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ENGG3490-PLC

PLCs Ref. [3];

1. Programming Timers

ENGG3490: Mechatronics W07. Adapted From Programmable Logic Controllers By F. D.Petruzella, McGraw-Hill

1

2. rogramm ng oun ers

There are very few industrial control systems that do not

need at least one or two timed functions. They are used to

activate or de-activate a device after a preset interval of

Timers

.

Time delay relays and solid-state timers are used to provide a time

delay. They may have displays, pots or other means of operator

interface for time settings and electromechanical or solid state

outputs.

Solid-State

ENGG3490: Mechatronics W07. Adapted From Programmable Logic Control lers By F. D. Petruzel la , McGraw-Hil l 2

Relay Timer

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On-Delay Timing Relay

Operating coil

NO Nontimed contacts are

controlled directly by

contacts

NC

e mer co , as n a

general-purpose

control relay.

When the coil is

energized, the timed

contacts are prevented

from opening or closing


Time control

contacts

NC

Time adjustment

until the time delay

period has elapsed.

However, when the coil isde-energized, the timed

contacts return

instantaneously to their

normal state.

Timed Contact Symbols

On-Delay Symbols

Normally open, timed

closed contact (NOTC)

Normally closed, timed

open contact (NCTO)


relay coil is de-energized

When relay is energized,

there is a time delay in

closing

relay coil is de-energized

When relay is energized,

there is a time delay in

opening

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Normall o en timed

Timed Contact Symbols

Off Delay Symbols

Normall closed timed

open contacts (NOTO).

Contact is normally

open when relay coil

is de-energized.

When relay coil is

closed contacts (NCTC).

Contact is normally

closed when relay coil

is de-energized.

When relay coil is


energ ze , con ac c oses

instantly.

When relay coil is de-

energized, there is a time

delay before the contact

opens.

energ ze , con ac opens

instantly.

When relay coil is de-

energized, there is a time

delay before the contact

closes.

On-Delay Relay Timer Circuit (NOTC Contact)

L1 L2S1

Sequence of operation

S1 open, TD de-energized,

L1

10 s

, .

After 10 s, TD1 closes, L1 is

S1 closes, TD energizes,

timing period starts,

TD1 still open, L1 is still off.

10 s


switched on.

S1 is opened, TD de-

energizes, TD1 opens

instantly, L1 is switched off.

OFF

ONInput

Output

Timing Diagram

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On-Delay Relay Timer Circuit (NCTO Contact)


Sequence of operation

L1 L2

S1

L1 L2

, .L1

10 s

After 10 s, TD1 opens,


timing period starts, TD1

is still closed, L1 is still on.

10 s


L1 is switched off.

S1 is opened, TD de-energizes,

TD1 closes instantly, L1 is

switched on.

On

Off

Input

Output

Timing Diagram

Off-Delay Relay Timer Circuit (NOTO Contact)

L1 L2

S1 Sequence of operation


L1

, .


TD1 closes instantly,

L1 is switched on.

S1 is opened, TD de-energizes,

10 s

10 s


,

still closed, L1 is still on.

After 10 s, TD1 opens, L1 is

switched off.

Input

OutputOff

On

Timing Diagram

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Off-Delay Relay Timer Circuit (NCTC Contact)

L1 L2

S1 Sequence of operation


L1

, .


TD1 opens instantly,

L1 is switched off.

S1 is opened,

-

10 s

10 s


period starts, TD1 is still

open, L1 is still off.

After 10 s, TD1 closes,

L1 is switched on.

Input

OutputOn

Off

Timing Diagram

Programmed Timer Instructions

PLC timers are output instructions that provide the

same functions as timing relays and solid state timers.

Some advantages of PLC timers:

their settings can be altered easily

the number of PLC timers used

can be increased or decreased by

ENGG3490: Mechatronics W07. Adapted From Programmable Logic Controllers By F. D. Petruzella, McGraw-Hill 10

programming changes withoutwiring changes

timer accuracy and repeatability

are extremely high

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RSLogic Timer Commands

TON

Command Name Description

TON Timer On-Delay Counts time base


instruction is true


TOF


TOF Timer Off-Delay Counts time base


instruction is false

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Timer/Counter

RTO RES


RTO Retentive TimerON

Counts time base

intervals when the

instruction is true and

retains the accumulated


value when the

instruction goes "false" or

when power cycle occurs

RES ResetWhen this instruction is

"true" it resets the count

of the RTO counter

Quantities Associated with the Timer Instruction

Preset Time Represents the time duration of the timing

circuit. For example, if a time delay of 10 s is required,

the timer will have a preset of 10 s.

