.3 V )
Product size：W70 * H33 "D13.8 (mm)

Remember that although Covid has raised interest in oxygen concentrators, they are old technology. Many people with routine medical conditions (e.g. asthma) which are assisted by breathing oxygen enriched air, have been buying and using them for years (see, for example https://www.portableoxygen.co.uk).


LATER ADDITION; here's what I was refering to for $48 https://www.aliexpress.com/item/33030006090.html?spm=a2g0o.productlist.0.0.1e36472aYVbR97&algo_pvid=65de0d2c-dacc-4ec7-9f10-c86d51affcff&algo_expid=65de0d2c-dacc-4ec7-9f10-c86d51affcff-2&btsid=0b0a555a16214822517298144e852c&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_  sure there are several others

[Adhith]

How are you proceeding - do you need more help/advice etc..??

Things are going great. We almost completed our second prototype. the sensor is working pretty good. Medical testing needs to be done now. However rolling this thing out at present maybe tough due to the time delay for proper testing. We are now looking this to introduce into the 3rd wave, which unfortunately is most certain here in India according to reports.

I was planning to leave this thread open for a while so that I can update you guys and probably get more advice along the road.

[Adhith]

Some of the oxygen concentrators on the commercial market use an ultrasound method of measuring the nitrogen / oxygen ratio, which I think is what you actually want to do if you are using molecular sieve to achieve concentration. It's actually sensing gas density.

These ultrasound sensors were available on ali express last year, but I no longer have a link to them. However, these are the notes I made about their technical function;

Detection principle：Principle of ultrasonic measurement
Detection range：20.9%~100%
precision：±1.8%FS@ (10-45
Distinguishing rate：0.1%
The response time：30s
The working conditions：- 10% - 50 ° c, 0-95% RH (condensation)
Storage conditions： - 20% - below 60 ° c, 0-95% RH in T (condensation)
Working voltage：DC 5.0 V to 12.0 V
Working current：Average operating current <40mA
Signal output：UART_TTL (3.3 V )
Product size：W70 * H33 "D13.8 (mm)

Remember that although Covid has raised interest in oxygen concentrators, they are old technology. Many people with routine medical conditions (e.g. asthma) which are assisted by breathing oxygen enriched air, have been buying and using them for years (see, for example https://www.portableoxygen.co.uk).


LATER ADDITION; here's what I was refering to for $48 https://www.aliexpress.com/item/33030006090.html?spm=a2g0o.productlist.0.0.1e36472aYVbR97&algo_pvid=65de0d2c-dacc-4ec7-9f10-c86d51affcff&algo_expid=65de0d2c-dacc-4ec7-9f10-c86d51affcff-2&btsid=0b0a555a16214822517298144e852c&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_  sure there are several others

Thank you very much for the info. The website link is broken but I'll try to find the sensor and probably get back to you. However, Importing from china is a bit problematic now, as India have banned Ali express and also imposed few new rules to Chinese import

[Adhith]

This is my attempt on the codes. I don't kow if it works or not. Plus I dont know how I could calibrate with ambient air sensing.

I can offer help with calibration, but you need to add a push button inside your device. Can you do that?

Great! Thank you. I could include a push button

[zampa]

Hello guys, I need you support on this one
As the conditions in our country, India is getting bad, me and few of my friends are planning to build an O2 concentrator. We have done our initial trial testing we are getting good results. Now we are moving towards the electronic part where, we need to analyse the O2 percent that we generated using the OOM202  oxygen sensor and display on a 7 segment display. This goes on to each system that we produce. could anyone guide me how to use this O2 sensor module with arduino ?

any help is appreciated, We will be pushing lots of these in this week, if we could figure out this electronic part. Thank you

Hello all,

With regard to the same subject, I have been working on an Oxygen concentrator where I am using an OOM202 oxygen sensor from Envitec for measuring the oxygen concentration at the output.

When I subjected the sensor with 99% oxygen concentration from a known source for calibrating, the sensor reading drastically increased and almost reached 200mV within no time.
So, as I went through these threads the values that are mentioned here for 100% oxygen concentration is somewhere around 75-80mV.
There is confusion in this aspect of the sensor.
Any help with this regard will be greatly appreciated
Thanks in Advance