Introduction to Industrial Automation

7.5.3   Programming with Timers and Counters

As already mentioned in Section 7.4.3, each timer can implement various kinds of time functions, 

each one of which is determined by the corresponding activation instruction. Figure 7.48 shows 

the most basic time functions as a result of executing the same program:

A

I0.0

L

‘T sec’

SX

T8

A

I1.0

R

T8

A

T8

=

Q4.0

BE

The only difference is the SX activation instruction that becomes:

 

◾

SP for the pulse timer

 

◾

SE for the self-holding pulse timer

 

◾

SD for the ON-delay timer

 

◾

SS for the self-holding ON-delay timer

 

◾

SF for the OFF-delay timer

and for the various cases of the input change (I0.0 or I1.0) that cause the set or reset of timers 

respectively. In these cases, every possible behavior of the output of a timer is clarified. The output 

of a timer, which has a real graphical form in the LAD language, will be presented subsequently. 

In Boolean language, it is the RLO of executing the instruction “A T8”, which is a logical “1” 

when the timer has measured the time that has been set according to the time function that 

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  Introduction to Industrial Automation

OFF-delay timer

I0.0

Q4.0

Reset

T

T

Self-holding ON-delay timer 

▪ 

This timer requires always reset

I0.0

Q4.0

Reset

T

T

T

I0.0

Q4.0

Reset

T

ON-delay timer

T

Self-holding pulse timer

I0.0

Q4.0

Reset

T

T

T

Pulse timer

I0.0

Q4.0

Reset

T

T