Magnetostrictive Level Transmitter

Magnetostrictive level transmitter
Image courtesy Jogler, LLC

Physical properties of certain materials can be applied using ingenuity and creativity to create useful appliances. Magnetostriction, a physical property of ferromagnetic materials, produces a change in shape or dimension in the subject material when it is magnetized. This basic principle is integrated into a liquid level transmitter by extending a sensing wire along the interior length of a tube immersed in a process tank or other vessel containing the liquid to be measured. The transmitter pulses the sensing wire with an electrical current, creating an electromagnetic field. A magnetic float, travelling along the outside of the sensing tube, rises and falls as the liquid level in the tank changes. As the float moves along the length of the sensing tube, it creates a torsional stress in the sensing wire, starting at the position of the float, which matches the level of liquid in the tank. A sensing element converts the torsional stress in the wire to an electrical pulse. The transmitter measures the time differential between the initial pulse it sent down the sensor wire and the pulse resulting from the torsional stress and then calculates the position of the float and the liquid level.

These devices are very accurate and operate on a standard 2-wire loop. There are numerous options and variants that allow configuration for each application.

More information is included in the data sheet below. Your best source for current product and application information is a product specialist. Combining your process knowledge with their application expertise will produce the best outcomes.

Magnetostrictive Liquid Level Transmitter for Process Measurement and Control from Alliance Technical Sales, Inc.

Direct Reading Level Indicator Gauge for Process Tanks

Direct reading level gauge continuously indicates
tank liquid level
Image courtesy Jogler

Anytime there is a process tank, there is a need to know how full it may be. There are numerous methods and technologies that can be applied, with varying levels of complexity and accuracy, to provide a measure and indication of tank liquid level.

A direct reading tank level gauge is essentially an extension of the tank that provides a visible indication of liquid level. The level is not inferred from a pressure reading or tank weight, nor is it represented by the movement of a float or other device. The actual process liquid can be seen by an operator or technician by looking at the clear display area of the gauge.

A direct reading level gauge connects to tank fittings at significantly high and low points along the tank side wall. The connections permit process liquid to flow into the gauge, with the level in the gauge being the same as that in the tank. A scale on the gauge provides a reference point for liquid level that can be recorded or used in other ways in the process. The simple device has no moving parts, requires no calibration, demands little to no maintenance. It can be the primary level indicating device for a manually operated fill, or act as a backup or local indicator for an automated process.

There are pressure limitations for these indicators. Higher pressure applications, or those with liquids that may foul the clear viewing area of the indicator are better handled with a magnetic level indicator. Like all instruments, proper application is the key to getting the best performance.

Share your level measurement and indication requirements and challenges with process measurement specialists, combining your own process knowledge and experience with their product application expertise to develop effective solutions.

Level Gauges, Flow Sight Glasses, and Analyzers from Alliance Technical Sales, Inc.

Liquid Level Measurement Using Hydrostatic Pressure

Hydrostatic pressure can be used to measure liquid level
in tanks or other vessels.

Pressure measurement is an inferential way to determine the height of a column of liquid in a vessel in process control. The vertical height of the fluid is directly proportional to the pressure at the bottom of the column, meaning the amount of pressure at the bottom of the column, due to gravity, relies on a constant to indicate a measurement. Regardless of whether the vessel is shaped like a funnel, a tube, a rectangle, or a concave polygon, the relationship between the height of the column and the accumulated fluid pressure is constant. Weight density depends on the liquid being measured, but the same method is used to determine the pressure.

A common method for measuring hydrostatic pressure is a simple gauge. The gauge is installed at the bottom of a vessel containing a column of liquid and returns a measurement in force per unit area units, such as PSI. Gauges can also be calibrated to return measurement in units representing the height of liquid since the linear relationship between the liquid height and the pressure. The particular density of a liquid allows for a calculation of specific gravity, which expresses how dense the liquid is when compared to water. Calculating the level or depth of a column of milk in a food and beverage industry storage vessel requires the hydrostatic pressure and the density of the milk. With these values, along with some constants, the depth of the liquid can be calculated.

The liquid depth measurement can be combined with known dimensions of the holding vessel to calculate the volume of liquid in the container. One measurement is made and combined with a host of constants to determine liquid volume. The density of the liquid must be constant in order for this method to be effective. Density variation would render the hydrostatic pressure measurement unreliable, so the method is best applied to operations where the liquid density is known and constant.

Interestingly, changes in liquid density will have no effect on measurement of liquid mass as opposed to volume as long as the area of the vessel being used to store the liquid remains constant. If a liquid inside a vessel that’s partially full were to experience a temperature increase, resulting in an expansion of volume with correspondingly lower density, the transmitter will be able to still calculate the exact mass of the liquid since the increase in the physical amount of liquid is proportional to a decrease in the liquid’s density. The intersecting relationships between the process variables in hydrostatic pressure measurement demonstrate both the flexibility of process instrumentation and how consistently reliable measurements depend on a number of process related factors.

Solutions to process instrumentation and measurement challenges are most effective when developed in concert with a product application specialist. The combination of user knowledge and experience with product application expertise will lead to a successful project.

