|| Flow Meter Types
Plate - An orifice plate helps measures flow
through the differences in pressure from the upstream
side to the downstream side of a partially obstructed
pipe. The plate offers a precisely measured obstruction
that narrows the pipe and forces the flowing substance
to constrict. A DP cell allows the comparison
of the pressure on the upstream (unobstructed)
side and the downstream (constricted) side.
the flow, the greater the difference in pressure
as the substance maintains its constricted state
for a longer distance, passing the downstream
element. Different kinds of orifice plates include
concentric, eccentric, and segmental, each of
which has different shapes and placements for
measuring different processes. Orifice plates
are in common use in many installations.
|Orifice Plate Calculator
||Orifice plate pressure drop calculator is used for flow rate measuring in pipe systems. With orifice plate, pressure drop is created. Based on the magnitude of pressure drop, flow rate can be calculated. The pressure drop calculation formula for the pipe is explained in more detail below .Practical for larger tube diameters and for dirty fluid where other methods are impractical.
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An orifice plate
is a very simple device installed in a straight run
of pipe. The orifice plate contains a hole smaller than
the pipe diameter. The flow constricts, experiences
a pressure drop, and then the differential pressure
can be related to a flow.
Figure 1: Orifice Plate Arrangement
For a discussion of how pressure drop is related to
liquid flow for concentric orifices,
Engineering. They have a very good explanation on
It is also important to note that relating differential
pressure to flow across an orifice depends on the location
of the pressure taps in relation to the orifice. In
Figure 2 below, the pressure taps are designated as
P1 and P2. "D" is the diameter of the pipe
and "d" is the diameter of the orifice.
Figure 2: Various Tap Positions for Orifice Plates
The principle of differential pressure
measurement as an inferred measurement of rate of flow
is well established and widely used in many specific
The use of more sophisticated electronic readout equipment
has enabled the effect of other process variables to
be taken into account in computing rate of flow.
Probably the most widely used differential pressure
device is the orifice plate , the characteristics of
which as a flow measurement device have been researched
for over a 100 years , leading to the publication of
many national and international standards. A whole measurement
cult has emerged around orifice plate technology.
Available in an infinite number of sizes to suit an
almost infinite number of application conditions. Can
be readily made from a wide variety of materials to
fulfill costs of applications requirement criteria.
More widely used for gases where it is utilized as a
primary measurement element.
In larger sizes it is available as a removable assembly
which can be interchanged under line pressure. For custody
transfer applications in gas it is common to see such
large orifice plate metering set ups with higher accuracies
referred to as senior orifice plate meters.
This is used as a primary measuring element for air
and gas flow, for a number of industrial applications.
The flow nozzle is also available cheaply manufactured
from plastics with simple manometer readout as the basis
for an effective cheap measurement system where rangeability
requirements are small and where limited accuracy is
Traditionally used for water measurement and water based
chemicals including corrosive fluids
Annubars and Pitot Tubes
The use of the pitot tube is restricted to a point velocity
measurement but these are occasionally employed to traverse
pipe velocity profiles for the purpose of inferring
volumetric flow rate. However the Annubar , or multi-orifice
probe is widely used as a flow measurement device. By
virtue of the disposition of the dynamic pressure measurement
holes across the velocity profile , an averaging effect
is obtained. The position of the sensing holes on the
velocity profile is thus critical to the accuracy of
the device, as is the shape of the profile itself.
|| Flow Indication & Control