With the largest selection of agency-approved level products available in the market today, the ABB K-TEK level product line has the technology to provide effective solutions for the most complex level applications.
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Why Level Measurement?
Smarter measurement supports safer, more efficient, and more sustainable operations in any industrial sector, improving uptime and extending service life. On a larger scale, it also assists in the delivery of reliable global infrastructure operations. In this setting, the value of level measurement cannot be overstated, especially in industrial process measurement and control or in inventory tank gauging.
For custody transfer applications, measurement accuracy is a critical parameter; however, in the other process industrial applications, safety and reliability are salient parameters to ensure the overall success of operation.
Level measurement becomes challenging in a dynamic system, since process vessels or tanks continually undergo changes in the behaviors of the measured process fluids. These behavioral changes are brought about by agitation, mixing, or chemical reactions, depending on application needs. In a number of applications, these processes occur at high temperature or pressure levels that pose safety risks for both the operators and equipment, making level measurement even more critical.
Any improper and inadequate control setting may cause tank- or vessel-levels to be excessively higher or lower than their safe operating limits. This may result in equipment damage, final product quality, overflow, or hazardous setups that ultimately result in financial losses.
ABB’s Smart Level Measurement solutions for continuous and point level detection can measure a wide range of liquids, including corrosive, flammable, and toxic materials, while ensuring consistent safety, reliability, and performance.
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Figure 1. Why Level Measurement?
A Complete Solution: Point Level Versus Continuous Level
Different technologies are utilized to cater to the every-growing requirements for level measurements in different applications. Some instruments measure level directly, while others do so indirectly by detecting another variable that is related to level. In liquid level measurement, instruments may either be point level and continuous level sensors. Figure 2 presents a table of commonly-used technologies per category.
What are Point Level Instruments?
Point level instruments are devices that detect variation in liquid levels based on the presence or absence of liquid media at various points in a vessel or tank. They could detect single-, dual-, or multi-point. Often, point level sensors are used for high or low level alarms, spill-prevention, and pump protection or its components.
The following are the most common point level technologies used in the industry:
- Thermal dispersion
- Buoyancy
- Vibrating fork
- RF capacitance
- Magnetic coupled
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Figure 2. Level Measurement Solutions
What are Continuous Level Instruments?
Continuous level instruments consistently transmit the accurate level of a vessel or tank over the full measurement span. Often utilized in process control, absolute precision and accuracy are of crucial importance when working on these instruments.
The following are the most common continuous level technologies used in the industry:
- Magnetic level gauge
- Magnetostrictive
- Guided wave radar
- Laser
- Ultrasonic
- Differential pressure
While such instruments may be structurally similar to each other, they are utilized in various needs and applications. As such, some instruments may not be best suited in certain conditions over others.
Level Measurement: Seeing Is Believing
Magnetic Level Gauge (MLG) was primarily developed as a replacement solution for the costly and dangerous direct contact sight glasses-based level indicators. Over time, however, this device has become a measuring tool for a wide range of processes.
Through technological advancements, MLGs were developed as safe-to-use devices for flammable, corrosive, or toxic liquids, or in applications where the safety limits of glass are being exceeded. The rugged construction of magnetic level gauges make them suitable for use in operating environments where extreme temperature (-1,950 °C or 5,380 °C) or pressure (344 Bar/5,000 Psi) may be encountered.
How Do Magnetic Level Gauges Work?
Presented in Figure 3, a basic MLG system is made up of a float, float chamber, and indicator assembly. Containing a magnet assembly, the float is designed and weighted to float in the process liquid at a level of 70% to 80% submersion. Meanwhile, the float chamber is directly connected to the process vessel. The indicator assembly is made up of a hermetically-sealed glass or polycarbonate tube that encapsulates the shuttle or magnetic bar graph indicator.
It also contains a graduated scale corresponding to the desired operating range. The indicator assembly is placed close to the float chamber. Magnetic coupling exists between the float and the indicator, so that when the float follows the changing liquid level, the indicator changes its position to reflect that level based on the magnetic coupling action.
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Figure 3. Magnetic Level Gauge Principle
Safety and Hazardous Risk May Be Evident
In many industrial applications, operational processes often require the use of extremely aggressive devices and the storage of highly corrosive or acidic chemicals. As such, it is inadvisable to utilize level devices that are made up of standard materials, as these can degrade quickly, leading to imprecise data and potential danger.
For such applications, non-contact continuous level measurement technology may be used. However, this solution does not provide a reliable visual indication that the process is working well. This mechanism also requires vessel or tanks to have an opening where the device could be mounted, which leads to the risk of the solution being exposed to the aggressive media during maintenance or repair procedures.
In addition, such devices also require wetted materials to be constructed from expensive exotic alloys, similar to titanium, which are resistant to the aggressive chemicals during measurement, leading to high costs.
A cost-effective and reliable alternative in such applications is a chemical or corrosion resistant coating, placed within the MLG, that can withstand extreme chemical reactions. Gauges, including floats coated with chemical resistant materials such as Tefzel® and Halar®, can improve the level measurement solution’s performance and shelf life.
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.