Dynasonics TFX Ultra Transit Time Flow Meters - Manual (Page 97)

Finally, if the flow rate is two gpm, then the accumulation of 1000 counts would take place in 30 seconds because the flow
rate, and hence the speed that the 1000 counts is accumulated, is twice as great.
Calculating K factors
Many styles of flow meters are capable of measuring flow in a wide range of pipe sizes. Because the pipe size and volumetric
units the meter will be used on vary, it may not possible to provide a discrete K factor. In the event that a discrete K factor is
not supplied then the velocity range of the meter is usually provided along with a maximum frequency output.
The most basic K factor calculation requires that an accurate flow rate and the output frequency associated with that flow
rate be known.
Example 1
Known values are:
Frequency = 700 Hz
Flow Rate = 48 gpm
700 Hz × 60 sec = 42,000 pulses per min
42,000 pulses per min
K factor
48 gpm
875 pulses per gallon = =
Example 2
Known values are:
Full Scale Flow Rate = 85 gpm
Full Scale Output Frequency = 650 Hz
650 Hz × 60 sec = 39,000 pulses per min
K factor
39,000 pulses per min
85 gpm
458.82 pulses per gallon = =
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 one 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.
K FACTORS EXPLAINED
Page 97 March 2014