What is Level Measurement?

As a key market leader in level measurement solutions with the widest selection of agency approved level products, the ABB K-TEK level products line has the established technology to provide solutions for the extremely difficult level applications.

Why Level Measurement?

Smarter measurement supports more efficient, safer and more sustainable operations, extending service life and enhancing uptime, whatever the industry sector. Behind the scenes, it is also helping to maintain global infrastructure operating reliably, day-in and day-out. The significance of level measurement in this context cannot be overstated whether for Industrial Process Measurement and Control or in Inventory Tank Gaging. In Applications like Custody transfer, the accuracy of the measurement becomes the vital parameter whereas in the other Process Industrial applications, along with a reasonable accuracy the Safety and Reliability factors are vital for ensuring the complete success of any business.

In a dynamic system, the Level measurement becomes challenging with the process tanks/vessels which constantly undergoe modifications in the behaviors of the measured process fluid due to mixing, chemical reaction, agitation or emptied out for downstream processes based on the application requirements. In such applications, these processes integrated with the fact that these occur at high temperature and/or high pressure pose a safety risk for the personnel and equipment, which makes the Level Measurement even more critical.

Any inadequate and improper control can cause levels in the tanks or vessels to be excessively lower or higher than their safe operating limits resulting in the damage to equipment, causing overflow or affecting the quality of the final product and potentially developing environmental and safety hazards resulting in financial losses.

ABB’s Smart Level measurement solutions for Continuous and Point level Detection can be employed for measuring a wide range of liquids, including flammable, toxic and corrosive materials while guaranteeing increased safety, performance and reliability with lower total cost of ownership for the operations. ABB’s smart Level measurement Solutions can be used for writing the future.

Figure 1. Why Level Measurement?

A Complete Solution: Point Level vs Continuous Level

Modern instrumentation uses a number of different technologies in order to satisfy the ever-growing requirements for level measurement in a wide range of applications. Some instruments are capable of measuring level directly, while others indirectly measure by sensing another variable that is related to level. In Liquid Level Measurement, it is possible to divide instruments into two basic categories: Point level and Continuous level sensors. Figure 2 displays the table of the most commonly used technologies in each category.

What are Point Level Instruments?

Point level instruments refer to those senses of variation in liquid levels based on the presence or absence of liquid media at different points in a tank or vessel. Point Level Instruments are capable of detecting either Dual pint, Multi-point or single point. Most often, the function of point level sensors are low level or high level alarms, pump protection alarms, spill-prevention sensors or as pump control components.

Following are the most common Point Level Technology used in the Industry:

• Buoyancy
• RF Capacitance
• Vibrating Fork
• Magnetic Coupled
• Thermal Dispersion

Figure 2. Level Measurement Solutions.

What are Continuous Level Instruments?

Continuous level instruments are those that transmit the accurate level of a tank/vessel continuously, over the full span of measurement. This is most frequently used for process control via a level absolute precision and accuracy is of extreme importance. Following are the most common Continuous Level Technology used in the Industry:

• Laser
• Ultrasonic
• Magnetostrictive
• Guided Wave Radar
• Magnetic Level Gage
• Differential Pressure

While these technologies and the instruments may have overlaps and similarities with one another, they suit a wide range of applications and meet the requirements, some technology may not be suitable or not best suited in specific conditions over the other. If one needs a liquid level solution for an industrial or other application, but is not sure of which point-level or continuous instrument to select, one can contact the nearest ABB Level Measurement expert for support.

Level Measurement: Seeing is Believing

This is true with the Magnetic Level Gage (MLG) which was originally developed as a replacement solution for the dangerous and costly direct contact sight glasses based level indicators. But over time, this technology has indeed become much more than a simple replacement measuring device; it has now become the method of choice for measurement in a variety of processes. With the improvements in the technology over the period of time the Magnetic Level Gages can safely be employed with flammable, toxic or corrosive liquids; or where operating conditions exceed safety limits of glass. The rugged construction of these level gages make them perfectly suited for use in operating environments where extreme temperature (538 °C/1000 °F or -195 °C/-320 °F) and/or pressure (344 Bar/5000 Psi) may be encountered.

