This article provides detailed information about Frequency
Meters and Types of Frequency Meters, Electrical Resonance Frequency Meter,
Mechanical Resonance Frequency Meter, Weston Frequency Meter, and Digital
Frequency Meter. Also, the structure, working principle, working method, and
benefits of all these instruments are explained.
Frequency Meters
Frequency meters are meters that are used to directly
measure the frequency of power circuits. The meters or instruments used are
called frequency meters. Such frequency meters are designed to measure the
frequency of electronic circuits. Which can measure very high frequencies.
Because the frequency range in electronics circuits can be up to several
megahertz. Electrical circuits have a very low-frequency range (25c/s to 60c/s).
Each country's power system has its standard frequency. The standard frequency
s 50c / s / 600 is being used in most countries. The standard frequency of the
power system in Pakistan is 50c/s±1%.
Types of Frequency Meters
- Electrical Resonance Frequency Meters
- Mechanical Resonance Frequency Meters
- West or Moving Iron Frequency Meters
- Ratio Type Frequency Meters
- Digital Frequency Meters
Electrical Resonance Frequency Meters
Working Principle
Electrical resonance frequency meter, frequency meter works
based on the principle of electrical resonance. Teaching frequency in an AC
circuit increases the inductive activity "XL". While the
capacitor activity "XC" is low. The special frequency at
which the XL and XC of the circuit are equal is called
electrical resonance. And the frequency at which the resonance occurs is called
the frequency correlation frequency. The movement of the moving coil in the
electrical resonance frequency meter changes its XL.
Construction
The structure of this instrument is shown in the figure
below. This instrument consists of a fixed or magnetizing coil and a moving
coil. The magnetizing coil is winded with a single wire bar at one end of a
curved laminated core. This coil is connected parallel to this supply. The
frequency of which has to be measured. The second moving coil is pivoted near
the core of the fixed coil in such a way that when the torque acts on it, it
can be near or far from the fixed coil. A pointer with a peanut coil is also a
fix. Indicates the relative value of the frequency by moving on the scale
calibrated in the frequency. Unlike moving coil power factor meters, it also
does not have control torque. There is also a capacitor of appropriate value
parallel to the moving coil.
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| Frequency Meter |
Working Method
This meter contains different quantities of the value supply
frequency of the moving coil castor action (CX). Because the moving
coil is not directly connected to the supply. But its inductance varies
depending on the movement of the value moving coil of inductive reactance (XL).
As the moving coil gets closer to the fixed coil its inductance activity
increases and when the moving coil moves away from the fixed coil (magnetic
tying coil) its value of XL decreases. When the fixed coil is
connected to the supply, a current I starts running in it. Due to this current, a flux ɸ
runs in the iron core. Which is in the phase of the current. Due to this flux,
a voltage (e) is induced in the moving coil. These voltage fluxes are leaking
from ɸ
to 90.
The current flowing due to voltage (e) in the moving coil
can also lead to its voltage α angle. And this α
angle can also be leading. As shown in Figures a and b. Angle α
Refers to the phase angle between the voltage (e) and current generated in the
moving coil. The value of angle α depends on whether the inductance of
the moving coil is high or the capacitance is high. (Because the inductance of
the moving coil may vary depending on its position.) The torque coming on the
coil (90±
α) is directly proportional to i.Cos, i.e. the torque depends on the
angle α.
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| Angle Working Method |
Advantages
- This instrument can be made very sensitive to different amounts of frequency.
- They are simple in structure.
- Don't use too much power.
Mechanical Resonance Frequency Meters
Mechanical resonance frequency meters are also called
vibration radio frequency meters. Because the leaves in it show the
corresponding frequency by vibrating.
Working Principle
The working principle of the mechanical resonance frequency
meter is based on the mechanical resonates of the fine particles. And all the
leaves try to tremble. But most of them are vibrations that have a natural mechanical
frequency that matches the frequency of the magnetic field.
Construction
These instruments are very simple in structure. They contain
an electromagnet. It is made by winding a steel bar on a single laminated iron
core and winding a copper bar with a single wire. A resistor is attached to the
series and it is connected to the supply sides (Across). And the frequency is
determined. In this sense, the external connections of this meter are like a
voltmeter. Numerous steel sheets or reeds on one side of the core are fixed in
a line along with a base plate. These metal sheets are about 4 mm wide and 0.5
mm thick. These leaves are not the same but their length and width are slightly
different. They have weights or flags of different values on their upper
ends.
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| Construction/Parts |
Digital Frequency Meters
Like other digital instruments, digital frequency meters
have many advantages over analog frequency meters (mentioned earlier). (Details
can be found in the Digital Instruments chapter). For example, they are free
from parallax error, zero adjustments, and the position of use. They are more
sensitive, more accurate, and have higher resolution. In addition, they are
light in weight and smart, use less power, and set their polarity and range.
Digital signals can be further processed.
Explanation & Working Principle
The figure shows the block diagram of a digital frequency
meter. The basic working method of this meter is to determine the frequency of
the supply source. The units of this supply are converted into Train of Pulses
through a special type of trigger circuit. A pulse is formed from one cycle of
supply. In this way, the supply sine wave cycles are converted to square wave
pulses in the shape shown on Sine (Wave Cycles). Therefore these square wave
pulses are considered as alternatives to the supply cycle. These pulses
appearing are counted by an electronic counter, and the supply frequency is
displayed directly on the screen in decimal geometric form. In the block
diagram shown, the source indicates the frequency to be determined.
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| Digital Frequency Meter Diagram |
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