Photodetector Health – The photodetector converts the scattered light as photons into electrical pulses by creating a charge for each received photon. As the amount of scattered light increases with the particle’s size and the scattered photons arrive at the same time, a current pulse proportional to the particle’s size is generated. If a photodetector is defective, some less technologically advanced particle
counters will continue reporting zero counts and no scattered light will be picked up and therefore no counts will be registered.
Even if particles are present they will go through the particle counter sensor undetected. In normal cleanroom environments reporting of zero counts for several hours is not uncommon. There is a false sense of security if the photodetector is not monitored. Therefore using a particle counter with advanced technology that monitors the photodetectors health mitigates from false zero counts. This issue is difficult to detect especially when you expect to see zero counts. Routine testing can detect if a photodector is faulty if the particle counter does not signal an error to the user.
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, then how confident are you in your data for the last 12 months?
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 your batches.
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