PROGRAMMABLE LOGIC CONTROLLERSlogic controller. PROCEDURE o Learner reads workbook for PLC-1. o...

PROGRAMMABLE LOGIC CONTROLLERS

(PLC)

Facilitator Guide

TABLE OF CONTENTS INTRODUCTION PAGE 1 PROCEDURE OF CONDUCTING A PROGRAMME / LESSON PAGE 2 TRAINING OBJECTIVE AND TRAINING AIDS PAGE 3 PROGRAMME NO.1: PLC-1 OBJECTIVES PAGE 4 MODEL ANSWERS: SELF-TEST NO. 1 PAGE 5 SELF-TEST NO. 2 PAGE 6 SELF-TEST NO. 3 PAGE 8 SELF-TEST NO. 4 PAGE 9 PROGRAMME NO.2: PLC-2 OBJECTIVES PAGE 10 MODEL ANSWERS: SELF-TEST NO. 1 PAGE 11 SELF-TEST NO. 2 PAGE 12 SELF-TEST NO. 3 PAGE 14 PROGRAMME NO.3: PLC-3 OBJECTIVES PAGE 17 MODEL ANSWERS: SELF-TEST NO. 1 PAGE 18 SELF-TEST NO. 2 PAGE 19 SELF-TEST NO. 3 PAGE 20 PROGRAMME NO.4: PLC-4 OBJECTIVES PAGE 22 MODEL ANSWERS: SELF-TEST NO. 1 PAGE 23 SELF-TEST NO. 2 PAGE 25 SELF-TEST NO. 3 PAGE 26 PLC LADDER DIAGRAM OF BLOCK SORTING MACHINE PAGE 29

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Back to Table of Contents 1

INTRODUCTION This PLC series is aimed at providing first level instruction to learners entering the field of automatic control from an electrical background, This series comprises of 4 separate programmes which should be presented in numerical sequence for the desired effect. We have striven to provide clear visual demonstration of concepts and principles using typical components and popular trade names. We are painfully aware of deviances which exist between certain manufacturers, especially in respect of PLC software design. It is envisaged that the examples provided in this series will by typical of those you and your learners will have available at your workstations and equipment. This series has been designed to address the "understanding" factor of how PLC's function in relation to existing "Relay Control" technology. The series comprises of:

o Video Programme. o 1 Learner's workbook. o 1 Facilitator's Guide.

OTHER RESOURCES Other resources may be obtained by contacting:

o Tech AV for training material. o PLC Direct for PLC products.


PROCEDURE FOR CONDUCTING A PROGRAMME (LESSON)

IMPORTANT NOTE This series has been presented purely as a TRAINING AID and in no way replaces an experienced Tutor or Facilitator. SUGGESTED LEARNING METHOD

o The learner is provided with a personal copy of the workbook. o The learner reads through the workbook and is guided by the written instructions

(e.g. View a video section, perform a self-test etc.). o Learner views video section and then completes self-test exercise as dictated in the

workbook. NOTE: For the best effect it is strongly recommended that learning begins at PLC-1 and programmes are attempted in numerical sequence. SUGGESTED LEARNING ENVIRONMENT The ideal learning environment would be a workstation comprising of:

o PLC simulator. o PC unit. o All necessary work tops etc. o A quiet surrounding.

Learners should be able to learn at their own pace and for this reason the PLC series is not particularly suited to group learning.


TRAINING OBJECTIVES AND AIDS

TRAINING OBJECTIVE The overall training objective of this series is: Upon successful completion of this series the learner will be able to demonstrate his / her ability to describe the fundamental principles of PLC control systems and interpret ladder logic diagrams. TRAINING AIDS

o The Learners Workbook is the primary aid. o The video programmes supplement the workbook references.

OPTIONAL TRAINING AIDS

o Manufacturers catalogues and manuals. o Models and simulators (see back pages for examples available). o PLC controlled equipment in your plant, factory etc. o Operators manuals where applicable.


