Demands for increased safety and improved efficiency in processing facilities have made the magnetic level indicator an indispensable level control device. With the ability to perform reliably under extreme process conditions and offer redundant technology for safety-critical applications, magnetic level indicators, can make a smart alternative for a wide range of level measurement and control needs. Here’s a closer look at the applications and operating principle of MLI technology. In our next blog article, we’ll feature the advantages for using MLIs.

Overview
The magnetic level indicator ("also known as a magnetically coupled liquid level indicator or a magnetic level gauge") is in widespread use throughout process industries around the world. Originally designed as an alternative to sight glass gauges, MLIs are now commonly utilized in both new construction and plant expansions.

Typical applications/locations include:

Alkylation units

Boiler drums

Feedwater heaters

Industrial boilers

LNG facilities

NGL storage vessels

Oil / Water separators

Process vessels

Propane vessels

Storage tanks

Surge tanks

Wastewater tanks

Principle of Operation

Utilizing a combination of proven buoyancy principles along with the benefits magnetism, MLIs can provide liquid level information. They can activate a switch or provide continuous level data via a transmitter. Unlike a sight glass, magnetic coupling allows the MLI to measure liquid levels without direct contact between the externally mounted visual indicator and the fluid in the vessel.

A magnetic level indicator is mounted in-line with its respective process vessel.  It is exposed to the process media inside the vessel along with the process pressure and temperature. A float containing an array of magnets is sealed inside the MLI chamber. The float’s magnetic field interacts with the flags located in the visual indicator securely mounted on the outside of the chamber. As liquid rises and falls within the MLI, the float follows the changing level with the magnets remaining in the same plane as the liquid surface. The magnetic field causes the visual indicator flags to rotate, thereby revealing the liquid level inside the MLI.

In an MLI, the magnets within a float and an indicator are magnetically coupled. The float, located inside the chamber, dynamically tracks the surface of the liquid as it rises and falls. The magnet assembly inside the float generates a magnetic field that penetrates through the chamber wall to couple with the visual indicator.

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