I-9PSL displays dash/hyphen for PM2.5 intermittently when air quality is good about arduino

[pnt325]

Hi @hsugene
If display show - mean communication with PM sensor failed. Some time we also get issue. Could you please check the sensor connection to PCB. If so you have two or more PM sensor please attach and do some double check to make sure the sensor is worked well.

From your log it's look the communication to PM sensor always failed.

[hsugene]

Hi @pnt325, thank you for the reply. I can try to check the connection, but I bought a pre-assembled version and I’m honestly not very comfortable with opening it. I suppose it’s possible that something got knocked loose in transport.

With that said, I do not believe it’s a connection issue because, if I open my windows and let some outside air into the room, the PM sensor will report data reliably the entire time (like 12+ hours). The issue only occurs when the PM levels in the room are close to zero. The way I can reproduce it is by shutting my windows and turning on my air purifier for an hour or so.

Achim on the AirGradient forum also mentioned that this was not an isolated issue:

In general this has been an issue we have been fighting with for quite some time. Normally we show a “-” when we get an error from the PM sensor. It seems that at very very low concentrations the sensor module itself sends that error message instead of the correct (very low) reading.

I think what we have already implemented is a 3x retry in these cases that seem to help a lot but might not catch all cases.

Given this information, do you still think it would be worthwhile to replace the sensor?

Thank you!

[pnt325]

Hi @hsugene
if you have other sensor that would be good to check and compare result.

And thank for your information we will procedure to test it