Parts Per Million?

[EN0]

Hi Everyone,

I've researched ppm a little, but it doesn't seem to click for me. Would someone please elucidate it in greater detail? I've heard that it can be associated with noise, but that doesn't make sense to me.

I'd appreciate any help!

Thanks,

Austin

 

[JimB]

Parts per million, just a way of expressing very small "percentages".

Consider a resistor, it may have a tolerance of +/- 5%, so a 100 Ohm resistor could be anything between 95 and 105 ohms.

Now consider a 1Mhz crystal, if it had a tolerance of 5% it would be a very bad crystal, but if it had a tolerance of 0.005% it would be a reasonable crystal and the frequency could be anything between 999,950 and 1,000,050 hz.
We could also express the tolerance of the crystal as 50 parts per million.
A good crystal may have a tolerance of 1ppm, much easier in the head than 0.0001%

Working out these fraction percents has made my head hurt, but ppm - no problem.

JimB

 

[EN0]

Hi Jim,

Thanks for the informative reply! I think I grasp a better understanding of ppm now, but I have a few questions and observations.

I take it that ppm is generally used to express the error fluctuation that a part may have?

For your example of the tolerance of 0.005%, with the frequencies varying from 999,950 to 1,000,050Hz, the set frequency of the crystal is evidently 1MHz. Since you said that this error rate could be expressed as 50ppm, you simply took the deviation of 50, correct? If that's the case, I'd like to know the set frequency of the crystal to observe how much my frequency fluctuates, given the ppm. But I do admit, using ppm does simplify things greatly. I guess ppm isn't as difficult as I thought it would be.

Thanks for your help!

Austin

 

[smanches]

PPM is generally used to describe fluid mixtures. It's used for very small ratios, as was mentioned above. I rarely see it used in electronics at all.

 

[HarveyH42]

It's the amount of man-made CO2 in the atmosphere...

 

[JimB]

For your example of the tolerance of 0.005%, with the frequencies varying from 999,950 to 1,000,050Hz, the set frequency of the crystal is evidently 1MHz. Since you said that this error rate could be expressed as 50ppm, you simply took the deviation of 50, correct? If that's the case, I'd like to know the set frequency of the crystal to observe how much my frequency fluctuates, given the ppm.

Everything in engineering has a nominal value and a tolerance.
So, consider a 5.000Mhz crystal with a tolerance of 10ppm, 5.000Mhz is the nominal value and the actual value could be somewhere between 4.999950 and 5.000050Mhz. Simple!

We could if we wish, describe the tolerance of the average resistor in ppm, not a good idea but we could do it.
A 5% resistor would be a 50,000ppm resistor. Mathematically correct but it makes my brain hurt.

As mentioned by other posters, ppm is often used to describe the concentration of some component of a mixture.
So if we have 1000 litres of water which is contaminated by 1ml of oil, the concentration of the oil in water is 1ppm. Equally simple!

JimB

 

[Dynamite]

hi ive been trying to understand this too. thx!

 

[EN0]

Hey Jim,

I'm happy to say that I understand ppm now.

Thanks for all your help and time, I truly appreciate it! Also, thanks to everyone else who contributed!

Austin

 

[Hayato]

For example.

If I mix 1 kg of lead in 999,999 kg of iron, I'm gonna have 1 ppm of lead. =D

 

[Hayato]

Or, if I have 1 german among 99,999 chineses, then I'm gonna have 10 ppm of germans!