PLCs_part1_printout

PLCs_part1_printout - 1 LAB LAB 11 11 INTRODUCTION TO PLCs...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 1 LAB LAB 11 11 INTRODUCTION TO PLCs INTRODUCTION TO PLCs Rajesh Rajamani ME 4231 Department of Mechanical Engineering University Of Minnesota PLCs A PLC (Programmable Logic Controller) works by looking at its inputs, and depending upon their state, turning ON/OFF its outputs The logic that determines the outputs is entered by the user, usually through a software program. User Entered Program Inputs Outputs 2 PLCs PLCs were invented to replace the sequential relay circuits used in machine control. What is a relay ? A relay is an electrically operated switch. INTRODUCTION TO RELAYS This circuit would not work too well for starting your car +- Starter motor Consider the following starter circuit 3 INTRODUCTION TO RELAYS Problem: A massive amount of current is required to turn the starter motor and crank your engine That much current would burn out the contacts of an ordinary switch Also You want shortest path from battery to starter You dont want that many amps near you +- INTRODUCTION TO RELAYS Solution: Use a relay The contacting plate is big enough to carry the amps. +- switch Starter motor solenoid 4 INTRODUCTION TO RELAYS A relay is an electrically operated switch It is made up of a coil that can be energized with just a little power a moving armature(plunger) of some sort that pulls in when the coil is energized. one (or more) pairs of contacts that the plunger makes an electrical connection with. These contacts usually carry the high power. PLCs - HISTORY PLCs were introduced in the late 1960s Primary Motivation Eliminating the large cost involved in replacing the complicated relay based machine control systems In machine control systems, when production requirements changed, so did the control system. Changing the control system was time consuming and expensive when relay circuits were being used 5...
View Full Document

Page1 / 18

PLCs_part1_printout - 1 LAB LAB 11 11 INTRODUCTION TO PLCs...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online