Experiment: Voltage Divider in a Wheatstone Bridge Circuit

This experiment demonstrates the use of a voltage divider within a Wheatstone bridge circuit, a common setup for precise measurement of unknown resistances, often used with sensors.

Objective

To understand the operation of a Wheatstone bridge circuit and its application in measuring unknown resistances or sensor outputs.

Materials

Circuit Diagram

Connect the circuit as shown below, with two voltage dividers forming a Wheatstone bridge. The bridge is balanced when the ratio of resistances on each side is equal.

Wheatstone bridge circuit diagram

Theory

A Wheatstone bridge circuit consists of two voltage dividers connected in parallel. The output voltage, or bridge voltage (V_out), is measured between the midpoints of the two dividers. The circuit is balanced when the ratios of resistances on each side of the bridge are equal, resulting in zero voltage across V_out:

(R1 / R2) = (R3 / R4)

If one resistance changes (for example, a sensor in place of R4), the bridge becomes unbalanced, and V_out varies proportionally to the change. This configuration is commonly used for precise measurements in strain gauges, temperature sensors, and more.

Procedure

  1. Choose known values for R1, R2, and R3. Connect them as shown in the circuit diagram.
  2. Set R4 as the unknown resistor or a variable resistor that you can adjust to simulate a changing sensor value.
  3. Connect the output of the power supply to the bridge, with one side to the top of R1 and R3 and the other side to the bottom of R2 and R4.
  4. Connect a multimeter across the midpoints of the two dividers to measure V_out.
  5. Adjust R4 and observe how V_out changes in response to resistance changes. Find the point where V_out is zero, indicating the bridge is balanced.

Observations

Record the resistance values of R1, R2, R3, and R4. Note the bridge output voltage V_out at various resistance settings for R4. Observe the conditions under which the bridge is balanced (i.e., when V_out is close to zero).

Conclusion

This experiment demonstrates how a Wheatstone bridge circuit can precisely measure changes in resistance. When one resistor is unknown or varies (e.g., a sensor), the circuit can detect small changes by monitoring V_out. This setup is widely used for precise sensor applications, such as in load cells or temperature sensing.