Accumulated Time Represents the amount of time that

has elapsed from the moment the timing coil became

energized.


several different time bases: 1 s, 0.1 s, and 0.01 s are

typical time bases. For example, if you enter 0.1 for the

time base and 50 for the preset time the timer would

have a 5 s delay (50 x 0.1 s = 5 s).

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Coil-Formatted Timer Instruction

The timer assigned

an address

The type of timer

Contact determines

rung continuity

TON

s spec e

Preset value PR:YYY

Time base 0.1 s

Accumulated value AC:000


When the timer rung has logic continuity, the timer's

accumulated value increases. When accumulated value equals

the preset value, the output is energized and and the timedoutput contact associated with the output is closed. The timed

contact can be used as many times as you wish throughout the

program as a NO or NC contact.

Generic Block-Formatted Timer Instruction

Timers are most often represented by boxes in a ladder

logic.

Control line controls the actual timing operation of the timer.

Preset time

Time base

Retentive timer block

Whenever this line is true the timer will time.


Reset line resets the the timer's accumulated value to zero.

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Generic Block-Formatted Timer Instruction

Timers are most often represented by boxes in a ladder

logic.

Preset time

Time base

Retentive timer block


The timer continuously compares its accumulated time with itspreset time. Its output is logic 0 as long as the accumulated time is

less than the preset time. When the two become equal the output

changes to logic 1.

On-Delay Timer Instruction

Theon-delay timer operates

so that, when the rung

containing the timer is true,TimerInput

the timer time-out period

commences.

Rung conditionFalse

TrueTimer Sequence

The timed output

becomes true


Timed periodOn delay

time duration

Timed output bitFalse

OFF

True

ON

timer rung becomes

true; hence the timer

is said to have an on

delay.

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Allen-Bradley On-Delay Timer Instruction

The Timer-Timing (TT) bit is true whenever the

accumulated value of the timer is changing, which

means the timer is timing.

TIMER ON DELAY

TON

Timer T4:0

Preset 50

Accumulated 10

EN


TT

T4:0 Timer-Timing bit true


The Done-Bit (DN) changes state whenever the

accumulated value reaches the preset value. Its

state depends on the type of timer being used.

TIMER ON DELAY

TON

Timer T4:0

Preset 50

Accumulated 10

EN

DN

50


DN

T4:0 Done-bit changes state

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The preset value (PRE) wordis the set point of the

timer, that is, the value up to which the timer will

time.

The accumulated value (ACC) wordis the value that

increments as the timer is timing. The accumulated

value will stop incrementing when its value reaches

the preset value.


TIMER TABLE

T4:0

/EN /TT /DN .PRE .ACC

0 0 0 0 0


TON

TIMER ON DELAY

The information to be entered includes:

DN

Time base 1.0

Preset 15

Accumulated 0


Time base which is expressed in seconds.

Preset value which is the length of the time delay.

Accumulated value which is normally entered as 0.

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On-Delay Timer Program

Ladder Logic Program

L1 L2

Input A TON

Input A

T4:0

T4:0

EN

Timer T4:0

Time base 1.0

Preset 10

Accumulated 0

EN

DN

Output B

Output B

Output C

Output COutput D

G

R

Y

10


T4:0

TT

DN

Output D


Timing Diagram

Input condition A

On

Off

Timer-enable bitn

Off

Timer-timing bitOn

Off

Timer-done bitOn

4 s 10 s


Timer accumulated

value

0

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Timers are 3-word elements

0

1

2

EN TT DN Internal use

Preset value PRE

Accumulated value ACC


Word 0 is the control word

Word 1 stores the preset value

Word 2 stores the accumulated value

On-Delay Timer With Instantaneous Output

Relay Ladder Schematic Diagram

Sto Start

1TD

-

1TD


M(instantaneous

contact)

1TD-2

(5 s)

(timed contact)

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On-Delay Timer With Instantaneous Output

