Controlling Level Measurement Remotely

Shouldn’t Your Level Measurement Solution Meet the Same Design Requirements as Your Vessel or Piping System And Safety Standards?

With current advancements in design and manufacturing, as well as the customizability of engineering solutions, an MLG level solution that could meet design and vessel requirements is possible. Each MLG float chamber can be designed to meet the ANSI/ASME B31.1, B31.3 or ASME Section VIII standards, depending on which is most applicable.

Certifications such as PED, ASME, and ATEX Constructional Safety also increase the device reliability for extreme applications. The hermetically-sealed float that is created for certain conditions, as well as the scale assembly tested to meet the highest standards of ingress protections, increases device accuracy, reliability and performance under any working condition.

Figure 4. KM26 Series MLG & Switches

Figure 5. ABB Ability^TM - Level Measurement Solutions

Power of Integration

Magnetic Level Gauge (MLG) technology provides users with continuous level indication through integrated float and scale assembly, a mechanism that promises confidence in measurement through visual indication. In some instances, operators may feel challenged with level measurement and isolated control over the MLG. As a result, a magnetostrictive technology that complements MLG technology has been developed as a solution.

The magnetostrictive loop powered transmitter, featuring continuous level measurement capability with 4-20 mA HART output, offers a complete, integrated, and efficient way to facilitate level measurement.

Figure 6. Integrated LMT200 with KM26 MLG

Using the latest advanced signal processing mechanism from its built-in advanced diagnostics with waveform display and signal conditioning, the magnetostrictive transmitter provides reliable measurements that ensure optimal performance and increased up-time.

When externally mounted onto an MLG, this device empowers users with the flexibility to install and modify on-site, with the device easily able to adjust from top to bottom mounting, or from left to right of the MLG chamber, without modification of the equipment. The external mounted transmitter is based upon the magnetostrictive principle that is shown in Figure 7.

Figure 7. KM26 MLG with LMT200

1. The device electronics generate low energy current pulses at fixed intervals.
2. The electrical pulses create a magnetic field which travels down a specialized wire inside the sensor tube.
3. The interaction of the magnetic field around the wire and the magnetic float causes a torsional stress wave to be induced in the wire. This torsion propagates 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 converts the received mechanical torsion into an electrical return pulse.
5. The microprocessor-based electronics measure the elapsed time between the start and return pulses, and convert it into a position measurement which is proportional to the level of the float.

In order to achieve more reliability and safety in the level measurement system using an MLG with an externally-mounted magnetostrictive transmitter, the addition of one or two magnetically-coupled point level switches is recommended. In such cases, one technology shall be used for continuous measurement, while the other will be utilized as a high-level switch for overfill prevention.

When the magnetic level gauge switch is mounted on an MLG or an external chamber that contains a magnetic float, it can determine high or low level points within a vessel. Through its unique magnetic coupling action, the need for seals, diaphragms, springs, or torque tubes is avoided.

Magnetic coupling cuts out contact and connections within the process, ensuring total isolation from the method. Mounting and adjustment are often achieved via a small screw driver, thus possessing an easy field replaceable core assembly.

Figure 8. KM26 MLG with LMT200

The compact design of these switches fits in tight places on chambers, thereby allowing flexible mounting options. Depending on the amperage rating of this externally mounted point level switch, the device could be used for alarming or controlling pumps directly or through the PLC/DCS systems.

The three major groups of MLG switches are as follows:

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

MLG switches are magnetically-actuated level switches that do not require power for operation. They are externally mounted on level gauges and have no direct contact with the process media. This mechanism is opposed to in-process or insertion type point level switch technologies such as thermal dispersion, vibrating fork, or RF capacitance.

An MLG with external magnetostrictive transmitters and external mounted point level switches is the safest solution in applications that have aggressive media because these are non-invasive solutions that can provide reliable continuous level measurement and overfill protection.

Figure 9. KM26 MLG with LMT200 and TX Switches

Some critical application designs may require the MLG with Point Level switches to be operated independently from the float. The thermal dispersion switch or the vibrating fork-based switch that is directly mounted onto the MLG chamber with separate process connections for each is the best solution to overcome challenges in such critical applications.

This solution provides safety via the redundancy and independent switch technology. Industry requires that such types of installation are made using an extruded outlet which can be met by superior manufacturing capabilities of a modern factory. Any other joint design would cause distortion to the chamber that would interfere with float travel, ultimately affecting level measurement.

Safe and Reliable Solutions to Increase Productivity and Profitability

ABB's Smart Level Measurement Solutions are safe to use and could measure a wide range of liquids, including corrosive, flammable, and toxic materials. The superior range of ABB level measurement solutions provides users with flexibility in integrating next-generation or advanced continuous level transmitters or point level switches in an MLG to ensure increased safety, reliability and performance whilst reducing the total cost of ownership.

This is in comparison with the cost of older technology or multiple separate solutions, associated accessories and maintenance schedules. As a result, the customer is able to save money and space, reduce weight, minimize leak potential, and limit on-site fabrication and calibration.

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.