In this experiment, we will use AS35 , which is an electronic temperature sensor that will produce output voltage that is proportional to the temperature around it to a scale factor of 10mV/degree C. The device only operate at 4-20V and an external resistor to provide an appropriate load.
First, we will verify that the AS35 work. By making the circuit on the breadboard we were able to obtain the temperature of the room is around 22.8 degree C (Vc=0.228V)
We want to convert the temeprature in degree Celsius to Fahrenheit by using the equation
T_F=(1.8Tc)+32
which means we want to scaled the voltage with a factor of 1.8 then shift upword with 320mV
by puting the terms into voltage, we obtain
V_f=(1+(R2/R1))Vc-(R2/R1)Vref
where Vref is 320mV
by using the nodal anlysis at the inverting and non-inverting output we obtain two equations
1+R2/R1=1.8
-R2*Vref/R1=320
we can solve the variable R2 and R1 by choosing R1 to be 1Mohm
thus, R2 will be 0.812Mohm
One thing we need to make sure is output current need to be small. That is the reason why we choose big value of resistor
After device the circuit
and we measure the output voltage
which is 0.711V
By assuming the Vc is exact, we can compute the theoretical value of degree Fahrenheit
Theoretical Value of Tf = (1.8*0.228+0.32)*100=73.04 degree Fahrenheit
% error = (73.04-71.1)/73.04*100% = 2.66%
which is extremely small
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