Programmed Circuit

Ladder logic program

Motor

Motor

M

Internal

relay

Internal

relay

Stop

Stop

Start

Start

M

L1 L2

Inputs Output


Timer

PR: 5

TB: 1 s Output

line

Start-Up Warning Signal Circuit

Relay Ladder Schematic Diagram

L1 L2Start-up

PB1Reset

PB2 CR1

CR1-1

1TD


CR1-2

1TD-1

(10 s)

CR1-3

Horn

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InputsLadder logic program

Programmed Circuit

Start-Up Warning Signal Circuit

TON

TIMER ON DELAY

Timer T4:0

Time base 1.0

Preset 10

Accumulated 0

Output

Horn

Horn

Start-up

Reset

PB1

PB1

PB2

PB2

EN

DNT4:0

EN10


DN

:

EN

:

Timed Closed Solenoid Valve Program

Input

L1

Ladder logic programOutput

L2

w c

SW_1

_

Valve

Valve

EN

DN

timer_1.dn

Timer On Delay

Timer timer_1

Preset 12000

Accumulated 012000


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Automatic Sequential Control System

Relay Ladder

Schematic

Diagram

L1 L2Stop

PB1

Start

PB2 Lube oil

pump motorOL

M1

M1-1

PS1

(lube oil

Main drive

motor

M2

OL


1TD

1TD-1

(15 s)

Feed

motor

OL

M3

Automatic Sequential Control System

Programmed Circuit

Inputs Outputs


OL

M1

PB1

PB1 PB2

OL

OL

M1

M2M2

M3

TON

TIMER ON DELAY

PB2

PS1 PS1

M1


M3

Timer T4:0Time base 1.0

Preset 15

Accumulated 0

DN

T4:0

DN

15

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Off-Delay Programmed Timer

Theoff-delay timer (TOF) operation will keep the output

energized for a period after the rung containing the timer

has gone false.

EN

DN

TOF

TIMER OFF DELAY

TIMER T4:3

Time base 1.0

I:1.0/0

I:1.0/0

O:2.0/1 PL

L1 L2Input Output


S1


Preset 15

Accumulated 0

O:2.0/1T4:3/DN

15

Off-Delay Programmed Timer

Timing Diagram

True

Input condition

S1 False

Timed period

Off delay

timed duration


Timed output

O:2.0/1

True (logic 1)

False (logic 0)

Preset value = accumulated value

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L1

Off-Delay Timer Used To Switch Motors Off

InputL2

OutputLadder logic program

5000

10000

15000


Pneumatic Off-Delay Timer

L1 L2

Relay Ladder

Schematic

Diagram


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Programmed Pneumatic Off-Delay Timer

Equivalent Programmed Circuit

L1 L2

Input OutputsLadder logic program

5


Fluid Pumping Process

When the pump start button is pressed, the pump starts. The

Operation

Before starting, PS1 must be closed.


When the stop button is pushed, the pump stops.

PS2 and PS3 must be closed for 5 s after the pump starts. If

either PS2 or PS3 opens, the pump will shut off and will not not

be able to start again for another 14 s.

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Fluid Pumping Process Program

Inputs Output


L1 L2

50


Retentive Timer

Aretentive timer accumulates time whenever the device

receives power, and maintains the current time should

power be removed from the device. Once the device

,

the device change state. The retentive timer must be

intentionally reset with a separate signal for the

accumulated time to be reset.

Electromechnical Retentive Timer


Cam operated

contact

Motor-driven

cam

Once power is applied, the motorstarts turning the cam. The

positioning of the lobes determines

the time it takes to activate the

contacts. If power is removed from

the motor, the shaft stops butdoes

not reset.

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Retentive On-Delay Timer Program

The PLC-programmed RETENTIVE ON-DELAY timer

(RTO) operates in the same way as the nonretentive on-delay timer (TON), with one major exception. There is a

.

Unlike the TON, the RTO

will hold its accumulated

value when the timer rung

goes false and will continue

timing where it left off when


the timer rung goes true

again. This timer must be

accompanied by a timer reset

(RES) instruction to reset the

accumulated value of the

timer to zero.

Same address

Retentive On-Delay Timer Program

390


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Retentive On-Delay Timing Chart

Enable bit is reset when

input pushbutton PB1 is

opened

=Accum value retained

when rung goes false


When reset PB2 is closed,

the T4:2/DN bit is reset to

0. Accumulated value is

reset and held at zero until

the reset pushbutton is

opened.

