Dynasonics TFX Ultra Transit Time Flow Meters Manuel d'utilisateur télécharger pdf (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

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Dynasonics TFX Ultra Transit Time Flow Meters Manuel d'utilisateur Page 97