Table of Contents
Advertisement
TM
K-Factors Explained
The K-factor (with regards to flow) is the number of pulses that must be accumulated
to equal a particular volume of fluid. You can think of each pulse as representing a
small fraction of the totalizing unit.
An example might be a K-factor of 1000 (pulses per gallon). This means that if
you were counting pulses, when the count total reached 1000, you would have
accumulated 1 Gallon of liquid. Using the same reasoning each individual pulse
represents an accumulation of 1/1000 of a gallon. This relationship is independent of
the time it takes to accumulate the counts.
The frequency aspect of K-factors is a little more confusing because it also involves
the flow rate. The same K-factor number, with a time frame added, can be converted
into a flow rate. If you accumulated 1000 counts (one gallon) in one minute, then
your flow rate would be 1 GPM. The output frequency, in Hz, is found simply by
dividing the number of counts (1000) by the number of seconds (60) to get the output
frequency.
1000 ÷ 60 = 16.6666... Hz. If you were looking at the pulse output on a frequency
counter, an output frequency of 16.666...Hz would be equal to 1 GPM. If the
frequency counter registered 33.333...Hz (2 × 16.666...Hz), then the flow rate would
be 2 GPM.
Finally, if the flow rate is 2 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 achieved, is twice as great.
Calculating K-factors for Ultrasonic meters
Many styles of ultrasonic 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 is not possible to provide a discrete K-factor. Instead 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
1) 700 Hz × 60 sec = 42,000 pulses per min
2) K-factor = 42,000 pulses per minute / 48 GPM = 8.75 pulses per gallon
Z205739-0D
PAGE 51
Alta Labs, Enercept, Enspector, Hawkeye, Trustat, Aerospond, Veris, and the Veris 'V' logo are trademarks or registered trademarks of Veris Industries, L.L.C. in the USA and/or other countries.
FSRxxxx SERIES
©2013 Veris Industries
INSTALLATION GUIDE
Example 2:
Known values are:
Full Scale Flow Rate = 85 GPM
Full Scale Output Frequency = 650 Hz
1) 650 Hz x 60 sec = 39,000 pulses per min
2) K-factor = 39,000 pulses per minute / 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 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 = π * r
2
Area = π * (3.068/2)
2) Find the volume in 1 ft of travel.
7.39 in
* 12 in = 88.71 in
/ ft
2
2
3) What portion of a gallon does 1 ft of travel represent?
88.71 in
/ 231 in
= 0.384 gallons
3
3
So for every foot of fluid travel 0.384 gallons will pass.
What is the flow 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 flow 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) K-factor = 42,000 pulses per minute / 99.1 GPM = 423.9 pulses per gallon
2
= π * 2.353 = 7.39 in
2
05131
Advertisement
Table of Contents
