Temperature Measurement System

In addition to the lab, we conducted three exercises.

First, we analyzed a cascaded op amp circuit consisting of two

non-inverting amplifiers, determining the resultant output

We also evaluated the relation of several input-output

configurations for a 3-bit digital analog converter circuit

In preparation for the lab, we derived the output of a

wheatstone bridge in which one resistor is allowed to vary

Proceeding with the lab, we produced a diagram for out temperature measurement circuit, in which a wheatstone bridge containing the thermistor supplies a difference amplifier. Given a desired minimum output swing and expected input variation, we derived necessary resistances for a consistent gain. Also shown are the measured values of the resistors used in our implementation

The implemented circuit

Collected data, including thermistor resistance seen by the bridge,

voltage supplied by the bridge, and output voltage of the amplifier

Video of the wheatstone bridge in operation

Video of the completed circuit in operation

Summary

The circuit behaved mostly as expected. The efficacy of the wheatstone bridge is difficult to judge, as biasing it is more fiddling calibration than direct implementation of theory. Nonetheless, we get output voltage ranging from 0 to 0.5, in line with expectations. We are let down, however, by the final output of the amplifier, falling short of the desired 2V range. Possible explanation for this could be input/output impedance between the bridge and amplifier. Regardless, it is a simple failure to rectify as the gain of the amplifier can be adjusted to yield desired results.