What is a Weston Type Frequency Meter & Its Working

Electric power systems comprise the networks of electrical components, which supply, transfer, deploy the electric energy when required. Power Systems can be classified into two types like AC power systems and DC power systems.AC power system runs efficiently based on the frequency parameter. This frequency parameter can be measured using a device named frequency meter, which displays the value of the periodic electric signal in frequency form on the display. There are 3 types of frequency meters they are, electrical resonance frequency meter (like Ferro dynamic type frequency meter, electrodynamometer type frequency meter), Weston type frequency meter, and ratiometer type frequency meter. This article explains about Weston type frequency meter.

What is a Weston Type Frequency Meter?

Definition:  Weston type frequency meter is based on the principle of the deflection, where the unknown value of the frequency of an input signal can be determined using this meter. It consists of 2 main coils they are, inductive coil and resistive coil. The current in these coils changes, whenever the signal frequency deviates from known frequency.


Different Types of Frequency Meters

The different types of Frequency meters are

  • Electrical resonance frequency meter
  • Ratiometer type frequency meter

Electrical Resonance Frequency Meter

It is based on the principle of electrical resonance, that is when inductive reactance XL and capacitive reactance XC becomes equal then the circuit is said to be at electrical resonance.

Ratiometer Type Frequency Meter

It consists of a ratio meter, which shows the relationship between current ration and their reflections. The main advantage of the radiometer type frequency meter is that the deflected pointer and the measured frequency exhibits a linear relationship. It can measure up to 5KHz.

Working Principle of Weston Type Frequency Meter

Weston type frequency meter works when the current is passed through 2 coils that are 90 degrees to one another. This flow of current generates some magnetic field and thus deflecting the needle towards a higher magnetic field.  This needle indication is a representation of the unknown frequency of the signal.

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Construction

Weston type frequency meter construction is as follows

It consists of 2 coils inductive coil and resistive coil, which are the right angle to one another. The 2 pairs, resistor RA, and coil A and inductor LA and coil B pair are placed in series, other pairs, LA and coil A, and RB, and coil B are placed parallelly.

Weston Frequency Meter
Weston Frequency Meter

The meter consists of a soft pointer made up of iron and a magnetic needle which is placed at the center. The inductor “L” connected is in series with “LA and RB ” minimizes the errors.

Working of Weston Type Frequency Meter

  • Case1: On applying current to the circuit, it flows through the 2 perpendicular coils, coil A & coil B. Thereby setting up the magnetic field, where the field magnitude is directly proportional to its current in the coil.
  • The coil A & coil B magnetic fields act on the magnetic needle as well as on soft iron, where the position of the needle is based on the magnetic fields, and the relative magnitude that acts on it.
  • Case2: At the condition where the normal frequency is applied to the meter, there will be a voltage drop in resistance and reactance, LA, and RB of the same magnitude. This results in an equal flow of current through the coils A and B.
  • The circuit is designed in a proper manner that the voltage drop remains the same across LA, LB RA, RB, whenever normal frequency is passed. This allows the magnetic needle pointing at 45 degrees concerning, both coils and soft iron needle pointing at the center.
  • Case3: Whereas on passing high-frequency trough the circuit, there will be an increase in reactance LA and LB of the coil, and the resistances on another side  RA, RB, remain the same. In other words, the inductance increases the impedance of the coil A, and if the current magnitude in coil A decreases, the field developed due to coil A current also decreases.
  • We can observe that more current follows in coil B than coil A, since coil B is connected parallelly. Hence coil B has a stronger magnetic field compared with coil A, and the pointer moves towards the strongest magnetic field that is coil B.
  • Finally, the frequency which is to be determined reduces from its normal value, and the pointer indicates the value of unknown frequency towards the left side.

Advantages

The following are the advantages

  • Highly sensitive
  • Construction is simple
  • The frequency scale is linear
  • Readings are independent of voltages
  • It is suitable for measuring a wide range of voltage.

Disadvantages

The following are the disadvantages of Weston frequency meter

  • Sensitive to temperature variation
  • The presence of rectifiers results in distortion producing inaccurate frequency output.

Applications

The following are the applications

  • Used for testing radio equipment’s
  • Used for measuring transducers.

A frequency meter is a device that is used to measure the unknown frequency of a given signal. There are 3 types of frequency meter they are, electrical resonance frequency meter (like Ferro dynamic type frequency meter, electrodynamometer type frequency meter), Weston type frequency meter, and ratiometer type frequency meter. A Weston type frequency meter is based on the principle of deflection. It consists of 2 coils, that are resistive coil and inductive coil. The current in the coil’s changes, whenever the signal frequency deviates from standard frequency. The deflection of the pointer will move towards a higher magnetic field. Weston type frequency meter is suitable for measuring a wide range of voltages.

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