How does the Magnetic Level Gages Work?

The basic Magnetic Level Gage system (Figure 3) comprises of a Float, Indicator assembly and a Float chamber. The float chamber is attached directly to the process vessel. The float comprises of a magnet assembly and is designed and weighted to float in the process liquid submerged approximately 70 to 80%. The indicator assembly comprises of a hermetically sealed glass or polycarbonate tube comprising of the shuttle or magnetic bar graph indicator and a graduated scale corresponding to the preferred operating range. The indicator assembly is mounted in close proximity to the float chamber. Magnetic coupling exists between the indicator and the float.

As the float follows the changing liquid level, the indicator changes position in order to reflect that level based on the magnetic coupling action.

Figure 3. Magnetic Level Gage Principle.

Safety and Hazardous Risk to All Equipment and Everyone in the Ecosystem!

In a number of industrial applications, the process is frequently required to have majorly aggressive media and often needs the bulk storage of highly corrosive or acidic chemicals that react with standard materials of the level measuring equipment. Thus, it is not advisable to use such level devices, developed from the standard materials for measuring such tank levels, as those would quickly degrade and, subsequently, provide inaccurate information and possibly end up in a disaster.

Non-contact continuous level measurement technology is considered to be an option for such applications. However, this solution does not provide the reliable mechanical visual indication that one may prefer as “Seeing is Believing”. In addition, these solutions also need the tanks or vessel to have an opening where these can be mounted that expose the risk to the aggressive media during the maintenance and repair. It is also necessary for these devices to have the wetted material made of exotic alloys similar to titanium or others, which are resilient to these aggressive chemicals measured, making these solutions extremely expensive.

A safe and cost effective alternative in such applications with aggressive media is a chemical or corrosion resistant coating on a Magnetic level gage such that it can withstand the extreme chemical reactions of the process. Gages including the floats coated with chemical resistant materials such as Halar^® and Tefzel^® shall enhance the performance and life of the level measurement solution operating reliably for extremely long time periods.

Shouldn't Your Level Measurement Solution Meet the Same Design Requirements as Your Vessel/ Piping System and Safety Standards?

With the customized Engineered Solutions and with the developments in design and manufacturing technologies, the MLG Level Solution is capable of meeting this requirement by having each MLG float chamber designed to meet the ANSI/ASME B31.1, B31.3 or ASME Section VIII whichever is most applicable. In addition, certifications like PED, ASME and ATEX Constructional Safety increases the confidence and reliability of solutions for such extreme applications. The hermetically sealed float designed for particular conditions of the applications and the Scale assembly tested to meet highest standards of the Ingress Protections like IP68 increases the reliability, performance and accuracy in all weather types.

Figure 4. KM26 Series MLG & Switches.

Figure 5. ABB Ability™ - Level Measurement Solutions.

Power of Integration

The Magnetic Level Gage (MLG) technology provides the user a constant level indication using the integrated float and scale assembly that provides the user the confidence in the measurement as it offers the visual indication to believe the measurement. At times, this poses the challenge for operators while referring to the possibility of level measurement and control remotely. The Magnetostrictive technology complements the MLG technology and provides an exceptional solution to this problem. The magnetostrictive loop powered transmitter with nonstop level measurement capability with 4-20 mA HART output when strapped externally on the MLG can presently offer an easy and complete level measurement and control solution. Integrated Level measurement solutions provide users the capability to believe what they see.

Figure 6. Integrated LMT200 with KM26 MLG.

With the recent advanced signal processing capabilities, the magnetostrictive transmitter offers consistent measurements having built-in advanced diagnostics with waveform display and signal conditioning alowing the user to guarantee optimal performance and increased uptime without the need for additional equipment or tools. When externally mounted on to a MLG, this transmitter provides users with installation flexibility and simple modification on site as they can be effortlessly changed from top to bottom mount or from left to right of the MLG chamber orientation without the need for modifying the equipment.