Retentive On-delay Alarm Program

L1

L2Ladder logic program

600000


The purpose of the RTO timer is to detect whenever a piping

system has sustained a cumulative overpressure condition of 60 s.

At that point, a horn is sounded automatically. You can silence the

alarm by switching the key switch to the rest position.

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Bearing Lubrication

Program

Sequence Of Operation

To start the machine, the operator turns SW on.

Before the motor shaft starts to turn, the bearings are supplied

with oil by the pump for 10 s.

The bearings also receive oil when the machine is running.

When the operator turns SW off to stop the machine, the oil

pump continues to supply oil for 15 s.


A retentive timer is used to track the total running time of the

pump. When the total running time is 3 h, the motor is shut down

and a pilot light is turned on to indicate that the filter and oilneed to be changed.

A reset button is provided to reset the process after the filter and

oil have been changed.

Bearing Lubrication Program

100

15


10800

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Cascading Timers

The programming of two or more timers together is

calledcascading. Timers may be interconnected, orcascaded to satisfy any required control logic.

Three motors started

automaticall in

Relay Schematic

Diagram


sequence with a 20-s

time delay betweeneach motor startup.

Equivalent Time-Delayed Motor-Starting Program

20000


20000

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Annunciator Flasher Circuit

Two timers can be interconnected to form an oscillator

circuit. The oscillator logic is basically a timing circuit

programmed to generate periodic output pulses of any

duration. They can be used as part of an annunciator

system to indicate an alarm condition.

The oscillator circuit output

is programmed in series with


the alarm condition. If the

alarm condition is true, the

appropriate output

indicating light will flash.

Annunciator Flasher Circuit


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Cascading of Timers for Longer Time Delays

30000

12000


Control of Traffic Lights in One Direction

A typical application for PLC timers is the control of

traffic lights.

Control of Traffic in One Direction

Sequence of Operation

Green


30 s 5 s25 s

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Control of Traffic Lights in One Direction

30

25

5


ENGG3490-WEEK9-11

PLCs Ref. [3];

1. Programming Timers

ENGG3490: Mechatronics W07. Adapted From Programmable Logic Controllers By F. D.Petruzella, McGraw-Hill

56

2. rogramm ng oun ers

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Counters

Common applications of counters include keeping trackof the number of items moving past a given point, and

determining the number of times a given action occurs.

A preset counter can control an

external circuit when its


coun e o a ma c es e

user-entered preset limits.

Mechanical Counters

Programmed counters can serve

the same functions as mechanical

counters.

Every time the actuating lever is moved


over e coun er a s one num er,while the actuating lever returns

automatically to its original position.

Resetting to zero is done with a

pushbutton located on the side of the

unit.

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Coil-Formatted Counter And Reset Instruction

Same address

ENGG3490: Mechatronics W07. Adapted From Programmable Logic Controllers By F. D. Petruzella, McGraw-Hill 61Resets counter when true

Block-Formatted Counter Instruction

Type of

counter

Preset value

Count lineOutput

line

Accumulated

valueReset line


input signal. The counter will either increment or decrement

whenever the count input transfers from an "off" state to an

"on" state. The counter will not operate on the trailing edge,

or on-to-off transition of the input condition.

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Counter Counting Sequence

PLC counters are normally retentive. Whatever

count was contained in the counter at the time of a

processor shutdown will be restored to the counter on

power-up. The counter may be reset, however, if the

reset condition is activated at the time of power

restoration.


PLC counters can be designed to count up to a presetvalue or to count down to a preset value.

The up-counter is incremented by 1 each time the rung

containing the counter is energized.



equal to or greater than the preset value, at which time an

output will be produced.

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The down-counter decrements by 1 each time the rung

containing the counter is energized.



A counter reset is always provided to cause the counteraccumulated value to be reset to a predetermined value.

Simple Up-counter Program

7


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Up-counter Program Timing Diagram


C5 Counter Data File

Each counter address is made of a 3-word element

Bit 0-9: Internal Use

-


.

Bit 11: UN - Underflow bit.

Bit 12: OV - Overflow bit.

Bit 13: DN - Done

Bit 14: CD - Count down is enabled.

