30 | February 2019
In air quality applications, where we're converting size
channels and counts into mass having a large number of
accurate channels is very important in arriving at a mass
estimate. If the instruments are measuring aggregate mass
then they are assuming a typical distribution of particulates
by mass (which is often not the case).
3. Counting efficiency
This requirement states that our particle counts have to
roughly match those on a NIST traceable instrument sam-
pling calibrated particles in a common air stream.
Omitting all the details of how this is done, we're essential-
ly ensuring that the counts we see on our instrument match
those taken on a more sensitive NIST traceable instrument.
For cleanroom applications this ensures that two in-
struments report largely the same counts when sampling
simultaneously from the same air stream. In order to pass
this test an instrument has to accurately: control the air vol-
ume, process all the particles within that volume, size and
count these particles, limit system noise, etc. So, this can
be a very challenging spec to meet.
For air quality applications we need to arrive at a require-
ment that ensures that instruments from multiple vendors
report similar results under the same conditions and that
these do so without intermediation. At present many of these
sensors compensate for poor quality sensing by doing sig-
nificant manipulation of the sensor data in the cloud to turn
sometimes nonsensical readings into something vaguely
akin to an expected reality. This can grossly misrepresent
