# PPM error calculate formula

Discussion in 'Homework Help' started by sen_embedded, May 10, 2010.

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1. ### sen_embedded Thread Starter New Member

May 9, 2010
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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

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
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.

3. ### sen_embedded Thread Starter New Member

May 9, 2010
4
0
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: May 10, 2010
4. ### Markd77 Senior Member

Sep 7, 2009
2,803
594
Crystal frequency is irrelevant.
Max error per day is (60*60*24) * (20/1000000) = 1.728
........................seconds in day * error

Last edited: May 10, 2010
5. ### rjenkins AAC Fanatic!

Nov 6, 2005
1,015
69
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.

Dec 5, 2009
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May 1, 2015
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8. ### RRITESH KAKKAR Senior Member

Jun 29, 2010
2,831
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What is PPM here?

Apr 2, 2009
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771
10. ### RRITESH KAKKAR Senior Member

Jun 29, 2010
2,831
89
anyway what is it?

11. ### R!f@@ AAC Fanatic!

Apr 2, 2009
8,791
771
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.

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.....!

RRITESH KAKKAR likes this.
12. ### WBahn Moderator

Mar 31, 2012
18,087
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MOD NOTE: Thread closed -- necroposting.