Chat with us, powered by LiveChat 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 - Writeden


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



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


FIGURE 12-3 An LVDT used to measure the weight of materials flowing on the conveyor belt

Fluid Flow Measurement

Pipe flow principles




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


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



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.)


Power sources


Static-pressure yanks


Transfer systems


Conveyor systems

Methods of Measurement


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.)


Point level measurements

Continuous level measurements

Level-Measurement Methods

Selection of a specific method of measuring level is often based on:


Accessibility and cost




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


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



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




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


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:


Excess gain



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



















Pressure Systems

Chapter 10

Note: Slides are an adaption of the publisher resources



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


Measured as force per unit area

Defined mathematically

FIGURE 10-1 Pressure

Properties of a Liquid


Head: height above measurement point


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


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


Liquid column gauges


Mechanical gauges

Bourdon tube gauge

Diaphragm gauge

Bellows gauge

Nonelectrical Pressure Sensors (cont’d.)

FIGURE 10-15 A differential pressure manometer

Electronic Pressure Sensors


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



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