Dynasonics TFXL Clamp-On Ultrasonic Flow Manuel d'utilisateur télécharger pdf (Page 33)

06-TTM-UM-00158 8/2012 33

The calculation is a little more complex if velocity is used because you  rst must convert the velocity into a volumetric  ow

rate to be able to compute a K-factor.

To convert a velocity into a volumetric  ow, the velocity measurement and an accurate measurement of the inside diameter

of the pipe must be known. Also needed is the fact that 1 US gallon of liquid is equal to 231 cubic inches.

Example 3:

Known values are:

Velocity = 4.3 ft/sec

Inside Diameter of Pipe = 3.068 in

1) Find the area of the pipe cross section.



Area r



§·

 

¨¸

©¹

3.068

2.353 7.39

Area x in

2) Find the volume in 1 ft of travel.





88.71

7.39 12 (1 )

in x in ft

3) What portion of a gallon does 1 ft of travel represent?



88.71

0.384

231

gallons

So for every foot of  uid travel 0.384 gallons will pass.

What is the  ow rate in GPM at 4.3 ft/sec?

0.384 gallons × 4.3 FPS × 60 sec (1 min) = 99.1 GPM

Now that the volumetric  ow rate is known, all that is needed is an output frequency to determine the K-factor.

Known values are:

Frequency = 700 Hz (By measurement)

Flow Rate = 99.1 GPM (By calculation)

1) 700 Hz × 60 sec = 42,000 pulses per gallon

42,000 min

423.9

99.1

pulses per

K factor pulses per gallon

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Dynasonics TFXL Clamp-On Ultrasonic Flow Manuel d'utilisateur Page 33

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