Level Switches How Level Switches with Built–In Diagnostics Reduce Maintenance Costs
Learn how the diagnostics built into Emerson’s latest generation vibrating fork level switches provide information that enables operators to resolve problems before they impact productivity and quality.
Vibrating-fork level switches are widely used in the process industries and are suitable for virtually all liquid applications. Operating on the principle of a tuning fork, an internal piezoelectric crystal oscillates an external fork at its natural frequency. The frequency changes depending on the medium in which it is immersed — the denser the liquid, the lower the frequency. Thus, the frequency varies depending on whether the fork is immersed or dry. Changes to this frequency are monitored.
A short fork with a high natural frequency — approximately 1,400 Hz — is used to avoid interference from other plant vibrations which otherwise could cause false switching. The fork is shaped in such a way that liquid quickly drips off as the level subsides. By monitoring the frequency it is also possible to determine the condition of the fork.
Unaffeceted Sensing of Vibrating Level Switches
Vibrating-fork level switches can be used in applications with liquids and slurries, including coating and aerated liquids. Sensing is virtually unaffected by flow, turbulence, bubbles, foam, vibration, solid particles, build-up, or fluid properties. Applications include high and low level detection in liquid tanks as a backup to a continuous level transmitter, activating pumps based on level, and starting or stopping mixers based on level around the blades. Unlike many other level switch technologies, vibrating-fork technology does not have parts that can get stuck and therefore is less prone to failure.
One Technology, Many Opportunities: Vibrating Fork Level Switches
Opportunities to deploy this technology are common. For example, many tanks around a plant may initially not have been fitted with instrumentation connected to the control system. Similarly, coolant and lubricant levels in various machines may have not been monitored continuously.