Q Meter MCQ Quiz - Objective Question with Answer for Q Meter - Download Free PDF

Explanation:

Q-Meter

Definition: A Q-meter is an instrument used to measure the electrical properties of inductors and capacitors, specifically focusing on the quality factor (Q) of a circuit. The quality factor is a measure of the sharpness of resonance in a circuit and is mathematically defined as the ratio of the reactive power to the resistive power in the circuit. The Q-meter is primarily based on the principle of a series resonant circuit, where the resonance condition is utilized to calculate the Q-factor and other related parameters.

Working Principle: The Q-meter operates based on the characteristics of a series resonant circuit. In a series resonant circuit, resonance occurs when the inductive reactance (XL) and capacitive reactance (XC) cancel each other out, leaving only the resistive component to determine the circuit's impedance. At resonance, the current in the circuit reaches its maximum value, and the voltage across the inductor or capacitor becomes significantly larger than the applied voltage. This property is exploited in the Q-meter to measure the Q-factor and other parameters of the circuit or component under test.

Advantages of Series Resonant Circuit in Q-Meter:

• High Sensitivity: At resonance, the current in the circuit is maximized, making it easier to measure small variations in circuit parameters accurately.
• Direct Measurement: The Q-factor can be directly calculated using the voltage readings across the inductor or capacitor and the applied voltage.
• Simplicity: The series resonant circuit is simple in design and easy to implement in a Q-meter.

Applications of Q-Meter:

• Measurement of the Q-factor of inductors and capacitors.
• Determination of inductance and capacitance values.
• Testing and characterization of RF and microwave components.

Correct Option Analysis:

The correct option is:

Option 3: Series resonant circuit

This option is correct because the Q-meter relies on the properties of a series resonant circuit to measure the quality factor and related electrical parameters. At resonance, the impedance of the series circuit is purely resistive, and the current reaches its maximum value, enabling accurate measurement of the Q-factor and other parameters.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 1: Shunt resonant circuit

This option is incorrect because the Q-meter does not rely on the principles of a shunt resonant circuit. In a shunt resonant circuit, the components (inductor and capacitor) are connected in parallel, and the resonance condition results in a minimum impedance. This configuration is not suitable for Q-meters, which require the maximum current condition achieved in a series resonant circuit.

Option 2: Series-parallel circuit

This option is incorrect because a series-parallel circuit involves a combination of series and parallel connections of components, which complicates the resonance condition. The Q-meter specifically uses the simpler and more effective series resonant circuit to achieve accurate measurements.

Option 4: Inductive reactance circuit

This option is incorrect because an inductive reactance circuit alone does not provide the resonance condition required for the Q-meter's operation. The Q-meter relies on the cancellation of inductive reactance and capacitive reactance in a series resonant circuit to achieve accurate measurements.

Conclusion:

In summary, the Q-meter is a specialized instrument that utilizes the characteristics of a series resonant circuit to measure the quality factor and other electrical properties of inductors and capacitors. The series resonant circuit is ideal for this application due to its high sensitivity and simplicity. By understanding the principles of resonance and the operation of the Q-meter, engineers and technicians can accurately measure and analyze the electrical properties of various components and circuits.

Q - METER:

Q meter is an instrument that is designed to measure the value of quality factor directly and it is useful in measuring the characteristics of coils and capacitors.

Important:

• Q meter works on the principle of series resonance.
• At series resonance, the voltage across the capacitor is equal to Q times of applied input voltage. Thus, we can measure the value of Q directly by connecting a voltmeter across capacitors.
• It is used for the measurement of properties of the coils such as quality factor, inductance, self-capacitance, inductance, bandwidth and capacitance of a coil.

Concept:

Q - METER:

Q meter is an instrument that is designed to measure the value of quality factor directly and it is useful in measuring the characteristics of coils and capacitors.

Important:

• Q meter works on the principle of series resonance.
• At series resonance, the voltage across the capacitor is equal to Q times of applied input voltage. Thus, we can measure the value of Q directly by connecting a voltmeter across capacitors.
• It is used for the measurement of quality factor, inductance, self-capacitance, inductance, bandwidth and capacitance of a coil.

