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I think it is OMEGA. a company that makes temperature stuff. you can find its website on google easily. it has all the charts in pdf. I am on my palmpilot at this time, otherwise would have given you the full url.
The ASTM standard E1137 deals with RTD's. You can buy the standard from ASTM
Omega offers their "The Temperature Handbook", which contains conversion charts. It is free, but shipping is not cheap.
Try using this .pdf. I don't know how accurate these coefficients are. I can check them on Monday, when I get back to work. Note that for temperatures above 0C, the formulas are simpler. www.atpsensor.com/pdfs/rtd.pdf