Programmable logic controllers 5ed P8

Programmable logic controllers 5edtion This outstanding book for programmable logic controllers focuses on the theory and operation of PLC systems with an emphasis on program analysis and development. The book is written in easy-to-read and understandable language with many crisp illustrations and many practical examples. It describes the PLC instructions for the Allen-Bradley PLC 5, SLC 500, and Logix processors with an emphasis on the SLC 500 system using numerous figures, tables, and example problems. New to this edition are two column and four-color interior design that improves readability and figure placement and all the chapter questions and problems are listed in one convenient location in Appendix D with page locations for all chapter references in the questions and problems. This book describes the technology so that readers can learn PLCs with no previous experience in PLCs or discrete and analog system control.

Sensor for item

ready for loading

I:012/10

O:012/01

I:012/10

O:012/01I:012/11

Timing diagram

CU

DN

Items counterCTUCOUNT UPCOUNTER C5.0PRESET 100ACCUM 0

Proximity sensorI:012/10

C5.0 DN

100 units completedsignal lamp

Reset buttonI:012/11

Counter resetC5.0RES

Figure 14.20: Conveyor belt counting of products

(X404/I0.4 input) The other inputs could be start (X400/I0.0 input) and stop (X401/I0.1 input) switches for the conveyor and a signal (X405/I0.5 input) from the packaging

machine as to when it is operating and has received four bottles and so is not ready for any further caps Figures 14.22 and 14.23 show a possible ladder program that could be used in Mitsubishi format and in Siemens format, respectively.

Start

X400

Stop

conveyor X400 is the start button,X401 the stop button - externally setclosed The conveyor is

stopped by Y232, M100,X404 or X405 being activated

Y431 is the output to thealarm It is triggered whenthe conveyor stops

M100

T450 is a timer whichstops the conveyor fortime taken to cap thebottle Y432 energizesthe capping machine andstops the conveyor

M100M100

RST

Reset for the counterwhen packagingmachine has 4 bottles

END

M100 is an internal relayactivated by X402 closingwhen a bottle is not full Itthen stops the conveyor

X404 input when bottledetected X405 opens whenpacking occurring 4 bottlescounted

Y433 energizes packingmachine when C460 hascounted 4 bottles

ConveyorY430

Bottle not full

X402

Bottle not fullX404

ConveyorstopX405

Bottle present

X403

TON TimerT450

Capping

Y432

CappingY432

4 bottles

X405

CounterC460

CounterC460 K4

Packing machineY433

CappingY432

TimerT450

Figure 14.22: Bottle-packing program (Mitsubishi format)

www.newnespress.com Programs 353

The Mitsubishi program in instruction list is as follows:

Q2.0 is the output to theconveyor I0.0 is the start button,I0.1 the stop button - externallyset The conveyor is

stopped by Q2.2, F0.0,I0.4 or I0.5 being activated

Q2.1 is the output to thealarm It is triggered whenthe conveyor stops

F0.0

T1 is a timer whichstops the conveyor fortime taken to cap thebottle

F0.0F0.0

END

I0.4 input when bottledetected I0.5 opens whenpacking occurring 4 bottlescounted

Q2.3 energizes packingmachine when counter hascounted 4 bottles

Q2.2 energizesthe capping machine andstops the conveyor

QCounter C0

TONQSTV

S_CU

StopI0.1

Start

I0.0

CappingQ2.2

Bottle not fullI0.4

ConveyorQ2.0

ConveyorstopI0.5

Bottle not full

Packing machineQ2.3

Bottle present

I0.4

Packing occurring I0.5

4 bottles

I0.5

F0.0 is an internal relayactivated by I0.2 closingwhen a bottle is not full Itthen stops the conveyor

Figure 14.23: Bottle-packing program (Siemens format)

The Siemens program in instruction list is:

Limit switch 5

(b)

Figure 14.25 shows the sequential function chart program When the start switch is activated, fill 1 and fill 2 occur simultaneously as a result of the actions of pumps 1 and 2 being

switched on When limit switch 1 is activated, fill 1 ceases; likewise, when limit switch 3 is activated, fill 2 ceases We then have the containers for fluid 1 and fluid 2 full The action that occurs when both limit switch 1 and 3 are activated is that the containers start to

empty, the action being the opening of valves 1 and 2 When limit switches 2 and 4 are

