I have a problem.From various software FB blocks where one concret output Qx.x is activated, and is indicated in the TIA portal as active, but the physical output does not activate.

I activate a specific output Qx.x of PLC S-7 1200 CPU214 from one FC block by my software and the corresponding physical output of the PLC S-7 1200 CPU214 is activated.

But from another FC block in my software the same physical output - Qx.x is not activated.

Apparently there is some problem with the software code I am loading the PLC-1200 with, but what could it be?

Thank you

Hello yordcherc;

The PLC scan typically starts by reading inputs, applying these inputs in the PLC program to determine the values that will be sent to the outputs, and finally writing these values to the actual outputs. There are other tasks performed by the CPU, but this is enough to possibly explain your problem.

As the scan works therough the PLC program the last logic block to access an output will determine the actual value of the output, until the next scan changes it if the logic has changed. Very often beginners are frustrated because they have 2 different logics applied to the same output, and only the last one that is treated by the CPU appears on the physical output.

I suggest you read the following discussion, and apply the suggestions by members Jeff Casagrande and Piotr.M so that the output is activated/deactivated only once in the program:

https://support.industry.siemens.com/forum/sa/en/posts/activating-an-output-(valve)-multiple-times/178497/?page=0&pageSize=10

Hope this helps,

Daniel Chartier

Hi yordcherv,

fault finding is often a process of elimination. The first step is to simplify. Only scan test code that activate that output. If the output comes on then you can deduce that the problem might be in the full code.

Dear Mr.dchartier,

Thank you very much for your answer.

But the problem is that when a segment of the program is activated, the PLC output is not activated.

For example, I have made screen shots to the problem and insert them in the file "The my problem.docx".

At the Fig.1 in the program block "Regimes_Changes", Network 4 is activated the program block "MAN" (Fig. 1).

At the Fig.2 in the program block "MAN", Network 29 is activated the output D44 Q - (Address %Q12.2) .

End finally the output D44Q (Address %Q12.2) - is not active. This is shown at Fig.3 "PLC tags".

I have attached the file The my problem.docx with Fig.1, Fig.2 and Fig.3 inside.

Please, loock at figures attached in docx format.

Thank you

Yordan Chervenkov

Dear bit7,

I've tried without success.

I'll try again, but it's straight

Thank you very much

Yordan Chervenkov

Hi Yordan Chervenkov,

as Daniel Chartier has already mentioned, the last write access to the PLC output is crucial. Once each PLC cycle, the process image of the outputs will be written to the hardware. This happens at the beginning of a cycle.

When monitoring a program block, the values written in the seen network / program line are shown. Since it is possible to write the same variable later again, the process image can be different to your expectation. When monitoring a PLC tag list, the value of the process image at cycle start should be shown. And as I mentioned above, these are the values written to the hardware. To be absolutely sure, you can use a watch table in extended mode and select "Permanently, at end of scan cycle" for the trigger.

You should take a look at the cross-references for your output tag. In the worst case, you have to take a look at all write accesses for the tag. In your screenshots, the data blocks "MAN_DB" and "MAN_DB_1" are shown. This looks like you have two instances of your function block "MAN". If so, you must ensure, only one of the instances is active.

Kind regards
Stefan

Dear Stefan Arcularius,

Thank you for the tips.

I have done absolutely everything according to your advice.

But still it doesn't work.

I should add that I control the PLC outputs via a touch panel that is networked with the PLC.

Not that the problem lies in the exchange of data.

All the tags on the touch panel are correct.

For example, the activation of a button in manual mode by touch panel is read correctly in the PLC program, but the corresponding output is not activated.

I don't know what else to do?Could I use some kind of interrupt to necessarily record the state of the outputs in the PLC hardware?

With kind regarda,

Yordan Chervenkov

Dear Mr.V,

I used the advice above but to no avail.

With kind regards

Yordan Chervenkov

Hello Yordan.

The FB called "MAN" has control over the outputs that you are asking about. That FB is being enabled and disabled by code. This is the cause of your problem.

The code inside the FB stays in a 'frozen' state when the FB is not enabled. Find a way to do the control so that the FB stays enabled.

Regards.