What is Digital Frequency Meter and Its Working

An electric signal can be represented as a sinusoidal waveform, where each wave has a positive edge and a negative edge. The basic parameters for measuring the strength of the wave is amplitude and frequency, where the amplitude is the maximum vibration taken from an equilibrium position of a sinusoidal wave and frequency is the reciprocal of the time period. Frequency can be measured using different types of frequency meters like deflection type which can measure frequency in the range of lower frequencies to 900Hz, Weston frequency meter which is usually not deflection type, it can measure frequency in the range 10 to 100Hz, and the advance frequency meter named digital frequency meter, which can measure the approximate value of frequency in binary digit form up to 3 decimals and displays on the counter. The advantage of these kinds of frequency meter is that they can measure the lower value of frequency.

What is Digital Frequency Meter?

Definition: A digital frequency meter is an electronic instrument that can measure even the smaller value of frequency up to 3 decimals of a sinusoidal wave and displays it on the counter display. It counts the frequency periodically and can measure in the range of frequencies between 104 to 109 hertz. The entire concept is based on the conversion of sinusoidal voltage into continuous pulses ( 01, 1.0, 10 seconds) along a single direction.


Frequency-Wave
frequency-wave

Construction of Digital Frequency Meter

The main components of digital frequency meter are

Unknown Frequency Source: It is used to measure the unknown value of input signal frequency.

Amplifier: It amplifies low-level signals to high-level signals.

Schmitt Trigger: The main purpose of the Schmitt trigger is to convert the analog signal into a digital signal in a pulse train form. It is also known as ADC and basically acts as a comparator circuit.

PCBWay

And Gate: The generated output from AND gate is obtained only when the inputs exist at the gate. One of the terminals of the AND gate is connected to Schmitt Trigger output, and another terminal is connected to a flipflop.

block-diagram
block-diagram

Counter: It operates based on the clock period, which starts from “0”. One input is taken from the output of the AND gate. The counter is constructed by cascading many flip flops.

Crystal Oscillator: When a DC supply is given to a crystal oscillator (frequency of 1MHz) it generates a sinusoidal wave.

Time-Based Selector: Depending on reference the time period of signals can be varied. It consists of a clock oscillator which gives an accurate value. The clock oscillator output is given as input to Schmitt trigger which converts sinusoidal wave into a series of a square wave of the same frequency. These continuous pulses are sent to frequency divider decade which is in series that are connected one after the another, where each divider decade consists of a counter decade and the frequency is divided by 10. Each decade frequency divider provides respective output using a selector switch.

Flip Flop: It provides output based on input.

Working Principle

When an unknown frequency signal is applied to the meter it passes on to amplifier which amplifies the weak signal. Now the amplified signal is now applied to Schmitt trigger which can convert input sinusoidal signal into a square wave. The oscillator also generates sinusoidal waves at periodic intervals of time, which is fed to Schmitt trigger. This trigger converts sin wave into a square wave, which is in the form of continuous pulses, where one pulse is equal to one positive and one negative value of a single signal cycle.

The first pulse which is generated is given as input to the gate control flip flop turning ON AND gate. The output from this AND gate count decimal value. Similarly, when the second pulse arrives, it disconnects AND gate, and when the third pulse arrives the AND gate turns ON and the corresponding continuous pulses for a precise time interval which is the decimal value is displayed on the counter display.

Formula

The frequency of the unknown signal can be calculated by the following formula

F = N / t …………………..(1)

Where

F =frequency of the unknown signal

N = Number of counts displayed by the counter

t = time interval between the start-stop of the gate.

Advantages

The following are the advantages of digital frequency meter

  • Good frequency response
  • High sensitivity
  • The production cost is low.

Disadvantages

The following are the disadvantages

  • It does not measure the exact value.

Digital Frequency Meter Applications

The following are the applications

  • The equipment’s like radio can be tested using a digital frequency meter
  • It can measure parameters like pressure, strength, vibrations, etc.

FAQs

1). Define is Frequency?

A frequency is the reciprocal of the time period. It is given by “F = 1/T”.

2). Define is Amplitude?

Amplitude is the maximum vibration taken from the equilibrium position of a sinusoidal wave. It is denoted by “ A ”.

3). What are the different types of digital frequency meter?

There are different types of frequency meter like

  • Deflection type which can measure lower frequencies to 900Hz,
  • Weston frequency meter usually not deflection type, which can measure frequency in the range 10 to 100Hz,
  • An advance meter named digital frequency meter can measure in the range of 104 to 109 hertz.

4). What are the components of the digital frequency meter?

The main components of digital frequency meter are

  • Unknown frequency source
  • Amplifier
  • Schmitt Trigger
  • AND gate Trigger,
  • Counter,
  • Crystal oscillator,
  • time-based selector.

5). At what range does digital frequency meter measure?

Digital frequency meter can measure in the range of 104 to 109 hertz.

6). What is the use of Schmitt Trigger in a digital frequency meter?

The main purpose of Schmitt’s trigger is to convert an analog signal into digital signals in a pulse rating form. It is also known as ADC and it acts as a comparator circuit.

A frequency meter is used to measure the value of the frequency of a periodic signal. There are different types of frequency meters to measure frequency like Deflection type, Weston frequency meter, digital frequency meter. This article gives an overview of digital frequency meter which can measure smaller values of frequency in the range of 104 to 109 hertz. Every component of digital frequency meter has its own function, where the entire concept is based on converting the sinusoidal signal into a square wave and the AND gate turning ON and OFF based on the arrived signal at its input, which is used to determine the unknown value of frequency. The main advantage of this is it can measure smaller values of frequency.

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