Introduction to Industrial Automation

Figure 3.8  Machine operation with a stop delay.

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  Introduction to Industrial Automation

3.2.5   Periodic Operation of Machine with Two Time Constants

In Section 2.3, basic time relays (also called timers) were presented, while, apart from those, there is 

a big variation of more specific time relays. One of them is the time relay with two time constants T

1

 

and T

2

, which can be utilized for achieving the periodic operation of a machine, where the machine 

will continuously operate for a T

1

 time interval and will stop for a T

2

 time interval. The same func-

tionality can also be achieved through the utilization of two simple time relays of ON-Delay type. 

The corresponding automation circuit and the time response of the relay C, which controls the 

machine, are indicated in Figure 3.9. The selective switch RS

1-0-2

 allows the normal operation of the 

machine without pauses in position 1. In position 2, the machine is operated for a time interval T

1

 

and stops for T

2

 repetitively, while in position 0 the machine stops. The second pole of switching 

contacts of the selective switch have been introduced in order to isolate properly the time relays and 

to avoid their unwanted operation, while the machine is in normal operation.