1.
Topic 3.1: Process Measuring
Instruments
Faculty of Chemical and Process
Engineering Technology
BVF2124 FIELD
INSTRUMENTATION DEVICES &
CONTROL

2.
Elements of a Process Control System
4) Final
Control
Element
3)
Controller
2)
Measuring
Element
1) Process

3.
Process Instrumentation & Measurement
• Flow Measurement
• Level Measurement
• Pressure measurement
• Temperature measurement

4.
Chapter 3.1:
FLOW MEASUREMENT

5.
OBJECTIVES
After you study this sub-chapter, you should be able to:
1. Define flow measurement.
2. Describe the importance of flow measurement.
3. Explain the basic operation, list the advantages and
disadvantages of each flow measurement device.

6.
TOPIC COVERED
• Fundamental of Flow Measurement
• Flow Measuring Devices:
1. Differential Pressure Flowmeter
- Orifice
2. Velocity-type Flowmeter
-Turbine, Electromagnetic, Ultrasonic Flowmeters
3. Variable area Flowmeter
- Rotameter
• How to Choose the right Flowmeter?

7.
Fundamental of Flow Measurement
• What is flowrate?
- Amount of material passing one point for
certain time.
• Give one simple method to measure water
flowrate from tap water.
• Flowmeters help to determine how much fluid
is passing through

8.
• Why flow is an important parameter?
- Most process involves moving material from one
part of the plant to another.
• A fluid can be defined as any substance that can
flow and thus the term applies both to liquids and
gases.
Fundamental of Flow Measurement

9.
Why
Custody Transfer
• Measure material present in a tank
• Billing purposes
Monitor the process
• Provide information about the process
• Ensure that the process is operating
satisfactorily
Safety
• Ensure that critical portions of the
process operate safely
• Over/under flow
WHY MEASURE FLOW ?

10.
FUNDAMENTAL OF
FLOW MEASUREMENT
Fluid type
Viscosity
Specific Gravity
Density
Flow Profile
Reynold’s
Number
Mass per unit volume of a fluid
Ratio of the density of a fluid to the density of a reference fluid
Measure of fluid’s tendency to resist a shearing force or to resist flow
Clean Fluid, Dirty Fluid, Slurry, Steam
Characterizes the behavior of a fluid as it flows through a pipe (e.g: smooth or
turbulent, symmetrical or asymmetrical)
Ratio of the inertial force to the viscous force in the flow stream.

11.
Clean Fluid
Dirty Fluid
Slurry
Steam
High
viscosity
Fluid
Foam
TYPE OF FLUID

12.
TYPE OF
FLOW MEASUREMENT
Volumetric Flow
Q = A V
= ft
=
ft sec
*
*
²
ft sec
³
where:
Q = volumetric flow
A = cross sectional area ( ft )
V = average fluid velocity ( )
ft sec
ft sec
³
²

13.
TYPE OF
FLOW MEASUREMENT
Mass Flow
where:
m = mass flow ( )
 = density ( )
Q = average fluid velocity ( )
A = cross sectional area ( ft )
V = average fluid velocity ( )
 lbs sec
²
ft sec
ft sec
m = Q  = A V 
= ft
=

* *
*
² ft sec
* *
lbs
ft³
lbs sec
lbs
ft³

14.
CLASS OF
FLOW MEASUREMENT
Differential
Pressure (DP)
Flowmeter
Velocity
Flowmeter
Mass
Flowmeter
Volumetric
Flowmeter
• Orifice plate
• Venturi tube
• Flow nozzle
• Wedge
• V-cone
• Rotatometer
• Pitot tube
• Annubar
• Magnetic Flowmeter
• Vortex Flowmeter
• Turbine Flowmeter
• Ultrasonic
Flowmeter
• Coriolis
Flowmeter
• Thermal
Flowmeter
• Positive
displacement
flowmeter

15.
FLOW MEASUREMENT USING
Differential Pressure (DP) Transmitter
Based on Bernoulli
Principle - Velocity is
increased after passing
the obstruction while
pressure is decreased.
Primary element -->
Placed in the process
pipe to restrict the flow
and create a differential
pressure
Measure the differential pressure (ΔP)
caused by an obstruction in the flow
stream
Secondary element --> Measures the
differential pressure and transmits the
result to a control system

16.
DP
Flowmeter
Venturi tube
Orifice plate
Flow nozzle
Rotatometer
V-cone
Pitot tube
FLOW MEASUREMENT USING
Differential Pressure (DP) Transmitter

17.
FLOW MEASUREMENT USING
Differential Pressure (DP) Transmitter
Venturi Orifice
Nozzle V-cone
l
Rotatometer
Pitot Tube

18.
FLOW MEASUREMENT USING
Differential Pressure (DP) Transmitter
& Orifice
Fluid velocity increases and pressure decreases as fluid passes through the
orifice, which creates a pressure drop.

