Profisafe on non-safety PLC?

[jesusvasquez]

Hello everybody,

Does anybody knows if a conventional (non safety) siemens PLC, for example a S7-315 support the ProfiSafe protocol?

I know it does not have much sense to send safety information from a non-safety PLC, but I was wondering if was something possible to do.

Thanks!

 

[JesperMP]

I think that Profisafe is 'merely' information embedded in regular Profibus or Profinet data.
The safety data is transferred to and from the safety components via regular bus network. If the data fails to transfer, the safety system goes to a safe state.

A safety PLC contains a special safety CPU (the safety logic is executed in two technically different ways).

Do you intend to use safety IO as regular IO ?
Or what ?

Never thought of if safety IO can be used as regular IO.
I think it is not possible. In my non-safety STEP7 projects, I cannot add ET200S safety modules to an ET200S rack.

 

[jesusvasquez]

Do you intend to use safety IO as regular IO ?

No. I was thinking, for example, if you have two separated PLC systems: one with a fail-safe CPU (e.g. 315F) and the other with a standard CPU (e.g. 315). The safety system is in charge of safety related functions while the standard system is in charge of controlling a process (a vacuum system, for example).

In this case, would it be possible to communicate both PLC using Profisafe over a Profinet/Profibus link? For example, if the safety PLC need to knows a vacumm level in order to perform some safety function?

Thanks!

 

[JesperMP]

For example, if the safety PLC need to knows a vacumm level in order to perform some safety function?

I am not an expert in safety PLC programming. But as far as I know, you can only connect the standard safety program blocks to safety inputs and outputs.

 

[tim2]

I am also no expert in the safety programming, but have used it a little.

If you have a safety PLC, you can connect non-safe I/o to the PLC. To actually have any level of safety though, those I/O should not be a part of the plc's safety block.

The PLC can run non-safe blocks, as well as safe blocks. the level of safety is all determined by the safety I/O used in the safety blocks. The safety blocks are limited in the instructions you can use and the data types that you can use.

Data can be shared between the non-safe and safe-blocks using a safety data-block. You can create a safety data-block and store a signal form the non-safe block then can then be used in the safe block. It doesn't make that I/O "safe" I/O, it's just how it's shared between the blocks.

As far as Profisafe between a standard and safe PLC, I think Profisafe can only be accomplished by devices that have specific hardware/firmware to use the Profisafe protocol. The standard PLC won't have that, so it would just be Profinet between the two PLC's, and then Profisafe between the safe PLC and any connected safety devices.

 

[Mike_RH]

In a safety PLC, you will have to sections of code:
1. The safety code, it will communicate using PROFISAFE to the Safe IO on either DP or PN. Once commissioned / certified this code is not easily changed.

2. Your process logic, it will control your process through normal (non safe) IO. You could use safe IO as normal IO, but why? The cost is much higher and the IO density will be lower.

If you are considering using a safe PLC, you should be familiar with the non safe version, and then take a course on the safe PLC. Plus you should be know the regulations / code for the country you will be deploying the equipment to.

 

[tim2]

Would definitely recommend a safety course if you have access to one.

I did not. It's quite a bit different than the just the standard PLC stuff and some of the questions you come up with along the way if trying to teach yourself, it's not necessarily easy to find the answers to.

Siemens does have it all documented, but then again, it's Siemens documentation. It's all in there somewhere, but not necessarily explained well enough for you to connect all of the dots.

 

[adisharr]

I agree with Tim, you might find a course useful as the programmable safety controllers and PLC's I've used in the past have some interesting rules that go along with their use.

 

[jesusvasquez]

Thank you all very much for your answers and advices.

Yes, I'm considering taking a safety course from Siemens. as you said, if more difficult to teach yourself on safety applications. Also, the resulting system must be very well programmed in order to satisfy the certification requirements and, more importantly, that nobody result injured.

Thanks!

 

[JesperMP]

Also, the resulting system must be very well programmed in order to satisfy the certification requirements and, more importantly, that nobody result injured.

The programming bit is trivial.
It is the risk analysis and decision about how safety is to be implemented that is the part where you have to take care everything is correct.
When you are done designing and programming the system, you have to document that the achieved safety is good enough. The Sistema software can help you with that in combination with a library for Siemens products.