thanks for the feedback,
Dan,
I did indeed have a typo in the 720 (need to be more careful in the future).
In all of my process runs, I record the number of amphours consumed and I know the target process area very precisely (most of the runs are done using 12" x12" coupons of 7075 or 6061)
To find my thickness discrepancy i rearrange the 720 as follows
thickness = (CD x time)/720
= (Amps x time)/(area x 720)
= (Amphours x 60)/(area x 720)
one run I did yesterday consumed 46.0 amphours on 2 sqft.
thickness = (46.0 x 60)/(2 x 720) = 1.92 mils
using the isoscope however, I measured 2.26 mils for a discrepancy of about 18%
(18% is the largest discrepency I have see, and as I have stated, most are within 7%)
I alway thought temperature, concentration, anode/cathod ratio, and alloy would change things, and so now I wonder.....
If all of the variables were held constant, I should get consistant result and be able to compensate accordingly.....
and
what is acceptable in industry? If 1 mil is required what is the acceptable tollerance? As sswee stated, +-7% maybe very accuate, but is it accurate enough? (trick question that can only be answered by the person that asks)
thanks
kevin