54
Chapter 2
X~. is 4.056 zc so that
X~c = zmax -
4.056 ~c = 0.01/~x + 0.01
0.01/~x + 0.01
4.056
and
0.01(~ +~t~)
001
Cvz - -
(100) = ~(100)
/~z 4.056(#~,_
Cz = 0.24654%
for the second part of Example 2.9 and expanding for seven cards with
X= 8.2516 Fig. 2.4 and Table 2.2
~c 0.01 ~/~xi (100)
Cw
#_~ 8.2516 ~ #xi
Cv = 0.12119 percent
The stack up dimension is/~z---28 in
0.12119
~- 1-~ (28) =- 0.03393
the stack up dimension will be
i=7
z = ~
2.576(0.03393)
i=1
z = 28 in -4- 0.087404 in
the percent error is in the tolerance
0.11832 - 0.087404
percent error=
0.11832
× 100
= 26.13%on the low side.
Example 2.9 is considered to be the exact solution.
EXAMPLE 2.11. Find the Rr for two 10% resistors in parallel (Fig.
2.5) whose mean and standard deviations are (~q, ~1)= (10,000; 300)
and (#2, ~2)-~(20,000; 600) ohms. Use Eq. (2.16).
R~- is
1
1
1 R1 +R2
R7 ~ R~ ~-R2
R~R2