Pm2.5 Sensor replacement

I have one PA monitor that continues to have less than 100% agreement between sensors. I’ve twice replaced both sensors using new sensors, and even replaced the sensor data cables.

Can this be caused by the control board itself?

How far apart are they reading?

There will not be 100% agreement, especially in short time spans.

Replacing the cables will do no good, the sensors output digital data. If one sensor stops reporting entirely then I would suspect connections.

It varies with time, between, say, 45% and 82%.

With no further changes to that system it has now ran at 100% agreement for about three days. I put it all back together and will have it redeployed to the field. Will keep a close eye on it once it returns to service.

82% is a lot, assuming we’re talking about large readings (more than 10-20μg range). US EPA requires the sensors to be within 70% or 5μg over the averaging interval to accept the data, and uses the average of the two sensors. Could be that the location is poor so the two sensors aren’t sampling the same air (i.e., unit exposed to wind or partially blocked by building, post, etc.).