## Outline

## Introduction

## Now, what are signals?

Signals are the main source of communication and in this age of development and inventions, there are various types of signals and these signals are measured by Resistance, Induction, and capacitance.

## What is Resistance?

### For Example:

- Light Dependent Resistor or LDR is the simplest device to mention in the example of resistance, so as the name suggests, LDR is a device whose resistance changes according to the light supplied to it or fallen on it.

### TYPES :

- Low Resistance Measurement
- Medium Resistance Measurement
- High Resistance Measurement

### NOTE :

## What is Wheatstone Bridge?

### Examples:

#### 1: Thermistor ;

#### 2: Strain Gauge ;

### NOTE :

## RESISTORS IN WHEATSTONE BRIDGE:

For finding the Unknown Resistance accurately this Bridge if used by measuring it with the known value of resistance. Indirectly, a Null or Balanced condition is used to find the unknown resistance through this Bridge.

In Balanced conditions, the output voltage of the Bridge at points A and B must be equal to 0. As compared to the above circuit:

VOUT = 0 V

For a detailed study of the above circuit, let’s redraw it with more deals and clarity.

For finding the Unknown Resistance accurately this Bridge if used by measuring it with the known value of resistance. Indirectly, a Null or Balanced condition is used to find the unknown resistance through this Bridge.

In Balanced conditions, the output voltage of the Bridge at points A and B must be equal to 0. As compared to the above circuit:

VOUT = 0 V

For a detailed study of the above circuit, let’s redraw it with more deals and clarity.

V1 = V2

V3 = V4

The voltage ratio can be written as:

V1 / V3 = V2 / V4

From Ohm’s law, is:

I1 R1 / I3 R3 = I2 R2 / I4 R4

Hence, I1 = I3 and I2 = I4, we get:

R1 / R3 = R2 / R4

Now from the above equation, it is clear that if we know the values of three Resistors then it’s easy to find the value of the fourth one.

### Alternative Way to Calculate Resistors:

In the redrawn circuit, if VIN is the input voltage, then the voltage at point A is:

VIN ( R3 / (R1 + R3))

Similarly, the voltage at point B is:

VIN ( R4 / (R2 + R4))

For the Bridge to be Balanced, VOUT = 0. But we know that VOUT = VA – VB .

So, in Balanced Bridge Condition,

VA = VB

Using above equations, we get:

VIN ( R3 / (R1 + R3)) = VIN ( R4 / (R2 + R4))

After simple manipulation of the above equation, we get:

R1 / R3 = R2 / R4

To find a conclusion from the above equation, if R1 is an unknown resistor, then its value can be calculated from the known values of R2, R3, and R4. Generally, the unknown value is known as RX and of the three known resistances, one resistor (mostly R3 in the above circuit is a variable Resistor called RV.

## Find Unknown Resistance using Balanced Wheatstone Bridge

From the above circuit, let’s assume that R1 is an unknown resistor. So, it is known as RX. The resistors R2 and R4 have a fixed value. This means the ratio R2 / R4 is also fixed. Now, from the above calculation, the ratio of resistors must be equal to create a balanced condition i.e.

RX / R3 = R2 / R4

As the ratio R2 / R4 is fixed, we can easily adjust the other known resistor (R3) to achieve the above condition. Hence, it is important that R3 to be a variable resistor, which is known as RV.

But here the question arises, How to make the Balanced Condition? Now Galvanometer (an old-school Ammeter) can be used by placing the Galvanometer between points A and B, then we can detect the Balanced Condition.

With RX placed in the circuit, it adjusts the RV until the Galvanometer points to 0. At this point, note down the value of RV. By using the following formula, you can calculate the unknown resistor value RX.

RX = RV (R2 / R4)

## Unbalanced Wheatstone Bridge

In the case of transducers, it must be of a different resistive type i.e. the resistance of the transducers changes accordingly when the quality of temperature, strain, etc changes. Hence its proved that in place of the unknown resistor in the above resistance calculations we can also connect the transducer.

## Wheatstone Bridge for Temperature Measurement

## Wheatstone Bridge for Strain Measurement

## Applications

- For studying very low resistance values accurately the Wheatstone Bridge is used.
- Its also used for measuring the physical parameters like Temperature, Strain, light, etc when it’s placed next to the operational Amplifier.
- The variations on Wheatstone Bridge also help to measure quantities, capabilities, Inductance, and impedance.

### Conclusion

### About Author

#### Aizaz khan

Aizaz was the first person to get a byline on his blog on technology from his home in Bannu in 2017. Then, he went on to a career in breaking things professionally at my electric sparks which is where he eventually took over the kit as a hardware editor. Today, as the senior editor of hardware for my electric sparks, he spends time reporting about the most recent developments in the hardware industry and technology. If he’s not reporting on hardware or electronics, you’ll see him trying to be as remote from the world of technology as possible through camping in the wild.