Lab 6 - Op Amps 1

Objective:
The purpose of the lab understanding how an inverting op-amp functions in a circuit.

Pre-Circuit Information:
Before the circuit can be assembled, the values of resistors connected to the op-amp and sensor must be determined.  The resistors connected to the op-amp are Ri and Rf.  The sensor has resistors RX and RY (the potentiometer/variable resistance).

Given :
Output range: 0 to +1V
Gain between 0 and -10V
Current through sensor cannot exceed 1 mA
Power Supply current into op-amp cannot exceed 30 mW
For the sensor, the Vsupply = 12V & VNode between Rx & Ry = 1V

Calculation:

Op-Amp

Schematic without sensor &  Ri

Rf

Sensor

Schematic with sensor &  RX

 RX  with a 1/8W Power Rating

RY & RTH

Ri = 1000Ω

Rf = 10000Ω

RX = 110000Ω

RX @ 1/8W = 1152Ω   ≈ 1300Ω 

RYmax = 108.33Ω   ≈ 130Ω

RTH = 118.182Ω

Measurements of the Components:

Note: Used RX = 10000Ω instead of calculated value since the calculated value did not allow the circuit to function correctly

The Circuit Model:

The Data collected by adjusting the potentiometer (RY):

After these measurements, the current being supplied to the op-amp was measured for each power supply:

IV1 = 1 mA

IV2 = 1 mA

Using the measurements of the current through each power supply, the power being supplied was by the power supply was calculated. 

The current through Rf 

The power supplied into the op-amp from the power supplies were PV1 = 12.08 mW  and PV2 = 12.13 mW. Since the power supplied are below 30 mW, the power supply constraint was satisfied.  A way to reduce the power drawn by the power supply without changing the gain of the op-amp is to increase the values of the resistors.