Introduction to Reliability Prediction standards

Reliability Basics

Introduction to Reliability Prediction standards The Reliability Prediction standard is a method to predict the reliability of systems and components (mostly electronic products) based on the failure rate estimates published by globally recognized military or commercial standards. In the early stages of R & D, real fault data cannot be obtained, or when the manufacturer is forced to use recognized standards for reliability prediction, the reliability prediction standards are particularly important. This article introduces the Reliability Prediction standard and how to use itLambda predictSoftware. Assumptions and Applicability Reliability hotwire50th introduced the criteria for reliability prediction, and discussed the applicability of this method and the assumptions used. The general prediction criteria and analysis methods are described in the 51st period. We recommend that you review these articles to lay a solid foundation for this article. Estimated Standard Common expected criteria include: MIL-HDBK-217, Bellcore/telcordia (SR-332), NSWC-98/le1 (for mechanical components), 299b (GJB/z-299B), and RDF 2000 (IEC 62380 ). Analysis Method: Typical analysis methods: Component count analysis method. Component stress analysis method. Besides the common methods in all these standards, Bellcore also uses three other methods (method I, method II, Method iii ). The above analysis methods are introduced in section 51st. Computing and Measurement The standard generally estimates the reliability of the system based on the basic failure rate of components in the system. The basic failure rate describes how a part works under "normal" conditions (determined by the standard. The basic failure rate can be multiplied by various factors (called pi factors, with a value between 0 and 1). These factors describe the specific conditions/stresses of the component during use, in some standards (such as Mil-217), there are also factors that describe part quality. The standard calculation failure rate of reliability is estimated by adding, or accumulating the failure rate of all components and components until the system level. Failure rates related to Part welding points and other types of structures, such as surface assembly and Printed Circuit Board (PCB) or hybrid devices, may also be added (depending on the method used by the analysis. The following metrics can be calculated: Failure Rate, λ: Condition failure rate, which is defined as the total number of failures in the total project at a certain measurement interval under a specific condition, divided by the total time consumed. The expected reliability is generally described as the number of failures per million hours, fpmh. In Bellcore, the failure rate is usually expressed as a failure per billions of hours, Fi. MTBF: The average interval between failures is the expected hours of work between failures under specific conditions. No availability: In the Reliability Prediction standard, this term will be used in turn for unrecoverable systems. Reliability is defined as 1-r (t ). R (t) indicates reliability. Because the standard assumption that the failure rate is determined and all calculations are based on the failure rate or MTBF Value, this assumption indicates that the reliability function is described using the exponential distribution model. The following equations describe the exponential distribution model. Time variables can be used to calculate the reliability of systems/subsystems under a specific time value. R (t) = E-λ tOrR (t) = E-T/MTBF Contribution: The failure rate of an item or block (collection of items) accounts for a certain percentage of the failure rate of the next higher level or hierarchy. the is the item or block's contribution. this may be (a) The percent contribution of a component's failure rate to the total failure rate of the block (collection of components) to which it is connected, (B) the percent contribution of a component or block's failure rate to the total failure rate of the top level hierarchy or system (collection of blocks or components) to which it is connected or (c) the percent contribution of a system's failure rate to the total overall project (collection of Systems) failure rate. First-year-multiplier This performance is only applicable to the Bellcore/telcordia standard. Bellcore emphasizes the Early Life Cycle elimination rate of electronic products (in infancy). manufacturers use aging to reduce the severity of early stages of elimination by screening vulnerable components with early life problems. The Bellcore standard uses the first-year-multiplier factor in the prediction of failure rates to demonstrate the risk of early elimination. The first-year-multiplier factor is defined as the average failure rate during the first year of operation, indicating the product of the failure rate in the stable state. The Bellcore standard also makes sense for the use of the aging stage, and correspondingly reduces the first-year-multiplier factor (that is, the longer the aging stage, the smaller the multiplication factor .) Task Section The reliability is expected to be consistent with the field use conditions, and the use conditions may sometimes change over time. The task section can be divided into multiple work stages of the same nature, and the conditional stages of the product over time. The performance of the specified task section is only available in the rdf2000 standard. The