Frequency Measurement MCQ Quiz - Objective Question with Answer for Frequency Measurement - Download Free PDF

Explanation:

• Electrical resonance frequency meter is used only for power frequency measurements and it is used in power systems for monitoring the frequencies
• Ratiometer type frequency meter us used up to a frequency of 5000 Hz
• Saturable core frequency meter can measure frequencies over a wide range and a specially well suited for use in tachometer systems
• Reed vibrator frequency meter is used for the measurement of low frequencies
• Heterodoxy frequency meter is suitable for the measurement of radio frequencies

Concept:

Lissajous patterns on a CRO are used to determine the frequency ratio of two sinusoidal signals. The ratio of frequencies is given by:

\( \frac{f_y}{f_x} = \frac{\text{Number of vertical tangencies}}{\text{Number of horizontal tangencies}} \)

Given

Number of vertical maximum values = 8

Number of horizontal maximum values = 4

Horizontal frequency (\( f_x \)) = 1600 Hz

Calculation

\( \frac{f_y}{1600} = \frac{8}{4} = 2 \)

\( f_y = 2 \times 1600 = 3200\ \text{Hz} \)

However, the number of vertical loops (or vertical maxima) is **8**, and horizontal is **4**, so:

\( \frac{f_x}{f_y} = \frac{8}{4} = 2 \Rightarrow f_y = \frac{f_x}{2} = \frac{1600}{2} = 800\ \text{Hz} \)

Concept:

The following is a procedure to measure the frequency of a Lissajous pattern obtained form CRO.

• For a given Lissajous figure, draw both horizontal and vertical lines passing through the Lissajous figure (Never draw either horizontal line (or) vertical line via pre-existing intersection in the Lissajous figure)
• Count the number of cuts made by both lines
• The unknown to known frequency ratio can be measured as follows.

\(\frac{{{f_v}}}{{{f_h}}} = \frac{{{n_h}}}{{{n_v}}}\)

Where

fv = unknown vertical frequency

fh = known horizontal frequency

nh = no. of cuts as made by horizontal line

nv = no. of cuts as made by a vertical line

Calculation:

From the given Lissajous figure,

n_v = 8

n_h = 10

The frequency ratio of the vertical signal to the horizontal signal is

\(\frac{{{f_V}}}{{{f_H}}} = \frac{{10}}{{{8}}} = \frac{5}{4}\)

Concept:

The following is a procedure to measure the frequency of a Lissajous pattern obtained form CRO.

• For a given Lissajous figure, draw both horizontal and vertical lines passing through the Lissajous figure (Never draw either horizontal line (or) vertical line via pre-existing intersection in the Lissajous figure)
• Count the number of cuts made by both lines
• The unknown to known frequency ratio can be measured as follows.

\(\frac{{{f_v}}}{{{f_h}}} = \frac{{{n_h}}}{{{n_v}}}\)

Where

fv = unknown vertical frequency

fh = known horizontal frequency

nh = no. of cuts as made by horizontal

nv = no. of cuts as made by a vertical line

Calculation:

From the given Lissajous figure,

Vertical tangencies (NV) = 2

Horizontal tangencies (NH) = 1

The frequency ratio of the vertical signal to the horizontal signal is

\(\frac{{{f_V}}}{{{f_H}}} = \frac{{{N_H}}}{{{N_V}}} = \frac{1}{2}\)

⇒ f_V = 30 Hz

According to the Nyquist criterion, f_s ≥ 2f_m is required to characterize the waveform

where f_s is the sampling frequency and

f_m is the maximum signal frequency

Given sampling frequency = 10⁸ samples per second = 100 MHz

The maximum frequency (in MHz) of a signal that can be monitored DSO

Given that,

Horizontal tangencies (n_H) = 3

Vertical tangencies (n_V) = 2

Horizontal frequency (f_H) = 3 kHz

n_Hf_H = n_Vf_V

\(\Rightarrow {f_V} = \frac{{{n_H}{f_H}}}{{{n_V}}} = \frac{{3 \times 3 \times {{10}^3}}}{2} = 4.5\;kHz\)

Concept:

Lissajous patterns on a CRO are used to determine the frequency ratio of two sinusoidal signals. The ratio of frequencies is given by:

\( \frac{f_y}{f_x} = \frac{\text{Number of vertical tangencies}}{\text{Number of horizontal tangencies}} \)

Given

Number of vertical maximum values = 8

Number of horizontal maximum values = 4

Horizontal frequency (\( f_x \)) = 1600 Hz

Calculation

\( \frac{f_y}{1600} = \frac{8}{4} = 2 \)

\( f_y = 2 \times 1600 = 3200\ \text{Hz} \)

However, the number of vertical loops (or vertical maxima) is **8**, and horizontal is **4**, so:

\( \frac{f_x}{f_y} = \frac{8}{4} = 2 \Rightarrow f_y = \frac{f_x}{2} = \frac{1600}{2} = 800\ \text{Hz} \)

Decibel Scale:

• A decibel scale is used for measuring voltage covering the wide frequency ratio.
• The decibel (dB) is used to measure sound level.
• It is also widely used in electronics, signals, and communication.
• The dB is a logarithmic way of describing a ratio.
• The ratio may be power, sound pressure, voltage or intensity, or several other things.