Bit 15: CU - Count up is enabled.

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pec es e va ue, w c e coun er mus reac e ore e con ro er

sets the done bit. When the accumulated value becomes equal to or

greater than the preset value, the done status bit is set. You can use thisbit to control an output device.




This is the number of times of false to true transitions that have occurredsince the counter was last reset.

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PLC-5 And SLC 500 Count-Up Counter Instruction


ControlLogix Count-Up Counter Instruction

The counter address in the PLC-5 and SLC 500 is a data table

address, whereas in the ControlLogix it is a predefined

structure of the data type.


In the PLC-5 and SLC 500, the max value for the preset and

accumulated values is 32,767 and the min value is 32,768; for

the ControlLogix controller the max value is 2,147,438,647 and

the min value is 2,147,438,648.

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RSLogic Counter Commands


CTU Count-UpIncrements the accumulated

value at each false-to-true


accumulated value when

power cycle occurs

RSLogic Counter Commands


CTD Count-DownDecrements the accumulated

value at each false-to-true


accumulated value when

power cycle occurs

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Parts Counting Program

Counter C5:2 counts thetotal number of parts coming

off an assembl line for final

packaging

Each package must contain 10 parts

When 10 parts are detected, counter C5:1 sets bit B3/1 to

initiate the box closin se uence


Counter C5:3 counts the total number of packages filled per day

A pushbutton is used to restart the total part and package count

from zero daily

Parts Counting Program

9100

91010


1

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One-Shot, Or Transitional, Contact Program

The transitional or one shot contact program can be used to

automatically clear or reset a counter. The program is designedto generate an output pulse that, when triggered, goes on for

the duration of one ro ram scan and then oes off.


One-Shot, Or Transitional, Contact Program

The transitional or one shot contact program can be used to

automatically clear or reset a counter. The program is designed

to generate an output pulse that, when triggered, goes on for

the duration of one ro ram scan and then oes off.


The one-shot can be

triggered from a

momentary signal, or

one that comes on and

stays on for some time.

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Types Of Transitional Contacts

Off-To-On Transitional Contact

OnIs programmed to

provide a one-shot

Symbol

Off

Off

On

One

scan

referenced trigger

signal makes a

positive (off-to-on)

transition

On-To-Off Transitional Contact


Symbol Onescan

Off

Off

On

On

Is programmed to

provide a one-shot

pulse when the

referenced trigger

signal makes a negative

(on-to-off) transition

Proximity

switch

Conveyor Motor Circuit That Uses A

Programmed One-Shot Reset Circuit

Sequential Task:

Case

Conveyor motorCount reset

button

Cases move pass the proximity

switch and increment the

counter's accumulated value

The start button is pressed

to start the conveyor motor


tart top stat on

After a count of 50, the conveyor motor stops automatically

and the counter's accumulated value is reset to zero

The conveyor motor can be stopped or started manually at

anytime without loss of the accumulated count

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Conveyor Motor Circuit That Uses A

Programmed One-Shot Reset Circuit

50


One-Shot Rising (OSR) Instruction

Triggers a one-time event.

The OSR instruction is a retentive input instruction

that triggers an event to occur only one time. Use the

OSR instruction when an event must start based on


.

When the input instruction goes from false to true, the

OSR instruction conditions the rung so that the output

goes true for one scan. The output goes false and

remains false for successive scans until the input makes

another false to true transition.

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Alarm Monitor Program

The alarm is triggered by the closing of liquid level switch

LS1

The light will flash whenever the alarm condition is triggered

and has not been acknowledged, even if the alarm condition

clears in the meantime


The alarm is acknowledged by closing selector switch SS1

The light will operate in the steady mode when the alarm

trigger condition exists but has been acknowledged

Alarm Monitor Program


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Down-Counter

The down-counter output instruction will count down

or decrement by 1 each time the counted event occurs.

Each time the down-count event occurs, the

accumulated value is decremented. Normally the down-

counter is used in conjunction with the up counter to

form an up/down counter.


Generic up/down

counter program

Up/Down Counter Timing diagram

Preset Value = 3


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Parking Garage Counter Program

As a car enters, it triggers the up-counter output instruction and

increments the accumulated count by 1.

As a car leaves, it triggers the down-counter output

instruction and decrements the accumulated count b 1.


