Dynasonics TFXL Clamp-On Ultrasonic Flow - Manual (Page 33)

06-TTM-UM-00158 8/2012 33
The calculation is a little more complex if velocity is used because you fi rst must convert the velocity into a volumetric fl ow
rate to be able to compute a K-factor.
To convert a velocity into a volumetric fl 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.
S Area r
S S
§ ·
¨ ¸
© ¹
2
3.068
2.353 7.39
2
Area x in
2) Find the volume in 1 ft of travel.
2
2
88.71
7.39 12 (1 )
in
in x in ft
ft
3) What portion of a gallon does 1 ft of travel represent?
3
3
88.71
0.384
231
in
gallons
in
So for every foot of fl uid travel 0.384 gallons will pass.
What is the fl 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 fl 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
2)
42, 000 min
423.9
99.1
pulses per
K factor pulses per gallon