In a message dated 98-01-04 21:24:44 EST, you write:

>  I have a question about some SIR results that I got. I made a few
>       consecutive SIR tests on a coupon and found that the ohm reading kept
>       on increasing the longer I left the coupon inside the humidity chamber
>       (35C, 85%RH). My understanding is that the reading should normally
>       decrease with the elapsed time, indicating the lowering of surface
>       resistance, right? I ran the coupon for 1 week, at first the ohm
>       reading looked OK (~2-5e11 ohm), but at the end of the week the
>       reading esceeded 1e12 ohm. I am confused.
>

What you are seeing is fairly common.  SIR readings can decrease over time if
you have metal migration and corrosion.  Normally, when the readings increase,
it means that you have / had some other surface contaminant that is / was
volatilized during the test.  A polyglycol is one such material.  The levels
you note would be considered as acceptable by most standards, provided the
measurements were taken correctly.

Doug Pauls
CSL

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