Experiment 8 Report - Experiment 8 Op Amp Design Project...

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Experiment 8 Op Amp Design Project: “Temperature Sensor for Display and Control” Eugene Gallagher Introduction The basic challenge in this design is to convert the current from the temperature sensor (1 ºK = 1uA) into a voltage. More specifically, we want two separate voltages, one which is .01* ºK and the other .1* ºF. Then in the second part we need to design a temperature controller that will light up a red LED if the temperature drops below 68 ºF (6.8 V) and green if it goes above 72 ºF (7.2 V).
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Schematic 1: Temperature Sensor for Display and Control Circuit Design and Analysis For the circuit design, we used LF412 operational amplifiers. Signal Conditioning for ºK: In order to model the temperature sensor output, we simply used a DC voltage source with a 10 kΩ resistor, which means a 1 V input will produce 100 uA (this should correspond to 100 ºK). We used a simple inverting amplifier used as a current to voltage converter, where V O / I S = - R F. Since we want 0.01 ºK at the V 01 output when I S = 1 uA, R F should be 10 kΩ. This is an inverting amplifier, so in order to get a positive voltage we simply reversed the polarity of the DC source, so the positive terminal was toward ground (I S would be going toward ground). In order to adjust for any error, we had to incorporate a +-1 ºK offset adjustment. This was done by adding a 1.5 MΩ resistor connected to the inverting terminal, then
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connecting the other side of the resistor to the center pin of a 10 kΩ potentiometer. The other pins of the pot were connected to +15 V and -15 V respectively. This is modeled on the schematic as a simple voltage divider with 5 kΩ resistors. By choosing a 1.5 MΩ
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