Ok that is pretty sane. I'll submit my full patchset for the driver marked RFC to see if my use of types and modifiers makes sense. Well once I get the module off the slow boat from Taiwan and test it Sent from my iPhone > On Aug 31, 2015, at 01:06, Lars-Peter Clausen <lars@xxxxxxxxxx> wrote: > >> On 08/28/2015 06:27 PM, Matt Ranostay wrote: >> Ah true but we could add a few IIO_MOD* modifiers for CO2, tVOC, VOC, >> etc, etc. I think Jonathan was suggesting that. > > What I meant was CO2 measured in what unit per what unit. > > Like is it weight per volume or volume per volume or weight per weight or > molecules per volume ... > > - Lars > >> >> Thanks, >> >> Matt >> >>> On Fri, Aug 28, 2015 at 2:16 AM, Lars-Peter Clausen <lars@xxxxxxxxxx> wrote: >>>> On 08/28/2015 11:05 AM, Matt Ranostay wrote: >>>>> On Thu, Aug 27, 2015 at 11:34 PM, Lars-Peter Clausen <lars@xxxxxxxxxx> wrote: >>>>>> On 08/27/2015 11:40 PM, Matt Ranostay wrote: >>>>>>> On Thu, Aug 27, 2015 at 8:58 AM, Lars-Peter Clausen <lars@xxxxxxxxxx> wrote: >>>>>>>> On 08/27/2015 05:40 PM, Lars-Peter Clausen wrote: >>>>>>>>> On 08/27/2015 08:45 AM, Matt Ranostay wrote: >>>>>>>>> There are air quality sensors that report data back in parts per million >>>>>>>>> of VOC (Volatile Organic Compounds) which are usually indexed from CO2 >>>>>>>>> or another common pollutant. >>>>>>>>> >>>>>>>>> This patchset adds an IIO_PPM type because no other channels types fit >>>>>>>>> this use case. >>>>>>>> >>>>>>>> Hm, I'm not sure if parts-per-million is a good channel type. It's more of a >>>>>>>> scale. The type would be concentration.[...] >>>>>>> >>>>>>> Reading a bit more[1], concentration doesn't actually seem to be the right >>>>>>> term in this case, the correct term is mole fraction. Maybe we can use that >>>>>>> as the type. That also makes it clear that the unit is molecules per molecule. >>>>>> Actually we can't use mole fraction for this because we aren't in a >>>>>> chemistry lab, and know the other compounds that make up the local >>>>>> atmosphere. Besides you'd have to include some insane lookup table for >>>>>> molar mass of carbon or whatever VOC being measured :) >>>>> >>>>> I don't think you'd need that. Mole fraction tells you the number of >>>>> molecules of something per total number of molecules. You don't need the >>>>> mass for this. >>>>> >>>>> But what exactly is the sensor measuring? CO2 (or VOC) molecules per total >>>>> number of molecules or number of CO2 molecules in a particular volume? >>>> CC'ed my Swiss colleague on this because he knows much on the >>>> interworkings of VOC sensors than I could hope to. >>>> So simply these sensors are finding VOCs (which the sensor in question >>>> does CO2 and tVOC indexes.. probably not too independent of each >>>> other) >>>> >>>> But molecules are not parts.. think of taking an X volume of air and >>>> figuring what is precent of oxygen is verses nitrogen, argon, etc, >>>> etc. Sure the highest is nitrogen at atomic weight 14.01 with ~78% of >>>> the "air", oxygen is ~20% at the weight of 16.00, and etc. >>>> >>>> Think about cutting cube into a millions of pieces and figuring an X% >>>> is Y substance which you can detect, but can't detect X, Y, and Z >>>> (think any particles in 'air' that aren't bonded with carbon). So mole >>>> fractions are impossible here, and you could only take a parts in a >>>> known volume. >>>> >>>> Most VOCs (if not all, bit of newbie here) use UV LEDs to ionize >>>> particles, and with some maths calculate the parts-per-million. >>> >>> But what per what? PPM is a completely ambiguous unit if you don't specify >>> parts of what per million of what. > -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
