vibration calibration system and vibration pick up life time

[Kyoungmin Kim]

how r u doing guys??
I calibrate vibration pick up these days.
I use 9610 vibration calibration system.
I wonder about vibration pick up's life time. As u know that system check reference frequency sensitivity. I tried more than hundred times but I still didnt make any dicision about pick ups condition. The sensitivity is only  5mV/in/sec less than reference. Some People said to me I have to tried more.
I want to know how many times make measurement when u calibrate vibration pick up and when u make it condemn.

I will wait ur reply. Thanks.