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How do you measure Q? (how to measurement of Q)

Hello friends, in this article we will know what is Q? And how is it measured (measurement of Q)? Learn about the different methods of connecting electrical components using a Q meter. And learn about many facts related to it.


Measurement of Q

Video Frequency Coils (RFC), inductors And at the time of testing the capacitors in the laboratory, their storage factor or quality factor Q is often measured. Storage factor Q = of a coil0is L/R where0, the resonance frequency, L is the inductance and R is its effective resistance. The effective resistance R of a coil is never measured directly because its value depends on the frequency.


The value of effective resistance is different on AC and DC because there is also skin effect and Eddy current effect on ac. Due to the change in the value of resistance R with frequency, it is measured indirectly in terms of Q. The instrument used for measuring Q is called Q-meter.



Measurement of Q

A simple block diagram of a Q-meter is given in the figure. The principle of Q-meter is based on resonance in RLC series circuit. An oscillator is used in the instrument, whose frequency range is from 50KHz to 50MHz. A resonating capacitor C with unknown impedance is applied. Resonance in a circuit is produced by changing the frequency of the oscillator or by changing the capacitance of the capacitor.


The operation of a Q-meter is based on the characteristics of a series-resonant circuit, for example, the voltage across the coil or capacitor ends is equal to the product of the voltage applied to the circuit and the Q of the circuit. If a fixed voltage is applied to the circuit, then a voltmeter connected across the terminals of the capacitor can be calibrated directly for measurement of Q.

In the measurement of unknown components (L, C, R) by a Q meter, there are three ways to connect the components –


  1. Direct Method
  2. Series Method
  3. Parallel Method

The method of connection depends on the type and size of the component.


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