CHAPTER 5 FUNCTION OF OUTPUT CONTROLLER AND APPLICATION.

CHAPTER 5

FUNCTION OF OUTPUT CONTROLLER AND

APPLICATION

TIMERS

• Many applications in industrial control systems need timer functions.

• Timer is used to activate or de-activate a device after a preset time interval.

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

Time Delay Relay

Solid-StateTimer

TIMERS

QUANTITIES IN TIMER INSTRUCTION

Preset Time •Represents the time duration of the timing circuit.• e.g. 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 since it is energized.

Time Base • Timers can typically be programmed with

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

• E.g. 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).

Generic Block-Formatted Timer Instruction

Timers are most often represented by boxes in a ladder logic.

Preset timeTime baseAccumulated time

Retentive timer block

Control line controls the actual timing operation of the timer.Whenever this line is true the timer will time.

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

Output line

The timer continuously compares its accumulated time with its preset 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 Timing Relay

Operating coil

Instantaneous contacts

NO

NC

Nontimed contacts are controlled directly by the timer coil, as in a general-purpose control relay.

Time control contacts

NO

NC

Time adjustment

When the coil is energized, the timed contacts are prevented from opening or closing until the time delay period has elapsed. However, when the coil is de-energized, the timed contacts return instantaneously to their normal state.

Normally open, timed closed contact (NOTC)

Contact is open when relay coil is de-energized

When relay is energized, there is a time delay in closing

Timed Contact Symbols

On-Delay Symbols

Normally closed, timed open contact (NCTO)

Contact is closed when relay coil is de-energized

When relay is energized, there is a time delay in opening

On-Delay Timer Program

Ladder Logic ProgramL1 L2

Input A

Input A

T4:0

T4:0

T4:0

EN

TT

DN

TONTIMER ON DELAYTimer T4:0Time base 1.0Preset 10Accumulated 0

EN

DN

Output B

Output B

Output C

Output COutput D

Output D

G

R

Y

10

On-Delay Relay Timer Circuit (NOTC Contact)

L1 L2S1

L1

Sequence of operation

10 s

S1 open, TD de-energized,TD1 open, L1 is off.

After 10 s, TD1 closes, L1 is switched on.

S1 closes, TD energizes,timing period starts,TD1 still open, L1 is still off.

S1 is opened, TD de-energizes, TD1 opens instantly, L1 is switched off.

10 s

OFFON

Input

Output

Timing Diagram

On-Delay Relay Timer Circuit (NCTO Contact)

S1 open, TD de-energized,TD1 closed, L1 is on.

Sequence of operationL1 L2

L1

S1

10 s

After 10 s, TD1 opens,L1 is switched off.

S1 closes, TD energizes,timing period starts, TD1is still closed, L1 is still on.

L1 L2

S1 is opened, TD de-energizes,TD1 closes instantly, L1 isswitched on.

10 s

On

Off

Input

Output

Timing Diagram

?

Normally open, timed open contacts (NOTO).

Contact is normallyopen when relay coilis de-energized.

When relay coil is energized, contact closes instantly.When relay coil is de-energized, there is a time delay before the contact opens.

Timed Contact Symbols

Off Delay Symbols

Normally closed, timed closed contacts (NCTC).

Contact is normallyclosed when relay coilis de-energized.

When relay coil is energized, contact opens instantly.

When relay coil is de-energized, there is a time delay before the contact closes.

Off-Delay Programmed Timer

The off-delay timer (TOF) operation will keep the output energized for a period after the rung containing the timer has gone false.

EN

DN

TOFTIMER OFF DELAY

TIMER T4:3Time base 1.0Preset 15Accumulated 0

I:1.0/0

I:1.0/0

O:2.0/1

O:2.0/1T4:3/DN

PL

L1 L2Input OutputLadder logic program

S1

15

Off-Delay Relay Timer Circuit (NOTO Contact)

L1 L2S1

L1

Sequence of operation

S1 open, TD de-energized,TD1 open, L1 is off.

S1 closes, TD energizes,TD1 closes instantly, L1 is switched on.

S1 is opened, TD de-energizes,timing period starts, TD1 isstill closed, L1 is still on.

10 s

After 10 s, TD1 opens, L1 isswitched off.

10 s

Input

OutputOff

On

Timing Diagram

?

Off-Delay Relay Timer Circuit (NCTC Contact)L1 L2

S1

L1

Sequence of operation

S1 open, TD de-energized,TD1 closed, L1 is on.

S1 closes, TD energizes,TD1 opens instantly, L1 is switched off.

S1 is opened, TD de-energizes, timingperiod starts, TD1 is stillopen, L1 is still off.

10 s

After 10 s, TD1 closes,L1 is switched on.

10 s

Input

Output On

Off

Timing Diagram

?

NONRETENTIVE TIMER

• Is also known as TMR• Has only 1 input• Timer enabled if the input

logic is ON• Timer reset if the input logic

is OFF• Non-retentive - loss of power

flow to the timer causes the timer instruction to reset.

TMR TIMER0

T0

K40

INPUT

RETENTIVE TIMER• Also known as TMRA• Has two inputs• Timer starts timing when

ENABLE is ON• Timer stops when ENABLE is OFF

without resetting the current value to 0.

• Timer continues timing when it is enabled again.

• The timer resets when RESET is ON (RES instruction is true)

• Once RESET is OFF, timer enable to start

TMRA TIMER2

T2

K50

ENABLE

RESET

Retentive Timer

A retentive timer accumulates time whenever the device receives power, and maintains the current time should power be removed from the device. Once the device accumulates time equal to its preset value, the contacts of 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 operatedcontact

Motor-drivencam

Once power is applied, the motor starts 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 but does not reset.

