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Roshan kumar
Joined: 29 May 2008
Posts: 2
Location: India
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 22 Sep 2009 12:55 what does PPm/deg celcius denoted when mentioned in spec. |
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Pls explain what does PPM/celcius denotes(means) when it is mentioned in the specification of
a) Resistance
b) Capacitor
For example
a) 200ohm,0805,+/-5%,100ppm
b)27pf,0805,0 +/- 60ppm/deg celcius
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treitmey
Joined: 23 Jan 2008
Posts: 36
Helped: 4
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22 Sep 2009 15:41 Re: what does PPm/deg celcius denoted when mentioned in spec |
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PPM is parts per million.
I've seen it used in oscillators.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=X062-ND
where its rated at 20MHz ±30ppm/deg C
So your value(20MHz) can be off by +-30 hertz per million hertz per deg C.
Which is deceiving, because at reference temp you still have that tolerance.
so for this example
http://www.ecsxtal.com/store/pdf/hc49u.pdf
at 25C(the reference temp) the crystal is within spec if
from 20,000,600 to 19999400 that is 30*20=600
now if we move 1C away from reference.
so at 26C the crystal is within spec if
from 20,001,200 to 19998800 that is 30*20*2=1200
the is 2 is coming from 1 + change from ref temp.
for the resister I would guess that it is ohms per million ohms per deg C
for the cap I would guess that it is pF per million pF per deg C((just a guess))
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Kral
Joined: 28 Mar 2005
Posts: 1182
Helped: 187
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22 Sep 2009 17:26 Re: what does PPm/deg celcius denoted when mentioned in spec |
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Roshan kumar,
Let Xi be the value at an initial temperature Ti. Then for every 1 Deg C change in temperature from the initial temperature Ti, X will change by an amount equal to [ppm/1000000] * Xi.
Regards,
Kral
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