Continuing from the previous three articles, this article mainly explains the Retentive on-delay timer.

1. Overall working principle

When the signal at the input is 1, the timer starts to time according to the set value, and the timing time is 1 at the output terminal, and stops when the output is 1 (during which this output will not be affected even if the input signal turns to 0); Reset to stop output within any period of time.

What it looks like in ladder chart programming:

Stay on timer

 In the above figure, the S end is the signal input terminal; The TV side is the preset value  input side, which is the timing time you want to set, and IOS is set here; The R end is the  reset end; Bl and BCD are output to display the current time value, the display value type is  different, Bl is a hexadecimal format without a time reference, and BCD is S5T# format.  

2. PLC programming examples and timing diagram explanations  

Programming examples

In the above figure, 10.1 is the start button, used to control the signal interruption, when  pressed, the IOS timing starts the timing as shown in Figure 3 below, the timing time is up to  the signal output (QO.O gets the signal), the 10.1 input signal stops the Q end and continues  to output without stopping until the reset end 10.0 is 1, the output is stopped as shown in  Figure 4 below. When the 10.1 reset button is pressed, the timer output switches to 0 and the  signal output stops (as shown in Figure 5 below).  

The timing time is up to the signal output

No input signal, output hold

After resetting, the output stops

The above is the corresponding timing schematic. In order to help friends deepen their  impression, here is also a small question for everyone to think about: when the start button  is released, the timer is halfway (5s), when the start button is pressed again, does the timer  start from the beginning (IOS) or from the half (5s)? 

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