This experiment requires us to perform level-shifting and scaling processes of an operational amplifier to convert the temperature-proportional voltage in centigrade exiting out of the LM35 into voltage that is proportional to fahrenheit.
Procedure:
We first start by testing the LM35, applying 9 volts into it relative to ground and seeing what voltage we get as output. Sure enough, we obtained 220 mA, or room temperature.
Now that the LM35 was shown to work, we solved for the output voltage of the op amp circuit according to this diagram.:
We also knew the formula for temperature conversion from celcius to fahrenheit, and we solved for the equation to be in terms of voltage.
Calculation:
Solving for the circuit diagram, we figured the output voltage to be related to the input voltage and the reference voltage by this relation below. Then we solved to find the reference voltage. We also took out resisters from the box that had the correct proportions to our calculated value.
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Pictures of the experiment:
Materials: 3 variable power supplies (9V, 9V, .4V) , lots of wires, breadboard, LM35 temperature sensor, OP amp, potentiometers...
The complete circuit.
Error calculation. the .716 mA came from calculation from the value obtained through converting the output of the LM35 voltage into fahrenheit voltage using the celcius-temperature equation.
Conclusion
The experiment successfully demonstrated the practical uses of an operational amplifier's ability to multiply and add. The conversion had an error of 9.2, which was probably due to the disproportion of the resistors to the actual ratio (18/22 isn't exactly .8) and the uncertainty of the resistors.
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