MSRs – Understanding monitoring and system responses in FMEA

MSRs – What are they all about?

Decades ago, engineers started to make tasks associated with the application of products more secure by means of MSRs.

In more specific terms, what happens here is that a technical system is upgraded with a diagnostic capability. When this system detects that certain threshold values have been exceeded or certain undesirable system states have occurred, an automated system response is initiated.

This enables the system and/or the user to minimize the severity of the effects that occur.

A specific example: A temperature sensor detects an abnormally high temperature in a medium and generates a warning message for the user of the system. The user becomes a part of the control circuit and intervenes in a failure-effect chain.

For example, they interrupt a car trip in order to minimize the effects of a dangerously overheated brake system: Instead of facing a dangerous situation (B=10 in FMEA), by interrupting their trip they reduce the effect to a system failure (B=8).

These system responses are by no means limited to just warnings. In some system responses, for example, the MSR component might automatically switch off the system or reduce its power level.

For years, there were intense discussions in FMEA expert circles as to whether such “detection measures in the field” should be treated as prevention or detection measures in FMEA.

It was obvious that an additional category here requires a different conceptual model. All the more so since the previous idea that the severity of effects was constant led to further questions and debate, because it seemed evident that the B value changed as a result of MSRs.

In actuality, the B value does not change! MSRs lead to the occurrence of a different effect, which of course has a different B value.

The AIAG/VDA FMEA methodology description represents a methodological approach.

The Probability of Occurrence (O) and Probability of Detection (D) categories have now been replaced by Frequency (F) and Monitoring (M). Of course, behind this change are MSR-specific evaluation catalogs (for F and M).

The general idea is: A malfunction is identified through diagnostics and a system response (another function) is used to reach a state that leads to a different (lower-threshold) failure effect.