The external mounted transmitter is based upon the magnetostrictive principle (Figure 7).

Figure 7. KM26 MLG with LMT200.

1. The device electronics produces a low energy current pulse at fixed intervals.
2. The electrical pulses produce a magnetic field which travels down a specialized wire within the sensor tube.
3. The interaction of the magnetic field around the wire and the magnetic float results in a torsional stress wave to be induced in the wire. This torsion transmits along the wire at a known velocity, from the position of the magnetic float and toward both ends of the wire.
4. A patented sensing element placed in the transmitter assembly transforms the received mechanical torsion into an electrical return pulse.
5. The microprocessor-based electronics measures the elapsed time between the start and return pulses (Time of Flight) and transforms it into a position measurement which is proportional to the level of the float.

To attain a higher level of reliability and to have additional safety in the level measurement system with the MLG with the externally mounted Magnetostrictive transmitter is recommended to add one or two magnetically coupled point level switches. In this case, one technology (Magnetostrictive) is employed for the constant measurement and the other (Magnetically coupled point level switch) as a high level switch for overfill prevention.

When the magnetic level gage switch is mounted on a MLG or an external chamber that comprises of a magnetic float, it can sense low or high level points within a vessel. Its unique magnetic coupling action avoids the requirement for seals, springs, diaphragms or torque tubes. Magnetic coupling eradicates process contact and connections, guaranteeing total isolation from the process. Mounting and adjustment is frequently achieved through a small screw driver and have an easy field replaceable core assembly.

Figure 8. KM26 MLG with LMT200.

Compact design of these switches fits in tight places on chambers permitting flexible mounting options. Based on the amperage rating of this externally mounted point level switch, it can be employed for Alarm or to Control Pumps directly or via the PLC/DCS systems.

Three Major Groups of Magnetic Level Gage Switches are:

• High Current – 10 Amp rated (MS41)
• Low Current – 1 Amp rated (LMS100)
• Pneumatic Switches (PS45)

MLG Switches are magnetically actuated level switches which require no power to operate; they are externally mounted on the Level Gages and have no direct contact with the process media as opposed to in-process or insertion type point level switch technologies such as Vibrating Fork, Thermal Dispersion or RF Capacitance. The MLG with the external mounted point level switches and external magnetostrictive transmitters is the safest solutions in critical applications with aggressive media as these are non-invasive solutions reliably providing the constant level measurement and overfill protection.

Figure 9. KM26 MLG with LMT200 and TX Switches.

A few critical application designs may be the MLG with Point Level switches operated with float independent technology. The Thermal Dispersion Switch or the Vibrating Fork based switch mounted directly onto the MLG chamber with separate process connections for each is considered to be the best solution to overcome the challenges in such serious applications. This solution provides safety via the redundancy and independent switch technology. Industry demands that this type of installation is made with an extruded outlet which can be met by the greater manufacturing capabilities of a modern factory. Any other joint design would cause distortion to the chamber that would interfere with float travel affecting the Level measurement.

Safe and Reliable Solutions to Increase Profitability and Productivity.

ABB's Smart Level Measurement Solutions can be safely used for measuring a variety of liquids, including corrosive, toxic and flammable materials. The wide and superior range of Level Measurement Solutions provides the flexibility of incorporating next generation advanced continuous level transmitters and point level switches in a Magnetic Level Gage as one powerful integrated platform guaranteeing increased safety, performance and reliability while reducing the total cost of ownership compared to the cost of older technology or multiple separate solutions, maintenance schedules and the associated accessories, saving the customer a lot of money, saves space, minimizes leak potential, reduces weight and since this is completely factory assembled and tested, no onsite fabrication and calibration is needed. ABB’s Smart Level measurement Solutions are now ideal for futuristic growth.

This information has been sourced, reviewed and adapted from materials provided by ABB Measurement & Analytics.

For more information on this source, please visit ABB Measurement & Analytics.