Switches Indicators & Gauges

Magnetostrictive Tank Gauging

There are different ways of measuring levels in a tank, whether it be hydrostatic, magnetic float, capacitance, ultrasonic or conductance. Tank gauges are used to determine different variables including levels, condensation, density, or temperature.

Magnetostrictive tank gauges use magnetic tracking to determine the fluid pressure in a closed body of liquid. Magnetostrictive materials change their shape when subjected to a magnetic field, converting magnetic energy into kinetic energy. Magnetostriction is the property of ferromagnetic materials, which have a structure that is divided into domains. Each domain is a region of uniform magnetic polarisation. When a magnetic field is applied, the boundaries between the domains shift, rotating them, causing a change in the material’s dimensions.

LabkoMax and LabkoFlex

The LabkoMax and LabkoFlex systems are designed for reliable, accurate and inexpensive fuel storage monitoring, in applications such as service stations, terminals, refineries and other fuel distribution sites.  These systems easily intensify logistics, optimise storage, detect condensated water and control leaks. They measure product level, temperature and eventual condensed water level. They are based on the magnetostrictive measuring principle, so are ideal for applications demanding high accuracy and good repeatability.

The sensor’s wetted parts are of stainless steel and PVDF, suitable for fuels like gasoline, diesel, fuel oil, various additives and industrial chemicals. They can take measurements from tanks up to 15 m high, are very easy to install and have an IP 68 structure. The LabkoMax is best for tanks that are less than 5 m high, while the LabkoFlex is most suitable for tanks between 5 – 15 m high. LabkoMax sensor can be equipped with one or two floats and optionally with 1 – 5 temperature sensors.

The MPS-4 is the interface and barrier unit of both systems, transforming the measurements into digital information. It is compatible with most common pump controllers, cash registers and outdoor payment terminals. It is also possible to observe the level information of containers in real time online with the LabkoNet® service site.

Hydrostatic Tank Gauging

Fluid pressure is the pressure at some point within a fluid, hydrostatic pressure being the pressure at any given point of a non-moving (static) fluid. Fluid pressure occurs in open conditions, such as the ocean, and closed conditions, such as a tank. Pressure in open conditions is usually static, as the motion of waves and currents create only negligible changes in pressure. Closed bodies of water are either static (when non-moving) or dynamic (when moving, or compressed by air).

After determining the pressure within the fluid, the pressure’s constant of integration is equal to some reference pressure within the system. The properties (such as pressure) of a fluid can be determined from a control volume analysis of a cube of water. Since the stress of all sides of the cube must be normal and equal in magnitude, the pressure gradient can be found to be linearly increasing in a potential gradient. The pressure within a fluid will increase linearly as the product of the fluid’s density and gravity.

Purge Control

Hydrostatic level transmitters measure hydrostatic pressure using an air purge connection to the tank. An integral specialised airflow regulator ensures a linear response throughout the entire operating range. LiquiSeal™ or Purge Control differential pressure air flow regulators are highly refined versions of the basic bubbler air control. ‘Bubblers’ are usually a length of open pipe that extends downwards into the tank.

Semrad’s Purge Control offers continuous level measurement with pneumatic or electronic output, and is suitable for corrosive or aggressive liquids. The electronic transmitter can be applied to a maximum depth of 49m in water, while the pneumatic transmitter has a maximum depth measurement of 91m. Both have a flow rate of one nominal cubic foot per hour, and a temperature range between -18° and +82° C (though the actual process temperature limits may be significantly higher depending on the material used for the downpipe and purge airline).

Tank Level Measurement

There are many methods for measuring tank levels, so identifying which technology or instrument to use can be difficult. Some of the common types of level measurement methods include RF capacitance, conductance, hydrostatic tank gauging, radar and ultrasonic.

• Radio Frequency capacitance uses the electrical characteristics of a capacitor to measure the level. The amount of capacitance is determined by the spacing and area between two conductors and the electrical characteristic of the insulating medium between them.
• Conductance is based on the electrical conductivity of the liquid, used for point level detection.
• The radar or microwave method uses electromagnetic waves for continuous level measurement. A sensor beams down a microwave from the top of the vessel. The time it takes for the beam to reach the bottom is used to calculate the level.
•  Ultrasonic  and sonic methods uses sound waves to determine the level of a liquid. A transducer sends waves downwards onto the surface of the material, then the echoes return to the trasducer which calculates the distance and converts it into a measurement.

Automatic Tank Gauge (ATG)

Hydrostatic tank gauging with an automatic tank gauge (ATG) is one of the oldest and most common methods of measuring liquids. The density of liquid varies with temperature, so the pressure exerted by a column (or head) of liquid in the tank is measured and expressed in relation to the actual temperature of the measured liquid. Through hydrostatic tank gauging transfers in tank farms can be monitored, and accurate information on tank level, mass, density and volume can be provided.

Semrad Pty Ltd provides level transmitters that measure hydrostatic pressure using an air purge connection to the tank. A downpipe or ‘bubbler’ of open ended pipe that extends downward into the tank measures the differential pressure.