Op-Amps - LM358 & AS35 - Temperature Sensor

PROBLEM
Op-amps are often used in scaling and level-shifting applications. Scaling is simply the process of multiplying a signal voltage/current by a constant in order to change its amplitude, and level-shifting is the process of adding a constant positive or negative voltage/current to a signal. This lab uses scaling and level-shifting of a circuit to process the output signal from an electronic temperature sensor so that it produces temperature readings in Fahrenheit degrees. The sensor produces an output voltage that is proportional to the ambient air temperature according to a scale factor of 10mV/C

METHODS
A circuit is constructed similar to the scaling and level-shifting circuit shown in the figure. The output voltage is converted from a 10Mv/C scale to a 10MV/F scale.

Scaling and level-shifting circuit -- Rvar is used to create the appropriate voltage at the inverting input for the level-shift

The scaling and level-shifting equation. Tf=1.8Tc+32 -- Vc = (1+R2/R1)Vc - (R2/R1)Vref

Hence, R2/R1 = .8 -- R2 = 800 Ohm, R1 = 973 Ohm

The ambient temperature in the room that day was 23C. Tf = 1.8*23 + 32 = 73.4 F

Voltage reading Vf -- 720 mV = 72 F degrees

 The percent error is calculated: absval(actual - theoretical)/theoretical*100% = (72-73.4/72)*100 = percent error = 1.9%err