Closed stevevance closed 1 year ago
Looks like you already found this, but for reference, it comes from here in the code: the SCD4x (CO2 sensor) reading did not return an error, but the reported CO2 value was 0 ppm (which is an invalid response).
I've seen this happen a few times, typically when I was handling the Adanet device during a measurement. I think it's related to the way photoacoustic NDIR sensors work, but can't remember where I read that.
Did it go back to normal operation on the next update?
It went back to normal operation on the next update.
I wonder if the shopping cart caused an issue: The cart's wheels or axle had flat spots and the car was making the Adanet bounce on that rack.
Why is 0
an invalid response? Couldn't the device plausibly detect the absence of CO2? Or is it not sensitive enough to confidently measure that?
Agreed, that's probably it re: the shopping cart. Good question re: why 0
is an invalid response. The data sheet even says that 0
is within the valid range.
An uninformed guess: part of the sensor's measurement cycle is probably some sort of calibration of the microphone part of the photoacoustic assembly relative to the current ambient noise. If it got a particularly large reading due to a disturbance during this step, it might set its baseline noise level too high, and be unable to detect any CO2 signal on top of it, causing it to report 0
.
If that's correct, it would be able accurately detect the absence of CO2, at least in a relatively quiet environment...
thanks for the discussion! I'm gonna close this since I'm satisfied with the answer and I don't think it's worth refactoring the error message/detection.
Today I saw an error message for the first time.
“Invalid sample detected”. I checked the code: it looks like the error is thrown if the reading is zero.
check out the photo