Timers are commonly used instructions in PLC programming, but sometimes we often confuse their functions, resulting in subsequent program debugging or maintenance work. A friend once lost production because he didn't figure out this timer, so he was embarrassed in front of customer leaders and colleagues. In order to avoid friends repeating the same mistakes, the next 5 articles will sort out the functions and uses of these 5 commonly used PLC timers. 

This article will talk about the Extended Pulse Timer. 

1. Overall working principle 

When the signal at the input end is 1, the output is 1, the output time length is the set time, and the output is stopped when the set time reaches 0. Even if the input signal changes from 1 to 0 within the set time, the output continues to output the signal 1, the time length is the set time, and the output stops when the set time reaches 0. 

Compared with the Pulse Timer function mentioned in the previous article, it will be clearer: the basic condition for the pulse timer to have a signal output is that there is an energy current signal at the input end, and when the input signal is disconnected, the output is also disconnected. 

2. What it looks like in the ladder diagram of PLC programming. 

PLC Extended PulseTimer PLC

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. 

3. Programming examples and timing diagram explanations 

PLC programming example application

In the above figure, 10.1 is the start button, the control signal is interrupted, when pressed, the IOS timing starts as shown in Figure 3 below, and there is a signal output (QO.O gets the signal), the IOS timing ends, stop the output, if you release the button within the set IOS time, continue to output until the set IOS time reaches 0, stop the output when the current time is 0, QO.O has no signal as shown in Figure 4 below. When the 10.1 reset button (when pressed, the timer output is 0, the signal output stops) is shown in Figure 5 below. 

Green indicates the PLC energy flow opening state

The timer continues even if the input is disconnected

When the reset button is pressed, the current value is set to 0 and the input is stopped

The corresponding timing diagram on the PLC

The above is the timing schematic diagram of their counterparts. In order to help friends deepen their impression, here I leave you two small questions to think about: When the timer is halfway through, release the start button iO.1, does the timer stop output? When the start button is released and the timer is halfway through (5s), when the start button is pressed again, does the timer start from the beginning (IOS) or from the middle (5s)? 

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