19.
Orifice plate
• An orifice plate is a thin disk diameter which is inserted in the pipe
perpendicular to the flow stream. It acts as the primary element of a DP
flowmeter.
• Fluid velocity increases and pressure decreases as fluid passes through
the orifice, which creates a pressure drop .
• It is commonly used when the flow is continuous and occupies the entire
pipe
• Typical orifice meter has a concentric, eccentric and segmental

20.
Figure 2: schematic diagram of orifice meter
Figure 1: Orifice meter
Video

21.
Advantages Disadvantages
• Recommended for clean and
dirty liquids and some slurry
services
• Most commonly used flow
sensor - inexpensive, easy to
install, no moving part, simple
configurations, required less
maintenance.
• Compatible with most pipe sizes
• Accuracy are poor at low
flowrates
• Easily gets clogged due to
impurities in gas or in unclear
liquids
Orifice plate

22.
• Variable area flow meters operate at a constant
differential pressure (ΔP) and the area changes with
the flowrate.
• The area will increase as the flowrate through the
meter increases to preserve a constant ΔP.
FLOW MEASUREMENT USING
Variable area type flowmeter

23.
• An industrial flowmeter used to measure
the flowrate of liquids and gases.
• The rotameter consists of a tube and
float.
• The direction of flow in the vertical conic
tube is from the bottom to the top
• Falling and rising action of float provides a
measure of flowrate.
• The upward flowing media lifts the float
for as long as necessary to reach an
equilibrium.
Rotameter

24.
TYPE OF MATERIALS
• The two basic components of every rotameter
are the tapered metering tube and float
• Tapered tube may be made of :
 Glass tubes (for accurate reading)
 Metal tubes (for corrosive conditions)
 Plastic tubes ( for low cost)

25.
Advantages Disadvantages
• All rotameters are low cost
compared to other flow
measurement devices
• Reliability combines for an
extremely low cost ownership.
• Long last expectancy brings low
life cycle cost.
• Simple to install and maintain.
• When opaque fluid is used,
float may not be visible
• It must be installed in vertical
position only
• Limited to low temperatures
Rotameter

26.
Typical units used
to represent
velocity are ft/s and
m/s
Velocity is the speed of a fluid
flowing past a stationary point in a
process pipe
Producing an output
based upon fluid
velocity that is linear
to the volumetric
flow rate
FLOW MEASUREMENT USING
Velocity type flowmeter

27.
In a vortex flowmeter an obstruction, or “bluff body,” is
placed across the pipe bore perpendicular to the fluid
flow.
FLOW MEASUREMENT USING
Velocity type flowmeter
Vortex flowmeter

28.
A slow moving putt barely displaces
the molecules of air
The higher velocity of a chip shot
causes irregular eddies to form
behind the ball
The velocity associated with a drive is
sufficient to cause a strong, regular
vortex formation behind the ball
The analogy of a golf ball moving through the air is useful
in describing vortex formation:
FLOW MEASUREMENT USING
Vortex flowmeter
Principle of operation

29.
When a flowing medium strikes a non-streamlined bluff object, it separates, moves around
the object and passes downstream. At the point of contact with the object, vortex swirls
separate from the body on alternating sides.
This separation causes a local increase in pressure and a decrease in velocity on one
side and a decrease in pressure and an increase in velocity on the opposite side.
FLOW MEASUREMENT USING
Vortex flowmeter
Principle of operation

30.
FLOW MEASUREMENT
MASS FLOWMETER
The continuing need for more accurate flow measurements in
mass-related processes (chemical reactions, heat transfer, etc.)
has resulted in the development of mass flowmeter.
Some of the most common mass flowmeter are:
Coriolis flowmeter
Thermal flowmeter

