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# Operational Amplifier

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An operational amplifier (Op-Amp) circuit is built to measure the temperature of an exothermic process in a lab. The circuit uses a thermistor (Resistance Temperature Detector) to monitor the target temperature and a voltmeter to measure the output voltage of the Op-Amp ciruit. Since the thermistor is a passive device, it requires and external battery to provide useful input, as shown in the ciruit diagram in attachment. The relationship between the resistance and temperature in the thermistor is relatively linear over a Temperature (T) range of 0deg Celsius and 200deg Celsius and is defined by Rt = 100 + 0.005*T. What will the Voltmeter read if the temperature of the reaction is 150deg Celsius? What are the potential sources of error in theis circuit and what might be done to improve any error that exists?

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#### Solution Preview

First to calculate the voltage:

Essentially what you have here is an inverting amplifier. A picture of this is shown in pic1.jpg. I will refer to the labels in this picture throughout this answer.

The output voltage Vo from the amplifier is given by:

Vo=-(R2/R1)Vin

where Vin is the input voltage.

What the question is asking you to do is to find Vo (which is what the voltmeter would read) when the temperature is 150 degrees Celsius.

Vin=1.5V
R2=2000ohm
R1=100+Rt ohm

And you know that at T=150, Rt=100+0.005*T=100.75

so ...

#### Solution Summary

Essentially what you have here is an inverting amplifier. A picture of this is shown in pic1.jpg. I will refer to the labels in this picture throughout this answer. The output voltage Vo from the amplifier is given by: Vo=-(R2/R1)Vin where Vin is the input voltage. What the question is asking you to do is to find Vo (which is what the voltmeter would read) when the temperature is 150 degrees Celsius.

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