Limit switch 1 AND 3

Limit switch 2 AND 4

MixerMix

liquidsTime elapsed 100 sValve 3Mixed

liquidsLimit switch 5

End

Figure 14.25: The mixing operation program

www.newnespress.com Programs 357

activated, the containers are empty The next stage, the mixing of the liquids, is then determined when limit switch 2 and limit switch 4 are both activated After a time of 100 s, the mixing ceases and the mixed liquids empty through valve 3 When limit switch 5 is activated, the program reaches the end of its cycle and the entire sequence is then repeated.

Problems

1 This problem is essentially part of the domestic washing-machine program Devise a ladder program to switch on a pump for 100 s It is then to be switched off and a heater switched on for 50 s Then the heater is to be switched off and another pump is

to be used to empty the water.

2 Devise a ladder program that can be used with a solenoid valve-controlled double-acting cylinder, that is, a cylinder with a piston that can be moved either way by means of solenoids for each of its two positions, and moves the piston to the right, holds it there for

2 s, and then returns it to the left.

3 Devise a ladder program that could be used to operate the simplified task shown in Figure 14.26 for the automatic drilling of workpieces The drill motor and the pump for the air pressure for the pneumatic valves must be started The workpiece has to be clamped The drill then must be lowered and drilling must be started to the required depth Then the drill has to be retracted and the workpiece unclamped.

Solenoid 1

Solenoid 2

MotorMoves drill up or down

Solenoid 3

Limit switch 1,open when drill

up, closed whendown

Limit switch 2,normally closed,opened whendrill at requireddepth

Limit switch

3 normallyclosed, openwhen piececlamped

Limit switch 4normallyopen, closedwhen piececlamped

4 What are the principles to be observed in installing a safe emergency stop system

with a PLC?

5 The inputs from the limit switches, the start switch, and the outputs to the solenoids of the valves shown in Figure 14.27a are connected to a PLC that has the ladder program shown in Figure 14.27b What is the sequence of the cylinders?

6 The inputs from the limit switches, the start switch, and the outputs to the solenoids

of the valves shown in Figure 14.28a are connected to a PLC that has the ladder program shown in Figure 14.28b What is the sequence of the cylinders?

7 Figure 14.29 shows a ladder program involving a counter C460, inputs X400 and X401, internal relays M100 and M101, and an output Y430 X400 is the start switch Explain how the output Y430 is switched on.

8 Write a ladder program that will switch on two motors when the start switch is operated, then switch off one motor after 200 s and the other motor after a further 100 s When both motors have been switched off, a third motor is to be switched on for 50 s The cycle

is then to repeat itself unless a stop switch has been activated.

9 Write a ladder program to switch on a motor when the start switch is momentarily

activated, with the motor remaining on for 50 s At the end of that time a second

motor is to be switched on for a further 50 s A third motor is to be switched on 10 s before the second motor switches off and is to remain on for 50 s The cycle is then

to repeat itself unless a stop switch has been activated.

10 Suggest the control problem specification that might be required for a passenger lift that

is to operate between the ground floor and the first floor of a building, and devise a

ladder program to carry out the specification.

RESET

C460K10

OUT

M101X400

Appendix: Symbols

Ladder Programs

Semi-graphic form Full graphic form

A horizontal link along which power can flow

Interconnection of horizontal and vertical power flows

Left-hand power connection of a ladder rung

Right-hand power connection of a ladder rung

Normally open contact

Normally closed contact

Positive transition-sensing contact, power flow occurs

Negative tranistion-sensing contact, power flow occurs

Output coil: if the power flow to it is on then the coil

state is on

Retentive memory coil, the state of the associated variable

is retained on PLC power fail

© 2009 Elsevier Ltd All rights reserved.

doi: 10.1016/B978-1-85617-751-1.00039-2 363

Function Blocks

Semi-graphic form Full graphic formHorizontal and vertical lines

Interconnection of horizontal and vertical signal flows

Crossing horizontal and vertical signal flow

Blocks with connections

AV_WEIGHT

AV_WEIGHTAV_WEIGHT

Commonly Encountered Blocks

BOOL is a Boolean signal, INT is an integer, REAL is a floating point number, ANY is any form of signal

