2. What is Q –Meter ?
• 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.
3. Introduction
• 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 th e
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 = XL / R = ωL / R
4. 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.
5. Circuit diagram
Volt meter 1 shows the source voltage(E)
Volt meter 2 shows voltage across variable capacitor
Inductor and resister combine shows coil
6. 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
7. 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.
.
8. Operation
• 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 =ωL/R =1/ωCR
Q=VL/E =VC/E
This template can be used as a starter file for presenting training materials in a group setting.SectionsRight-click on a slide to add sections. Sections can help to organize your slides or facilitate collaboration between multiple authors.NotesUse the Notes section for delivery notes or to provide additional details for the audience. View these notes in Presentation View during your presentation. Keep in mind the font size (important for accessibility, visibility, videotaping, and online production)Coordinated colors Pay particular attention to the graphs, charts, and text boxes.Consider that attendees will print in black and white or grayscale. Run a test print to make sure your colors work when printed in pure black and white and grayscale.Graphics, tables, and graphsKeep it simple: If possible, use consistent, non-distracting styles and colors.Label all graphs and tables.
Give a brief overview of the presentation. Describe the major focus of the presentation and why it is important.Introduce each of the major topics.To provide a road map for the audience, you can repeat this Overview slide throughout the presentation, highlighting the particular topic you will discuss next.
This is another option for an Overview slides using transitions.
