Unformatted text preview: an
vi Calculate the voltage gain ( gain =
ideal op amp. Figure 2 + + − ! " =
= − = + − = = +
+ = + # $% "
− − = − −
& − =
− ' () + & − = & + − & − & "
+ = +
+
+ = +
+
* − & & & − & & − = & " = = & +
+
+ & − = , +
,
, − = ,
= −, , )
− ) /.&
. page 2 of 4 ENME 351 HW#5 Solutions Electronics & Instrumentation II Problem 3 For the circuit shown in Figure 3, assume the operational amplifiers are ideal.
v
(a) Calculate the voltage gain ( gain = out )
v in
(b) Calculate the input impedance. Solution page 3 of 4 ENME 351 HW#5 Solutions Electronics & Instrumentation II Problem 4
A strain gauge with gauge factor GF and nominal resistance R is used to measure strain
on a specimen as shown in Figure 4 (b). The strain gauge is connected to a bridge circuit
and an amplifier as shown in Figure 4 (a). Assume the opamp is ideal. Derive an
expression for the output voltage Vout. Is the relationship between the output voltage and
the change in gauge resistance linear or nonlinear? (a) Solution: Figure 4 (b) Since the op amp is ideal and there is negative feedback,
i− =i+ =0 V + =V − Summing point constraint i
V+ V− 0 i V
V
R
= in V − = in
R +R
2
2
Writing KVL at output loop:
V
V
V out = −RG i +V − = −(R + ∆R ) in + in
2R
2
V
∆R
V
= − in −
V in + in
2 2R
2
∆R
V out = −
V in
(V out is a linear function of ∆R )
2R
V + =V in Remark Recall that for a quarter bridge circuit with one strain gauge, the output voltage is a
nonlinear function of ∆R . Therefore, the op amp in the circuit linearizes the output
voltage as a function of ∆R . page 4 of 4...
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 Spring '14
 Amplifier, Instrumentation, Operational Amplifier, Electronics & Instrumentation II

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