- #1

Samuelriesterer

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Problem statement, work done, and equations:

A Wheatstone Bridge is often used in sensor circuits and other measurement circuits. The basic circuit is drawn below:

In the circuit, Rs is the sensor and might be a thermistor for measuring temperature or a photoresistor for measuring light intensity. These change resistance when the temperature or light intensity changes.

Ra is an adjustable resistor or potentiometer (pot for short). It will have a knob on it to turn for adjusting the resistance.

Real thermistors have a resistance which changes nonlinearly with temperature. For this question, we will assume the resistance is linear over the temperature range of interest.

(a)With the thermistor placed in ice, Ra is adjusted so that the volt meter in the center of the drawing reads zero. Figure out the relation among Rs, Ra and R1 when the meter reads zero. Assume the meter has a resistance of 10^13Ω (essentially infinite).

##\frac{Ra}{R1} = \frac{R1}{Rs} → Ra = \frac{R1^2}{Rs}##

(b) With Ra adjusted as above, the thermistor is then placed on a counter where the temperature is 20°C. With V = 9V, determine the meter reading. The resistance of the thermistor is given by R = 100 + 0.04T where T is the temperature in degrees Celsius and the resistance is in Ohms.

##Rs=100+0.04(20) = 100.8 ohms##

__I cannot figure how to get the other resistor values, seems like too few knowns__A Wheatstone Bridge is often used in sensor circuits and other measurement circuits. The basic circuit is drawn below:

In the circuit, Rs is the sensor and might be a thermistor for measuring temperature or a photoresistor for measuring light intensity. These change resistance when the temperature or light intensity changes.

Ra is an adjustable resistor or potentiometer (pot for short). It will have a knob on it to turn for adjusting the resistance.

Real thermistors have a resistance which changes nonlinearly with temperature. For this question, we will assume the resistance is linear over the temperature range of interest.

(a)With the thermistor placed in ice, Ra is adjusted so that the volt meter in the center of the drawing reads zero. Figure out the relation among Rs, Ra and R1 when the meter reads zero. Assume the meter has a resistance of 10^13Ω (essentially infinite).

##\frac{Ra}{R1} = \frac{R1}{Rs} → Ra = \frac{R1^2}{Rs}##

(b) With Ra adjusted as above, the thermistor is then placed on a counter where the temperature is 20°C. With V = 9V, determine the meter reading. The resistance of the thermistor is given by R = 100 + 0.04T where T is the temperature in degrees Celsius and the resistance is in Ohms.

##Rs=100+0.04(20) = 100.8 ohms##