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BASICS ON VIBRATING FORK LEVEL SWITCH

by Ragini Salampure
BASICS ON VIBRATING FORK LEVEL SWITCH

A vibrating fork level switch is otherwise known as a tuning fork switch and rod sensor. It is a low maintenance mechanical device, which works on the tuning fork principle and provides a point level detection; it ensures control over the material in question through constant monitoring. 

They are reliable in terms of preventing overfilling and ensure pump protection of the tank. A typical vibrating fork level switch contains two interconnected forks, which vibrate at their natural frequency. There will be variations in vibration, according to the medium one immerses it in. These forks vibrate at their natural frequency when they are free. 

This frequency will fluctuate when it comes into contact with any medium. The changes in frequency can be monitored and analyzed with the use of switch electronics. These switches can change the output either by setting off an alarm, a valve, or a pump and thus preventing any overflow.

The tuning fork switches are applicable in a variety of fields including medical diagnostics, chemical industries, and so on. Usually, they consist of a quartz crystal, in miniature form. These switches were a suitable substitute to the rotating paddle level switches from the 1970s. 

From the time of introduction to this decade, vibrating fork level switches continue to have a preference in the market. Many consider them as a compact and fast level switch among other types of point level switches available in the market. 

Mainly, they are popular for two reasons, that is they are comparatively more comfortable to operate and have a long life. 

How it Works

Vibration fork switches work on the principle of point level measurement. A fork level switch consists of a tuning fork—otherwise known as an oscillating fork—with two tines that acts as the sensing element. 

There will be changes in this resonance according to the difference in the medium. The two-pronged fork will oscillate at its natural frequency when left free. The fork level switch will be attached on the top or side of the tank using a flange—this aids in immersing the fork into the tank. 

Most commonly, the harmonic vibration is made possible by using piezoelectricity. The pressure applied to the forks using the piezoelectric stack will make them vibrate and will result in their separation. They will return to their previous position with the removal of the pressure applied. 

One can monitor the vibration of the tuning forks based on two parameters, the frequency of operation and amplitude of vibration. It is usual for them to vibrate at their natural frequency, and a detector circuit continuously monitors this vibration. 

There will be a decrease in the frequency of oscillation, when it moves to any other medium; liquid in this case. The natural frequency will drop when the material inside the tank coats the fork level switch. 

The switch will detect the change in frequency, and it will change the output state by operating an alarm, valve, or pump. One can choose the frequency of the switch operation before fitting, to avoid false switching; a possibility due to the regular vibrations present in the environment. 

Many industries prefer a fork level switch made of stainless steel as the material is highly durable, and they can use it in high-pressure and high-temperature conditions. Stainless steel is also highly resistant against rusting, making it an apt choice for monitoring the level of liquids and other fluids.

Advantages:

  1. They are cost-effective and durable for an extended period. Thus, it is budget-friendly.
  2. They are easy to manage and are user-friendly alternatives, in comparison to other point level switches. 
  3. Vibrating fork level switches are suitable to use in water and other fluids, and they can operate in bubbly or foamy solutions as well. They are perfect for conditions that involve high pressure and high temperature, being made from materials like highly durable stainless steel.  
  4. Proper checking and maintenance will help to ensure the long life of the tuning fork switches. 
  5. They work with high-level accuracy and provide reliable outputs. 
  6. They are easy to handle and can be mounted in any position and at any height. 

Limitations:

  1. Vibrating fork level switches cannot function in a very viscous medium.
  2. There are chances for the two prongs of the fork to connect, due to the material buildup between them, leading to false level detection or inaccurate outputs. 

The simplicity and effectiveness of the working principle and the operation makes the tuning fork level switches reliable and cost-effective, and also a popular choice in the detection of bulk solid materials and liquids. 

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