RTDs are more accurate and reliable than thermocouples. You should ?also understand that RTD’s sensing element is a resistor that changes ?resistance with temperature and it is
RTDs are more accurate and reliable than thermocouples. You should also understand that RTD's sensing element is a resistor that changes resistance with temperature and it is connected to the control circuitry through a wire.
Answer the following:
- In order to select the suitable detector, what materials should be used as sensing elements and wire materials for RTDs?
- How are thermocouples types and temperature ranges involved?
Flow Control
Chapter 12
Note: Slides are an adaption of the publisher resources
1
Objectives
Define flow
Describe the importance of measuring and controlling flow in industrial processes
List some types of materials measured for flow and how they are transferred
Explain the difference between volumetric flow rate and mass flow rate
Objectives (cont’d.)
List common measurement units of flow rate
Describe the method used for measuring the volumetric flow rate and mass flow rate of solid materials
List four factors that affect the flow rate of liquids
Calculate the Reynolds number for a liquid
Objectives (cont’d.)
Describe the operation of the following mechanical measurement instruments used to determine flow rate:
Differential pressure, rotameter, rotary-vane, lobed impeller, and turbine flowmeter
Objectives (cont’d.)
Describe the operation of the following electronic sensors used to measure flow:
Coriolis mass flowmeter, rotor flow detector, time-of-flight flowmeter, electromagnetic flow detector, thermal flowmeter, vortex flowmeter, ultrasonic flowmeter, and thermal mass meter
Objectives (cont’d.)
State a rule that describes the placement of flow sensors in a pipe system
Select the most appropriate flow-measuring device for a particular application
Systems Concepts
To operate, systems employ a(n):
Source, path, control function, actuator, and measuring instrument
Reasons for control:
Ensure correct proportions of raw materials are combined during manufacturing process
Ensure ingredients are supplied at proper rate
Prevent a high flow rate that may become dangerous
Flow Units of Measurement
Volumetric flow rate
Determine volume of material that flows during a specific period of time
Flow velocity
Distance a material travels per unit of time
Mass flow rate
How much actual mass flows past a location within a specific time period
(For further investigation review ELE2307 at the link.)
Solid Flow Measurement
Solids measured for mass flow rate
Typically in the form of small particles
Formula:
FIGURE 12-3 An LVDT used to measure the weight of materials flowing on the conveyor belt
Fluid Flow Measurement
Pipe flow principles
Velocity
Density
Viscosity
Pipe size
Reynolds number:
(For further investigation review ELE906 at the link.)
Fluid Flow Measurement (cont’d.)
Fluid flowmeter categories:
Differential pressure meter
(For further investigation review ELE1407 at the link.)
Positive displacement methods
Velocity meters
Direct reading mass
Fluid Flow Measurement (cont’d.)
FIGURE 12-12 Turbine flowmeter that measures velocity
Electronic Sensors
Include:
Coriolis mass flowmeter
Mass flowmeters
Thermal mass meters
Rotor flow detectors
Electromagnetic flow detectors
Thermal flowmeters
(For further investigation review ELE1107 at the link.)
Vortex flowmeters
(For further investigation review ELE1307 at the link.)
Ultrasonic flowmeters
(For further investigation review ELE5208 at the link.)
Time-of-flight flowmeter
(For further investigation review ELE2207 at the link.)
Electronic Sensors (cont’d.)
FIGURE 12-20 Time-of-flight flowmeter
Flowmeter Placement
Measuring device
Placed five to 20 pipeline diameters downstream from an obstruction
FIGURE 12-21 The swirling current produced by pipeline elbows
Selecting a Flowmeter
Consider the following:
Is the fluid a gas or a liquid?
Is the fluid corrosive?
Is the fluid electrically conductive?
Does the fluid contain a slurry or large solids?
What is the fluid viscosity?
Will the fluid density or viscosity change?
Selecting a Flowmeter (cont’d.)
Is there a need for a noninvasive approach?
What is the need for accuracy and repeatability?
What is the cost?
Level-Control Systems
Chapter 13
18
Objectives
Define level
Describe the importance of measuring and controlling level in industrial processes
Define interface and list three types of interfaces that may be measured for level indication
List four level-measurement units
Objectives (cont’d.)
Define direct level measurement, and list types and applications of this method
Define indirect level measurement, and list types and applications of this method
Explain the difference between continuous and point level measurements
Objectives (cont’d.)
Describe the operation of the following level-indicator devices:
Rod gauge and sight glass
Describe the operation of the following mechanical measurement instruments used to determine level:
Float, displacement, bubbler, paddle wheel detector, hydrostatic pressure detector, differential pressure detector, weight detector
Objectives (cont’d.)
