SIL3 for S71500

Dears

Please I need your support for the problem below:

I have a Normally closed contact (emergency contact) that I need to supervise it's 4 status: Healthy, Alarm, short circuit, open loop with a PLC S71500. Can you please propose to me an FAI that support these 4 status and the solution stay in SIL3!!!!!!!!

Thank you in advance

Wahbi012

Dears

Please I need your support for the problem below:

I have a Normally closed contact (emergency contact) that I need to supervise it's 4 status: Healthy, Alarm, short circuit, open loop with a PLC S71500. Can you please propose to me an FAI that support these 4 status and the solution stay in SIL3!!!!!!!!

Thank you in advance

 Dears

Please help me it's an emergency!!! Is there any F-DI module that can support the 4 cases (Healthy, Alarm, short circuit, open loop) in one time !!! It's not a problem if it the solution exist with other type of PLC!

Dear CaOd,

Why I need 2 contacts?

Dear CaOd,

The module you gave me don' support wire break according to page 58 of it's datasheet!!!

Can you please give me an explanation or another module?

And why we need 2 contactors?!

SIL 3 is all about assurance the proper safety function will happen even if a single fault occurs, like a single contactor, or single set of input contacts fails.

SIL 3 expects redundant input contacts and redundant output contactors. 

Wahbi012

Dear CaOd,

The module you gave me don' support wire break according to page 58 of it's datasheet!!!

Can you please give me an explanation or another module?

And why we need 2 contactors?!

Hello Wahbi;

The mdoule CaOd proposed does detect wire break, it is part of the discrepancy alarms, as shown in the following screenshot, taken from its manual:

SIMATIC ET 200MP digital I/O module F-DI 16x24VDC

https://support.industry.siemens.com/cs/ww/en/view/109482426

I will try to give a basic explanation of why it is suggested that for a SIL 3 configuration you would need 2 input contactors in a following post.

Hope this helps,

Daniel Chartier

Note: I just realized that we had a very similar discussion on the contents of the manual for this module, a few days ago. The original poster had asked for support (through a Support Request) on this issue, but has not come back to us to date on the solution.

https://support.industry.siemens.com/tf/ww/en/posts/wire-break-detection-in-the-digital-input-module-f-di-16x24vdc-6es7526-1bh00-0ab0/212385/?page=0&pageSize=10

Hello Wahbi;

Questioning why certain design specifications are required in Safety systems would require a lot of theory. I will attempt to show you the same visually.

Siemens has opted to use IEC 61508, Safety-related Systems (along with IEC 61511, Safety in Process Industry), and has developed a tool to help the user evaluate the safety level his design can attain, SIL 1 to SIL 3. This is the Safety Evaluation Tool (already mentioned by our friend CaOd); you can download it from the Safety Evaluation Tool conference, part of the Solutions, Applications and Initiatives directory in the navigation panel at the left of this page.

A competing standard, ISO 13849-1 (Functional Safety of machines) has been championned by TUV and is much used by manufacturers of safety equipment. This is the standard I have generally worked with.

Both standards are very close, I expect that at some point they will be resolved in a single encompassing standard. But for the moment we have to work within one or the other.

For the moment, equivalencies have been determined between both standards. If you look at the attached screenshot, you will see that a SIL 3 design (IEC 61508) corresponds to a PLe implementation (in ISO 13849-1).You could input the corresponding parameters for your safety inputs, logic solver and outputs in both SET and Sistema and obtain the same corresponding safety level (the parameters are slightly different for both systems though).

ISO 13849-1 has one advantage in my opinion. It has associated to the design phase some architectural guides, based on a preceding standard, EN 954.These are shown in the same screenshot below.  If you want to design a PLe (equivalent to SIL 3) system, you should use a CAT 4 architecture (some exceptions allow CAT 3). Both CAT 3 and CAT 4 architectures require dual, separate inputs, and dual outputs to the logic solver (Safety PLC), based on the mathematical basis for the evaluation of safety levels. If you are attempting to create a PLe design with a single input, Sistema will create a warning and stop its calculations, since the calculations to reach a PLe level will not compute. If you analyse the design for your SIL 3  implementation in the SET (Safety Evaluation Tool) with a single input contactor, no matter how safe this particular equipment is, calculations will fail, you will get the same result: an error, and will not be certified at SIL 3.

Hope this helps,

Daniel Chartier

Dear CaOd, dchartier and huggy_d1

Thank you a lot for the good explanation.

The problem is that the client request to make the SIL3 with only one contact (the emergency pushbutton). But according to your explanation, if i understand , that's not possible!