Instrument Selection

[Srinathgv]

Any one ther help me out with your suggestion, while selecting the instrument what considerations I need to take from SIL point of view.

[aidini]

Any one ther help me out with your suggestion, while selecting the instrument what considerations I need to take from SIL point of view.

Instruments are selected based on SIL Study requirements. The SIL level for each loop should be specified and according to that every element in the loop (sensing element, logic solver, final element) is assigned with a SIL level up to 3 or 4.

[aidini]

Any one ther help me out with your suggestion, while selecting the instrument what considerations I need to take from SIL point of view.

Instruments are selected based on SIL Study requirements. The SIL level for each loop should be specified and according to that every element in the loop (sensing element, logic solver, final element) is assigned with a SIL level up to 3 or 4.

[hasanbarim]

Before SIL study , HAZOP has been done.

Then you can make SIL study and select transmitters.

[Hix]

Hi, as previous comments the selection you are asking depends of different factors, the hazop is the first step of the safety lifecycle and the starting point for all the process. After you have identified the independent layers that can be taken into account on every risk scenario, you can identify the need for a SIF. This SIF must have a assigned SIL specified on the SRS (Safety Requirements Specification), this is usually done by a LOPA Analysis. The selection of the instrument depends of the LOPA results, assuming you have clear the SIL meaning you must identify the requirements each level has, discard SIL 4 as this is only adressed on IEC 61508, and the IEC 61511 and ISA 84 (IEC Mod) suggest a design change when this SIL is required. A chain is only as strong as it's weakest link, meaning that you must take into account all the loop, Sensor/transmitter, logic solver, and Final control element (even the fieldbus used to communicate now). This being said you can have a SIL 3 rated Sensor/Transmitter, but if you have a basic process control Logic Solver with no SIL rated certification, with no diagnostics you can achieve SIL 1, and hardly achieve SIL 2 with crazy numbers on calculations. So be aware that the PFD numers of all elements of the loop are added in the final calculations. FYI also you can use non rated SIL instruments using the proven in use clause, but this will require a lot of information about the operation of that instrument in safety related functions, and in the same process conditions.

[chen4]

Hello,
Is "specification sheet" same as "instrument data sheet"?
In API 520, the title of Fig 33 is "Sample of completed valve specification sheet". Is this the instrument data sheet for a valve?