I'm sure my PA-II sensors are dead, but I'd like more info

The sensor info line in the data box says A B x0% PA-II 7.02.
The pop-up over the A says “Laser counter channel A”.
The pop-up over the B says “Laser counter channel B is downgraded.”

I interpret the x0% to mean that there is no correlation, which leads me to think that sensor B is constantly reading zero.

But if I look at the graph, there is a black line that looks to be reporting accurately and there is no blue line. From reading forum posts, the blue line is sensor A and the black line is sensor B. So I’d expect the line with good data to be blue (sensor A), not black (sensor B).

And there’s another, dashed, black line that’s straight across at 51.5, which looks to be the average of the readings from the other line.

Note that I have powered down and vacu-sucked the sensors and powered up and confirmed that the red light is present and both fans are spinning.

What am I misinterpreting? Am I safe ordering the replacement PA-II sensors to get my unit back on-line?


Hi @Ellett

It is very possible that one of the laser counters has a broken fan. The simplest fix would be laser counter replacements. However, we would like to take a look. If you don’t mind, could you send an email to contact@purpleair.com with the Device ID included?