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ECET 211 Electric Machines & Controls

Lecture 4-2 Motor Control Devices:Part 3. Sensors

Part 4. Actuators

Text Book: Electric Motors and Control Systems, by Frank D.

Petruzella, published by McGraw Hill, 2015.

Paul I-Hai Lin, Professor of Electrical and Computer

P.E. States of Indiana & California

Dept. of Computer, Electrical and Information Technology

Purdue University Fort Wayne Campus

Prof. Paul Lin

Lecture 4 Motor Control Devices

Chapter 4. Motor Control Devices

• Part 1. Manually Operated Switches

• Part 2. Mechanically Operated Switches

• Part 3. Sensors

• Part 4. Actuators

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Part 3 Sensors

Sensors

• Devices that are used to detect, and often to measure, the

magnitude of real world parameters such as distance, position

velocity, acceleration, temperature, sound, force, light, etc

• Operated by converting mechanical, magnetic, thermal, optical,

and chemical variations into electrical voltage and currents.

• Sensors are categorized by what they measure

Proximity Sensors, Photoelectric Sensors

Hall Effect Sensors, Ultrasonic Sensors

Temperature Sensors, Velocity and Position Sensors

Flow Measurement, Magnetic Flowmeters

• Play an important role in modern manufacturing process control

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Part 3 Sensors

Figure 4-33 Typical sensor Applications

• Light sensor

• Pressure sensor

• Bard code sensor (reader)

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Part 3 Sensors: Proximity Sensors

Proximity Sensors

• Detect the presence of an object without

physical contact (non-contact)

• Object types: metal, glass, plastics,

most liquids

• Sensor measurement methods or

operating principles depends on the

type of matter being detected:

Inductive type:

• for ferrous metals (containing

iron), nonferrous metals (copper,

aluminum, brass)

Capacitive type:

• for sensing metal objects

• nonmetallic materials (paper,

glass, liquids, cloth, etc)

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Figure 4-34 Proximity sensor and symbols

Part 3 Sensors: Proximity Sensors

Inductive Proximity Sensors

• Detect the presence of a metal object using the principles of AC

inductance, where a fluctuating AC current induces an electromotive

force (emf) in a sensing target

• Figure 4-35 shows a block diagram of the Inductive proximity

sensors

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Figure 4-35 Inductive Proximity sensor

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Part 3 Sensors: Proximity Sensors

Inductive Proximity Sensors

• Operating point – the point at which

the proximity sensor recognize an

incoming target

• Release point – the point at which

the proximity sensor recognizes an

outgoing target

• Hysteresis

Specifies as a percentage of the

nominal sensing range

Needed to keep proximity

sensors from chattering when

subject to Shock and Vibration,

Slow-moving targets, or Minor

disturbances such as electrical

noise and temperature drift.

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Figure 4-36 Proximity sensor sensing range

Part 3 Sensors: Proximity Sensors

Inductive Proximity Sensors

• Sensor operating voltage levels: 24

V DC or 120 V AC

Figure 4-37 Typical two-wire and

three wire sensor connections

• 3-wire DC proximity sensor: Figure

4-37a has the positive and negative

DC line leads, and NO or NC

contact

• 2-wire AC proximity sensor: Figure

4-37b, the load is connected in

series with L1 and L2 power source

• Load type: starter, magnetic

contactors, relays, solenoids

• Should not be used to directly

operate a motor Prof. Paul Lin 8

Figure 4-37 Typical two-wire and three-wire sensor connections

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Proximity Sensors

Capacitive Proximity Sensors

• Detect the presence of a metal object using the principles of

capacitance (C = ε A/d); where C is the capacitance, ε is the

dielectric constant, A is the metal electrode area, and d is the

distance between the two electrodes

• Figure 4-38 Capacitive proximity sensor

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Proximity Sensors

Capacitive Proximity Sensors

• Figure 4-39 Capacitive proximity sensor liquid detection

• An application example for detecting empty container

Cardboard container: lower dielectric constant, εC

Liquid: higher dielectric constant, εLiquid

• Empty containers are automatically diverted via the push

rod

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Photoelectric Sensors

Photoelectric Sensors

• An optical control device that operates by detecting a visible or

non-visible beam of light and responding to a change in the

receiving light intensity.

