Application Note

5 Fluke Corporation Indoor air quality monitoring made easy with the Fluke 985 Particle Counter
The individual readings are well within the limitations for the
cleanroom; however, we can take the following steps to determine
the statistical validity of the readings:
The resulting mean count for all locations is within
the requirements of a Class 5 class cleanroom.
The Fluke 985 provides particulate data over six
channels on a single display, allowing the techni-
cian to view all readings at a glance. Though the
cleanroom exercise focused on 0.3 μm particu-
lates, the single display would immediately alert
the technician to anomalies in other particle size
concentrations. With the Fluke 985, the technician
can configure the number of channels displayed for
different particle sizes and also sets an alarm alert
via audio or highlighted text for count overconcen-
tration for the particular particle size in concern.
Once the cleanroom is certified, the technician
can also use the trend graph function of Fluke 985
to monitor particle concentration over specific time
period preset by the technician. This can be used
at “operational” stage of cleanroom. This allows
the technician to monitor manufacturing process
if there is any unusual spike of particle concen-
tration and track down the event that introduces
contaminates to the process. This also allows the
technicians to view the trend immediately on the
unit before data is exported; saving tremendous
time on data download. With the Fluke 985 USB/
Ethernet Cradle, the technician can quickly transfer
the data to computer via USB or over the network
for immediate data analysis so that corrective
actions can be quickly deployed. The Delay func-
tion of the Fluke 985 is useful for determining “at
rest” cleanroom particle concentrations after facil-
ity occupants have exited the cleanroom and the
room’s ventilation system has filtered the air and
the environment has stabilized.
Particle counting in perspective
The key to a successful IAQ investigation is to
be aware of the environment as a whole. Loca-
tion, building history, complaints, process records,
and measurable factors such as temperature and
humidity, pressure and particle concentration all
play a role in uncovering IAQ problems. When
using a particle counter, be aware that a particle’s
source may only be a symptom of a much larger
issue looming under the surface. Remediation of
the source may not address core problems of poor
filtration, ventilation, or excessive moisture. Left
unchecked, these conditions will cause the same
symptoms, or worse, to reoccur with certainty.
Particle Counting as part of the ongoing preventive
maintenance is critical to ensure a healthy environ-
ment and good production yield. The Fluke 985 is
a powerful, rugged, and easy to use tool to assist
the technician in identifying particulate problems
and authenticating the efforts to address their root
causes.
# Locations
Upper Control Limit (UCL) Factor for 95 % confidence
1 2 3 4 5 6 7 8 9+
95 % UCL Factor 6.31 2.92 2.35 2.13 2.02 1.94 1.9 1.86 NA
Step 1: Calculate the mean average particulate concentration
M = (AC
1
+ AC
2
+ AC
3
+ AC
4
+ AC
5
+ AC
6
) / L
995 = (674 + 1154 + 1097 + 841 + 828 + 1376) / 6
Step 2: Calculate the standard deviation of the averages
SD = ( (AC
1
-M)
2
+ … + (AC
6
-M)
2
) / (L-1)
116 = ( (674-995)
2
+ (1154-995)
2
+ (1097-995)
2
+ (841-995)
2
+ (828-995)
2
+ (1376-995)
2
) / (6-1)
Step 3: Calculate the standard error of the mean of the averages
SE = SD / ( L)
47.36 = 116 / ( 6)
Step 4: Establish the upper confidence limit (UCL)
UCL = M + (UCL Factor * SE)
1,087 = 995 + (1.94 * 47.36)