ANS: R i = 250 k? and R F = 125 M? The tachogenerator shown on specification sheet 1 is to be used with a display device, which has an internal resistance of 1 M ohm. The display device requires a minimum input voltage of 1V. The tachogenerator is measuring a rotational velocity of 400 r.p.m. when attached to a rotating shaft... Solution Closed loop gain of a common inverting DC op-amp circuit is given by -(Rf/Rin) Now the specs of tachogenerator shows 5mV/1000 rpm, so for 400rpm ,the corresponding voltage is 2mV. Ss, this 2mV is to be amplified to 1V, an amplification of 500 is required. So, -(Rf/Rin) = 500 , hence a choice of Rf = 125 MOhms & Rin = 250 kOhms is absolutely fine. .

1. ANS:
R i = 250 k? and R F = 125 M?
The tachogenerator shown on specification sheet 1 is to be used with a display device, which has
an internal resistance of 1 M ohm. The display device requires a minimum input voltage of 1V.
The tachogenerator is measuring a rotational velocity of 400 r.p.m. when attached to a rotating
shaft...
Solution
Closed loop gain of a common inverting DC op-amp circuit is given by -(Rf/Rin)
Now the specs of tachogenerator shows 5mV/1000 rpm, so for 400rpm ,the corresponding
voltage is 2mV.
Ss, this 2mV is to be amplified to 1V, an amplification of 500 is required.
So, -(Rf/Rin) = 500 , hence a choice of Rf = 125 MOhms & Rin = 250 kOhms is absolutely fine.