standard allows you to specify the temperature task profile for different stages. Each stage may have different temperatures, which may affect the failure rate of components. The phase can also be one of the following types of average external temperature changes that can be detected by devices: Switch phase Permanent Work Phase Static (storage) Stage The failure rate calculation is affected in different ways in different stages, because they impose different stresses on components. Repairable and/or Redundant System Analysis The typical Reliability Prediction standard emphasizes the use of devices and equipment as unrecoverable series systems. Any component failure will lead to system faults and the system will remain in the fault state permanently. Therefore, the model does not contain redundancy or repair. Lambda predict provides additional functionality to include system and/or module-level maintenance and redundancy in failure rate and availability calculations. In Lambda predict, you can simply input MTTR (average repair time) data for repair analysis. Analysts can also specify the number of redundant units and describe the relationships used: simple parallel structure (hot standby) or cold standby (Backup) structure. The initial availability can be calculated using the repair rate μ = 1/MTTR and failure rate λ. In a redundant system, the primary availability, failure rate, and number of available backup systems can be used for calculation. The failure rate can also be calculated for redundant systems. Allocate Generally, a design must meet a specific reliability goal. For a system composed of multiple components/subsystems, the reliability objective needs to be apportioned (allocated) to different components/subsystems in one way to ensure that the overall failure rate meets the reliability objective. The Reliability Prediction Method Standard usually uses one of the five allocation models to logically allocate product design reliability to lower-level design standards, so that the cumulative reliability can meet the requirements. The method depends on different allocation technologies, so different results are also obtained. The five allocation methods are as follows: Mean: This method is the simplest, regardless of any difference between elements. It only distributes the reliability target evenly to all elements. Agree: An expected probability of system failure caused by an element failure, taking into account the complexity and importance of each element. Feasibility: evaluates elements based on product complexity, technology development level, running time, and environment based on the data rate scale. ARINC: This method only focuses on the current failure rate of the subsystem. It allocates reliability by using the weighting factor calculated by the sum of the current failure rate of the subsystem and the failure rate of all subsystems. Recoverable system allocation: This method allocates the failure rate of the subsystem to meet the availability target of a repairable system. Assume that all subsystems can be identified and there is a fixed repair rate. The repair rate is determined by calculating the distribution failure rate and repair rate ratio of each subsystem based on the stable state availability, in this way, the failure rate assigned to each subsystem can be determined. Amount Reduction Analysis Most device faults are caused by stress. When the applied stress exceeds the inherent strength of the component, serious degradation or failure may occur. To ensure reliability, the device must be designed to withstand time-based stress without faults. In addition, the design stress parameters must be determined and controlled, and the components and materials under stress must be selected. The reduction is the selection and application of parts and materials, so the applied stress is less than the ratio of specific applications. Especially for temperature images, the decrease is the negative growth of efficacy. It shows that as the ambient temperature increases, the output power of a certain part will decrease to ensure reliable system operation. The descending curve provides a simple method to estimate the maximum output of a device at a given temperature. InLambda predict 2Medium, you can apply a scale-down standard to the Mil-217, Bellcore, or RDF 2000 systems. The following are available recognized criteria for downgrading: NAVSEA-TE000-AB-GTP-010: This standard is based on the naval electronic equipment parts demotion demand and application manual. MIL-STD-975M: electronic components, materials and processes for aerospace and ship equipment. MIL-STD-1547: The standard provides the selection of electrical, electronic, and mechanical electronic components (GSE) used in the design and construction of space mission aerospace vehicle hardware and basic ground support equipment ). Naval Air System Command as-4613: Application and demotion requirements of electronic components, general standard F. The scale-down is configured at the system level. It only affects the part types that are considered in the Fall standard. Because the scale-down criteria indicate different demand for scale-down, and do not fully accept the actual parameters or values, some reliability analysts hope to combine the accepted criteria with their own demand for scale-down.Lambda predict 2With this flexibility. After selecting a standard, each component will indicate whether its current stress level is within the standard of reduction.