Dynasonics TFXP Series Transit Time Ultrasonic Flow Meter User Manual
Page 108
Example 2
Known values are:
Full Scale Flow Rate
= 85 GPM
Full Scale Output Frequency = 650 Hz
650 Hz x 60 sec = 39,000 pulses per min
39,000 pulses per min
K-factor =
= 458.82 pulses per gallon
85 GPM
The calculation is a little more complex if velocity is used because you first must convert the
velocity into a volumetric flow rate to be able to compute a K-factor.
To convert a velocity into a volumetric flow 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
2
2
2
Area = r
3.068
Area =
= x 2.353 = 7.39 in
2
2) Find the volume in 1 ft of travel
3
2
88.71 in
7.39 in x 12 in (1ft) =
ft
3) What portion of a gallon does 1ft of travel represent
3
3
88.71 in
= 0.384 gallons
231 in
So for every foot of fluid travel 0.384 gallons will pass.