# Difference btw Inductance measurement,Capacitance measurement

This page compares Inductance measurement vs Capacitance measurement and mentions difference between Inductance measurement and Capacitance measurement.

There are different techniques used for resistance, inductance and capacitance measurement. The equipments used for such measurements are known as digital LCR meter or digital impedance meter or digital multimeter. The meter used only for inductance measurement is known as inductance meter. The meter used only for capacitance measurement is known as capacitance meter.

## What is Inductance, Inductive Reactance

The inductance is basically property of AC (Alternating Current) circuits which oppose any change in the amount of current.
The unit of inductance is Henry.
If a current of value I Ampere is passed through coil of 'N' turns and if it generates magnetic field of say 'φ' webers,
then inductance is expressed as follows:

L = (N*φ)/I ...Henrys

The inductance is further categorized into self inductance and mutual inductance. When an AC causes emf to be developed in the coil itself, the phenomenon is referred as self inductance. When an AC causes emf to be developed in the secondary coil, the phenomenon is referred as mutual inductance.

The inductive reactance is the opposition offered by inductor to flow of AC passes through it.
It is measured in Ohm and expressed as follows.

X_{L} = 2*π*f*L

## What is Capacitance, Capacitive Reactance

The capacitance is basically property of AC circuits which oppose any change in amount of voltage.
The unit of capacitance is Farad. The other units are µF (Micro farad) and pF (Pico Farad).

1 µF = 10^{-6} F and 1 pF = 10^{-12} F

C = Q/V , which says if a voltage of 1 volt causes 1 coulomb of charge tobe accumulated in a capacitor then its
capacity is 1 farad.

The capacitive reactance is the opposition offered by capacitor to flow of AC passes through it.
It is measured in Ohm and expressed as follows.

X_{C} = 1/ (2*π*f*C )

## Simple A.C. Bridge

The figure-1 depicts simple AC bridge circuit. When null detector indicates zero, bridge is balanced and in this condition, voltage across a and b is zero. This means voltage across Z1 is equal to voltage across Z2. Moreover voltage across Z3 is equal to voltage across Z4. Voltages are equal both in magnitude as well as phase in order to have bridge as balanced.

General equation for bridge balance is as follows:

Z1'*Z4' = Z2'*Z3'

➨|Z1|*|Z4| = |Z2|*|Z3|

➨θ1 + θ4 = θ2 + θ3

This concept is used to determine unknown inductance as well as capacitance as explained below.

## Inductance measurement

The figure-2 depicts simple bridge circuit used for
**inductance measurement**. This bridge can be balanced by varying R1 and either
R3 or R4. At balance Z1/Z3 equals Z2/Z4.

➨ (R1+j*w*L1)/R3 = (Rs+j*w*Ls)/R4

➨Equating only real components, we get R1/R3 = Rs/R4; which gives,
Rs = R1*R4/R3

➨Equating imaginary components, we get w*L1/R3 = w*Ls/R4;
which gives, Ls = L1*R4/R3

Inductance meter utilizes this and other bridge circuits such as Maxwell bridge, Hay bridge, Anderson bridge, Owen bridge etc. for inductance measurement. There are digital inductance meters are also available for such measurements.

## Capacitance measurement

The figure-3 depicts simple bridge circuit used for **capacitance measurement**.
In this circuit, let us say Z1 is standard capacitor C1,
Z2 is unknown capacitance Cx, Z3 and Z4 are known variable resistors.

When bridge is balanced, Z1/Z3 = Z2/Z4.

➨ { (-j1/w*C1)/R3 } = { (-j1/w*Cx)/R4 }

➨ 1/(C1*R3) = 1/(Cx*R4)

➨ Cx = (C1*R3)/R4

Capacitance meter utilizes this and other bridge circuits such as De-sauty's bridge, Schering bridge, series resistance capacitance, parallel resistance capacitance for capacitance measurement. There are digital capacitance meters are also available for such measurements.

## Links to useful Measurements

Following are the links to other useful measurements available on Test and Measurement World website.

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Current measurement vs Voltage measurement

Inductance measurement vs Capacitance measurement

Difference between Power and Energy measurements

EMC measurement vs EMI measurement

Electric and Magnetic Field Measurements

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