Dynasonics TFXL Clamp-On Ultrasonic Flow - Manual (Page 32)

32 06-TTM-UM-00158 8/2012
K-FACTORS EXPLAINED
The K-factor (with regards to fl ow) is the number of pulses that must be accumulated to equal a particular volume of fl uid. 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 fl ow rate. The same K-factor number,
with a time frame added, can be converted into a fl ow rate. If you accumulated 1000 counts (one gallon) in one minute, then
your fl ow 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 fl ow rate would be 2 GPM.
Finally, if the fl ow rate is 2 GPM, then the accumulation of 1000 counts would take place in 30 seconds because the fl ow 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 fl ow meters are capable of measuring fl ow 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 fl ow rate and the output frequency associated with that fl ow 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)
42, 000 min
875
48
pulses per
K factor pulses per gallon
GPM
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)
39, 000 min
458.82
85
pulses per
K factor pulses per gallon
GPM