Reliability Models and Predictions (MTBF)
Reliability Models and Predictions analytically predict the reliability of a product in terms of MTBF or Availability.
Reliability Models and Predictions estimate a product’s reliability to satisfy customer requirements, determine spares requirements, and diagnose weak points in the design.
Reliability Predictions are used during the component selection phase to:
- help assess the effect of product reliability on the quantity of spare units required which feeds into the life cycle cost model.
- provide necessary input to system-level reliability models (e.g. frequency of system outages, expected downtime per year, and system availability).
- assist in deciding which product to purchase from a list of competing products.
- drive design trade-off studies. For example, we can compare a design with many simple devices to a design with fewer devices that are newer but more complex. The unit with fewer devices is usually more reliable.
- set achievable in-service performance standards against which to judge actual performance and stimulate action.
VALUE TO YOUR ORGANIZATION
Reliability Models are used early in a design to help make initial assessments of complex systems and to help
- make early decisions as to the need for redundancy.
- understand how often different parts of the system are going to fail even for redundant components.
An example of Reliability Integration during Reliability Predictions is as follows:
Reliability Modeling and Predictions can be used as an early indicator if a design has the potential of meeting end-goal requirements
We can calculate a product’s reliability with a reasonable level of accuracy. From this, we can help determine how much testing and manufacturing screening will be necessary to then assure that the goals are met.
The following options are available for Reliability Modeling and Predictions. You can choose any combination of the following services to meet your specific situation.
Basic Analysis (parts count)
“Parts Count” Analysis estimates a product’s overall reliability using industry standard failure rates for each component. Telcordia SR-332 is commonly used for Commercial Products and MIL-HDBK-217F is commonly used for Defense Products. This analysis is typically performed at the assembly level but can also be performed at the system level.
Advanced Analysis (parts stress)
“Parts Stress” Analysis is performed after a Basic Analysis for a more accurate overall MTBF. It considers the influence of additional factors on each component (quality, temperature, electrical stress, environment, and first year reliability estimates based on proposed manufacturing screening). This analysis is typically performed at the assembly level but can also be performed at the system level.
End-of-Life Analysis estimates the onset of wear-out failures for consumables (electrolytic capacitors, fans, motors, drives, etc.). This can aid in planning In-Warranty costs and scheduling Preventive Maintenance. This analysis is typically performed on components within an assembly or system.
“Service-Affecting” Analysis can be performed after the Basic Analysis. Rather than considering every component failure, it discounts failures which do not affect system performance. Acceptable minimum level of performance is carefully defined and considered across the product. This analysis can be performed at the assembly level or system level.
Availability estimates uptime by considering failures that take down an entire system. The architecture, with redundancies, is modeled as a combination of series and parallel elements. Markov Analysis or Telcordia SR-TSY-001171 guidelines are used as appropriate. This knowledge can satisfy regulatory requirements, aid in setting spares strategies, and support marketing efforts. This analysis is typically performed at the system level.
Field Measured Reliability
We collect data from the field database and use analytical techniques such as Weibull Analysis to determine not only the current reliability figure but also where on the reliability life cycle the product currently is (see reliability “bathtub curve” below) – decreasing failure rate, constant failure rate, or increasing failure rate. This analysis can be performed at the assembly or system level.
RELIABILITY PREDICTION SOFTWARE
There are many different companies that sell reliability prediction software packages and there are many different reliability prediction methodologies, handbooks and guidelines (MIL-HDBK-217F, G, H, 217Plus, Telcordia SR332, etc). As consultants, we maintain an objective viewpoint in these areas and first evaluate our clients needs and then make recommendations as to the best sofware package and the best methodology.