• Two components: a transmitter (light source) and a receiver

(sensor), may or may not be housed in the same unit

• Figure 4-40 Photoelectric sensor

• Scan techniques to detect object

Through-Beam Scanning

Retro-reflective Scanning

Diffuse scanning

Fiber-optics

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Through-Beam Scanning Photoelectric Sensors

Direct scan, placed the

transmitter and receiver in

direct line with each other

Detect: Light being blocked -

Yes/No

Long range sensing: up to 300

feet

More reliable method in area

of heavy dust, mist, and other

types of airborne

contaminants

Figure 4-41 Through-beam

scan

An example: Garage door

opener

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Photoelectric Sensors

Retro-reflective Scan Sensor

(Figure 4-42)

• The transmitter and receiver

are housed in the same

enclosure

• Used for medium-range

applications

• May not be able to detect shiny

targets

• Because it cannot differentiate

the Light reflective back from

the reflector vs. Light reflective

back from the target

Polarized Retro-reflective Scan

Sensor (Figure 4-43): Over come

this problem

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Photoelectric Sensors

Diffuse Scan Sensor

• The transmitter and receiver are housed in the same enclosure.

• A light reflector is not needed.

• Receiver picks up some of the diffused (scattered) light.

• Maximum sensing length: 40 inch

• Figure 4-44 Diffuse scan sensor: inspect the presence of the

polarity mark on a capacitor (or any other mark inspection)

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Fiber Optics Sensor

Use a flexible fiber-optic cable that

channel light from emitter to receiver

Can be used with Through-beam,

Retro-reflective scan, or diffuse scan

sensors: Figure 4-45 Fiber optic

sensors

Immune from all forms of electrical

interference

Can be safely used in the most

hazardous sensing environment such

as:

• Refinery for producing gases

• Grain bins

• Mining

• Pharmaceutical manufacturing

• Chemical processing

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Part 3 Sensors – Hall Effect Sensors

Detect the proximity and

strength of magnetic field when

a current carry conductor is

placed into a magnetic field, a

voltage will be generated

perpendicular to both the current

and the field

Figure 4-46 Hall effect Sensor

Analog-Type Hall Effector

Sensor (Figure 4-47) – Current

transformer used in the clamp

meter for measurement current

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Part 3 Sensors – Hall Effect Sensors

Digital-Type Hall Effector Sensor

Figure 4-48 Monitoring speed using a Hall effect sensor

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Part 3 Sensors – Ultrasonic Sensors

Ultrasonic Sensor (operating

theory)

• Operates by sending high

frequency sound waves toward the

targets and measuring the time its

takes for the pulses to bounce back

Figure 4-49 Ultrasonic sensor with 4

to 20 mA output

• 1) Detecting the level of chocolate

• 2) Detecting transparent bottles

• 3) Liquid level detection

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Part 3 Sensors – Ultrasonic Sensors

Figure 4-50 Ultrasonic wind sensor

• Wind turbine system application for

determining wind speed and direction

• Four sensors, one at each major

compass point (N-S, E-W)

Operating Theory

• N S, E W: fire ultrasonic sound

pulses to opposing sensors

• In still air: all pulses’ time of flight are

equal

• Wind blow: it increases the time of

flight for pulses traveling against it

• System calculates the wind speed

and direction

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Part 3 Sensors – Temperature Sensors

Types of sensors

• Thermocouple:

High temperature measurement; output DC mV

Type B (870 °C to 1700 °C / 1000°F to 3100°F)

Type E (-200 °C to 900 °C / -330°F to 1600°F)

Type J (0 °C to 760 °C / 32°F to 1400°F)

Type K (-200 °C to 1260 °C / -330°F to 2300°F)

Types R, S, T, C, P

• Resistance Temperature Detector (RTD):

Positive temperature coefficient (PTC) R: Temp

increase => R increase

• Thermistor: negative temperature coefficient (NTC) R

• IC sensor

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Part 3 Sensors – Temperature Sensors

Types of sensors

• Thermistor:

Negative temperature coefficient (NTC) R

Temperature range: -100 °C to 500 °C

• IC sensor

RTD, Thermistor, Thermocouple Comparison Chart,

http://digital.ni.com/public.nsf/allkb/C50FA55B3B2F85D986257

2D00083350E

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Criteria Thermocouple RTD Thermistor

Temp Range -267 °C to 2316 °C -240 °C to 649 °C -100 °C to 500 °C

Accuracy Good Best Good

Linearity Better Best Good

Sensitivity Good Better Best

Cost Best Good Better

Part 3 Sensors – Temperature Sensors

Figure 4-51 Thermocouple

heat sensor

• Hot junction (measurement

junction)

• Cold junction (reference

junction)

• Type K (-200 °C to 1260 °C /

-330°F to 2300°F

• Hot junction at 300 °C =>

12.2 mV

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Part 3 Sensors – Temperature Sensors

Figure 4-52 Thermocouple tip

styles

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Figure 4-53 Typical thermowell

installation

Part 3 Sensors – Temperature Sensors

Resistance Temperature Detector (RTD):

• Positive temperature coefficient (PTC) R

• Temp increase => R increase

• Temperature Ranges: -50 ° C to 500 ° C for thin film RTD, -200

°C to 850 ° C for wire-wound RTD,

http://www.omega.com/temperature/pdf/rtd_gen_specs_ref.pdf

• Figure 4-54 Resistance temperature detector

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Part 3 Sensors – Temperature Sensors

