TON .DN bit confusion

ssas

Member
Join Date
Sep 2018
Location
Pakistan
Posts
3
Hello Members,
I am new learner of PLC and I am experimenting with Rockwell Automation Softwares.
I have attached my logic file, it is basic traffic signal program. According to my understanding, initially when the program start to run, Yellow_Timer.DN bit is 0 and hence XIO contact is high, which is causing Red_Timer to enable and it starts timing, meanwhile Red_Light OTE is high for 30 sec. After 30 sec, Red_Timer.DN bit will be high enabling Green_Timer, turning OFF Red_Light and turning on Green_Light for 25 sec. After 25 sec, Green_Timer.DN will be high to enable Yellow_timer, turning Off Green_Light and turning On Yellow Light for 5 sec. As soon as, 5 secs complete Yellow_Timer.DN bit will be high, causing Yellow Light to turn off, according to my understanding this bit should remain high and Red_Timer should not be enabled again. But in actually it goes back to 0 and Red_Timer get enabled again, what is causing this bit Yellow_Timer.DN to set to 0 after 5 secs. Please explain.Thank you
 
The yellow_timer.dn is XIC which will reset the red timer and that in turn will reset green timer which will reset the yellow timer and that will return the yellow-timer.dn to it's normal state of closed and starts the red timer.
 
Also, look at the timer.TT bit. It could simplify your light output rungs.
 

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