Every month, Control's editors take a specific product area, collect all the latest, significant tools we can find, and present them here to make your job easier. If you know of any tools and resources we didn't include, send them to [email protected], and we'll add them to the website.
LEVEL MEASUREMENT BASICS
Transactions in Measurement & Control, Vol. 4, Flow and Level Measurement, from Omega Engineering, is a 113-page, free, downloadable PDF covering the basics of level measurement. Beginning on p.age 72, level topics include level sensor selection, pressure/density, RF/capacitance and radiation-based instrumentation, and speciality level switches. The direct link is www.omega.com/literature/transactions/Transactions_Vol_IV.pdf.
"Methods of Detecting Water Level in Steam Boilers" is an online tutorial from Spirax Sarco that discusses the application of level controls and alarms, plus an overview of different level-detection methods, including float-type controls, conductivity probes and capacitance devices. The direct link is at http://preview.tinyurl.com/3al6ow9.
LEVEL BASICS—THE MOVIE
In this video, Control's editor in chief, Walt Boyes, talks about the basics of measuring level and how to select the correct level technology for your applications. Topics include wireless standards, hydrostatic level measurement, level measurement basics and more. Watch the video at www.controlglobal.com/multimedia/2008/024.html.
LEVEL LIMIT SWITCHES
This article discusses in detail the characteristics of a universal limit switch for liquids using a vibronic limit switch as an example. Starting with the general requirements of such an instrument, this switch may be used in approximately 80% of all applications occurring in practice. It demonstrates both the physical measurement principle and the electronic units for frequency evaluation and signal transmission. The focus is on using a limit switch for overspill protection to guarantee safe operation, even under extreme conditions. The direct link is http://preview.tinyurl.com/35yqvv8.
This is an online discussion that begins with a problem about horizontal-tank level measurement and logging. A customer has a horizontally mounted tank that is 144 in. long and 64 in. in diameter. The ends are flat. The customer would like to know the daily usage of the liquid in the tank via a measurement in the morning and another at the end of the day. The customer wants accuracy of up to 1 gallon changes in this tank measurement. Some say this is impossible, given it is a horizontally mounted tank and that the sensor cannot detect those extreme small changes. Follow the discussion and possible solutions at http://tinyurl.com/2fmlsju.
SOLIDS LEVEL MEASUREMENT
Blue Level Technologies
Continuous level measurement is about one thing, which is answering the question, "How much stuff do I have?" Usually the desired engineering unit is expressed in terms of volume or weight. "Measuring" volume or weight is not always the most practical approach. Sometimes it isn't even viable. This is where continuous level measurement sensors and systems come into play and offer a viable and cost-effective approach. "Application Considerations for Continuous Level and Inventory Monitoring of Powder and Bulk Solids" is a white paper from Blue Level Technologies that discusses the challenges of powder and bulk solid level measurement. The downloadable PDF is found at www.controlglobal.com/whitepapers/2010/046.html.