PPM error calculate formula

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sen_embedded

Joined May 9, 2010
4
Crystal frequency = 32.768KHZ
PPM =20 PPM
Temperature =25 C

I have used above crystal in RTC. I am getting 1.4 sec delay per day can you please let me know how calculate the error.

Please let me know PPM error calculate formula
 

t_n_k

Joined Mar 6, 2009
5,455
The error is 1.4 sec per 24 hours

Error[PPM]=1e^6*1.4/(24*3600)=16.2037 PPM

which is within the error spec. of 20 PPM @25C for your crystal.
 

Thread Starter

sen_embedded

Joined May 9, 2010
4
Actualfrequency = 32768 (Hz)

20 ppm frequency =32768-20 = 32748

Actualfrequency per day = 32768 * 3600 * 24 = 2831155200

20 ppm error frequency per day = 32748* 3600 * 24 = 2829427200


Error frequency per day = 2831155200 – 2831068800 = 1728000 Hz /per day


frequency = 1728000 /1000000 = 1.74 sec

20 PPM error in 32.768 Khz. crystal oscillator = 0.5 Sec per day


Pelase let me know my caluation is right or worng
 
Last edited:

Markd77

Joined Sep 7, 2009
2,806
Crystal frequency is irrelevant.
Max error per day is (60*60*24) * (20/1000000) = 1.728
........................seconds in day * error
 
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rjenkins

Joined Nov 6, 2005
1,013
If you want ultimate accuracy, use a crystal that needs a higher capacitive load that the oscillator in the chip provides; ie. the common crystal osc config with a capacitor to ground from either side of the crystal.

Now make the capacitor at the oscillator input side a variable one - a trimcap, of about twice the nominal fixed capacitor value.

You can then tune the oscillator to exact frequency and minimise any error.

If you need better stability still, you also need to temperature stabilise the crystal, or preferably the whole oscillator circuit.
 

R!f@@

Joined Apr 2, 2009
9,918
Open a new thread if you have a question.
Isn't that what you always do.
Better yet type that in google and read the articles for a change.
You are not a baby to ask things that you can find for your self.

https://www.google.mv/?gws_rd=ssl#q=PPM+crystal+error

I get tons of info and why can't you. Don't be lazy. Try to read for your self.
What makes you think you would understand any better here than from google.....!
 
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