SPEC gas sensor for NO2 (and CO, alcohol, air quality, etc.)
Rayman
Posts: 14,640
Was surprised the other day to hear how gas appliances might be bad for you, particularly due to high levels of NO2. Thought I'd buy a sensor and check it out... Came across these SPEC sensors:
https://www.spec-sensors.com/
The sensors themselves are cheap, $20. But, the helper electronics is expensive.
They have an analog demo board that is very simple. I'm copying ideas from that.
They have a digital version that looks better with AFE chip, but that AFE chip is out of stock...
Anyway, did quick work on this PCB for two SPEC sensors and hope to get it in ~1 week.
2585 x 713 - 235K
Comments
I2C temperature sensors seem to also be out of stock everywhere...
Going to try to use a 10k thermistor with ADC input instead...
Probably don't actually need a thermometer as doing this indoors, but wanted to see how well this works anyway...
How about this one - ADT7420 ? In stock at Mouser and comes with a nice dev board to play with as well.
Hmm.. thanks.
I clearly wasn’t searching right.
See all kinds now.
Hi,
interesting project!
Perhaps you can translate this paper for you somehow: https://www.toxikologie.de/fileadmin/user_upload/GT/Aktuelles/2019-02-26_Beratungskommission_GT_NO2.pdf
It might be helpful to judge, what a "high level of NO2" might be.
Is this this sensor: https://www.spec-sensors.com/wp-content/uploads/2017/01/DGS-NO2-968-043_9-6-17.pdf ?
I think, that for measuring our normal air you would need to have a sensor that can measure NOx< 40µg/m³, because this is the long time limit even for "weak" people. This translates to 0.02ppm.
At least in Stuttgart, Germany, it will be difficult to measure anything with a NOx sensor that can detect >= 0,1ppm = 200µg/m³:
https://www.stadtklima-stuttgart.de/index.php?luft_messdaten_ueberschreitungen
@"Christof Eb." It's a good question... I'm no expert on this, so don't really know if this sensor is going to work.
But, on their website for the SMT NO2 sensor: https://www.spec-sensors.com/product/no2-sensor/
They have this document: "Indoor Air Pollution from Natural Gas Stoves"
This seems to imply that it will work for this application, but who knows...
Built it with NO2 and CO sensors to start.
Did some tests next to stovetop and also tailpipe of car, but are inconclusive.
There's also a temperature affect, so hard to say for sure I was seeing anything.
Just testing with multimeter for now. Need to get the 14-bit P2 ADC going....
Replaced CO sensor with alcohol sensor (because it's easier to test).
Thought I did something very bad at first or the sensor was bad because it was reading 0 V when I fired it up.
But then read that the first time you put voltage on these sensors, you should wait up to an hour for it to settle.
Sure enough, after an hour it seems to work.
Testing with some pure ethanol for now. There's definitely a response when waiving a moist paper towel over it.
Only about 50 mV or so swing though. Have to figure out if that is right...
It's somewhat slow to respond though...
Datasheet is saying T90 response time is <60 seconds. I guess that's what I'm seeing...
Now, I'm thinking that the NO2/CO test may not have worked because I didn't have it powered up for an hour before testing.
Might do some breathalyzer type testing later on tonight
Been over an hour with alcohol sensor powered up, so testing again...
Output voltage with no alcohol ranges from 1.357 V to 1.369 V.
Surprisingly, this is below the reference voltage output that is steady at 1.449 V.
Manual does say that there can be an offset from the reference, but I assumed it was always positive.
Anyway, waiving moist paper towel soaked in pure ethanol over it, the output voltage slowly increases to around 1.570 V in about a minute.
So, that's a swing of about 200 mV.
One datasheet is saying ~4 mV/ppm, so that'd be around 50 ppm.
Looked at NO2 response again after being powered up for well over an hour...
Turned 3 of 4 cooktop burners up to full and sat 5 minutes.
Maybe there was a 2 mV increase, but can't be 100% sure that wasn't a thermal response.
Have to find a better place to test... Maybe the furnace or gas dryer...
@Rayman You might try a Coleman lantern. Those mantles are hot and should produce a mess of NO’s.
According to the specs the SPEC sensors respond to NO2 and mostly ignore NO. According to this, https://www.crcleanair.com/library-2/technical-articles/the-chemical-aspect-of-nox-scrubbing/ most of the pollution may be NO.
If you have a gas tank water heater that is a good place to put a sensor. My water heater generated a steady 40ppm NOx. That was with an automotive type NOx sensor that could certainly handle the heat. The flue gas might be too hot for the SPEC sensor.