As you know, the maximum amount of time that you can use on S7 or SIMATIC timers for timing is 2 hours 46 seconds. If you need larger timing values, one of the options might be using the IEC timers.
If you're not interested in using IEC timers, the other option is to build your own customized timer by combining S7 timers with S7 counters.
In the previous lessons, I wrote a PLC program that could easily extend timing to the desired amount for S7 timers by combining these timers with S7 counters. In this lesson, I'm going to write another PLC program with similar functionality but this time, I will make use of comparator operations as well.
So far I've inserted a timer and a counter in the first network and also a flip-flop in the second network to turn on the fan. Now I'm going to show you how these programming elements should work together to be able keep the output energized continually for 15 seconds.
The problem with this program is, when I press the start switch, the timer times the 5 seconds once but I need the timer to time the 5 seconds 3 times in a row. Let's fix this by adding some additional code.
As I said in the previous lesson, the program is complete but it still has an issue. Let's find out what the problem is.
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