Longer Timers than 2h 46m 30s

NevadaNewbie

Member
Join Date
Dec 2007
Location
Nevada
Posts
4
Hello everyone. I am new to PLC's and I am having some problems with my siemes simatic s7-400. I am trying to program it with step 7 and the longest timer I can find use s5time and will only let me go to 2h46m30s. I need to go out about 6 weeks this would require ~400 timers in series to do. I know there has to be a better way. Can anyone help me out?

Thanks in advance.
 
Last edited:
The #Time variable used by SFB4 for example, will time up to 24 days so it looks like you will have to roll your own code.
 
Can you please describe the functionality required first. Are you timing how long something is running or delaying before starting something or what. How accurate does the time have to be. What is to happen if the plc gets turned off for a time ?
 
I am delaying a notification light from turning on. Every 6 weeks the UV bulbs in my system need to be wiped and the light will notify when it is time to do this. The timing does not have to be super accurate. Pretty much just within the day would be fine.
 
One simple solution would be to use one of the Time-of-day interrupt organization blocks (OB10 - OB17) and set the interrupt time to once a day and then update a variable at each interrupt.
 
OB35 is a timed interrupt block. It normally runs every 100ms (check the h/w config for the CPU to confirm).

In OB35 increment a DINT variable (say MD100 or any free double marker). When the variable gets to
6 * 7 * 24 * 60 * 60 * 10 >= 36288000 it's time to wipe your bulbs and reset the variable to zero to start the next 6 weeks.
 
NevadaNewbie said:
Ok got that now how do I reset that variable?


Using the same logic that turns off the notification lamp with a move instruction as indicated in the previous post.
 
use the combination of counter and timer can easily solve the long timer peoblem(T=t*c),if you need i'll give you the program.
 
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