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Mean Time Before Failure

Calculations

Reverse Engineering Department

20/06/2019

Definition

of

MTBF

Mean Time Between Failure

-is the estimated time between inherent failures of a electronic or mechanical system

Goal is to design a product to increase the time between failures or increase the time before a failure

Mean Time Between Failure

In order to determine an effective MTBF duration is it critical to understand

the operating conditions the device is subject to in the field

Operating Conditions Include:

  • Operating (Ambient) Temperature
  • Component's Maximum Rating (max voltage/wattage)
  • Component's Applied Rating (applied voltage/ power dissipated)

  • When components are operated close to the maximum ratings, their mean time between failure can be reduced

Our

Approach

Our Approach to Calculating A Mean Time Between Failure

  • Electrical design of the prototype

  • Using analog circuit design methodologies

  • Develop a schematic of the design

  • Generate a Bill of Materials (BOM) of components used
  • Verify the alpha prototype has a mean time between failure that is greater than the specified legacy unit's value

4.

2.

Proceed to Design Alpha Prototype

Verify

Prototype

Meets Customer Requirement

Determine Customer

MTBF

Requirement

Perform

MTBF Analysis on the Bill of

Materials

Sample Components Used

3.

1.

  • Using the components used on the electrical sub assemblies (ESA's)
  • Perform a Failure in Time (FIT) calculation for each component using the MIL-HDBK-217F Standard
  • Sum the total FIT's to get the mean time between failure of the prototype
  • Technical specification defines a minimum MTBF in hours

  • Or customer provides legacy documentation , that illustrates the MTBF of the legacy unit

  • Kinectrics works toward a greater MTBF number than the customer imposes

Example of a Technical Specification

  • Specifies an operating temperature
  • Specifies a minimum MTBF requirement

Example of a Electrical Subassembly Drawing

Sample Bill of Materials

Sample MTBF Calculation

MIL-HDBK

217F

Standard

MIL-HDBK-217F Handbook

  • Developed by department of defense, with assistance with military departments

  • Standard reflects the latest information on reliability prediction procedures of electronics

  • Provides methods for estimating the inherent reliability of military electronic equipment

Contents

Component Failure's In Time (FIT)

Sample

Calculation

Sample Calculation for Capacitor

  • FIT Calculation for C12

  • Has an applied Voltage of 86 VDC

  • Component has a maximum voltage of 200 VDC

  • Operating temperature is 50C
  • Temperature rating is 125C

  • Capacitance is 22 micro farads

  • Capacitor material is ceramic

Following Section 10.1 of Standard

Failure in Time=

Mean Time Between Failure=

Calculation

Summary

Thank You

Any Questions

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