On the level: Dealing with non-linear shapes

A big advantage automation lends is the the ability to acquire data continuously rather than as discrete points in time. If consumption varies predictably, acquiring data at a couple of points in time can be fine. Otherwise, continuous measurement is practical and cost-effective.

03/01/2009


Many process applications require volume/level measurement to be automated. A big advantage of automating is the data can be acquired continuously rather than as discrete points in time. If consumption varies predictably, acquiring data at a couple of points in time can be fine. Otherwise, continuous measurement is practical and cost-effective.

There are many technologies available to measure level either continuously or in discrete steps. There is even a larger variety of sensors that can measure level continuously. For example, some mechanical systems have been used for centuries.

If a cylindrical tank is installed on its side, the non-linearity of the volume is caused by the constantly varying diameter of the fluid as the level changes. The challenge is to compute the volume with respect to this change. The answer lies in geometry that calculates the level based on known parameters of height and diameter.

Deriving the equations isn’t necessary; one can go to a variety of sources and come up with an equation in terms of radius, liquid height and tank length. Typically, users don’t have to do the calculations. Sensors using several different measurement technologies have the capability to calculate volume of irregular geometries among other conversions for weight, mass, etc. By entering the known parameters %%MDASSML%% for example, vessel diameter and units %%MDASSML%% and the maximum scale corresponding to 100% output, the sensor can apply a standard algorithm for those parameters adjusting the output based on the level. When applying these algorithms, there is a reduction in the accuracy of the reading, albeit small. However, in situations requiring a low level of uncertainty such as inventory control applications, one may choose not to use these internal calculations.

Level technology

Level measurement technology is a key task of many control systems in chemical, petroleum and environmental technologies. In addition to determining limit values to protect against overfilling, min and max control systems, it is also protection against overflow or running dry. Continuous level measurement is of considerable significance for accurate inventory management.

In addition to availability and reliability, the important benefits of continuous level measurement are the accuracy of the measurement and cost of ownership. Today more than ever, each decision must be preceded by a careful evaluation of which measurement principle goes with which process and medium, and what the trend will be for long-term operating costs of the measurement system. No one technology satisfies all situations.

Guided microwave sensors

Guided microwave systems are offered in today’s market with increasing popularity. In contrast to radar or ultrasonic systems, measurements are performed in contact with the medium. The microwave pulses are not radiated freely, but are guided on a sensor rod or cable. The time-of-flight of the pulses corresponds to the distance measured between the process connection and the surface of the product.

Guided microwave sensors are time-of-flight instruments and work with the time-domain reflectometry (TDR) principle. They transmit repetitive pulses at microsecond intervals with pulse widths in the nanosecond range. These pulses are reflected off the surface of the medium and are evaluated by sampling with time offset as an echo profile.

Special algorithms and multiple sampling of the echo profiles allow an exact representation of the spatial situation between the source of the wave and the reflection. The echo is converted to a proportional distance or level signal at a resolution of just a few millimeters. The measurement is insensitive to temperature, pressure or gas layers in the container. The measurement accuracy is independent of changes of the medium in density or moisture. The advantages of the guided signal and the practical absence of external influences compensate for the disadvantage of being in contact with the medium.

Guided microwave sensors are well suited for use in almost all process-related systems in which filling levels of liquids or bulk goods must be measured. They are being used more frequently in applications involving chemicals, petrochemicals, water/wastewater and the basic materials processing industry. The advantages of guided microwaves are found in areas where reliable measurements have been problematic until now %%MDASSML%% for example, in small process containers with formation of froth or turbulence, or in media with a low dielectric value. These include:

  • Reliable measurements of powdery media even during filling

  • Measurements in liquids even with froth and drop formation

  • Reliable and accurate measurements in a bypass or still pipe

  • Practically no interference caused by installed elements or supports, textured container walls such as corrugated sheet metal or narrow silo cells

  • Independence of media properties in liquids/bulk materials such as density, dielectric value, chemical corrosiveness or conductivity

  • Largely independent of process influences such as pressure, temperature, movable surfaces or froth, mist and dust.

    • Economic considerations

      Versatility and range of applications, give guided microwaves a clear advantage and a promising alternative to other continuous level measurement technologies. Important considerations include uncomplicated operation, flexible installation and maintenance requirements. Simple front panel control with a menu-driven user interface and PC-interface make it possible to adjust other features such as saving a characteristic curve for tank linearization.

      Application conditions and the price/performance ratio are critical factors for the economical and successful use of measurement systems. No one level measurement system offers the optimal solution for all applications. However, most applications can be implemented with time-of-flight measurement systems.

      Go to www.plantengineering.com to read the full text of this article.


      <table ID = 'id4433300-0-table' CELLSPACING = '0' CELLPADDING = '2' WIDTH = '100%' BORDER = '0'><tbody ID = 'id4432823-0-tbody'><tr ID = 'id4432825-0-tr'><td ID = 'id4432827-0-td' CLASS = 'table' STYLE = 'background-color: #EEEEEE'> Author Information </td></tr><tr ID = 'id4432837-3-tr'><td ID = 'id4434152-3-td' CLASS = 'table'> Mike Mendicino is a product manager at Pepperl+Fuchs ( </td></tr></tbody></table>


No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
World-class maintenance: The three keys to success - Deploy people, process and technology; 2016 Lubrication Guide; Why hydraulic systems get hot
Your leaks start here: Take a disciplined approach with your hydraulic system; U.S. presence at Hannover Messe a rousing success
Hannover Messe 2016: Taking hold of the future - Partner Country status spotlights U.S. manufacturing; Honoring manufacturing excellence: The 2015 Product of the Year Winners
The digital oilfield: Utilizing Big Data can yield big savings; Virtualization a real solution; Tracking SIS performance
Getting to the bottom of subsea repairs: Older pipelines need more attention, and operators need a repair strategy; OTC preview; Offshore production difficult - and crucial
Digital oilfields: Integrated HMI/SCADA systems enable smarter data acquisition; Real-world impact of simulation; Electric actuator technology prospers in production fields
Improving flowmeter calibration; Selecting flowmeters for natural gas; Case study: Streamlining assembly systems using PC-based control; CLPM: Improving process efficiency, throughput
Putting COPS into context; Designing medium-voltage electrical systems; Planning and designing resilient, efficient data centers; The nine steps of designing generator fuel systems
Warehouse winter comfort: The HTHV solution; Cooling with natural gas; Plastics industry booming

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
This article collection contains several articles on the vital role that compressed air plays in manufacturing plants.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.
This article collection contains several articles on strategic maintenance and understanding all the parts of your plant.
click me