Magnetostrictive Level Transmitter Retrofit to Magnetic Level Gauge

This magnetic level gauge has been fitted
with a magnetostrictive transmitter to
provide a continuous process level signal
Jogler

A magnetic liquid level indicator provides a reliable and highly visible reading of its indirect level measurement in tanks and vessels. While useful for local visual indication of tank level, the instrument does not provide an electrical signal output that can be utilized for process control or other monitoring functions. Several magnetic level gauge manufacturers offer combination units that incorporate another measurement technology to provide an analog signal corresponding to liquid level.

What if your installation has an existing magnetic level indicator and you need an analog level signal?

One manufacturer, Jogler, offers a magnetostrictive level measurement instrument that can be retrofitted to an existing magnetic level gauge, even those from other manufacturers. The low profile waveguide mounts slightly away from the existing magnetic level unit to isolate it from temperature and vibration. It is specifically designed for use with an existing magnetic level indicator and provides an analog output signal that is accurate, stable, and responsive.

A magnetostrictive level measurement instrument employs a magnetic float that moves along a sensing wire as the tank level changes. Fixed interval current pulses are sent down the wire, with the resulting electromagnetic field being interrupted by the magnetized float. This interruption causes magnetostriction in the sensing wire, which is manifested as a torsional stress wave along the wire. A piezoceramic sensing element converts the torsional stress into an electrical signal and the transmitter produces an output signal based upon the time interval between the initial pulse and the return pulse produced as a function of the float position.

There is more to be learned, so share your liquid level measurement requirements and challenges with instrumentation specialists. The combination of your process knowledge and their product application expertise will produce effective solutions.

Magnetostrictive level transmitter added to magnetic level gauge from Alliance Technical Sales, Inc.

When Magnetic Level Indicators May Be Best Choice for Tank Liquid Level Measurement

Magnetic level gauge configured for sanitary installation
Courtesy Jogler

Fluid process control operations often involve vessel or tank storage of liquids. Continuous and accurate indication of the liquid level within the tank is an essential data point for process control decision making and safety. Several methods and instrument types are available for tank level measurement, each with its own set of attributes that may be advantageous for a particular installation. Selection criteria for a tank liquid level indicator may include:

• Direct or indirect measurement of level
• Level measurement accuracy and reliability
• Tank shape, regular or irregular
• Media compatibility with measurement device
• Requirements for maintenance or calibration
• Compatibility with process temperature and pressure range
• Local display and visibility
• Level indication signal type and transmission
• Level alarm switches or other indicators

The selection of a magnetic level indicator, also referred to as a magnetic level gauge, for the project will likely be based upon at least one of the instrument's strengths. Magnetic level gauges have a host of potentially positive features for level indication.

• Continuous level measurement
• Operable without electric power
• Direct visual tank fluid level indication, regardless of tank shape or profile.
• Wide range of operating temperature and pressure
• Breakage resistant construction
• Range of construction materials available to accommodate corrosive media
• Measuring indicators, switches, and transmitters mounted externally, without contacting the medium being measured.
• Low maintenance operation.
• Readable level indication from greater distance than glass sight gauges.
• Applicable to large fluid level ranges with a single instrument.

Magnetic level indicators have a strong position in the tank liquid level measurement field and should be considered as a candidate for fulfilling those application requirements. There are many options available to customize the level indicator for each specific application. I have included a technical data sheet from Jogler, a manufacturer of level instrumentation, for more detail. Share your application challenges with a sales engineer that specializes in level measurement. Combining your process knowledge with their product application expertise will yield positive solutions.

Jogler magnetic level gauge brochure from Alliance Technical Sales, Inc.

Magnetostrictive Level Transmitter for Process Measurement & Control

Magnetostrictive
Liquid Level
Transmitter
(Jogler)

Physical properties of certain materials can be applied using ingenuity and creativity to create useful appliances. Magnetostriction, a physical property of ferromagnetic materials, produces a change in shape or dimension in the subject material when it is magnetized. This basic principle is integrated into a liquid level transmitter by extending a sensing wire along the interior length of a tube immersed in a process tank or other vessel containing the liquid to be measured. The transmitter pulses the sensing wire with an electrical current, creating an electromagnetic field. A magnetic float, travelling along the outside of the sensing tube, rises and falls as the liquid level in the tank changes. As the float moves along the length of the sensing tube, it creates a torsional stress in the sensing wire, starting at the position of the float, which matches the level of liquid in the tank. A sensing element converts the torsional stress in the wire to an electrical pulse. The transmitter measures the time differential between the initial pulse it sent down the sensor wire and the pulse resulting from the torsional stress and then calculates the position of the float and the liquid level.

These devices are very accurate and operate on a standard 2-wire loop. There are numerous options and variants that allow configuration for each application.

More information is included in the data sheet below. Your best source for current product and application information is a product specialist. Combining your process knowledge with their application expertise will produce the best outcomes.

Magnetostrictive Liquid Level Transmitter for Process Measurement and Control from Alliance Technical Sales, Inc.