ISO 26262 Part 3.5: Item Definition

ISO 26262 Part 3.5: Item Definition

What is an Item definition?

• The Item Definitions draws out the identification of a E/E unit or a part of it, on which ISO 26262 life cycle process needs to be carried out.

How to identify an Item?

• Reference of previously existing Item on which Functional Safety compliance needs to be applied
• A completely new concept that needs to be developed in accordance with Functional Safety compliance.
• During the course of ISO 26262 life cycle Item Definition may has to be changed while some system/sub systems needs to be added or removed.

Determining Requirements for the Item that shall be used throughout Functional Safety Life Cycle

• Once the Item has been determined, the requirements related to it shall be identified.
• This requirements are necessary to analyse the Item from the Functional Safety point of view to be adhered during the Safety life cycle.

How to define Boundary of an Item?

An E/E unit may not be always performing independently to achieve a desired functionality. It is further supported/affected by

• User/Driver of the vehicle
• Or other Mechanical units which the E/E unit (under study) controls/ monitors.
• Or Environment where the functionality is expected to operate.

The boundary of the Item shall be determined based upon

• The Elements of the Item
• the assumptions concerning the effects of the item's behavior on the vehicle;
• the functionality of the item under consideration required by other items and elements;
• the functionality of other items and elements required by the item under consideration;
• the allocation and distribution of functions among the involved systems and elements; and
• the operational scenarios which impact the functionality of the item.

Based upon the Item boundary further division into System, Sub Systems, Software (SW)/Hardware (HW)/Firmware (FW) Components/Sub Components are determined.

Example of an Item - Antilock Braking System

Here Antilock Braking System (ABS) is considered as a E/E unit on which the Functional Safety life cycle shall be executed.
This ABS unit which perform a functionality of preventing locking of the wheel consists of

• E/E system (ABS Control Unit, Sensing units, Pump Motor Control Unit, Valve/Solenoid Control Unit), 
• Mechanical System (Actual Brake pedals, Brake Calipers, Brake Pads, Rotor, Brake hose, Brake Shoe, Brake Drum) and 
• Hydraulic System (Master Cylinder, Accumulator, Reservoirs, Piston, Valves, Pump Motor)

Preliminary Architecture Diagram/Assumptions:

The Item Diagram forms the basis of the Preliminary Architecture Diagram on which future System/Sub Systems are identified.