Crystal Life Expectancy

[garyq]

Hello all,

Unfortunately I am not a techie and only an operator of a PI detector.

I am not sure under what section of Geotech to post my question so I ended up here.

I read on another forum that due to the very nature of crystals they deteriorate with age.

Therefore I am looking for further advice on the expected life expectancy of crystals such as Minelab used in their early PI detectors?

Also if so is there certain signs during a crystals operation that will exibit it's deterioration?

Gary

[Carl-NC]

Hi Gary,

All electronic components age, including resistors, caps, and even ICs. Crystals are amongst the most stable component; most are specified with an initial tolerance and an "aging" tolerance, which are usually less than 100 ppm. For a 1MHz crystal, this results in a 100Hz error. Or, in terms of timing, for every 1us it's a 100ps error.

While a crappy crystal with several 100pm of age drifting might cause problems in an RF application, it just isn't going to affect a PI detector in any meaningful way.

- Carl

[garyq]

Thanks Carl for the clarification as I thought the Xtal may have been a weakness of all the components within.

If I may pose another question can lack of use or visa versa have an adding or lessening effect to the aging process of an electronic component?

Regards,
Gary.

[Carl-NC]

"can lack of use or visa versa have an adding or lessening effect to the aging process of an electronic component?"

Yes, ferinstance some caps are prone to piezoelectric effects that cause mechanical vibrations. ICs can undergo metal migration and thermal cycling stress. Generally, any component sitting on a shelf will last longer than a component in constant use, but they're no good sitting on a shelf, eh? Most components, when used within their intended spec, will last a really long time. The worst things happen when a component is taken to its limit (e.g. resistor wattage) or a wrong style component (e.g. cap) is used. I have lots of detectors from the 60's & 70's (including tubes!) still working fine.

- Carl

[Steve in MS]

Carl, while on this subject, one that comes up from time to time and some manufacturers state not to leave a detector in a vehicle, like in the summer time because of the extreme heat.
I was just wondering your take on this, even vehicles have radios, tape players, etc and they last a long time even in all that heat......
Still I usually don't leave my detectors in a hot car.