Rotary paddle level sensors are the most commonly used sensors for point level indication in powder & bulk solids applications. This is mainly due to their versatility in a variety of powder & bulk materials and reasonable price range. There are a number of styles out in the market to choose from, so how do you determine which one is best for your needs? Below are a few of the main factors to look at when selecting a rotary paddle level sensor:
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Application / Purpose - Rotary paddle level sensors work well as high-level, low-level and intermediate-level indicators for most powders, granules, pellets, aggregates and other bulk solid materials. If located properly, they can also be used for
high level detection in dust collection hoppers and for plugged chute detection (
more details on plugged chute).
How demanding the application is plays a big part in the type of rotary level sensor that is selected. For instance, "mini" rotary level switches are good for smaller bins/areas under light duty, low use conditions; However, if the level sensors are going to be used on a regular-basis or in critical applications, the standard version or fail-safe rotary paddle sensors would be recommended
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Examples of Paddle Assemblies
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(like Monitor's
Model KA/KAX or
SafePoint sensors).
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Paddle Assembly - In most cases you have a choice on the paddle assembly you can use. The paddle selected will help determine how successful the unit is for your specific target material. The major factors for picking a paddle assembly include: material density, material flow properties and sensor mounting location & method. The standard 3-vane paddle is the most commonly used because it works for the widest range of target materials. "Insertable" paddles, such as a 1-vane scimitar or 2-vane collapsible paddle, are useful when fitting a paddle through a pre-existing 1-1/4" NPT or 1-1/2" BSPT coupling hole from the outside of a bin or silo.
Click here for Monitor's paddle selection chart (PDF file)
Click here for article on selecting a paddle assembly (in PBE magazine - PDF file)>
Fail-safe Option - In most cases for rotary paddle level indicators, "the term fail-safe refers to the output signal condition that occurs with loss of power to the switch". However, there are some fail-safe rotary level indicators, referred to as "truly fail-safe", "self-validating" or "fail-safe plus", that in essence also monitor
their own ability to function. This self-analysis includes sensor health in addition to indication of a power failure. Click here for article regarding fail-safe rotary paddle sensors
(in PBS magazine)
More Information on Model KA / KAX Standard Rotary Paddle Level Switches: http://www.monitortech.com/product_p_rotary.shtml
