Failure in Time (FIT) is a unit of measure that quantifies the failure rate of a component or system, representing the number of failures expected to occur per billion (109) hours of operation.
Understanding Failure in Time (FIT)
FIT is a crucial metric in reliability engineering. It provides a standardized way to express how often a device is likely to fail. A lower FIT value indicates a more reliable component. For example, a component with a FIT rate of 10 will experience 10 failures for every 1 billion hours of operation. This is often extrapolated from accelerated testing or field data.
How FIT is Used
- Reliability Prediction: FIT values are used to predict the overall reliability of complex systems by combining the FIT rates of individual components.
- Component Selection: Engineers use FIT rates to compare the reliability of different components when designing a product.
- Warranty Estimation: Manufacturers use FIT data to estimate warranty costs and predict the lifespan of their products.
- Risk Assessment: FIT rates help in assessing the risk of failure in critical applications where reliability is paramount.
Calculating FIT
While calculating the exact FIT requires extensive testing and statistical analysis, the basic concept revolves around observing the number of failures over a specific period and scaling it to represent failures per billion hours. Common methods include:
- Accelerated Testing: Components are subjected to stress conditions (e.g., high temperature, voltage) to accelerate failures. The data is then extrapolated to normal operating conditions.
- Field Data Analysis: Failure data collected from real-world use is analyzed to determine the FIT rate.
Example of FIT
Let's say a power supply has a FIT rate of 50. This means you would expect 50 failures for every 1 billion hours of operation of identical power supplies. This doesn't mean that any single power supply will fail after 1 billion / 50 = 20 million hours (over 2283 years); it's a statistical average across a large population.
Why Use FIT Instead of Other Metrics?
FIT offers a consistent and standardized unit for comparison, especially when dealing with highly reliable components where failures are infrequent. Other metrics like Mean Time Between Failures (MTBF) are also used, and there's a direct relationship:
FIT = 1 / MTBF (if MTBF is expressed in hours)
MTBF is often a much larger number, which can be less intuitive when comparing highly reliable devices. FIT, expressing failures per billion hours, provides a finer-grained view.
Summary
Failure in Time (FIT) is a vital reliability metric that represents the number of failures expected per billion operating hours, offering a standardized approach to assess and compare the reliability of components and systems. It's used in reliability prediction, component selection, warranty estimation, and risk assessment, providing a consistent way to quantify and manage potential failures.