EXERCISE

CASE 1• Using a timer, a toggle switch and a buzzer. Write a ladder diagram

so that the buzzer will ON immediately, but OFF after 5 sec the input is OFF. Choose the type of timer necessary and assume the preset value for the timer is 0.1 sec.

TMR TIMER0

T0K50

INPUTX0

T0Y1=buzzer

Off Delay Timer (NOTO contact) is used

• When X0 ON the timer is enable, and starts timing. The buzzer starts.• When X0 OFF the timer enable is off, and stop timing. But it does not

reset to zero.

TMRA TIMER2

T2

K50

ENABLE

RESET

T2Y1=buzzer

X0= PB

Figure 5.1.1 (b) Timer with 2 inputs

CASE 2:

Q: Using a 2 inputs timer, a PB and a buzzer. The buzzer is needed to buzz for 5 sec. Assume that the preset value is 0.1 sec. Write the ladder diagram.

A: The ladder diagram is as below.

T2

X1

5.1.2 Cascading Timer• Applications sometimes require longer time

delays than one timer can accomplish.• Multiple timers can then be used to achieve a

longer delay than would otherwise be possible.

• One timer acts as the input to another.• When the first timer times out, it becomes the

input to start the second timer timing.• This is called cascading.

When X0 is ON, timer will start timing. After 99 sec, Timer 1will trigger T0 to open. Then T0 will initiate Timer 1, and timing

for another 51 seconds.Usually used when requirements demand more time than is

available from a single timer. Therefore, two or more timers can be programmed together to get the desire time.

TMRT0

K99

X0

T0TMRT1

K51Figure 5.1.2 (a) Cascading Timer

CASE 3:

Q: One maximum timer can be set for 99sec. Let say preset value is 1 sec. Time needed to set is 150. In this case cascading timer is used.

CASCADING

CASCADING TIMER

• The programming of two or more timers together is called cascading.

• Timers may be interconnected, or cascaded to satisfy any required control logic.

Cascading Timers

Three motors started automatically in sequence with a 20-s time delay between each motor startup.

Relay Schematic Diagram

For sequencing

Cascading Timers

30000

12000

For Longer Time Delays

T4:1 max of 30000 seconds+T4:2 of 12000 seconds= 42000 seconds/700 minutes

COUNTER

• Electronic counters can count up, count down, or be combined to count up and down.

• They are dependent on external sources, such as parts traveling past a sensor or actuating a limit switch for counting.

COUNTER APPLICATIONS

Block-Formatted Counter Instruction

Type of counter

Preset value

Accumulated value

Count line

Reset line

Outputline

PLC counters operate or count on the leading edge of the 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.

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 preset value or to count down to a preset value.

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

Counter Counting Sequence

The counter will increment until the accumulated value is equal to or greater than the preset value, at which time an output will be produced.

The down-counter decrements by 1 each time the rung containing the counter is energized.

Counter Counting Sequence

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

UP- COUNTER

Simple Up-counter Program

7

Up-counter Program Timing Diagram

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.

RSLogic Counter Commands

Command Name Description

CTU Count-UpIncrements the accumulatedvalue at each false-to-truetransition and retains theaccumulated value whenpower cycle occurs

CTD Count-DownDecrements the accumulatedvalue at each false-to-truetransition and retains theaccumulated value whenpower cycle occurs

HSC High-Speed Counter

Counts high-speed pulsesfrom a fixed controllerhigh-speed input

RES ResetResets the accumulatedvalue and status bit of the counter

Parts Counting Program

Counter C5:2 counts the total number of parts coming off an assembly 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 closing sequence

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

9

9

10

10

1

15

5

DOWN- COUNTER

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

Parking Garage Counter Program

As a car enters, it triggers the up-counter output instruction andincrements the accumulated count by 1.

As a car leaves, it triggers the down-counter output instruction and decrements the accumulated count by 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

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 instructionis true, C5:2/CU will be truecausing output A to be true

1

1

When the CTD instructionis true, C5:2/CD will be truecausing output B to be true

When the accumulated valueis greater than or equal to thepreset value, C5:2/DN will betrue, causing output C to betrue

10

10

Input C going true will cause both counter instructions to reset

In-Process Monitoring System

Before start-up, the system is completely empty of parts, and the counter is reset manually to zero.

When the operation begins, raw parts move through the in-feedsensor, with each part generating an up count.

After processing, finished parts appearing at the out-feed sensorgenerate down counts, so the accumulated count of the countercontinuously indicates the number of in-process parts.

In-Process Monitoring System

8

8

5

5

Counting Beyond The Maximum Count

15000

Counter Speed

The maximum speed of transitions you can count isdetermined by your program's scan time. Any counter input signal must be fixed for one scan time to be counted reliably.

If the input changes faster than one scan period, the count value will become unreliable because counts will be missed. When this is the case you need to use a high-speed counter.

CASCADING COUNTER

Cascading Counters

Depending on the application, it may be necessary to count events that exceed the maximum number allowable per counter instruction. One way of accomplishing this is by interconnection, or cascading, two counters.

Counting Beyond The Maximum Count

The output of the first counter is programmed into the input of the second counterThe status

bits of both counters are programmed in series to produce an output

These two counters allow twice as many counts to be measured

Cascading Counters For Extremely Large Counts

Whenever counter C5:1 reaches 500, its done bit resets counter C5:1 and increments counter C5:2 by 1

500

1

0

The output light turns on after 500 x 500, or 250,000 transitions of the count input