Concept:

Q-meter is an instrument used for the measurement of the Q-factor of the coil as well as for the measurement of self-inductance, self-capacitance and resistance. There are three methods to connect the unknown impedance to the testing terminals of the Q-meter:

1. Direct Connection
2. Series Connection
3. Parallel Connection

Parallel Connection of Q-meter:

In a parallel connection, the unknown impedance/coil is connected in parallel with the tuning circuit as shown in the figure below.

Measurement procedure:

1. Before connecting the unknown impedance, the circuit is resonated and we get the values of the tuning capacitor and Q-meter as C₁ and Q₁ respectively.
2. After connecting the unknown impedance, the circuit is resonated and we get the values of the tuning capacitor and Q-meter as C₂ and Q2 respectively.

Results:

Solving using resonance equations, we get

\(R_p = {Q_1Q_2 \over \omega C_1(Q_1-Q_2)}\) and \(X_p = {1 \over \omega (C_1-C_2)}\)

Hence, Q of the unknown coil is obtained as

\(Q_p = {R_p \over X_p} = {{(C_1-C_2)Q_1Q_2} \over C_1(Q_1-Q_2)}\)

\(Q_p = {{(C_1-C_2)Q_1Q_2} \over C_1(\Delta Q)}\)

Additional Information

Series Connection of Q-meter:

Using the resonance conditions before and after connecting the load impedance, we get

\(R_s = {C_1Q_1-C_2Q_2 \over \omega C_1C_2Q_1Q_2}\) and \(X_s = {C_1-C_2 \over \omega C_1C_2}\) 

Hence,

\(Q_s = {X_s \over R_s} = {{(C_1-C_2)Q_1Q_2} \over C_1Q_1-C_2Q_2}\)

Q-meter:

• Q meter is an instrument that is designed to measure the value of quality factor directly and it is useful in measuring the characteristics of coils and capacitors.
• Q meter works on the principle of series resonance.
• The Q-meter is based on the characteristic of the resistance, inductance, and capacitance of the resonant series circuit and is independent of the conductance of the coil.

​The quality factor for a Q-meter is given by:

\(QF = {X_L \over R}\)

\(QF = {ω L \over R}\)

where, QF = Quality factor

ω = Frequency

L = Inductance

R = Resistance

Q meter is an instrument which is designed to measure the value of quality factor directly and it is useful in measuring the characteristics of coils and capacitors.

Important:

• Q meter works on the principle of series resonance.
• At series resonance, the voltage across capacitor is equal to Q times of applied input voltage. Thus, we can measure the value of Q directly by connecting a voltmeter across capacitor.
• It is used for the measurement of quality factor, inductance, self-capacitance, inductance, bandwidth and capacitance of a coil.

• Q meter is an instrument that is designed to measure the value of quality factor directly and it is useful in measuring the characteristics of coils and capacitors.
• Q meter works on the principle of series resonance.
• At series resonance, the voltage across the capacitor is equal to Q times of applied input voltage. Thus, we can measure the value of Q directly by connecting a voltmeter across the capacitor.
• It is used for the measurement of the quality factor, inductance, self-capacitance, inductance, bandwidth, and distributed capacitance of a coil.

Q meter is an instrument which is designed to measure the value of quality factor directly and it is useful in measuring the characteristics of coils and capacitors.

Important:

• Q meter works on the principle of series resonance.
• At series resonance, the voltage across capacitor is equal to Q times of applied input voltage. Thus, we can measure the value of Q directly by connecting a voltmeter across capacitor.
• It is used for the measurement of quality factor, inductance, self-capacitance, inductance, bandwidth and capacitance of a coil.

