The Zone System (Linear Tone Curve?)

Hi, I've been learning the zone system by Ansel Adams.  I would like to take a photo and import it into photoshop so that each value in my scene matches the according grayscale measurements in photoshop (measured using Lab values).

1. I used my camera and took 11 exposures of a grey card: -5 ('Black'), -4, -3, -2, -1, 0 (Mid Grey), +1, +2, +3, +4, +5 ('White'). 
2. I then opened the files in Adobe Camera Raw (No adjustments)
3. I then opened them with Photoshop
4. I measured the Lightness values using Lab and plotted the points on a graph.

I see that somewhere along the line an S Curve has been applied to the input values!  I would like an even distribution of the input tonal values. 

How do I turn this S-curve off?  Or, how do I achieve a linear curve when importing photos to photoshop?   

Essentially:

I would like a linear response curve so that each tone (each 1 stop exposure from above) maps to the appropriate grayscale value in even increments (i.e., 10% steps).

Zone 0:     0% (Black)

Zone 1:     10%

Zone 2:     20%

Zone 3:     30%

Zone 4:     40%

Zone 5:     50%

Zone 6:     60%

Zone 7:     70%

Zone 8:     80%

Zone 9:     90%

Zone 10:   100% (White)

Can anyone shed any light on this issue?  I'm really stumped with this one!