Bachelor thesis - Scan time.

Hello.

I am writing a bachelor thesis on my university, where I need to recode an existing code to make the scan time be faster. I have written all sections in ST (not ladder). I need to find out how much time each section use, and the total scan time. How can I find that out? (I am using Unity xl, btw.)

Thanks.

A generic method to calculate average scan time is to set up a counter to increment every program scan. The elapsed time to count from zero to 1000 divided by 1000 is the average scan time.

On Allen Bradley PLC's, you can see the processor scan data such as average, min, and max scan times. I assume it is the same for Modicon. I would assume that you can disable portions of the program to check each section one by one and then re-enable all sections to get the total scan time.

Generally speaking your plc scan time will be made up of code execution and "housekeeping" (the plc handling tasks NOT directly related to code execution). The easiest way to determine what is what is to run only what you are interested in.

Allow the plc to scan with only one very simple instruction in it, an unconditional output for example. At that point the total scan time is for housekeeping and is a hard number you cannot get below. After that, conditionally execute your logic sections using the program control tools available to you, be that selective routine calls or simple program jumps. The total scan time minus the housekeeping time is your section scan time. Do this for all your program sections to find individual scan times. If you run into a resolution issue with your scan time reporting Steve Bailey's time over number of scans idea works well.

Keith

The scan time is available by clicking on the cpu in the configuration section of the project and selecting the animation tab. There are also some status words that may help
%SW27 system overhead time
%SW30 master task execution time
Make sure you do a rebuild all between changes as this will give a better indication of effect of your changes