confused about the difference between these two rungs

rscott9399

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Aug 2017
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Can someone explain the difference between these two rungs?
Dont they do the same thing?
If so what is the point of having the same thing two different ways.

2Timers.jpg
 
The top rung will only be off for 1 scan and the bottom rung will alternate on and off for 1 Sec each.
Edit:
Let me clearify...

The done bit on the top rung will be active for one scan only.
Timer[15].DN will be "ON" for one sec then "OFF" for one sec.
 
Last edited:
The first rung makes the .DN bit of Timer(14) true for one scan every second.

The second rung makes the .DN bit of Timer(15) false for 1 second, then true for one second, then false for one second, then true for one second ad infinitum as long as the PLC is running and the subroutine in which the rungs are located is called.
 
Last edited:
No they are not the same.
The first rung will cycle on for 1 program scan once every second.
The the first timer in the second rung will cycle on for 1 second then off for one second.
 
Thanks to all the constructive answers

Much appreciated.
As some of you have seen from my other posts i am an EE that works mainly in power, My job is changing a bit so now i need to learn this.
Thanks for the patience
 
One way to think about it:
With the first rung you have no on/off duty cycle control.
With the second, you do.
 
kwade said:
One way to think about it:
With the first rung you have no on/off duty cycle control.
With the second, you do.
Click to expand...

right so the first one is just an instantaneous triggr so to speak to possible give a quick authorization every one second.

The second one is literally a blink with a 50% duty cycle that remains hight for the alotted time and then low for the alotted time.
 
Yup, think of the first one as a "blip" that occurs once per second (or so, there is an overhead penalty that will make it trigger a little slower than that). So you could use this for a marker to tell the program to collect data every 1 second.

The second rung would often be used as part of a flasher.


BTW, pretty island that you live on.
 

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