Describe the operation of the following electronic sensors used to measure level:
Conductive probes, capacitive probes, and ultrasonic sensors
Select an appropriate level-measuring device for a particular application based on various considerations
A Level-Control System
FIGURE 13-1 A level-determination system
A Level-Control System (cont’d.)
Include:
Power sources
Pumps
Static-pressure yanks
Augers
Transfer systems
Pipes
Conveyor systems
Methods of Measurement
Interface:
Boundary between two media
Used to measure level
Level can be measured:
Directly or indirectly
At a point value or continuously across a range
Methods of Measurement (cont’d.)
Include:
Point level measurements
Continuous level measurements
Level-Measurement Methods
Selection of a specific method of measuring level is often based on:
Material
Accessibility and cost
Turbulence
Accuracy
Pressure
Level range
Level-Measurement Methods (cont’d.)
Visual methods
Rod gauge
Sight glass
Float and displacement methods
Buoyancy method: float-type level indicator
Displacement method: displacement sensor
(For further investigation review ELE2607 at the link.)
Purge method: bubbler
(For further investigation review ELE406 at the link.)
Level-Measurement Methods (cont’d.)
Rotational suppression method: paddle wheel detector
Optical liquid-level sensor
Hydrostatic-pressure method: hydrostatic-head level detector
Differential-pressure method: differential-pressure level measurement
Level-Measurement Methods (cont’d.)
FIGURE 13-9 Optical liquid-level sensor
Electronic Sensors
Conductive probes
Single- or multiple-point measurement systems
Detect presence of conductive liquid
(For further investigation review ELE2507 at the link.)
Capacitive probes
Continuous level measurement
(For further investigation review ELE2407 at the link.)
Ultrasonic sensors
Continuous level detector
(For further investigation review IAU106 at the link.)
Selecting a Level Sensor
Consider:
What are the physical properties of the medium?
What are the chemical and thermal properties?
Reliability, cost, and safety
Industrial Detection Sensors and Interfacing
Chapter 19
33
Objectives
Define industrial detection sensor and provide several examples of the types of applications for which it is used
List the parts of a limit switch, provide examples of the types of functions it performs, and list precautions that should be followed when connecting it to machinery
Objectives (cont’d.)
Explain the operation of an inductive proximity detector, describe the function of the sensor circuitry, and provide examples of its applications
Explain the operation of a capacitive proximity detector, describe the function of the sensor circuitry, and provide examples of its applications
Objectives (cont’d.)
Explain the operation of a Hall-effect sensor and provide examples of its applications
Describe the operational theory of the three components that make up a photoelectric sensor
Objectives (cont’d.)
Describe the operational theory, characteristics, and application examples of several photoelectric methods of detection
Properly interface electromechanical relays, solid-state relays, and analog sensor outputs to load devices
Objectives (cont’d.)
Define common terms associated with industrial detection sensors and interfacing
List the factors that determine the sensing distance from which a target can be detected by the sensors that are described in this chapter
Limit Switches
Most fundamental detection sensor
Converts mechanical motion into electrical signals
Main parts:
Electrical contacts
Actuating mechanism
Follow rules when wiring
Proximity Detectors
Electronic sensors
Indicate presence of an object without making physical contact
Commonly called proximity switches
Types:
Inductive
Capacitive
Inductive Proximity Switches
Detects presence of ferrous or nonferrous metallic materials
Parts: oscillator, sensor head, demodulator, trigger and output stages
Operation of an inductive proximity switch
Guidelines, dimensions, materials, distance, position, and applications
Analog inductive sensor
FIGURE 19-2 An inductive proximity switch
(For further investigation review IAU5707 at the link and IAU5307 at this link.)
Capacitive Proximity Switches
Detects presence of metallic and nonmetallic targets
Operation: dimension and shape, distance and position, dielectric constant, and applications
FIGURE 19-10 Relative dielectric constant of different materials
(For further investigation review IAU5607 at the link and IAU5207 at this link.)
Hall-Effect Sensor
Detects presence of magnetic field
Linear Hall-effect sensors
Digital Hall-Effect sensor
Modes of operation: head-on, slide-by, and stationary
Applications: well suited for harsh conditions
(For further investigation review IAU7407 at the link.)
Photoelectric Sensors
Use light to detect absence or presence of an object
Light source: supplies light beam
Light sensor: detects presence or absence of object
Sensor circuitry: emitter block and detector block
Methods of Detection
Most sensing applications rely on one of the following detection methods:
Opposed sensing method
Retroreflective sensing method
Diffuse sensing method
Convergent sensing method
Specular sensing method
Color-mark sensing method
Photoelectric Sensor Adjustable Controls
Important concepts:
Light/dark operation
Sensitivity
On-delay operation
Off-delay operation
One-shot operation
Photoelectric Package Styles
Styles: self-contained and remote
Fiber optics
Transparent strands of glass or plastic
Transfer light
FIGURE 19-33 Fiber-optic cables used to perform photoelectric sensing methods
Operating Specifications
Data sheets provide information on:
Sensitivity
Excess gain
Contrast
Field-of-view
Sensor response
FIGURE 19-37 Horizontal and vertical alignment adjustments
Operating Specifications (cont’d.)