31.
Thermal Flowmeter
Coriolis Flowmeter
FLOW MEASUREMENT
MASS FLOWMETER

32.
Electromagnetic Flowmeter
• Use Faraday’s Law of electromagnetic induction to
determine the flow of liquid in a pipe.
• In this flowmeter, a magnetic field is generated by
electric coils and channelled into the liquid flowing
through the pipe.
• Flow of a conductive liquid through the magnetic
field will cause a voltage signal to be sensed by
electrodes located on the flow tube walls.
• When the fluid moves faster, more voltage is
generated .
• The developed voltage is linearly proportional to
the volumetric flow rate
• The electronic transmitter process the voltage
signal to determine liquid flow.
Video

33.
Advantages Disadvantages
• Can be used in hazardous
environments or measure
corrosive or slurry fluid flow
• Low maintenance cost because
of no moving parts
• More accurate than differential
pressure meter (orifice, venturi
and flow nozzle) since this flow
meter does not introduce any
pressure drop
• Material must be liquid that
conduct electricity
• Requires electrical conductivity
of fluid higher than 3 µS/cm in
most cases, (particle caused
bias in reading).
• Expensive
Magnetic Flowmeter

34.
Turbine Flowmeter
• Turbine meters have a spinning rotor with blades that is mounted on
bearings in a housing on the central longitudinal axis of the pipeline.
• The rotor spins as water or other fluid passes over it.
• Blade movement is often detected magnetically, where the movement of
rotor generates a pulse
• The pulse frequency is proportional to the velocity of the fluid. When the
fluid moves faster, more pulses are generated
• Speed of rotation of rotor proportional to the volumetric flow rate.

35.
Advantages Disadvantages
• Turbine meter excel at
measuring steady, high-speed
flows of liquid and gas.
• Widely used in utility
applications to measure the
amount of water used in
commercial and industrial
buildings.
• Have excellent accuracy
• The size (diameter) same as the
pipe in which they are fitted, and
pressure loss is quite low.
• limited to clean fluid, require
maintenance at their bearing
from time to time and
expensive.
• Not suitable for high
viscosity fluids
Turbine Flowmeter

36.
Ultrasonic Flowmeter
• Ultrasonic flowmeters can be categorized into two types
based on the installation method: clamped-on and inline.
• The clamped-on type is located outside of the pipe and
there are no wetted parts. It can easily be installed on
existing piping systems without worrying about corrosion
problems.
• Clamped-on designs also increase the portability of the
flowmeter.
• The inline type, on the other hand, requires fitting flanges
or wafers for installation. However, it usually offers better
accuracy and its calibration procedures are more
straightforward.

37.
• A pair of transducers is placed on the pipe wall, one on
the upstream and the other on the downstream.
• Flowrate is measured based on the time for the sound
to travel between a transmitter and a receiver
• The time for acoustic waves to travel from the
upstream transducer to the downstream transducer, td
is shorter than the time it requires for the same waves
to travel from the downstream to the upstream, tu.
transmitter
receiver
Ultrasonic Flowmeter

38.
Advantages Disadvantages
• No obstruction in the flow path
• No pressure drop, no moving
parts
• Low maintenance cost
• Can be used to measure
corrosive or slurry fluid flow.
• Higher initial cost
• Measuring accuracy easy
influenced by the installation
and environment.
Ultrasonic Flowmeter

39.
How to choose the flowmeter?
• The purpose of the measurement and the
physical characteristics of the fluid being
measured are the two main considerations.

40.
Some specifics to consider are:
• Type of the fluid being measured (air, water, gas, oil,
etc.)
• Fluid condition (clean, dirty, viscous, slurry, corrosive,
conductive etc.)
• Measurement device accuracy, turndown ratio
(rangeability) and reliability
• Total cost involve (equipment cost, total cost
installation, maintenance cost, and operating cost)-
cheap or expensive?
• Type of construction materials (stainless steel,
fiberglass, etc.)
• Pressure loss (high, low, intermediate?)

41.
Orifice plate
Vortex Flowmeter
Venturi meter
Turbine flowmeter
Electromagnetic
flowmeter
Flow Nozzle
Time Transit Model
Doppler Electromagnetic flowmeter