Thermistors

• Thermally sensitive resistor

• NTC (Negative Temp

Coefficient): Temp increase,

R decrease

• Figure 4-55 Thermistors

IC Temperature Sensor

• Figure 4-56 Integrated circuit

temperature sensor

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Part 3 Sensors – Velocity & Position Sensors

Tachometer

• Figure 4-57 Tachometer

generator

Magnetic Pickup Sensor (Figure

4-58)

Encoder (Figure 4-9 Optical

encoder)

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Figure 4-58Figure 4-59

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Part 3 Sensors – Flow Measurement

Turbine Flowmeters

• Like windmills utilizes their

angular velocity (rotational

speed) to indicate flow

velocity

• Figure 4-60

Target Flowmeters

• Measure the drag force on

the inserted target flat disk,

and convert it to the flow

velocity

• Figure 4-61

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Part 3 Sensors – Flow Measurement

Magnetic Flowmeters

• Electromagnetic flowmeters or induction flowmeters

• Obtained the flow velocity by measuring the changes of

induced voltage of the conductive fluid passing across a

controlled magnetic field

• Figure 4-62 Magnetic flowmeter

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Part 4 Actuators

Relays

Solenoids

Solenoid Valves

Stepper Motors

Servo Motors

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Part 4 Actuators

Actuator

• A device that converts electrical signal to mechanical movement.

Actuator Types

• Relays

• Solenoids

• Solenoid Valves

• Stepper Motors

• Servo Motors

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Part 4 Actuators Figure 4-63 Electromagnetic

relay

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Figure 4-64 Relay motor

control circuit

Part 4 Actuators

Figure 4-65 Double-break contacts

• Relay contacts use two pairs of

contacts that open circuit in two

places, creating two air gaps

• Dissipate heat more rapidly =>

Longer life

• Enabling the contact to handle

higher voltages

• Benefits: Greater DC load

breaking capability and better

isolation of contact

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Part 4 Actuators

Dry contact

• A dry contact refers to one that

has both terminals available and

in which neither contact is initially

connected to a voltage source

Figure 4-66 shows a magnetic

starter with an extra dry contact

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Part 4 Actuators

Solenoid

• A electromechanical

solenoid is a device that

uses electrical energy to

cause mechanical control

action

• A solenoid consists of

A coil

Frame

Plunger (or armature)

• Types: AC or DC solenoid

• Categories: Linear, Rotary

• Action: energized vs

deenergized

• Figure 4-67 Solenoid

construction and operationProf. Paul Lin 34

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Part 4 Actuators

Solenoid

• A electromechanical

solenoid is a device that

uses electrical energy to

cause mechanical control

action

• A solenoid consists of a

coil, frame, plunger (or

armature), Figure 4-67

Solenoid construction and

operation

• Types: AC or DC solenoid

• Categories: Linear, Rotary;

Figure 4-68

• Actions: energized vs

deenergized

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Part 4 Actuators

Solenoid Valve

• A combination of a

solenoid coil operator and

value

• It controls the flow of

liquids, gases, steam, and

other media.

• Figure 4-69 Solenoid value

construction and principle

of operation

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Part 4 Actuators

Figure 4-70 Solenoid

valve operated tank

filling and empty

operation

• Tank filling operation:

Solenoid A

Fill tank sensor

Control relay

(1CR)

• Tank emptying :

Solenoid B

Empty tank sensor

Control relay

(2CR)

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Part 4 Actuators

Stepper Motors

• A brushless DC motor with the rotor

carries a set of permanent magnets,

and the stator has a set of coils.

Figure 4-72 Stepper Motor

operation

• The shaft of a stepper motor rotate

in discrete increments when

electrical command pulsed are

applied to it in proper sequence.

• An example: a stepper that 1.8

degree per pulse step, would take

200 pulses to make a 360 degree

rotation

• Stepper system are used most often

in “open-loop” control system

• Figure 4-71 Stepper motor/drive

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Part 4 Actuators

Servo Motors

• All servo motors operate in close-

loop mode with speed or position

feedback.

• Stepper system are used most often

in “open-loop” control system

• Figure 4-73 Open- and closed-loop

motor control system

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Part 4 Actuators

Figure 4-74 Closed-loop servo

system

Major component

• Controller

• Servo amplifier

• Servo motor

• Load

• Feedback devices (position, speed)

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Part 4 Actuators Figure 4-75 Brushless DC motor with integrated drive

Major component

• Reference, Run/Stop, FWD/REV

• Controller

• Driver

• Brushless DC motors (BLDCs), with three-phase stator (A-B-C)

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Summary & Conclusion

Questions?Contact Prof. Lin through:

Email: lin@ipfw.edu

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