memory latch with a timer

rogerhollingsworth · Aug 9, 2003

I want to take my foot off the foot pedal after I step on it and still have the timer finish it's cycle.

redmanrh

That is how a TOF or OFF timer works, it starts timing when you remove your foot from the foot-switch, you don't need to seal or latch it in. Sounds like you are just confused on the operation of the timed bits, look at your timer data table while operating the foot-switch and you will figure it out.
I do agree with the others, TON or on delay timers are much less confusing.

Roger

Eric Nelson · Aug 10, 2003

Notice his original logic Roger:



|    0

|---] [---+----------( TIMER )

|         |

|         |  TIMER

|         +---]/[-----( 15 )

.
Whether or not redman understood how an off-delay timer operates, he was still requiring that the foot switch be ON for the valve to fire. The off-delay timer would start timing, but its contact became useless once the foot switch input went false.

beerchug

-Eric

panic mode · Aug 10, 2003

I am not familiar with that PLC but here is
my suggestion:





  foot_sw              trigger 

----| |---[osr]----------( )







 trigger   timer        output  

----| |--+-|/|------+-----( )

         |          | 

  output |          |   timer

----| |--+          +-----( )









foot_sw : input ("O")

output  : output ("15")

timer   : on_timer

trigger : some spare bit

[osr]   : one shot (rising edge)

You can try to get rid of the first rung
and use input "O" instead of trigger.
in this case however output might stay on
for longer time than specified by timer
if operator decides not to remove foot
from foot switch. when using both rungs,
output would stay on for exactly same time
every time.

memory latch with a timer

rogerhollingsworth

Member

Eric Nelson

Lifetime Supporting Member + Moderator

panic mode

Member

Similar Topics