Edstructura y ejemplos

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Programmable Logic
Controller
Chapter 5
Mendoza Vázquez Raymundo
Mayo-Agosto 2014
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Summary
Timers
1. Introduction
2. Types of Timers
3. On-Delay Timers
4. Off-Delay Timers
5. Pulse Timers
6. Program Examples
7. References

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Timers
1. Introduction

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Timers
(Introduction)
 In many control tasks there is a need to control time.
For example a motor or a pump might need to be controlled to operate for a
particular interval of time or perhaps be switched on after some time interval.

 PLCs thus have timers as built-in devices.
 Timers count seconds or fractions of seconds using the internal CPU clock.
Timer function blocks can be programmed to carry out control tasks.

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Timers
2. Types of Timers

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Timers
(Types of Timers)
A common approach is to consider timers to behave like relays with coils that
when energized, result in the closure or opening of contacts after some preset
time.i.

The timer is thus treated as an output for a rung, with control being
exercised over pairs of contacts elsewhere.

ii.

Some treat a timer as a delay block that when inserted in a rung, delays
signals in that rung from reaching the output.

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Timers
(Types of Timers)
There are a number of different forms of timers that can befound with PLCs:
a) On-delay timmers (TON).
b) Off-delay timmers (TOF).
c) Pulse timers (TP).
With small PLCs there is likely to be just one form, the on-delay timers.

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Timers
(Types of Timers)
 On-delay timers (TON) come on after a particular time delay.


Thus as the input goes from 0 to 1, the elapsed time starts to increase, andwhen it reaches
the time specified by the input PT, the output goes to 1.

 An off-delay timer (TOF) is on for a fixed period of time before turning off.


The timer starts when the input signal changes from 1 to 0.

 Pulse timer (TP) gives an output of 1 for a fixed period of time


Starting when the input goes from 0 to 1 and switching back to 0 when the set time PT has
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Timers
(Types of Timers)
The time duration for which a timer has been set is termed the preset and is set
in multiples of the time base used. Some time bases are typically:
 10 ms,
 100 ms,
 1 s,
 10 s,
 and 100 s.

Thus a preset value of 5 with a time base of 100 ms is a time of 500 ms.

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Timers
(Types of Timers)

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Timers
(Types of Timers)
Ejemplo 22.- Elabore el siguiente diagrama en escalera en el simulador Step7
para el PLC S200 CPU 226:

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Timers
(Types of Timers)
Ejemplo 23-25.Elabore en el simulador Step7 para el PLC S200 CPU 226 utilizandoTemporizadores TON con las configuraciones de 1ms, 10ms y 100ms un circuito
de activación a los:
a) 3 seg.
b) 4 seg.
c) 5 seg.

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Timers
(Types of Timers – Exercises)
Ejemplo 26 .Elabore el diagrama en escalera en el simulador Step7 para el PLC S200 CPU
226 que genere la siguiente variación temporal en la salida Q1. Utilizando lacombinación de 2 temporizadores TON-TON, TOF-TOF & TON-TOF.

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Timers
(Types of Timers – Exercises)
Ejemplo 27.Elabore el diagrama en escalera en el simulador Step7 para el PLC S200 CPU
226 que genere la siguiente variación temporal en la salida Q1. Tip: Utilice
detectores de flanco positivos o negativos

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