Q meter ppt

Overview on Q Meter

1. Govt. Engineering College Ajmer Electronics & Communication EC-4 Submitted By Submitted To Pushkar Singh

2. An Overview Q-METER(RLC METER)

3. INTRODUCTION Q meter is design for measuring the Q factor of a coil and for measuring inductance, capacitance and resistance of an electric circuit at radio frequency. It is also known as RLC meter. A direct-reading instrument which measures the Q of an electric circuit at radio frequencies by determining the ratio of inductance to resistance, and which has also been developed to measure many other quantities. Also known as quality-factor meter.

4. Inductors, capacitors and resisters which have to operate at radio frequencies cannot be measured satisfactorily at lower frequencies. Inductors, capacitors and resisters which have to operate at radio frequencies cannot be measured satisfactorily at lower frequencies. The resonance methods are employed in which the unknown component may be tested at or near its normal operating frequency. We know that every inductor coil has a certain amount of resistance and the coil should have lowest possible resistance. The ratio of the inductive reactance to the effective resistance of the coil is called the quality factor   or Q-factor of the coil. Q = X L  / R = ωL / R

5. Q meter Tesla BM 560

6. Benchtop LCR meter with 4-wire ( Kelvin sensing ) fixture

7. CONSTRUCTION Q meter consist of the following major elements: Variable calibrated capacitor Variable –frequency ac voltage source Coil to be tested or measured All elements are connected in series . The capacitor voltage ( Vc ) and the source voltage ( E) are monitored by voltmeters. One terminal of the coil is connected to the signal generator (Ac voltage source) while the other terminal is connected to the variable capacitor.

8. WORKING PRINCIPLE The operations of this useful laboratory instrument is based on the familiar characteristics of a series-resonant circuit, namely, that the voltage across the coil or the capacitor is equal to the applied voltage times the Q of the circuit. If a fixed voltage is applied to the circuit, a voltmeter across the capacitor can be calibrated to read Q directly. VC = VL and I=E/R

9. CIRCUIT DIAGRAM Volt meter 1 shows the source voltage(E) Volt meter 2 shows voltage across variable capacitor Inductor and resister combine shows coil

10. OPERATION First of all The oscillator is set to the desired frequency Then  the tuning Capacitor is adjusted for maximum value under this condition and if the voltage is kept constant the voltmeter connected across the capacitor may be calibrated to read the value of Q directly. This measures value of Q in commonly regarded as the Q of the coil under test.

11. There is an error. The measured value of Q is the Q of the whole circuit and not of the coil. Thus the measured value of Q is smaller than the true value. Coils of high resistance are being measured the difference between the two value may be negligible but when measurements are done on low resistance coils, the error caused on this account may be serious. VC= VL and I = E/R Q = ω L/R =1/ ω CR Q=VL/E =VC/E

12.   APPLICATIONS OF A Q-METER The Q meter can be used for many purposes. As the name implies, it can measure Q and is generally used to check the Q factor of inductors. Unknown impedance can be measured using Q-meter, either by series or shunt substitution method. IF the impedance to be measured is small, the former is used and if its large, the latter method is used Characteristic impedance of a transmission line can be measured using series substitution method

13. Measurement of quality factor involving comparison of inductances and capacitances. Another use of the Q meter is to measure the value of small capacitors. The capacitor sample is resonated with a selected inductor by adjusting the source frequency and using the tuning capacitor set to a low value on its calibrated scale.

14. Thank You