Since both the up- and down-counters have the same address,

the accumulated value will be the same in both.

Whenever the accumulated value equals the preset value, the

counter output is energized to light up the Lot Full sign.

Parking Garage Counter Program

50

50

38

38

150

150


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PLC-5 And SLC-500

Count-Down Counter Instruction


If the accumulation value is below the

minimum range then the underflow

(UN) bit will be true.

Up/Down-Counter Program

When the CTU instruction

is true C5:2/CU will be true

1

When the CTD instructionWhen the accumulated value

10


causing output A to be trues rue, : w e rue

causing output B to be trueis greater than or equal to thepreset value, C5:2/DN will be

true, causing output C to be

true

Input C going true will causeboth counter instructions to

reset

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In-Process Monitoring System


Before start-up, the system is completely empty of parts, and

the counter is reset manually to zero.

In-Process Monitoring System

85


85

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Counter Speed

The maximum speed of transitions you can count isdetermined by your program's scan time. Any counter

counted reliably.

If the input changes faster

than one scan period, the

count value will become


unreliable because counts

will be missed. When this isthe case you need to use a

high-speed counter.

Cascading Counters

Depending on the

app ca on, may e

necessary to count events

that exceed the maximum

number allowable per

counter instruction. One way


interconnection, or

cascading, two counters.

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Counting Beyond The Maximum Count

15000


Counting Beyond The Maximum Count

The output of the

first counter is

programmed into

the input of the

second counterThe status

bits of both


coun ers areprogrammed

in series to

produce an

output

These twocounters allow

twice as many

counts to be

measured

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Incremental Encoder

The number of square waves obtainedfrom the output of the encoder can be

movement required.

To divide a shaft revolution into 100

parts, an encoder could be selected to


supply 100 square wave cycles per

revolution. By using a counter to

those cycles, we could tell how far

the shaft has rotated.

Cutting Objects To A Specific Size


The object is advanced for a specific distance and measured

by encoder pulses to determine the correct length for

cutting.

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Counter Used For Length Measurement

Count input pulses generated by the magnetic sensor, which

detects passing teeth on a conveyor drive sprocket. If 10 teeth perfoot of conveyor motion pass the sensor, the accumulated count of

.


The photoelectric sensor monitors a reference point on theconveyor. When activated, it prevents the unit from counting,

thus permitting the counter to accumulate counts only when bar

stock is moving.

Counter Used For Length Measurement

10


Photo sensor activated, therefore,

accumulated count remains at 10

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Combining Counter And Timer Functions

When the start button is pressed,

conveyor M1 begins running.

After 15 lates have been stacked

conveyor M1 stops and conveyor

M2 begins running.

After conveyor M2 has been

operated for 5 s, it stops and the

sequence is repeated

automaticall .


Automatic Stacking Process

The done bit of the timer resetsthe timer and counter, and

provides a momentary pulse to

automatically restart conveyor

M1.

Automatic

Stacking

Program


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Motor Lock-Out Program

Designed to prevent

a machine operator

from starting a

The normally open (OL) relay

contact momentarily closes

each time an overload current

motor that has

tripped off more

than 5 times in an

hour.

s sense .

Every time the motor stops

due to an overload condition,

the motor start circuit is

locked out for 5 min.


If the motor trips off more

than 5 times in an hour, the

motor start circuit is

permanently locked out and

cannot be started until the

reset button is actuated.

Motor

Lock-Out


rogram

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Product Flow Rate Program

This program is designed to indicate howmany parts per minute pass a given

rocess oint.

Parts

When the start switch is closed, both the counter and timer

are enabled.

The counter is pulsed for each part passing the sensor.

The counting begins and the timer starts timing through its

Sensor


1-min time interval.

At the end of 1 min, the timer done bit causes the counterrung to go false. Sensor pulses continue but do not affect the

PLC counter. The number of parts for the past minutes are

represented by the accumulated value of the counter.

Product Flow Rate Program

60


28

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Timer Driving A Counter For Long Time-Delay Period

Each timer T4:0

input closes for

10,000 s, its done

bit resets itself

and increments

10,0000

1


: y .

The output light turns on 10,000 x

100, or 1,000,000 seconds after the

timer input contact closes.

Assignments Chapter 7 and 8 (PLC) book: Problems

- -web page.


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engg3490 plc l4

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