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How to Test Bridge Circuits

A bridge circuit is a resistive circuit in which two branches are connected via a third branch. The most common is a Wheatstone bridge circuit. It is used to determine the value of an unknown resistor using a voltage source such as a DC battery and electrical components, including resistors, an ammeter or a galvanometer and a potentiometer. The voltage source provides power, the ammeter measures the circuit̵7;s current, and the potentiometer works as a variable resistance. To test a bridge circuit, use a simple equation: R2/R1 = Rx/R3.

Things You'll Need

Voltage source (9V DC battery or a dedicated power supply)
Resistors
Ammeter (or galvanometer)
Potentiometer
Digital multimeter (or ohmmeter)

Instructions

- 1
  Find the values for R1 and R2. These are on the color code of the resistor itself, or you can use a digital multimeter on the resistance setting. Use the values to calculate K, where K = R2/R1.
- 2
  Connect the components to create the bridge circuit. Check to see if the ammeter (or the galvanometer) reads zero. If so, this means that both sides of the bridge are balanced. If not, adjust the potentiometer until the ammeter reads zero.
- 3
  Turn off the power supply and disconnect the potentiometer. Measure its value and plug the value into your equation as R3. Calculate Rx, using K = Rx/R3 -- or, translated into a solvable equation, Rx = K(R3). You have just found the experimental value of the unknown resistor.
- 4
  Measure the unknown resistor (Rx) with a digital multimeter or an ohmmeter directly, and calculate the percent error with another simple equation: percent error = (Rx from Step 3 calculation - Rx from digital multimeter)/Rx from the digital multimeter. The percent error tells you the difference between the theoretical and the experimental values.
- 5
  Repeat with different resistances for Rx that are comparable to the maximum and minimum values of the potentiometer. Try different values to see how well the bridge circuit performs under different ranges of conditions. This shows you how well the bridge circuit can find unknown resistances.

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