Here is the system to analyze for our example

The system shall control automatically the water level in a tank

The technical functions frozen by the team are the following :

Filling flow is controled by a manual valve , handled by a rod + float.

When water is high , float + rod are closing the manual valve , reducing the filling flow.

When water level is low, Float + rod are opening the manual valve, increasing the filling flow.

Target is now to analyze the different failure modes of the technical functions and analyze their effects at system level

Fill the functional analysis of the system in the FMEA tool template by double click on <<ADD>> buttons.

ADD Life situations : Operating / System OFF / Maintenance / Installation

ADD Functions : "Manage level of water in tank"

ADD Technical functions : Valve / Rod / Float

To reduce number of failure modes and situations to analyze in FMEA table, the tool allows the setting of affectations matrices.

Eliminate from top level the situations that are not relevant to analyze, when technical functions are strictly independant from main functions , or when main functions are strictly independant from life situation.

Set "0" when independancy exists

Set "1" when no independancy exists

In our example, no independancy are present, 1 are set everywhere in the 2 affectation matrices

First , unhide the next columns to the right of the technical functions

Then fill the identified failure modes in front of each tecnical functions

VALVE >>

Stuck open / Stuck close/Stuck in middle position/Handling force too high/Handling force too low etc...

ROD >>

Tool long / Too short /Mechanical break / corrosion etc...

FLOAT >>

Floatability too high / FLoatability too low / Leak / float blocked etc...

Failure modes can be identified or extracted from sub-FMEAs or can be the result of generic failure modes identification: Loss of function/Unintended function activation/too much/too low/stuck in wrong position/mechanical failure/short cut to Vbat/Short cut to Ground etc...

Double click on <<Refresh button >> to create the FMEA table.

The tool will create one row per situation, mixing all life situations with all functions and all technical functions

The team shall then review row per row all the sitations listed in the table, assessing the effects of a failure mode at system level in each specific life situation with the 3 criteria - occurence / severity /detection - from 1 to 10

As a result of FMEA, team should come to the release of new specifications and specific validation plans such as min and max handling force of the manual valve, rod material and resistance to corrosion, endurance test.

But team should notice and report as well lack of design control in the life situations installation, maintenance and system OFF. System described in this example is not well designed for those situtaiond, so team should upgrade it

This is the main force of an FMEA study >> it drives the design of a system with robust and secured specifications book and drives the definition of a relevant validation plan.