PROGRAMME NO. 1 PLC-1

FUNDAMENTALS OF AUTOMATIC CONTROL OBJECTIVES At the end of this programme the learner will be able to:

o Identify the 3 basic stages of a typical automatic control system. o Describe the operation of a two state switch and a two state logic. o Explain the operation of a two state relay and describe the function as a control

device. o Explain the basic differences between a relay logic controller and a programmable

logic controller. PROCEDURE

o Learner reads workbook for PLC-1. o Learner views video PLC-1. o Learner stops at Review breaks and performs relevant exercise. o Learner checks her / his responses and reviews areas of non-performance. o Course Controller / Facilitator assists where necessary.

RESOURCES REQUIRED

o PLC Learner workbook. o PLC-1 video.


PLC-1: SELF TEST EXERCISE NO. 1

INSTRUCTIONS

o Without the aid of notes or other references answer the question below. o When completed, check your answers against your notes, the video or with your

Facilitators.

QUESTIONS YES NO

1. What are the 3 fundamental steps of any process? a) Information gathering. b) Decision making. c) Action.

2. What is the basis of all automatic control systems?(write answers in the blocks.)

3. On the simple block sorting machine what role does the height bar play, in respect of your answer to question No. 2? Decision Making.

4. A logic acts only upon what decision? Yes or No.

INPUT

INFORMATION

LOGIC

DECISION

OUTPUT

ACTION


PLC-1: SELF-TEST EXERCISE NO. 2

INSTRUCTIONS

o Without the aid of notes or other references answer the questions below. o When completed, check your answers against your notes, the video or with your

Facilitators.

QUESTIONS YES NO

1. With what have we replaced the height bar in our improved block sorter? Limit switch.

2. What device causes the ejector to operate? Solenoid.

3. What device decides when to cause the ejector solenoid to function? Relay.

4. From your answers of questions 1, 2 and 3 which device is: a) The input device: Limit Switch. b) The logic device: Relay. c) The output device: Solenoid.

5. In which of two possible inactive states can a simple switch exist? a) Normally Open. b) Normally Closed.

6. What signal or message does the logic see when, a) a N/O switch is activated: YES. b) a N/C switch is activated: NO.

7. What, basically, is a relay? An electrically activated switch.


8. Describe the symbols shown below.

Normally Open Contacts.

Normally Closed Contacts.

9. In what state, or conditions, are contacts always shown in a circuit diagram? In their normal, or inactive, state.

10. Describe the symbolised device shown below.

A Double Pole, Single Throw Relay.



INSTRUCTIONS

o Without the aid of your notes or other resources answer the questions below. o When completed, check your answers against your notes, the video or with your

Facilitators.

QUESTIONS YES NO

1. What, in basic terms, is logic (in terms of circuitry)? The combination of ON and OFF signals in an order.

2. What does a ladder logic diagram show us? How input, logic and output devices are identified and wired together in an order.

3. On the block sorting machine there are two primary input sensors. Name the function of each: (i.e. what they signal to.) a) Upper limit sensor – operates ejector solenoid via a control

relay. b) Lower limit sensor -triggers a counter which counts the

short blocks.

4. When a long block activates both sensors, which working device operates? Ejector solenoid.

5. Why does the counter not operate when a long block passes the sensors? Because the counter circuit is wired to the counter via the N/C contacts of the control relay. These contacts open when the relay is energised by the upper sensor, thereby preventing the trigger signal from reaching the counter.


PLC-1: SELF-TEST EXERCISE NO. 4

INSTRUCTIONS

o Without the aid of your notes or other resources answer the questions below. o When completed, check your answers against your notes, the video or with your

Facilitator.

QUESTIONS YES NO

1. For what reason do we not connect the lower limit-switch (short block counter) directly to the counter? Because it would count the long blocks as well as the short ones.