Up-counter counts the number of rising edges at input CU PV defines

the maximum value of the counter Each new rising edge at CU

increments CV by 1 Output Q occurs after set count R is the reset

CTUCURPV

BOOL

INT

BOOLBOOLINT

Q

CV

Down-counter counts down the number of rising edges at input CU

PV defines the starting value of the counter Each new rising edge at

CU decrements CV by 1 Output Q occurs when count reaches zero

CTDCDLDPV

BOOL

INT

BOOLBOOLINT

Q

CV

Up-down counter It can be used to count up on one input and down

on the other

CTUDCDQU

RBOOL

BOOLQD

On-delay timer When input IN goes true, the elapsed time at about

ET starts to increase and when it reaches the set time, specified by

input PT, the output Q goes true

TONBOOL

TIME

BOOLTIME

INPT

QET

TONBOOL

TIME

BOOLTIME

INPT

QET

Off-delay timer When input IN goes true, the output Q follows and

remains true for the set time after which the input Q goes false

TOFBOOL

TIME

BOOLTIME

INPT

QET

Pulse timer When input IN goes true, output Q follows and remains

true for the pulse duration specified by input PT

TPBOOL

TIME

BOOLTIME

INPT

QET

A

B

OutputInputs

NOR Gate

A

B

OutputInputs >1

A

B

OutputInputs

www.newnespress.com Appendix: Symbols 365

Sequential Function Charts

Start step This defines the step which will be activated when the PLC

Transition condition Every transition must have a condition One that

always occurs should be shown with the condition TRUE

Every step can have an associated action An action describes the behavior

that occurs when the step is activated Each action can have a qualifier: N

indicates the action is executed while the step is active If no qualifier is

indicated it is taken to be N

ActionNStep

Qualifier

Selective branching

D: time-delayed action whichstarts after a given time

Parallel branching when the transition occurs

Convergence when both transitions occur

Simultaneous convergence

Instruction List (IEC 1131-3 Symbols)

LD Start a rung with an open contact

LDN Start a rung with a closed contact

R Reset false

AND Boolean AND

ANDN Boolean NAND

ORN Boolean NOR

XOR Boolean XOR

NOT Boolean NOT

( ) Parenthesized (bracketed) expression

Function( .) List of parameters of a function

** Raising to a power

, NOT Negation, Boolean NOT

*, /, MOD Multiplication, division, modulus operation

þ,  Addition, subtraction

<, >, <¼, >¼ Less than, greater than, less than or equal to, greater than or equal to

www.newnespress.com Appendix: Symbols 367

¼, <> Equality, inequality

AND, & Boolean AND

XOR Boolean XOR

OR Boolean OR

Conditional and Iteration Statements

IF THEN ELSE is used when selected statements are to be executed when certain conditions occur.

The FOR DO iteration statement allows a set of statements to be repeated, depending

on the value of the iteration integer variable.

The WHILE DO iteration statement allows one or more statements to be executed while a particular Boolean expression remains true.

The REPEAT UNTIL iteration statement allows one or more statements to be executed and repeated while a particular Boolean expression remains true.

19 See Section 2.2.4 Consider the behavior of RL circuits.

20 Stepper motor with 5 step.

21 (a) Photoelectric transmissive system, (b) direction control valve operated cylinder.

12 (a) 0.110010
23, (b) 0.1100
24, (c) 0.1000 0100
24.

13 See Sections 3.7 and 3.8.

14 (a) 1 AND 1, (b) 1 OR 1, (c) 1 AND NOT 1.

21 See Sections (a) 4.5.5, (b) 4.5.2 and 4.5.3.

Figure A.1: Chapter 5, Problem 27

www.newnespress.com Answers 373

25 See Figure A.2

26. WHILE NOT (Level_switch1 AND Drain_valve)

Valve1 :¼1

END_WHILE

Openvalve 1Fill tank

START switch

Level switch 1Drain

tank

Openvalve 2Level switch 2Start

End

DNTimer

0.5 s DELAY

Figure A.3: Chapter 9, Problem 22d

www.newnespress.com Answers 377

8 C.

9 D.

10 (a) As Figure 11.1/11.2 with a constant input to In 1/X400, so entering a 1 at each shift, (b) as in Figure 11.3 but instead of a faulty item, a hook with an item, and instead of a good item, hooks with no items.

