What are Timers? || How to use Timers || Using Timers in Simatic manager

Timer Functions:

Timer functions are used to implement timing sequences. For example, waiting and monitoring times,

measuring of time intervals, generation of pulses. The timer functions are stored in system memory of

the CPU. The following timer types are available:

·         Pulse Timer

·         Extended Pulse Timer

·         On delay Timer

·         Retentive On Delay Timer

·         Off Delay Timer

Timers have an area reserved for them in the memory of your CPU. This memory area reserves one

16-bit word for each timer address. The ladder logic instruction set supports 256 timers. Please refer to

your CPU’s technical information to establish the number of timer words available. The following

functions have access to the timer memory area:

·         Timer instructions

·         Updating of timer words by means of clock timing.

This function of your CPU in the RUN mode decrements a given time value by one unit at the interval

designated by the time base until the time value is equal to zero.

For any timer there are three inputs and three outputs as shown in the below figure.

Time Value: Bits 0 through 9 of the timer word contain the time value in binary code. The time value

specifies a number of units. Time updating decrements the time value by one unit at an interval designated

by the time base. Decrementing continues until the time value is equal to zero. You can load a time value

into the low word of accumulator 1 in binary, hexadecimal, or binary coded decimal (BCD) format.

You can pre-load a time value using either of the following formats:

             W#16#wxyz

            Where w = the time base (that is, the time interval or resolution)

           Where xyz = the time value in binary coded decimal format

            S5T#aH_bM_cS_dMS

           Where H = hours, M = minutes, S = seconds, and MS = milliseconds; a, b, c, d are defined by the user.

·         The time base is selected automatically, and the value is rounded to the next lower number

             with that time base.

 

NOTE: The maximum time value that you can enter is 9,990 seconds, or 2H_46M_30S.

Time Base: Bits 12 and 13 of the timer word contain the time base in binary code. The time base

defines the interval at which the time value is decrement by one unit. The smallest time base is 10 ms;

the largest is 10 s.

Time Base                       Binary Code for the Time Base

10 ms                                      00

100 ms                                    01

1 s                                           10

10 s                                         11

Values that exceed 2h46m30s are not accepted. A value whose resolution is too high for the range

limits (for example, 2h10ms) is truncated down to a valid resolution. The general format for S5TIME has

limits to range and resolution as shown below:

Resolution                      Range

0.01 second                   10MS to 9S_990MS

0.1 second                     100MS to 1M_39S_900MS

1 second                        1S to 16M_39S

10 seconds                    10S to 2H_46M_30S

       

Bit configuration in the ACCU1: When a timer is started, the contents of ACCU1 are used as the time

value. Bits 0 through 11 of the ACCU1-L hold the time value in binary coded decimal format (BCD formats:

each set of four bits contains the binary code for one decimal value). Bits 12 and 13 hold the time base in

binary code. The following figure shows the contents of the timer cell loaded with timer value 127 and a

time base of 1 second:

 

S5TIME DATA TYPES for Time values:

Data Type                Length (bits)                      Format                          Format Examples

S5time                      16 bits                        s5t#_h__m__s__ms              s5t#10ms, s5t#2H30m45s

Choosing the right Timer: This overview is intended to help you choose the right timer for your timing

job

FR Enable Timer (free):

When the RLO transitions from "0" to "1", FR <timer> clears the edge-detecting flag that is used for

starting the addressed timer. A change in the RLO bit from 0 to 1 in front of an enable instruction (FR)

enables a timer. Timer enable is not required to start a timer, nor is it required for normal timer

instruction. An enable is used only to re-trigger a running timer, that is, to restart a timer. The restarting

is possible only when the start instruction continues to be processed with RLO = 1.

 

Time Specifications:

·         Fixed time values specified as time constants (e.g.: S5T#100ms, S5T#35s, S5T#5m2s200ms,

·         S5T#2h2m2s50ms).

·         Time values to be changed by the machine operator using push wheel buttons.

·         Process or recipe-dependent time values in memory words or data words.

Timer Cell: A special area of memory is reserved for timers in your CPU. This area contains a 16-bit word

for each timer address. bits 0 to 9 of the timer word contain the time value in binary code. When the timer

is updated, the time value is decremented by one unit at the interval defined by the time base.

L / BI: The address at the “BI” output contains the time value in the form of a 10-digit binary number

(without time base!).

LC / BCD: The address at the “BCD” output contains both the time value as a 3-digit BCD number (12bits) and the time format (bits 12 and 13).

Note: IEC-compliant timers can also be implemented in STEP7. The system function blocks need to be used for implementing IEC timers.

TYPES OF TIMERS:

Pulse Timer: S_PULSE (Pulse S5 Timer) starts the specified timer if there is a positive edge at the start

(S) input. A signal change is always necessary in order to enable a timer. The timer runs as long as the

signal state at input S is "1", the longest period, however, is the time value specified by input TV. The

signal state at output Q is "1" as long as the timer is running. If there is a change from "1" to "0" at the S

input before the time interval has elapsed the timer will be stopped. In this case the signal state at output Q

is "0". The timer is reset when the timer reset (R) input changes from "0" to "1" while the timer is running.

The current time and the time base are also set to zero. Logic "1" at the timer's R input has no effect if the

timer is not running. The current time value can be scanned at the outputs BI and BCD. The time value at

BI is binary coded, at BCD it is BCD coded. The current time value is the initial TV value minus the time

elapsed since the timer was started. 

