Page 49 - Servo Motors and Industrial Control Theory -

2.7 Bode Diagram 41

Fig. 2.22 An electronic R 2
proportional device

R 1
V 1 – + V
OP-AMP 0
+
–
R

Fig. 2.23 A proportional R 2
control for negative or posi-
tive feedback configuration R
V 1 1

- V
V 2 OP-AMP c
+
R 1
R

It should be noted that an OP-AMP changes the sign of the signal and for positive
gain two of them must be used in cascade. For positive and negative feedback con-
trol, they can be wired as shown in Fig. 2.23.
In this case,
V =− KV + V 1 )
(
2
o
R (2.30)
K = 2
R 1
For a negative feedback control, the direction of one of the signals is changed. In
design of control often a negative feedback is used. In this case,

V =− KV − V 2 ) (2.31)
(
o
1
When a capacitor is attached to the feedback loop of an operational amplifier, it
becomes an integrator (Fig. 2.24).