Searching for dB and ppm App data.

Thread Starter

tindel

Joined Sep 16, 2012
780
I recall seeing in an appnote somewhere (probably an old LT appnote) a graph of dB, gain, and ppm, but I can't find it anywhere with a google search. Can anyone help? I've seen a few related to audio, but I'd like one that is related to electronics specifically. Maybe Jim Williams did it, but I'm not 100% sure. Any community help out there?

It's possible I'm mistaken about what I saw since ppm is more accuracy and dB is ratios.
 

Papabravo

Joined Feb 24, 2006
16,195
There are two ways to do it depending on a constant.
ppm in dB, using 10 log (ppm / 1e6) this would be like treating the quantity like you would treat power
ppm in dB using 20 log (ppm /1e6) this would be treating the quantity like you would treat voltage

They are different by a factor of 2
Looks like this webiste uses 20
http://www.testips.com/dB_ppm.php
 

Thread Starter

tindel

Joined Sep 16, 2012
780
I understand how to do it. I'm specifically looking for the graphical representation so I can use it to teach.
 

Papabravo

Joined Feb 24, 2006
16,195
I understand how to do it. I'm specifically looking for the graphical representation so I can use it to teach.
You'll want to use graph paper with a log scale on one-axis. We used to call this semi-log paper.
The ppm range should be plotted on the linear scale with the corresponding dB value

https://en.wikipedia.org/wiki/Semi-log_plot

I can't tell you what it will look like without doing some work.
If you insist on a guess it would be a straight line
 

MisterBill2

Joined Jan 23, 2018
8,808
There is no reason ever to use dB and PPM in the same discussion. And teaching anything equating them is a very poor choice, and a way to spread confusion.
 

dendad

Joined Feb 20, 2016
3,840
There is no reason ever to use dB and PPM in the same discussion. And teaching anything equating them is a very poor choice, and a way to spread confusion.
I would have thought so too.
Having them both together is not a thing I've ever heard of. Is it some obscure use?
 

MisterBill2

Joined Jan 23, 2018
8,808
In addition, dB is a ratio normally used to compare magnitudes of voltage or power, while PPM is primarily used to express concentrations of substances. The only place thatI have seen PPM used in electronics is in describing crystal frequency accuracy and stability, and in those instances dB would not be at all applicable. And a graphical explanation seems non-applicable. Although a micrometer versus a surveyor's chain may be a fair comparison.
 
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