# What is PPM with regards to crystal tolerances

Discussion in 'General Electronics' started by kean, Jun 22, 2004.

1. ### keanGuest

Hi,
Looking at datasheets for crystals, they specify its tolerance as +/-
100 PPM. What does PPM stand for and how do you calculate the
tolerance of the crystal in terms of frequency?

Thanks,
Kean

2. ### ArtGuest

Parts Per Million: General reference to tolerance of the crystal frequency.
1.00 MHZ Xtal with +-1PPM would therefore be plus or minus 1 hertz to be
within that specific tolerance.

3. ### ExternetGuest

Hi Kean.
PPM is parts per million.

Is like percentage, but per million instead.

On a ±100 ppM tolerance, means a 1 MHz crystal can be anywhere in the
range of 999 900 Hertz to 1 000 100 Hertz.

Miguel

4. ### ZorknobGuest

PPM = parts per million

With a +/- 100ppm tolerance, a 1MHz crystal can range in frequency
from 999,900Hz to 1,000,100Hz. Where the crystal oscillates within
the range is primarly a function of temperature.

5. ### Rich GriseGuest

100 PPM == 0.01%

Cheers!
Rich

6. ### keanGuest

Okay!. Thanks a lot for the help guys.

7. ### Robert BaerGuest

Be advised that 100ppm is crappy; a good RailRoad watch does better...

8. ### David L. JonesGuest

PPM can refer to the temperature coefficient as well, so in this case
it's not just an absolute frequency error, but a variation with
temperature.
100ppm/degC will give you 0.01% change per degree C. A big change if
you are working over a wide temperature range.

Dave