All CMCs and Trainees:
I have been contacted by a number of distributors and PID users this week who were concerned about the advisory and looking for advice.
I spoke about this issue at the MCA Conference (without referring to any specific manufacturer).
Not all types of PID sensor failure are capable of being electronically detected. That’s why it’s so important to include the PID sensor when you perform the daily bump test.
We hope it takes two or three years, but all PID lamps eventually fail. One of the most common types of failure is when the lamp can’t initiate the production of photons. When the lamp fails to “ignite” it needs to be replaced. Failure of the PID lamp to ignite is an all or none failure condition. When you are right at the threshold, you can go from normal initiation to failure between turning the instrument off and turning it back on later the same day. It’s different than when the PID fails span calibration, shows a fluctuating response, or has become overly responsive to humidity. With these other types of failure, the lamp is still producing photons of UV light.
It takes more energy to initiate the production of UV light from the PID lamp than it does to keep the production going. It’s analogous to planing in a motorboat. It takes a lot more power to bring the boat up to the speed where it begins to plane than it does to maintain the speed once the boat is planing. PID instruments provide additional power to the lamp during the warmup process to initiate the process. When the PID startup process is complete, the instrument reverts to normal power operation.
As the lamp ages it can take more and more power to ignite the lamp or initiate the glow. Eventually the instrument may become unable to provide sufficient power for the glow to be initiated. This is the type of failure condition referred to in the advisory.
It’s VERY easy to perform a qualitative bump test on the PID by using a Sharpee Marker. I simply put a small dot of Sharpee ink on a business card and hold it against the PID sensor opening or inlet. If you see a response, the lamp is producing photons of UV light. To pass the bump test, you still need to activate the PID alarm. But most of the time the response of the PID to the Sharpee Ink is more than enough to activate the alarm. If you use a DS-404 Docking Station, the Daily Test includes verification of accuracy as well as verification that the PID lamp is igniting.
GfG takes special steps to identify PID lamps that may be subject to premature failure. We put all PID lamps and sensors through an additional two-week screening process in Ann Arbor to identify lamps that are likely to fail prematurely. We have confidence that the PID lamps and sensors we ship meet our quality requirements, and we have PID equipped instruments in stock.
Sincerely,
Robert E. Henderson
President
GfG Instrumentation, Inc.
1194 Oak Valley Drive, Suite 20
Ann Arbor, MI 48108
