Day 13 04/09/2015 Temperature Measurement system designed

Today we first talk about the cascaded op amp circuits

In the picture I know that understand that

Formula: Vout = -(Vf/Vi)*Vsource

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Lab

Temperature Measurement system designed

This lab is required us to use the preview's lab knowledge to make a overall temperature measurement system which require to make Thermistor connect with Wheatstone Bridge and difference amplifier.

And because real Wheatstone Bridge is expansive outside we build our own

This is circuit with thermistor and potential transistor 

To be able to make lab work we are required to test each system individually and on the Wheatstone Bridge we make Vab as close to zero as possible because we want to know what will Vout change when we increase the thermistor temperature.

On the different amplifier we first build the same circuit we built last lab which with 4 same resistors connect to amplifier and we suppose to get Vout = Vb - Va and by supply Vb with 2V and Va with 1V we got Vab = 0.996V

After all we connect two circuit together

And hold the thermistor to hope to see the Vab change by the ratio 

Formula Vout=R2/R1(Vb-Va)

Below is the video when we use R1=1k and R2=10k

The result end up

Even the ratio is not come out with Vf = 10times of Vi but the voltage did increase when the thermistor hold by our fingers.