1. Programmable Logic Controller

2. Transducer A transducer is any device that converts energy from
one form to another.
Input transducer
(microphone) converts
sound energy to electric
energy
Output transducer
(speaker) converts
electric energy to sound
energy
Amplifier

3. Sensors Sensors are input transducers used for detecting and
often measuring the magnitude of something. They
convert mechanical, magnetic, thermal, optical, and
chemical variations into electric voltages and currents.
Photoelectric
sensor

4. Sensors Sensors provide the equivalent of eyes, ears, nose,
and tongue to the microprocessor brain.
Microprocessor
Optical
sensor
Gas
sensor
Microphone
Probe

5. Proximity Sensor Proximity sensors or switches detect the presence of
an object without making physical contact with it.

6. Proximity Sensor Applications
The object being detected is too small, lightweight, or
soft to operate a mechanical switch.
Rapid response and high switching rates are required.
An object has to be sensed through nonmetallic barriers
such as glass, plastic, and paper cartons.
Hostile environments conditions exist.
Long life and reliable service are required.
A fast electronic control system requires a bounce-free
input signal.

7. Inductive Proximity Sensor Operation
Barrel type
Block diagram
As the target
moves into the
sensing area,
the sensor
switches
the output ON

8. Capacitive Proximity Sensor
A capacitive proximity sensor can be actuated by both
conductive and nonconductive material such as wood,
plastics, liquids, sugar flour and wheat.
Operation is similar to that of inductive
proximity sensor. Instead of a coil, the
active face of the sensor is formed by
two metallic electrodes – rather like an
"opened capacitor".

9. Magnetic Switch (Reed Switch)
A magnetic switch (also called a reed switch) is composed of flat contact tabs that are hermetically sealed (air-tight).
The switch is actuated by a magnet.
Magnet N S NO NC
Common

10. Reed Switch Activation
Magnet
Reed switch
Proximity motion – movement
of the switch or magnet will
activate the switch
Rotary motion – switch is actuated twice for every complete revolution
Shielding – the shield short circuits the magnetic field; switch is activated by removal of the shield

11. Photovoltaic Or Solar Cell
The photovoltaic cell, or solar cell, is a common light-sensor device that converts light energy directly into electric energy.
Solar cell
The solar cell converts light impulses directly into electrical charges which can easily be amplified to provide an input signal to a PLC.

12. Photoconductive Or Photoresistive Cell
The photoconductive cell, or photoresistive cell, is is another popular type of light transducer. Light energy falling on this device will cause a change in the resistance of the cell.
20 Ohms Light resistance 5,000 Ohms Dark resistance
Ohms

13. Photoelectric Sensor Operation
Most industrial photoelectric sensors use a light-emitting diode (LED) for the light source and a phototransistor to sense the presence or absence of light.
Light from the LED falls on the input of the
phototransistor and the amount of conduction through the transistor changes. Analog outputs provide an output proportional to the quantity of light seen by the photodetector.
Object
to be
sensed
Light detector
Light source

14. Reflective Photoelectric Sensor
Emits a light beam (visible, infrared, or laser) from its light emitting element and detects the light being reflected.
Retro-reflective type
Operating
range
Reflector
Operating
range
Diffused-reflective type
Emitter/receiver
Target

15. Through-Beam Type Photoelectric Sensor
A through-beam photoelectric sensor is used to measure the change in light quantity caused by the target's crossing the optical axis.
Operating
range
Target
Emitter
Receiver

16. Bar Code Systems Bar code systems can be used to
enter data much more quickly
than manual methods, and are
highly accurate.
Scanner
Decoder
PLC
Diverter
The decoder receives the signal from the scanner and converts these data into the character data representation of the symbol's code.

17. Ultrasonic Sensor
An ultrasonic sensor operates by sending sound waves towards the target and measuring the time it takes for the pulses to bounce back.
The returning echo signal
is electronically converted
to a 4 mA to 20 mA output,
which supplies flow rate to
external control devices.

18. Strain /Weight Sensors
A strain gauge transducer converts
a mechanical strain into an electric signal.
The load cell provides
sensor input to the
controller, which displays the weight and controls the hopper chute.
Load cell
Controller
Hopper
Chute
ON/OFF
Control
Force
Wire type
The force applied to the gauge causes the gauge to bend. This bending action also distorts the physical size of the gauge, which in turn changes its resistance.

19. Temperature Sensors
Temperature sensors convert heat into an electric signal. There are four basic types used: thermocouple, resistance temperature detector (RTD), thermistor, and IC sensor.
The thermocouple consists of a pair
of dissimilar conductors fused together at one end to form the "hot" or measuring junction, with the free ends available for connection to the "cold" reference junction. A temperature difference between the measuring and reference junction generates a small DC signal voltage.
The resistance temperature detector (RTD) varies in resistance value with changes in temperature.
RTD
The thermistor varies in resistance value with changes in temperature
The Integrated Circuit (IC) temperature
sensor produces changes in voltage or current with changes in temperature.

20. Flow Measurement
The usual approach used in measuring fluid flow is to convert the kinetic energy that the fluid has into some other measurable form.
Electronic Magnetic
Flow Meter
Can be used with electrically conducting fluids and offers no restriction to flow. A coil in the unit sets up a magnetic field. If a conductive liquid flows through this magnetic field, a voltage is induced and sensed by two electrodes.
Flow
Magnet
Turbine
Turbine Flow Meter
Coil
The turbine blades turn at a rate proportional to the fluid velocity and are magnetized to induce voltage pulses coil.

21. Velocity/RPM Sensors
A tachometer is a small permanent magnet DC generator which when rotated produces a voltage that is directly proportional to the speed at which it is driven.
Controller
Tach
Motor M
Load
Tachometers coupled
to motors are commonly used in motor speed control
applications to provide
a feedback voltage to the controller that is proportional to motor speed.

22. Velocity/RPM Sensors
The rotating speed of a shaft is often measured using a magnetic (inductive) pickup sensor.
0 V
Pickup coil
Pole piece
N S
Magnet
Sensor
output
A magnet is attached to the shaft. A small coil of wire held near the magnet receives a pulse each time the magnet passes. By measuring the frequency of the pulses, the shaft speed can be determined.

23. Output Control Devices
A variety of output control devices can be operated by the controller output module to control traditional processes. These include:
Pilot light
Solenoid
valve
Control
relay
Alarm
Heater
Motor starter
Small motor

24. Actuators
An actuator is any device that converts an electrical signal into mechanical movement. The principle types of actuators are relays, solenoids, and motors.
The solenoid converts electric current into linear motion.
AIR
Coil
Plunger
Solenoid
Symbol

25. Solenoid Valve A solenoid valve is a combination of:
a solenoid with its core or plunger
a valve body containing an orifice
in which a disc or plug is positioned
to restrict or allow flow
When SOL A is energized, the valve spool is shifted to redirect the fluid and move the cylinder forward
SOL A
Forward motion of piston
Directional
solenoid
valve
FWD CR

26. Stepper Motor
A stepper motor converts electrical pulses applied to it into discrete rotor movements called steps. They are used to provide precise position control of movement.
Module
Stepper-motor
translator
Step
motor
Stepper motor control system
Communicates with the PLC and responds with pulse trains
Enables control
of the stepper motor
The motor will move
one step for each pulse
received