Siemens 317F Strange happenings

Today I connected a new KT600 to a Siemens 317F safety PLC to display some basic information.

This all worked fine and was connected via Profibus.

Some time later I was called as the equipment was not in its ready state.
After some diagnostics:

There were inputs I57.0 etc showing true/green 24VDC on the input card.
Viewing the logic in the program I57.0 showed false.

In VAT table it mainly showed True and then occasionally flashed false.
No CPU diagnostics.

Reset the PLC and all returned to its normal operating state.

Why or what could possibly cause these this discrepancy between Input Card / Logic and VAT table.

Many Thanks for any suggestions

Is I 57.0 in the cpu's card stack or connected via profibus?

Any IO on profibus?

Kalle


Edit: And did you measure the input voltage? The LED can be lit even if the voltage is too low for being an '1'.

Hi,

24VDC measured on the card OK.
Configurations basically.
CPU
I/O
I/O
I/O
Profibus Card (Slave for DCS communications)
I/O Connected via Profibus to CPU
I/OConnected via Profibus to CPU
I/OConnected via Profibus to CPU

The last cards are connected via Profibus to the CPU.
The middle Profibus card is used as a slave to a Master within a DCS.

So I think to answer yes I 57.0 is on Profibus.
Adding a slave device should not cause this to happen to my knowledge?

Is I57.0 a fail safe input?
If so then the input card is passivated (Fail state caused by error)

Did you put the HMI as the last partner in the Profibus chain? If so did you terminate the Profibus correctly

Even if you did not enter the HMI last in chain make sure that the termination is correct in both ends of the Profibus chain.
Adding one node to a poor Profibus chain (Poorly terminated or poorly shielded) can cause strange sporadic errors even if the machine has worked properly for years.

Adding new nodes as "T drop off" from the Profibus chain can also cause strange errors.

The cabling was fine and terminated correctly.
The HMI was only a test and was piggy backed off of the 1st Profibus Plug.
Yes the I/O is a Safe Input Card. (Fail state caused by error)
If a sporadic error had happened the input led would stay green as seen.
Should there have been a diagnostics message available?
Can you see this in the logic?
Why is there a different between VAT and Logic
Thanks for all help

My guess is that it's passivated
Put the yellow data block for the module in a vat table

A passivated fail safe input flickers in the S7 program so that is most likely what happened.

The cause of the passivation should be visible in the module diagnostic for that input card.

There is also a Fail Safe DB for every fail safe module where diagnostic can be read.

My guess is that you increased the number of error telegrams on the Profibus by adding the new node but there can of course be an other cause.

Test to connect the HMI properly don't piggyback "T-drop" without a repeater this is known to cause errors.

Failsafe nodes are much less tolerant of errors on the Profibus because it has to do with safety

Many Thanks all, A few more quetions if you have time.

There was a communication problem indicated in the CPU buffer for all I/O on IM153-2.(Profibus)
I have set VAT table up and will replicate once I can have the PLC when the plant is down.
The DB's have Acknowledgement Nessacary. Where do you acknowledge from?

Also when I view the logic for the Fail Safe Program, the comments are highlighted in red and at the end have added "is not a fail safe address"?
There is also a grey triangle by the side, whta do these represent?

We don't have the S7 F systems/ S7 Distributed Safety software, this shouldn't be a problem when monitoring?
A good learning curve, many Thanks

Not all signals must be safety signals in a safety program. For instance the acknowledgment button is usually a normal input.

All signals from the safety program are indicated with red in the safety program because they can be a safety issue if you dont know what you are doing and program the standard signals wrong

To acknowledge passivation you could set the variable ACK_REI in each db for each node but we usually use FB 219 "F_ACK_GL": Global acknowledgment of all F-I/Os in an F-Runtime group.

Read the help file for FB219 for more information.

Many Thanks Bratt and all others
Very informative and helpful.