Basic information fot the instrumentation technician and the instrumentation engineer regarding the magnetic level indicators.


Companies in the process industry need the ability to visually monitor liquid levels in vessels (boilers, storage tanks, processing units, etc.). Traditionally, armored glass sight gauges have been used. However, many companies want an alternative to sight gauges to avoid problems such as breakage, leaks, or bursting at high pressures and extreme temperatures. In addition, the visibility of the sight glass can be poor and often affected by moisture, corrosion, or oxidation.

Magnetic level indicators (MLIs) do not have the shortcomings of glass sight gauges and are suitable for a wide variety of installations.


This handbook describes the configuration and operation of MLIs and provides information about their key components and features. Use this handbook as a resource when selecting the right MLI for a specific application.

Chapter 1 – Introducing the MLI

Provides an introduction to MLIs, describes the components, discusses the advantages of an MLI over a glass sight gauge, and offers some general questions to ask when selecting an MLI.

Chapter 2 – Indicator Types and Seals

Discusses principles of operation, MLI shuttle and flag indicator types, advantages and disadvantages of both indicator types, and guidelines for selecting an indicator for a specific application.

Chapter 3 – Floats and Chambers

Discusses the function of the MLI float and chamber, materials of construction and properties, and guidelines for selecting appropriate MLI floats and chambers.

Chapter 4 – Magnets

Provides an overview of magnets including properties, advantages and disadvantages; discusses the functions of magnets in an MLI; and provides guidelines to use when appraising magnets.

Chapter 5 – Transmitters

Describes the types of MLI transmitters available, presents an overview of the principles of operation for each type of transmitter, discusses the benefits and shortcomings of each, and provides guidelines for selecting an appropriate transmitter.

Chapter 6 – Accessories

Discusses typical accessories used with MLI devices and presents an overview of the operation of each accessory.

Chapter 7 – Orion MLIs

Describes the features of magnetic level indicators engineered and manufactured by Orion Instruments, presents information on various configurations of MLIs, discusses the benefits and limitations of each configuration, and provides guidelines for selecting the correct MLI configuration for a specific application.

Magnetrol (2003) Selecting the Right Magnetic Level Indicator
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