Concept:

• Q-meter works on the principle of resonance.
• At series resonance, the voltage across the capacitor is equal to Q times of applied input voltage. Thus, we can measure the value of Q directly by connecting a voltmeter across the capacitor.
• Q meter is an instrument that is designed to measure the value of quality factor directly and it is useful in measuring the characteristics of coils and capacitors.
  XL = XC   Or  VL = VC
  Q factor of Q-meter is given as:
  \(Q=\frac{V_C}{V}\)
  Where,
  VC = Voltage across capacitor
  V = Total applied voltage

• Variable calibrated capacitor C and its voltage(VC) is measured by Electronic Voltmeter.
• Variable frequency AC voltage source which is generated by the oscillator and measured by Thermocouple Voltmeter.
• Coil to be tested or measured is connected as tank circuit i.e. a capacitor Cd is connected across an unknown coil which is in series with negligible resistance R.

Impedance Measurement Using Q Meter:

• An unknown impedance can be measured using a Q meter, either by series or shunt substitution method.
• If the impedance to be measured is small, the former is used and if it is large the later method is used.

Concept:

Q-meter works on the principle of resonance i.e.

X_L = X_C   Or  V_L = V_C

Q factor of Q-meter is given as:

\(Q=\frac{V_C}{V}\)

Where,

V_C = Voltage across capacitor

V = Total applied voltage

Calculation:

V = 500mV

V_C = 10V

\(Q=\frac{V_C}{V}\)

\(Q=\frac{10}{500\times10^{-3}}\)

Q = 20

Heaviside bridge:

• Heaviside bridge is used to measure the mutual inductance.
• The bridge which measures the unknown mutual inductance regarding mutual inductance such type of bridge is known as the Campbell bridge.
• Mutual inductance is the phenomenon in which the variation of current in one coil induces the current in the nearer coil.
• The bridge also used for measuring the frequency by adjusting the mutual inductance until the null point is not obtained.

Important Points

Q-meter:

• Q meter is an instrument that is designed to measure the value of quality factor directly and it is useful in measuring the characteristics of coils and capacitors.
• Q meter works on the principle of series resonance.
• The Q-meter is based on the characteristic of the resistance, inductance, and capacitance of the resonant series circuit and is independent of the conductance of the coil.

​The quality factor for a Q-meter is given by:

\(QF = {X_L \over R}\)

\(QF = {ω L \over R}\)

where, QF = Quality factor

ω = Frequency

L = Inductance

R = Resistance

Q - METER:

Q meter is an instrument that is designed to measure the value of quality factor directly and it is useful in measuring the characteristics of coils and capacitors.

Important:

• Q meter works on the principle of series resonance.
• At series resonance, the voltage across the capacitor is equal to Q times of applied input voltage. Thus, we can measure the value of Q directly by connecting a voltmeter across capacitors.
• It is used for the measurement of quality factor, inductance, self-capacitance, inductance, bandwidth and capacitance of a coil.

LCR meter:

• An LCR meter is electronic test equipment used to measure the inductance (L), capacitance (C), and resistance (R) of an electronic component.
• It actually measures impedance internally and converted for a display to the corresponding capacitance or inductance value.
• It gives accurate readings if the inductor or capacitor device under test does not have a significant resistive component of impedance.
• An LCR meter can also be used to measure the inductance variation with respect to the rotor position in permanent magnet machines.

Operation:

Generally, the device under test is subjected to an AC voltage source. The meter measures the voltage across and the current through the device under test. From the ratio of these the meter can determine the magnitude of the impedance. The phase angle between the voltage and current is also measured in more advanced instruments, in combination with the impedance the equivalent capacitance or inductance, and resistance of the device under test can be calculated and displayed.

Important points:

• The automatic bridge balance method is is a circuit design that is used in the LCR meter.
• These can be easily operated, it can measure passive components with minimal error.
• By the use of an LCR meter, we can also measure parameters like dissipation factor, quality factor, conductance, susceptance.

Q - METER:

Q meter is an instrument that is designed to measure the value of quality factor directly and it is useful in measuring the characteristics of coils and capacitors.

Important:

• Q meter works on the principle of series resonance.
• At series resonance, the voltage across the capacitor is equal to Q times of applied input voltage. Thus, we can measure the value of Q directly by connecting a voltmeter across capacitors.
• It is used for the measurement of properties of the coils such as quality factor, inductance, self-capacitance, inductance, bandwidth and capacitance of a coil.