2. Through which relay contacts do we connect the counter circuit? The normally closed (N/C) contacts.

3. Explain, using a diagram and explanation, how the counter is not activated when a long block passes the two sensors.

DIAGRAM:

EXPLANATION: A long block activates both sensors. The upper limit switch closes, passing power to the control relay CR1. Two things now happen - (1) CR1 N/O contact closes, operating the ejector solenoid; and (2) CR1 N/C contacts open, interrupting the power flow in the counter circuit -thus preventing the trigger signal from the lower limit switch reaching the counter.


PROGRAMME NO. 2 PLC-2 RELAY LOGIC DEVICES AND LADDER DIAGRAMS

OBJECTIVES At the end of this programme the learner will be able to:

o Identify typical symbols in relay ladder logic diagrams. o Identify typical input, logic and output devices. o Describe typical circuit operation from a ladder logic.

PROCEDURE


RESOURCES REQUIRED




INSTRUCTIONS

o Without consulting the Resource Notes, or the video, answer the questions below. o When completed check your answers.

QUESTIONS YES NO

1. What do the rungs of a ladder logic diagram represent? Device circuits. They inform us how the various devices are wired together.

2. What do the rails of a ladder logic diagram represent? Power supply rails.

3. What is the primary purpose of setting out an automatic process system in ladder form? To indicate how the input, output and logical devices are wired together. This helps us follow the power flow in a logical and progressive sequence.

4. What are the most basic symbols used on a typical relay logic diagram? Contacts and coils.

5. In what state are all devices represented on a diagram? In their normal or inactive state.



INSTRUCTIONS

o Without consulting the Resource notes or the video, answer the questions below. o When completed check your answers.

QUESTIONS YES NO

1. What, in basic terms, is a discreet device? A two-state or an on / off device.

2. What, in basic terms, is an analogue device? A sensor that produces a voltage signal which varies according to the physical condition it is measuring.

3. List 3 typical discreet sensor devices. a) Limit Switch. b) Float Switch. c) Thermostat.

4. List 2 typical analogue sensor devices. a) Microphone (where sound pressure is converted to a

voltage signal). b) Temperature sensor.

5. What is the most fundamental device used in relay logic control circuits? The electro-mechanical relay.

6. Which part of a relay is represented with a circle? The coil.

7. What feature of a relay determines the "logic"? The state of its switching contacts.

8. When a relay's coil is energised, what state do the associated contacts change to? Their active state.


9. How do we associate (link) the relays contacts on a ladder diagram? By the coil designation or the operating device.

10. What type of electro-mechanical device will retain a circuit, even if the system is de-energised? A latching or ratchet relay.

11. A timer will "time out" causing its internal contacts to do what? Change from their inactive state to their active state.

12. An electrical timer or counter will reset only when what happens? When power to the device is interrupted.



INSTRUCTIONS

o Without consulting the Resource notes or the video, answer the questions below. o When completed check your answers.

QUESTIONS YES NO

1. In the space below sketch a relay ladder circuit to satisfy the following conditions: A base motor circuit with a:

o Stop and Start control. o Retain control. o Timer control.


2. In your own words explain the operation or power flow through rung No. 1. (Refer to your diagram.) KEYS: Series circuit; through 1 PB when closed; through the N/C contacts of 2PB to the motor relay M1. EXPLANATION: Once 1 PB is activated, power flows through the now closed contacts of 1 PB, through the normally closed contacts of 2PB energising the control relay. 1 PB and 2PB represent a series or "and" circuit since both 1 PB AND 2 PB must be closed in order for power to flow across the rung to coil 1M.

