S7-1200 - Cycle Time

Hi all!!

I have a S7-1200 with a quite simple software downloaded.

The cycle time is about 22 mSeconds. All the DBs are optimized but I have one not optimized (I need a direct addressing in this case).

Is there a way/settings to decrease the cycle time? Is it not too high??

Thanks in advance.

scan time is relative I suppose.  Is it fast enough to do what you want to do?

Several factors drive scan time

- floating point math functions
- interrupts
- nested loops
- motion control
- communication functions.

In my apps, I generally have 8-15ms scan times, which include many FP calculations, motion control (1 axis), comm functions and the usual bit/word operations.  It works and I'm happy with the scan time.

I do all of my FP calculations on change detect of variables, so they are not running continuously.  Interrupts should be coded as efficiently as possible.  Nested loops should be avoided unless there is no other solution.

You can try disabling some of your code and see where your scan time is coming from.

Jeff (thanks!) has said most of what needs to be said.
It really depends on what you are controlling.

Some more tips:
* If the PLC is processing some HMI related tasks - consider if those can be isolated as per HMI page. Then have the HMI tell the PLC which page is active so that only those HMI tasks are processed.

* Some tasks are not to much time critical (think: calculations). Have those update on a "clock" pulse. A simple example would be..

   scanPulse          scanPulse
----|  /  |------------(     )

   scanPulse       {task group 1}
----|  /  |------------(     )

   scanPulse       {task group 2}
----|     |------------(     )

....
If you expand on your thoughts relating to your control system, we might be more of service to you.

Greetings.
w

Hi,

if you want to know how much time needs a part of your PLC Code you can measure the time.

There is a nice FAQ called:

With S7-1200/S7-1500, how do you measure the total cycle time of a program?

https://support.industry.siemens.com/cs/ww/en/view/87668055

Regards,

Towome

hi Mike,

Hello Mike,

question is why you want short cycle time? Basically, if your system can work optimally without any problems (can communicate with external devices in optimal time, can calculate without timeouts, can drive outputs logic fine) you don't need optimize your code. Be calm, I got old project where I got 1s cycle time and everything is ok