Can the scan cycle time be calculated as described in chapter 19 of the system manual (doc no. A5E00267695-13) by simply adding up the execution time of each instruction, process image update portions and OS function?

Or is there a limit to how low it will go? What scan cycle time is achievable on for example a 417-5H with a minimal program?

Thanks.

Hi!

According to the guide you sent (or studied), the minimum cycle time can be organized and calculated if your system consists of:

1. Any S7-400 CPU

2. CPU don't have any connections

3. CPU don't have any interruptions

4. You have only one organizational block (OB1)

5. Besides the organizational block, you have nothing else

6. No modules connected to the PLC rack

And what do you get? - The smallest cycle time

However, as soon as you fill your program, add external connections, interruptions, add modules, add communication modules - you configure all this - and you increase the cycle time many times.

In this case its calculation PLC cycle timeis reduced to an approximate maximum and minimum value.

See the manual and its sections below. The calculation of time depends on a huge number of factors (there is a description in the manual)

The fact is that in STEP7 and TIA PORTAL I did not find the function of counting the number of instructions in the program

And then it turns out that the calculations come down to understanding how much and what will be used with PLC

An easy way to calculate is to drive your software onto the simulator without external connections configured and understand how fast it works (however, the simulator will also show an approximate value, since this is not a real controller)

S7-400H System Manual, 07/2014, A5E00267695-13

SIMATIC Fault-tolerant systems S7-400H (V6.0)

19.1 Cycle time

19.2 Calculating the cycle time

19.3 Different cycle times

19.4 Communication load 

K0ICHI

Anybody else?

 Yes)

Hello Again!

This is not a new topic for the forum however so ambiguous that there will be no simple answer to it!

See topics and FAQ below:

cycle time

FAQs:

S7-400 Instruction List CPU 412, 414, 416, 417

Clipping from FAQs:

Calculating the Execution Times for Area-Internal Memory-Indirect Addressing Example:

A I [DBD 12] with CPU 414

Step 1: Load the contents of DBD 12 (time required is listed in the table on page 20)

Step 2: AND the input addressed in this way (you will find the execution time in the tables in the chapter entitled “List of Instructions” on page 23 )

**********

There is a calculation method - you see it.

However, in order to fully use it, you need to:

1. Know how much instruction you have in one block
2. Know the types of these instructions
3. Know the types of accesses - to memory, to inputs / outputs and so on
4. Know how much indirect addressing you are using (and things like that)

Can you answer these questions? If you can - Yes, use Excel, create a table, count, and you will get what you need.

But unfortunately, again approximately.

Because, in addition to the instructions themselves, there are various interruptions and so on.

You Snooze, You Lose: Measuring PLC Cycle Times under Attacks

You can, of course, not worry, and buy the expensive and powerful PLC, but we have common sense!

We test our software on simulators and so on.

Try, study, do!

Regarding the calculation of the number of instructions.

I found a site on which to do this (Website in Russian).

Statistics of the use of instructions in the Step7 project

All you need is to download the source code of your program in STL language, and you will see the result.

Of course, in total this does not solve the problem of calculations, but it can simplify the understanding of how much time the PLC will spend on processing your program ...