onnect17
Established
I think the idea of overexposure, when it comes to PMTs, relates to the amount of light over a period of time, not a instantaneous occurrence.
About the 15 years life, I think it refers to continuous operation equipment. If I understood correctly, PMTs sort of "recovers" when is not in use so the life of the tube is substantially longer if the device operates intermittently, like a scanner, rather than a radar. In other words, the expected life of a PMT in a device which is operating 12 hours a day compared to 24 hours not only doubles, it is in fact many times longer.
Also, as the document reads, the MTBF of between 1000 and 10000 hours is while operating at the extreme conditions. On a more common environment/scenario the number is expected to be 400 times bigger.
Now, talking about scanners. The designs are so different. I am sure the temperature surrounding the PMTs, the size and use of the apertures, the speed, the light source type and power, electronics, etc. makes the PMTs in one scanner to last more than in others operating for the same number of hours.
A simple example that comes to mind is the way the auto adjustment works in the Howteks scanners, allowing a (technically speaking) bad PMT to still operate. To my knowledge, it's quite different in the Scanmates.
Understanding this, I think, is important because owners/users can extend the life of the equipment making sure it is operating on the cool side, rather than in a warm environment (remember that "noisy" fan?), filtering that extra IR and UV light coming from the lamp (IR-UV filter, anybody?), having the scanner ON only when is being used, etc.
