PLC Fundamentals

 PLC

FundamentalsModule 2: Hardware and Terminology

Module Objectives

Upon successful completion of this module, students will be able to:

Name the PLC hardware parts.Differentiate between analog and digital inputs, and give examples for each.List the inputs and outputs for a given application, and categorize them as analog and digital.Name the LOGO! Basic module parts.Connect input and output devices and program the LOGO! to perform simple tasks.

2.1 PLC Inputs and Outputs

PLC is a device that can be programmed to perform control functions.

It is a Digital Device, it stores information in the form of ON/OFF conditions referred to as binary digits or bits.

Even though the PLC uses both digital and analog signals, the CPU can understand only digital signals.

The Hardware parts of a PLC consists of:

Input ModuleThe Input Module consists of the Digital Inputs and the Analog Inputs

Go to section “2.1 PLC Hardware” and find the meaning of:

Digital Input

Analog Input

Digital and Analog Signals

Logic 1 a signal is present switch is ON.

Logic 0 signal is absent switch is OFF.

Is the switch a digital input or an analog input? What do you think?

What do we mean by Logic 1 and Logic 0 ?

What is the type of PB that is used in the circuit ?

What are the types of PBs ?

Symbols of PBs

A level transmitter checks the level of liquid in the tank and provides a varying voltage to the PLC input.

Is a level transmitter a digital or an analog input?

Video

http://www.plcedge.com/plc-inputs.html

Analog Inputs Digital Inputs

2.4 Lab Activity 1 – Page 12

Objective: To identify the difference between normally open (NO) and normally closed (NC) pushbuttons.

All sensors can be connected as inputs to a PLC, some examples

are given

Classify which are Analog and which are digital

Inputs …

The Table below shows more examples of Inputs. Classify them as digital and analog.

Output ModuleThe output module is used to connect output devices to the PLC unit. Examples of output devices include Lamps, Motors, Solenoids and Buzzers.All of these outputs can be turned ON/OFF by the PLC output module.

Central Control UnitThe Central Control Unit contains

the Central Processor which is the brain of the PLC. The CPU monitors the inputs and makes decisions based on instructions in its program memory. It performs:

Counting TimingData comparison Sequential operations

Analog or Digital Output?

Class ActivityRefer to the Case Study on page-4, and list all the inputs and outputs and classify them as analog and digital.

https://sites.google.com/site/automatedmanufacturingsystems/Home/hardware#50499799_61119

Input Output Analog/ Digital

2.4 Sensors and Actuators

A SENSOR: is an input device that senses a physical condition and converts it to an electrical signal.

The pushbutton sends an electrical signal to the PLC’s input informing the condition of the pushbutton’s contacts.

ACTUATORS: convert Electrical Signals from PLC outputs into physical conditions.

A motor starter is an example of an actuator. It will either start or stop the motor depending on the state of the PLC output.

Conduct Lab Activity 1

LOGO! Basic Module

LOGO!12/24 RC is the LOGO! Controller.

LOGO! Basic module

componentsInputs: The LOGO! Basic Module has:8 inputs and they are designated as I1, I2, I3, …. I8. Inputs I1 to I6 are digital inputs.Inputs I7 and I8 can function as digital or analog.

Outputs: The LOGO! Has: 4 digital outputs Q1, Q2, Q3, Q4.

Display Unit (LCD)

Control Panel

Module Slot: to connect the programming cable from the PLC to computer

2.5 PLC Wiring Connecting the power supply:

PLC devices need an electrical power supply that can be either an AC, or DC supply. LOGO! 12/24RC needs a DC supply.

Connecting LOGO! Inputs

Figure shows the hardware/wiring details of connecting the inputs to the LOGO! Switch S1 is connected to I1 and switch S2 is connected to I2.

Connecting sensors to the LOGO!

For two wires sensor the connection can be done easily by taking one wire to the positive terminal of the power supply and the second wire to the LOGO! Input.

For three wire sensor, sensor’s type must be taken into consideration while programming.

Connecting LOGO! Outputs

LOGO! is equipped with relay outputs. As shown in fig 2.22, various loads can be connected to the relay outputs, for example, lamps, motors, relays etc.

Lab Activities2.4 Lab Activity 1

2.4 Lab Activity 2