The Vibrating Fork Industrial Liquid Level Switch: Operation and Application

Vibrating Fork Level
Switch (Hawk)

When asked the primary reason to remember the year 1711, the event probably not on the minds of many is the invention of a device called the tuning fork. The tuning fork has been used as an source of resonating pitch for over three hundred years, and is still used to tune musical instruments today. While the tuning fork was initially applied to tune musical instruments, the concept of resonant frequency of a material or object has been utilized in numerous commercial, scientific, and industrial applications to provide feedback or insight into a process or operation. The vibrating fork level switch is one such industrial application where resonant frequency is used to deliver a data point or provide a control output for process operation.

The operating principle of the vibrating fork is based on the oscillating fork resonating at a known frequency in air when it is set in motion. Upon contacting a medium other than air, the resonant frequency is shifted, depending on the medium contacting or immersing the fork. Typically, fork-type level switches are installed on either the side or the top of a liquid process tank. An exciter keeps the fork oscillating, and a detector circuit monitors fork vibrating frequency, providing a change in the output signal when the frequency changes. Contact or immersion of the fork in liquid will change the fork vibrating frequency sufficiently to produce a change in output signal. Depending on the configuration of the level switch, it can function as a liquid level alarm, or provide a control output for a pump, valve, or other device. Sensor response, the change in fork vibration frequency, is a function of liquid density. Liquids with greater density will generally produce a larger frequency shift in the vibrating fork.

The wide use of vibrating level switches across various process industries is a testament to the reliability of the technology. The devices protect against overfill, indicate high and low points inside tanks, and are useful over a wide range of temperatures. A sturdy design, coupled with product variants that include a variety of sensor materials, selectable probe length, and specialized output features make vibrating fork switches applicable in many operations where level indication is needed. Chemical processing, mining, food and beverage, plastics, and other industries utilize the switches, thanks to their customizable designs and consistent performance. An advantage offered by vibrating fork level switches is a resistance to factors that sometimes confound other technologies employed for level indication. The devices will reliably function despite flow, bubbles, foam, vibration, and coating complexities related to the subject liquids. Additionally, vibrating fork switches are reliable in both high level and low level indication scenarios.

Highly viscous liquids are generally not good candidates for the application of a vibrating fork level switch. Some liquids present the potential for material accumulation between the forks, possibly resulting in poor performance. Both of these limitations are addressed by various design features incorporated by different manufacturers.

For more information, visit Power Specialties web site here or call (816) 353-6550.

Industrial Steam Boiler Optimization Toolkit

Steam generation

The primary function of a utility boiler is to convert water into steam to be used by a steam turbine/ generator in producing electricity. The boiler consists of a furnace, where air and fuel are combined and burned to produce combustion gases, and a feedwater tube system, the contents of which are heated by these gases. The tubes are connected to the steam drum, where the generated water vapor is drawn. In larger utility boilers, if superheated steam (low vapor saturation) is to be generated, the steam through the drum is passed through superheated tubes, which are also exposed to combustion gases. Boiler drum pressures can reach 2800 psi with temperatures over 680°F. Small to intermediate size boilers can reach drum pressures between 800 and 900 psi at temperatures of only 520°F if
superheated steam is desired. Small to intermediate size boilers are only being considered for this application note.

With oil‐burning and gas‐burning boiler efficiencies over 90%, power plants are examining all associated processes and controls for efficiency improvements. Between 1 and 3% of the gross work produced by a boiler is used to pump feedwater. One method of improving overall efficiency is by controlling feedwater pump speed to save on pump power.

Read the entire optimization toolkit below (courtesy of Yokogawa).

Industrial Boiler Optimization Toolkit from Power Specialties, Inc.

New Power Specialties Company Video

Here is a new, short, introductory video about Power Specialties.

Celebrating our 50th year in business, Power Specialties was founded on the concept that customer service is of primary importance. Our staff of Sales Engineers are well trained in the application and selection of instrumentation and control products. Specializing in providing instrumentation and control solutions for industry:

• Ethanol / BioFuel 
• Agricultural and Specialty Chemical 
• Power 
• Pharmaceutical 
• Manufacturing 
• Oil and Gas Production

Basics of Load Cells Used in Process Weighing

Load cell with many industrial uses
including the weighing of hoppers,
mixing/blending tanks, and conveyors.
(Courtesy of BLH Nobel)   

In industrial application of process measurement and control, principles of the physical sciences are combined with technology and engineering to create devices essential to modern high speed, high accuracy system operation.

Load cells are the key components applied to weighing materials in modern processing. Load cells are utilized throughout many industries in process weighing operations. In application, a load cell can be adapted for measurement of items from the very small to the very large.

In essence, a load cell is a measurement tool which functions as a transducer, predictably converting force into a unit of measurable electrical output. While many types of load cells are available, the most popular cell in multiple industries is a strain gauge based cell. These strain gauge cells typically function with an accuracy range between 0.03% and 0.25%. Pneumatically based load cells are ideal for situations requiring intrinsic safety and optimal hygiene and, for locations without a power grid, there are even hydraulic load cells, which function without need for a power supply. These different types of load cells follow the same principle of operation: a force acts upon the cell (typically the weight of material or an object) which is then returned as a value. Processing the value yields an indication of weight in engineering units. For strain gauge cells, the principle of deformation applies, where extremely small amounts of deformation, directly related to the stress or strain being applied to the cell, are output as an electrical signal with value proportional to the load applied to the cell. The operating principle allows for development of devices delivering accurate, precise measurements of a wide range of industrial products. Advantages of load cells include their longevity, accuracy, and adaptability to many applications, all of which contribute to their usefulness in so many industries and applications.

For more information on any process weighing application, visit Power Specialties at http://www.powerspecialties.com or call (816) 353-6550.