3. In your own words explain how the "latching" circuit operates. KEYS: M1 N/O relay contacts (1 M) in series with timer relay contacts (HMR); power flows via contacts 1 M on parallel branch; branch in parallel with 1 PB; power continues via 2PB to motor coil; contacts 1 M remains closed when 1 PB is released. EXPLANATION: Once relay coil 1 M is energised, its contacts M1 on rung 2 change to their active state and close. At this point in time, timer contacts TMR1 have not yet changed state and therefore remain in their inactive state i.e. closed. Power now flows through M1, TMR1 and 2PB to 1M maintaining the coil in its energised position even after the start switch 1 PB has been released. We can see that power to the coil is retained and contact M1 on rung 2 is referred to as the latching contact. The circuits on rungs 1 and 2 represented by the contacts 1PB, M1 and TMR1 form a parallel orOR circuit since the closure of either 1PB OR M1 will pass power to the relay coil via the stop switch 2PB.


4. In your own words explain how the timer circuit controls the motor, i.e. how it stops the motor. KEYS: N/C timer contacts on rung 2; timer coil on rung 3 will "time out" when N/C contacts become activated; power flow interrupted in rung 2; power flow interrupted in rung 3 as 1 M contacts change to N/O ; timer re-sets. EXPLANATION: Once relay 1M has energised, power passes to timer 1TMR through the now closed contacts M1. The timer now begins its timing cycle and after the pre-set delay time has elapsed, its contacts (TMR1) on rung 2 open. The retain circuit is interrupted and the relay coil is unlatched causing the relay coil to de-energise. Both sets of contacts (1M) now return to their normal or inactive state and open. Power flow to the timer is interrupted, and the timer is automatically reset ready for the next timing cycle. The retain circuit is also rendered inoperative.



PLC HARDWARE AND LADDER LOGIC OBJECTIVES At the end of this programme the learner will be able to:

o Describe the purpose and function of I / O's. o Decipher address locations and devices involved in PLC ladder logic diagrams. o Describe how a CPU processes input signals to control the state of outputs device. o Explain the basic differences between a relay logic controller and a programmable

logic controller. PROCEDURE

o Learner reads workbook for PLC-3. o Learner views video Learner stops at Review breaks and performs relevant exercise. o Learner checks her / his responses and reviews areas of non-performance. o Course Controller / Facilitator assists where necessary.

RESOURCES REQUIRED




INSTRUCTIONS

o Without consulting your notes or the video answer the questions that follow. o When completed check your answers.

QUESTIONS YES NO

1. What is the term we use to refer to the input and output interfaces on a PLC unit? I / O’s.

2. What prevents external input signal voltage from entering the Processor circuits? An isolating circuit.

3. What do we call the references that are marked at each PLC input or output point? Address locations.

4. What devices are usually connected to the inputs? Discrete or analogue sensing devices (sensors).

5. What devices are typically connected to the outputs? Motors, indicator lamps, solenoids, alarms.



INTRODUCTION

o Without consulting your resource notes or video, answer the following questions. o Check your answers when completed.

QUESTIONS YES NO

1. In a PLC ladder logic diagram what symbols are used to denote the following: a) An input device

Normally Open and Normally Closed contacts.

b) An output device.

A coil symbol.

2. What information is always provided, on a ladder diagram, along with a symbol? The device address location.

3. As far as a Processor is concerned it needs only know two details, which are? a) The address location of each device. b) What to do with the on / off signals appearing at each input

point.



INSTRUCTIONS

o Without consulting your notes, or the video, answer the following questions. o Check your answers when completed.

QUESTIONS YES NO

1. How does the Central Processing Unit of a PLC see an input location? As a normally closed or normally open relay contact.

2. How does the CPU see a contact symbol entered in the user programme? As an instruction to examine the state of a specific input location for an ON or an OFF voltage signal.

3. How does the CPU interpret this symbol? Examine the input location for an ON voltage signal.

4. How does the CPU interpret a N/C symbol? Examine the input location for an OFF voltage signal.

5. Where does the CPU look for voltage signals? At the input address location.

6. If the CPU finds a voltage or an ON signal at an address location, what does it do in respect of the contact entered in the user programme? It will treat the contact as if it were in its active state / or ON.

7. If the CPU finds an ON voltage signal at the address location where N/O contacts are programmed into the logic, it will? (tick correct answer) a) Pass power in the rung. b) Interrupt power in the rung.


