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Active Contributor

Join Date: Jun 2011
Posts: 20

Level Calculation

02/26/2012 12:16 AM

please explain me displacer level calculation formula? what is the formula of displacer level transmitter. thnk you

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#1

Re: level calculation

02/26/2012 1:00 AM
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#2

Re: level calculation

02/26/2012 2:18 AM

P=ρgh

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Join Date: Sep 2011
Location: Bellingham, WA
Posts: 187
Good Answers: 46
#3

Re: Level Calculation

02/26/2012 2:25 PM

In answer to this and your previous question: a float is a device that floats on top of the liquid, while a displacer is a device that is too heavy to float, and experiences a buoyant force that varies with the liquid level. Float sensors are often (but not always) connected to a cable and reel system for mechanically sensing the liquid level:

Displacer instruments often use a spring-steel tube called a "torque tube" to couple the slight motion of the displacer to a mechanism outside the pressurized cage where the displacer resides:

The most important difference to recognize is that floats sit on the top of the liquid, and so move with the liquid as it changes height. Displacers merely experience different amounts of upward force as they become more or less submerged by the rising and falling liquid -- the displacer element itself does not actually float on the liquid, and in fact does not move much at all.

Displacers operate on Archimedes' Principle, which states that the buoyant force experienced by any object is equal to the weight of the liquid it displaces. Therefore,

(Buoyant force) = (weight density of liquid) * (volume of displacer submerged)

Based on this and previous posts, I'm guessing you could use a general reference on instrumentation to explain how various instruments work and the principles of operation for them. You might find this book helpful in your studies:

http://www.openbookproject.net/books/socratic/sinst/book/liii.pdf

Another set of references are these worksheets which I use to teach level-measurement instrumentation at Bellingham Technical College:

http://www.openbookproject.net/books/socratic/sinst/output/INST240_sec3.pdf

http://www.openbookproject.net/books/socratic/sinst/output/INST240_sec4.pdf

You may also find this document helpful -- it's a worksheet of practice problems I give to my students so they may practice performing calculations on hydrostatic and displacer level-sensing instruments:

http://www.openbookproject.net/books/socratic/sinst/output/level.pdf

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Active Contributor

Join Date: Jun 2011
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#4
In reply to #3

Re: Level Calculation

02/26/2012 7:11 PM

thank a lot sir

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