Guidelines for selecting an optical sensing method
Target shape and size
Distance between the emitter and detector
Physical object characteristics
Unwanted ambient light or background
Rate of speed at which the target passes the light beam
Ultrasonic Sensors
Uses high-frequency sound waves to detect objects
Categories: proximity switches and analog sensors
FIGURE 19-39 Ultrasonic sensor
(For further investigation review IAU106 at the link.)
Sensor Interfacing
Switched signal
Electromechanical relay
Resistive and inductive loads
Solid-state relays
Two-, three-, and four-wire systems
Hints on connecting three- and four-wire sensors
Analog signal
Usually used in process-control applications
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Pressure Systems
Chapter 10
Note: Slides are an adaption of the publisher resources
1
Objectives
Define pressure and fluid
Given force and area, calculate the pressure exerted by a fluid
Identify five factors that affect the pressure exerted by a liquid
Calculate pressure by using specific gravity and depth values for a liquid in a container
Objectives (cont’d.)
Identify three factors that affect the pressure exerted by a gas
List the reference value for gage, absolute, and vacuum pressures
Convert psia to psig, and psig to psia
Calculate differential pressure
Identify the difference between direct and indirect measurements
Objectives (cont’d.)
Describe the operation of the following nonelectrical measuring devices:
Barometer, manometer, Bourdon tube, diaphragm, bellows, and capsular
Describe the operation of the following electronic pressure sensors:
Semiconductor strain gauge, transverse voltage strain gauge, and variable capacitor pressure detector
Pressure Laws
Pressure
Measured as force per unit area
Defined mathematically
FIGURE 10-1 Pressure
Properties of a Liquid
Height
Head: height above measurement point
Weight:
Density: weight of a certain volume of liquid
Expressed in pounds per unit volume
Hydrostatic pressure:
Pressure = Height x Density
(For further investigation review ELE606 at the link.)
Properties of a Liquid (cont’d.)
Specific gravity:
Indicates liquid weight
Compared to water at 60 degrees Fahrenheit
Temperature
Affects pressure exerted
Properties of a Liquid (cont’d.)
Atmospheric pressure
Weight of a one-square-inch column of air from the top of the layer to sea level is 14.7 psi
Mechanical machines
Can change pressure of a liquid
Properties of a Gas
Temperature of the gas
Pressure increases proportionately with rise in temperature
Volume of the gas container
Compression: space between gas molecules is reduced
Gas removal from a container
Vacuum: reduction of pressure
Compared to atmospheric pressure
Pressure Measurement Scales
Gage pressure scale
Reference point is atmospheric pressure
Absolute pressure scale
Referenced to absolute zero
More accurate
Convert gage to absolute pressure
Add atmospheric pressure to psig pressure value
Pressure Measurement Scales (cont’d.)
Inches of water column
How many inches of water in a vertical column will create the pressure
Differential pressure scale
Difference in pressure between two measured pressures
Vacuum pressure scale
Based on a barometer tube
(For further investigation review IAU3806 at the link.)
Pressure Measurement Instruments
Used to monitor pressure conditions
So that corrective action can be taken if necessary
Classified by whether they make the measurements directly or indirectly
Inferred measurement
Nonelectrical Pressure Sensors
Include:
Liquid column gauges
Manometer
Mechanical gauges
Bourdon tube gauge
Diaphragm gauge
Bellows gauge
Nonelectrical Pressure Sensors (cont’d.)
FIGURE 10-15 A differential pressure manometer
Electronic Pressure Sensors
Include:
Semiconductor strain gauges
Transverse voltage strain gauge
Variable capacitor pressure detector
FIGURE 10-20 Transverse voltage strain gauge
Pressure Control Systems
Hydraulic systems
Powers most machinery used in the manufacturing industry
Pneumatic systems
Mass production assembly lines
Vacuum systems
Enclosed space containing air or other gas at a pressure lower than atmospheric pressure
Pressure Control Systems (cont’d.)
Static pressure systems
Industrial applications where fluids are distributed during the manufacturing process
Steam pressure systems
Used in industry for a variety of purposes
Temperature Control
Chapter 11
18
Objectives
Define thermal energy
Explain the law of thermodynamics
List the three types of heat transfer
Describe the operation of the following heat sources of thermal energy:
Blast furnace, electronic heat element, arc, and resistance induction
Objectives (cont’d.)
Describe the operation of a cold thermal energy source (refrigeration system)
Define temperature
Identify the Fahrenheit and Celsius scales and convert specific values from one scale to another
Objectives (cont’d.)
List several reasons for monitoring
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