8. If the CPU finds an ON voltage signal at the address location where a set of N/C contacts have been specified, it will? (tick correct answer) a) Pass over the rung. b) Not pass over the rung.

9. If the CPU finds an OFF (NO) voltage signal at the address location where N/C contacts have been entered into the logic, it will? (tick correct answer) a) Pass power in the rung. b) Not pass power in the rung.

10. If the CPU finds an OFF (NO) voltage signal at the address location where N/O contacts have been entered into the logic, it will? (tick correct answer) a) Pass power in the rung. b) Not pass power in the rung.

11. In your own words describe what is meant when we say a circuit is true. When all conditions relating to the “active” state of all contacts on a particular rung are met.



THE PLC AS AN INFORMATION PROCESSOR OBJECTIVES At the end of this programme the learner will be able to:

o Describe how the PLC processes information by a process called SCAN. o Describe the basic operation of the CPU and its memory circuits. o Describe the internal logic devices that exist in the virtual world of the PLC. o Explain the operation of contacts, coils, timers and counters that appear in a typical

PLC ladder logic diagram. PROCEDURE


RESOURCES REQUIRED




INTRODUCTION


QUESTIONS YES NO

1. Name the three main sections of a CPU. a) The Processor. b) Memory. c) Power Supply.

2. What is the function of the processor? It does the thinking and calculating.

3. Name the three things a processor does during a scan cycle. a) Checks the state of the circuits. b) Solves the user programme. c) Sets the state of the outputs.

4. What are the two main functions of the memory section? a) Storing instructions. b) Storing data.

5. Name the two kinds of memory in the CPU a) System memory or ROM. b) Application memory or RAM.

6. What is the function of the ROM? It initializes (activates) the processor.

7. What is the function of the RAM? It stores information concerning the input, output and logic processing.


8. The system memory arranges the memory cells into groups of cells. How many cells are usually found in a group, and what do we call this group of cells? a) 16. b) A Register.

9. Why does a register need to have a specific address? So that the processor knows where to find it.

10. A binary digit or bit can have either one of two values. Name them: 0 or 1.

11. Name the fundamental unit of information used in most computer systems. Word.



INTRODUCTION


QUESTIONS YES NO

1. Name one important characteristic of internal logic devices They are imaginary.

2. Name three internal logic devices a) Relay. b) Counter. c) Timer.

3. When a normally open contact is entered into the logic by the user programme, what is its function? It examines the input for an "on" voltage condition, and if it finds it there, it passes power.

4. What is the function of a normally closed contact when written into the PLC programme? It examines the input for an "off" voltage condition, and if it finds it there, it passes power.

5. What is the basic function of a coil? It passes power (via its contacts) to other circuits.



INTRODUCTION


QUESTIONS YES NO

1. What is the purpose of the normally closed contact Y2 (refer diagram below)?

Without contact Y2 (inhibit), the counter would count the long blocks as well as the short blocks.


2. In your own words, explain the operation of the "equal to" contact on rung 6 of the diagram below.

When the value in the counter is equal to the pre-loaded value (10), the contacts will close passing power along the rung to output coil Y3.

3. In your own words, explain how the counter is reset.

When the "end of cycle" timer times out, contact T1 closes resetting the counter.


4. Explain the purpose of the retain circuit on rung 6.

It ensures that coil Y3 remains energised after the closure of the "equal to" contact i.e. when 10 short blocks have been counted. Because timer T1 must have an uninterrupted supply of power (via contacts Y3) to complete its timing cycle, this condition is ensured by the latching the coil Y3.

5. Explain the function of the "end" coil on rung 8 of the diagram.

When the processor sees this instruction (coil), it knows that it must return to rung 1 and commence a new scan cycle.


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PROGRAMMABLE LOGIC CONTROLLERSlogic controller. PROCEDURE o Learner reads workbook for PLC-1. o...

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