Red light O:013/02

C5:0 DNI:012/ 01

CU

DN

C5:0DN

T4.0

COUNT UPCOUNTER C5.0PRESET 10ACCUM 0

TIMER ON DELAYTIMER T4.0TIME BASE 1.0PRESET 5ACCUM 0TONCTU

(b)

T4:0DN

RES

C5.0DN

OutputO:013/01

Figure A.4: Chapter 10, (a) Problem 20c, (b) Problem 20d

www.newnespress.com Answers 379

9 Power failure, supply off, power tripped.

10 Wiring fault, device fault.

LESInput

LESS THAN A<BSOURCE A TempSOURCE B Set temp

NEQNOT EQUALSOURCE A DataSOURCE B 100

Start for Out 1 Out 1 Start switch closes and starts

Out 1, which in theabsence of a fault takes acertain time to complete

for other outputs

Plus similar rungs for the

other outputs

Timer 1 is set for slightlylonger than completiontime for Out 1

END

Stop for Out 1

If any output takes longerthan expected, theinternal relay is energized

When this happens it switches off all the outputrungs in which it islocated

IRIR

Figure A.6: Chapter 13, Problem 11

The output B+ produces ashort duration pulse at

IR 2 as a result of thetimer setting

The above part of the programgives the sequence A+, B+, B–, A–and the following part the diagnostics

The output B–produces ashort duration pulse at

IR 5 as a result of thetimer setting

Chapter 14

1 See Figure A.8

2 See Figure A.9

3 See Figure A.10 for a basic answer.

4 Hardwired emergency stop button, not dependent on software.

5 A þ and Bþ, Cþ, A– and B–, C–.

6 Aþ, Bþ, A, B, Aþ, A.

7 M100 and M101 activated Ten pulses on X401 counted Then output.

8 See Figure A.11

LED A+

IR 2 IR 3 IR 4 Reset If A+ output occurs, IR 1 closes

and is latched on LED A+ isthen on LED A+ is not onunless IR 1 closed

LED B+

If B+ output occurs, IR 2 closesand is latched on LED B+ isthen on LED B+ is not onunless IR 2 closed

If B– output occurs, IR 4 closesand is latched on LED B– isthen on LED B– is not onunless IR 4 closed

Figure A.7: Cont’d

www.newnespress.com Answers 383

Start Y431 Y432 Y430

T450Y430

K100T450 is supply pumptimer

Y432 is the heaterT450 T451 Y431 Y432

Y432

K50T451 is the heatertimer

Y431 is the discharge pumpT451 T452 Y430 Y431

Y431

T452 is the discharge pump timer

Y430 is the supplypump

Y430

Figure A.8: Chapter 14, Problem 1

Start Stop Y430

Y430 is air pressure supply

Y431Sensor 1 Sensor 1 is a limit switch for

piston at left Y431 is solenoid

to move piston to rightSensor 2 T450 Sensor 2 is a limit switch for

piston at right T450 has K2Y432

T450

Y432 is solenoid to moveY430

Motor 1 switched off after 200 s

Motor 3Timer 2

Timer 2

Timer 3

Motor 2 switched off after 300 s

Motor 3 runs when timer 2 is onand timer 3 off

Timer 3Timer 2

Timer 3 switched on when timer 2goes on

END

Figure A.11: Chapter 14, Problem 8

www.newnespress.com Answers 385

9 See Figure A.12

10 A basic specification might be as follows: The lift can only move when both access doors are closed and the lift door is closed The lift will move from the ground floor

to the first floor when a call command is given from the first floor and move to the ground floor when a call command is received from the ground floor Signal lamps

at each floor will indicate on each floor which floor the lift is at See Figure A.13 for

a possible program You might like to refine the program by adding a timer which will sound an alarm if the lift takes too long between floors.

Motor 2

Timer 1 is set running when STARTactivated Motor 1 is switched on untiltimer 1 goes on Timer 1 is set for 50 s

Timer 1

END

Timer 2Timer 2

Timer 4Timer 4

on Timer 4 is set for 50 s

Figure A.12: Chapter 14, Problem 9