Hi John!
I wouldn't say that you're misinformed at all... It's just that the XRF method of PMI is mostly limited to detecting most elements without being able to isolate carbon, yet some can determine certain specific grades of CS up to the most common grades say 20 to 25 different grades with about a 95% accuracy which is not so bad and yet in comparison to OES, it's very limited...
Having said that, the OES method of PMI can detect and isolate carbon and measure it much more precisely than an XRF PMI instrument can because all the XRF gun can do is to acknowledge that it is present without any capability of isolating and therefore being able to measure with any sort of accuracy - CAPECHE???
An OES PMI gun can accurately measure the carbon content in the material being analyzed, so it all boils down to which method is being used in order to accurately measure the carbon content in an unknown piece of material ,and then there are different types of OES portable PMI systems as well where some do not require some sort of sampling at all and others that do require some sort of lifting of a very minute sample of the material in question yet smaller than something that one would be required to cut out.
So you're not incorrect all together when it comes to PMI! I hope this clarifies somewhat the differences between the two portable methods of PMI being used currently out in the field.
On another note; Isn't it kind of late concerning yourself now with how you rate with the diamond system 3.? I mean if it really did concern you that much wouldn't you show it in the way you respond to most people in here? Just some food for thought, because I certainly will not debate this nor discuss this with you any further since I'm only offering you a different prespective for you to consider - that's all.
Respectfully,
Henry