Basics of Wheatstone Bridge

In the year 1833, Samuel Hunter Christie invented the Wheatstone bridge. But in the year 1843, the device became popular when Sir Charles Wheatstone started working on it. Wheatstone bridge is the most widely used device because the accuracy with its measurement of resistance is very good. The initial use of the Wheatstone bridge was for analysing and comparing the soils.

What is a Wheatstone bridge?

Wheatstone bridge is defined as the device which is used for the measurement of minimum resistance by comparing the resistance known resistance with the unknown resistance.

Elements of Wheatstone bridge

Wheatstone bridge consists of elements as listed below:

• A resistor with an unknown resistance value.
• Two resistors with known resistance value.
• A variable resistor such as rheostat.
• A DC source.
• Connecting wires.

Applications of Wheatstone bridge

Following are the applications of Wheatstone bridge:

• It is used for measuring very low resistance values with more precision.
• Physical parameters such as temperature, light, and strain can be measured using the Wheatstone bridge.
• Other quantities such as capacitance, impedance, and inductance can be measured using the Wheatstone bridge.

Even Wheatstone bridge has flaws and they are discussed further in the article.

Flaws in Wheatstone bridge

• The error in measurement is a result of the difference in true and mark value of the three resistances.
• Inaccuracy is found in the balance point, as the galvanometer is less sensitive.
• Errors are generated because of the self-heating of the resistance.
• Low-value resistance cannot be measured due to thermal emf.
• The errors in galvanometer occur either because of taking a reading or by finding the null point.

The above-mentioned flaws can be rectified by using good quality resistors and galvanometer. By connecting a reversing switch between the battery and bridge, the thermal effect can be reduced. Also, by measuring the resistance within a short period of time, the self-heating can be decreased.

Limitations of Wheatstone bridge

• When there are unbalanced conditions, the reading might be inaccurate.
• The range of the measured resistance is between ohms to megaohms.
• There is no susceptibility for high DC current.

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