Photodetector health: If a photodetector (the
electronic device that picks up scattered light
from the particle passing through the laser beam)
is defective, some less technologically advanced
remote particle counters will continue reporting
zero counts and no light will be picked up and
therefore no counts will be registered. Even if particles are present they will go through the particle
counter optics undetected. In normal clean environments reporting of 0 counts for several hours is
not uncommon. There is a false sense of security if
the photodetector is not monitored.
Solution: Choose a sensor where the photodetector is monitored so zero count errors are not
going to be an issue due to a dead photodetector.
Sensor health: One of the biggest problems with
particle counter data integrity occurs when contamination builds up around the sensors optics and
mirrors. This normally happens during cleaning
operations when the inlet is not capped, causing
cleaning solution to coat the optics, which cause the
sensor to fail calibration. If you are on annual calibrations and there is a calibration failure, how confident are you in your data for the last 12 months?
Solution: A particle counter that monitors sensor health is a good choice and assists in sending
out service notifications when background contamination becomes an issue. These advanced instruments can mitigate failed calibrations and assist in
maintaining data integrity. These sensors can be
pulled from service, tested, and recalibrated before
failed calibration issues could potentially ground
Flow integrity: Flow is critical to accurate sizing of particles that scatter light. A remote particle
counter with the most accurate flowrate must have
a low +/- flow error tolerance. If the flowrate is
not accurate, the count data will not be accurate
and wrong particle sizing can occur.
Solution: Considering particle size and count
data are crucial factors in determining alarm limits, choose a sensor with the highest flow accuracy
available for flowrate control.
Data storage redundancy: Having data records
backed up on the remote particle counter assures
redundancy in case a software issue occurs in the
transmission of real time data.
Solution: Choosing a remote particle counter
with sufficient buffering in data collection will
enable critical data to be downloaded at a later
stage back into the monitoring system software.
Audit trail: In order to follow the ALCOA standard, an audit trail built into the equipment or software is an absolute must. (21CFR11 in monitoring
systems are required).
Solution: Seek particle counters with built in
audit trails to satisfy ALCOA requirements for who,
when, what, and where attributions.
User security levels: The system must conform
to 21CFR11 guidelines. Up to three security levels
from operator to manager and administrator must
be available with the usual compliant parameters
such as password length, password aging, and password control.
Solution: User security levels are a 21cfr11
requirement and particle counters should have the
ability to manage and control user access.
System validation: A complete validation of
the data records must be conducted by verifying
the accuracy of the data to the location of where
the data is generated. This is a must do exercise
and should be rolled into the Installation and
Operational Qualifications IQ/OQ protocols.
Solution: Seek particle counters with built-
in IQ/OQ protocols and always conduct a
Performance Qualification (PQ) to verify accuracy
before going into production.
Calibration ISO 21501: The particle counter
must be calibrated to meet ISO 21501 standards.
The new revision of ISO 14644-1 requires particle
counters to be calibrated to ISO 21501. It is cur-
rently the most accurate particle counter calibration
and must be the calibration standard followed.
Solution: Make sure the supplier or distributor
can offer local accredited ISO 21501 calibrations
that are traceable.
Service level agreements: When the system is up
and running it is required in PIC’s Annex 11 to have