Exp 1. Wheatstone bridge

Concept : To observe the working of a Wheatstone bridge

 

Explanation: A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one of which includes the unknown component.

How It Works:

  1. Components: The bridge consists of four resistors arranged in a diamond shape. Three of these resistors have known values (R1, R2, and R3), and one resistor (Rx) is the unknown resistance to be measured.

  2. Balancing the Bridge: By adjusting one of the known resistors (usually R2), the bridge is balanced when the voltage between the two midpoints (B and D) is zero. At this point, the ratio of the resistances in one leg is equal to the ratio in the other leg:
    R1R2​=R3Rx​
    From this, the unknown resistance ( Rx ) can be calculated as:
    Rx=R3⋅R1R2​

 

Simulation Mode: Transient/DC Sweep

 

Simulation Parameters: Any reasonable values would work. For example:

 

Reference Circuit Schematic: 

 

Make the circuit diagram with the exact pin-to-pin connection as shown below to practice. This will help you to complete the experiment successfully.

 

Reference Circuit Details:

Input=COM.1

Graph Output 1

Reference Netlist:

 

* Capacitor Voltage Divider Circuit

V1 COM.1 0 DC 0 

R1 COM.1 COM.2 1 

R2 COM.1 COM.3 1 

R3 COM.2 0 2 

R4 COM.3 0 2 

R5 COM.3 COM.2 1 

 

.dc V1 0 5 1    

 

.control 

run 

plot  V(COM.2)-V(COM.3) 

.endc 

.end

 

Reference Output:

After the simulation is done, the following output graph appears at the screen showing the voltages and currents across all the nodes.

 

Graph Output 2

Reference Netlist:

 

* Capacitor Voltage Divider Circuit

V1 COM.1 0 DC 0 

R1 COM.1 COM.2 1 

R2 COM.1 COM.3 1 

R3 COM.2 0 2 

R4 COM.3 0 2 

R5 COM.3 COM.2 1 

 

.dc V1 0 5 1    

 

.control 

run 

plot  V(COM.2)-V(COM.3) 

.endc 

.end

 

Reference Output:

After the simulation is done, the following output graph appears at the screen showing the voltage  V(COM.2)-V(COM.3).

Thus in the bridge balanced condition the potential difference between com.2 and com.3 is 0V.

 

Conclusion:
Thus, we have seen the behavior of the Wheatstone Bridge which can be used to measure the unknown resistance among R1, R2, R3 and R4.

 

Assignment:

Change the components, sources and analysis values and get different results. Please verify the theoretical and practical results.

 

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