Explanation:

• Electrical resonance frequency meter is used only for power frequency measurements and it is used in power systems for monitoring the frequencies
• Ratiometer type frequency meter us used up to a frequency of 5000 Hz
• Saturable core frequency meter can measure frequencies over a wide range and a specially well suited for use in tachometer systems
• Reed vibrator frequency meter is used for the measurement of low frequencies
• Heterodoxy frequency meter is suitable for the measurement of radio frequencies

Concept:

The following is a procedure to measure the frequency of a Lissajous pattern obtained form CRO.

• For a given Lissajous figure, draw both horizontal and vertical lines passing through the Lissajous figure (Never draw either horizontal line (or) vertical line via pre-existing intersection in the Lissajous figure)
• Count the number of cuts made by both lines
• The unknown to known frequency ratio can be measured as follows.

\(\frac{{{f_v}}}{{{f_h}}} = \frac{{{n_h}}}{{{n_v}}}\)

Where

fv = unknown vertical frequency

fh = known horizontal frequency

nh = no. of cuts as made by horizontal line

nv = no. of cuts as made by a vertical line

Calculation:

From the given Lissajous figure,

n_v = 8

n_h = 10

The frequency ratio of the vertical signal to the horizontal signal is

\(\frac{{{f_V}}}{{{f_H}}} = \frac{{10}}{{{8}}} = \frac{5}{4}\)

Given that,

Horizontal tangencies (n_H) = 3

Vertical tangencies (n_V) = 2

Horizontal frequency (f_H) = 3 kHz

n_Hf_H = n_Vf_V

\(\Rightarrow {f_V} = \frac{{{n_H}{f_H}}}{{{n_V}}} = \frac{{3 \times 3 \times {{10}^3}}}{2} = 4.5\;kHz\)

Concept:

Lissajous patterns on a CRO are used to determine the frequency ratio of two sinusoidal signals. The ratio of frequencies is given by:

\( \frac{f_y}{f_x} = \frac{\text{Number of vertical tangencies}}{\text{Number of horizontal tangencies}} \)

Given

Number of vertical maximum values = 8

Number of horizontal maximum values = 4

Horizontal frequency (\( f_x \)) = 1600 Hz

Calculation

\( \frac{f_y}{1600} = \frac{8}{4} = 2 \)

\( f_y = 2 \times 1600 = 3200\ \text{Hz} \)

However, the number of vertical loops (or vertical maxima) is **8**, and horizontal is **4**, so:

\( \frac{f_x}{f_y} = \frac{8}{4} = 2 \Rightarrow f_y = \frac{f_x}{2} = \frac{1600}{2} = 800\ \text{Hz} \)

Concept:

The following is a procedure to measure the frequency of a Lissajous pattern obtained form CRO.

• For a given Lissajous figure, draw both horizontal and vertical lines passing through the Lissajous figure (Never draw either horizontal line (or) vertical line via pre-existing intersection in the Lissajous figure)
• Count the number of cuts made by both lines
• The unknown to known frequency ratio can be measured as follows.

\(\frac{{{f_v}}}{{{f_h}}} = \frac{{{n_h}}}{{{n_v}}}\)

Where

fv = unknown vertical frequency

fh = known horizontal frequency

nh = no. of cuts as made by horizontal line

nv = no. of cuts as made by a vertical line

Calculation:

From the given Lissajous figure,

n_v = 8

n_h = 10

The frequency ratio of the vertical signal to the horizontal signal is

\(\frac{{{f_V}}}{{{f_H}}} = \frac{{10}}{{{8}}} = \frac{5}{4}\)

Decibel Scale:

• A decibel scale is used for measuring voltage covering the wide frequency ratio.
• The decibel (dB) is used to measure sound level.
• It is also widely used in electronics, signals, and communication.
• The dB is a logarithmic way of describing a ratio.
• The ratio may be power, sound pressure, voltage or intensity, or several other things.

Low-frequency measurement in frequency mode gives low accuracy. So period measurement is used.

Note:

Frequency counter counts the number of times a signal passes a given voltage point or a zero-crossing point.

• It usually measures the number of cycles of oscillation i.e. time interval between two pulses.
• It also measures the pulse width of a signal.
• It can only measure the fundamental component of a signal, not a harmonic component.