If the signal state of 0.7 changes from "0" to "1" (positive edge in RLO), the timer T4 will be

started. The timer will continue to run for the specified time of thirty-five seconds (35 s) as long as I0.7

is "1". If the Signal State of I0.7 changes from "1" to "0" before the timer has expired the timer will be

stopped. If the Signal State of input I0.5 changes from "0" to "1" while the timer is running, the time is

reset. The output Q8.5 is logic "1" as long as the timer is running and "0" if the time has elapsed or

was reset.

Extended Pulse Timer: S_PEXT (Extended Pulse Timer) starts the specified timer if there is a positive

edge at the start (S) input. A signal change is always necessary in order to enable a timer. The timer

runs for the preset time interval specified at input TV even if the signal state at the S input changes to

"0" before the time interval has elapsed. The signal state at output Q is "1" as long as the timer is

running. The timer will be restarted ("re-triggered") with the preset time value if the signal state at input

S changes from "0" to "1" while the timer is running. The timer is reset if the reset (R) input changes

from "0" to "1" while the timer is running. The current time and the time base are set to zero. The

current time value can be scanned at the outputs BI and BCD. The time value at BI is binary coded, at

BCD is BCD coded. The current time value is the initial TV value minus the time elapsed since the timer

was started.

If the signal state of 0.7 changes from "0" to "1" (positive edge in RLO), the timer T4 will be

started. The timer will continue to run for the specified time of thirty five seconds (35 s) even if I0.7 is

"0". If the Signal State of input I0.5 changes from "0" to "1" while the timer is running, the timer is reset.

The output Q8.5 is logic "1" as long as the timer is running and "0" if the time has elapsed or was

reset. Also the output Q8.5 does not depend on the Input I0.7.

On-Delay Timer: S_ODT (On-Delay S5 Timer) starts the specified timer if there is a positive edge at

the start (S) input. A signal change is always necessary in order to enable a timer. The timer runs for

the time interval specified at input TV as long as the Signal State at input S is positive. The signal state

at output Q is "1" when the timer has elapsed without error and the signal state at the S input is still "1".

When the Signal State at input S changes from "1" to "0" while the timer is running, the timer is stopped.

In this case the signal state of output Q is "0". The timer is reset if the reset (R) input changes from "0"

to "1" while the timer is running. The current time and the time base are set to zero. The signal state at

output Q is then "0". The timer is also reset if there is a logic "1" at the R input while the timer is not

running and the RLO at input S is "1". The current time value can be scanned at the outputs BI and

BCD. The time value at BI is binary coded, at BCD is BCD coded. The current time value is the initial

TV value minus the time elapsed since the timer was started.

If the signal state of input I0.7 changes from "0" to "1" (positive edge in RLO), the timer T4 will be

started. The timer will continue to run for the specified time of thirty-five seconds (35 s) as long as if I0.7

is "1". If the Signal State of input I0.5 changes from "0" to "1" while the timer is running, the timer is

reset. The output Q8.5 is logic "1" only when timer is elapsed and "0" if the input I0.7 is “0”.

Retentive On-Delay S5 Timer: S_ODTS (Retentive On-Delay S5 Timer) starts the specified timer if

there is a positive edge at the start (S) input. A signal change is always necessary in order to enable a

timer. The timer runs for the time interval specified at input TV even if the signal state at input S changes

to "0" before the time interval has elapsed. The signal state at output Q is "1" when the timer has

elapsed without regard to the signal state at input S. The timer will be restarted (re-triggered) with the

specified time if the signal state at input S changes from "0" to "1" while the timer is running. The timer is

reset if the reset (R) input changes from "0" to "1" without regard to the RLO at the S input. The signal

state at output Q is then "0". The current time value can be scanned at the outputs BI and BCD. The

time value at BI is binary coded, at BCD it is BCD coded. The current time value is the initial TV value

minus the time elapsed since the timer was started.

If the signal state of I0.7 changes from "0" to "1" (positive edge in RLO), the timer T4 will be started.

The timer runs without regard to a signal change at I0.7 from "1" to "0". If the signal state at I0.7

changes from "0" to "1" before the timer has expired, the timer will be re-triggered. The output Q8.5 will

be "1" if the timer elapsed. If the signal state of input I0.5 changes from "0" to "1", the time will be reset

irrespective of the RLO at S.

Off-Delay Timer: S_OFFDT (Off-Delay S5 Timer) starts the specified timer if there is a negative edge

at the start (S) input. A signal change is always necessary in order to enable a timer. The signal state at

output Q is "1" if the signal state at the S input is "1" or while the timer is running. The timer is reset

when the signal state at input S goes from "0" to "1" while the timer is running. The timer is not restarted

until the signal state at input S changes again from "1" to "0".The timer is reset when the reset (R) input

changes from "0" to "1" while the timer is running.The current time value can be scanned at the outputs

BI and BCD. The time value at BI is binary coded, at BCD it is BCD coded. The current time value is the

initial TV value minus the time elapsed since the timer was started.

If the signal state of I0.7 changes from "1" to "0" (negative edge in RLO), the timer T4 will be started.

The timer runs without regard to a signal change at I0.7. If the signal state at I0.7 changes from "0" to

"1" before the timer has expired, the timer will be re-triggered. The output Q8.5 will be "1" as soon as

I0.7 is “1” & resets only when timer is elapsed. If the signal state of input I0.5 changes from "0" to "1",

the time will be reset & output becomes zero.

To watch the tutorial video click : What are Timers? || How to use Timers || Using Timers in Simatic manager