At2 H 01 Introduction Improved

DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY SENSORS TECHNOLOGY Introduction

a.

Transducer :

Terms - A transducer is a device, usually, that converts one type of energy to another. Most

transducers are

either sensors or actuators. Example of transducer :

Type of Sensor or Transducer Type of Energy Source

That Produces Voltage or Current

Type of Sensor or Transducer That Produces a Change of Resistance or Impedance

Motion

Generator

Linear potentiometer

Light

Solar cell, photovoltaic

Cds Cell

Force (pressure)

Piezoelectric

Strain gauge

Temperature

Thermocouple

RTD

Magnetic

Transformer hall effects

Magneto resistive

Chemical

Batteries, fuel cells

Different concentrations

Sensors : Terms : A sensor is defined as a device that is sensitive to motion, heat, light, pressure, electrical, magnetic and other types of energy.

An

example of sensory part and the

actuators

in the human body

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY

1. An Open loop system :

Close loop system :

CONTROL PART

OPERATIVE PART SENSORS

INPUT INTERFACE

PROCESSOR (PLC) 1.

Actuators

STRUCTURE OF AN AUTOMATED SYSTEM

output interface Handout

AT2-222 – Sensors & Fiber Optic Technology Chap. 1 – Sensors : Introduction

Preactuators

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UT OMA TION T ECHNOL OGY 2.

INDUSTRIAL CONTROL

LV electrical distribution

Machine or process

Actuators

Data acquisition Power Control

Data processing

Man machine dialogue Assessment

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UTOMA TION TECHNOL OGY 3.

TYPES OF SIGNALS

Generally a processor in industrial automation receives and send three types of signal. There are: 3.1. Discrete signal All signals that can have only two logical states i.e. ON/OFF or bit 1/0 are called discrete signals. Example: The circuit is open, the lamp is OFF. It receives 0V from the 0V

supply.

The circuit is closed, the lamp

24V

is ON. It receives 24V from the supply. 24V

The 24V/0V is called discrete signal. The lamp is said at logic 1 when it receives 24V, and on

24V

the other hand, if it receives 0V, it is said at logic 0. V (volt)

V (volt)

24

0

t (s)

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0

t (s)

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UTOMA TION TECHNOL OGY Sensors that produce ON/OFF signals are called discrete sensors. Examples: 

Limit switch



Proximity sensor

3.2. Digital signal All signals that are the combination of 0s and 1s (in BCD) are called digital signals. However these signals can be converted to Hexadecimal or Decimal value. Example: In PLC communication the letter P is represented by 1010000. The bit 1s are at 5mA and the bit 0s are at 0mA. i (mA) (MSB)

1

(LSB)

0

1

0

0

0

0

5

0

t (s)

Remark: Certain author doesn’t differenciate digital and discrete signals. Both are treated as digital signals. Sensors that produce digital signals are called digital sensors. Example: 

i (mA)

Absolute rotary encoder 20

3.3. Analog signal Analog signals are continuous signals. Example: A signal sent by a level sensor is analog signal from 4mA to 20mA. Sensors that produce continuos signals are called

0

30

d (m)

analog sensors. Examples: Handout

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UTOMA TION TECHNOL OGY

4.



Level transducer



Temperature transducer

General principle of sensors:

ENERGY INPUT

INFORMATION ACQUISITION

OUTPUT SIGNAL

SENSOR 4.1. Discrete Sensors: The output signal has only two states -high level (24V or logic 1) or low level (0V or logic 0).

ELECTRIC ENERGY

OBJECT PRESENCE

INFORMATION ACQUISITION

ELECTRIC OUTPUT SIGNAL

DISCRETE 0V-24V

DISCRETE SENSOR

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DEPT. of ELECTRICAL EQUIPMENT AND INSTALLATION TECHNOLOGY AT - A UTOMA TION TECHNOL OGY 4.2. Digital Sensors: The output signal is combination of 1s and 0s.

ELECTRIC ENERGY OBJECT POSITION

INFORMATION ACQUISITION

ELECTRIC OUTPUT SIGNAL

DIGITAL

DIGITAL SENSOR 4.3. Analog Sensors: The output signal is a continuos signal.

ELECTRIC ENERGY OBJECT POSITION

INFORMATION ACQUISITION

ELECTRIC OUTPUT SIGNAL

ANALOG 4mA –

ANALOG SENSOR

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