We will be elaborating Mean Time Between Failure and Mean Time to Repair in this article. We will be examining their effects on Reliability, Availability, otherwise as known as RAMs analysis.

 

What is MTBF?
 

Mean Time Between Failures is the arithmetic mean or average amount of time between failures of an electronic or mechanical system. In other words, the average amount of time until the device or system simply doesn’t work.

In system engineering, the definition of MTBF is dependent on the device or system under consideration and what constitutes a failure. A complex and repairable system, in most cases, defines failure as an event that removes the device or system from service. The redundancy approach is the most commonly used technique to increase MTBF value of systems.

 

How to calculate MTBF?
 

MTBF is the arithmetic mean or average amount of time between failures of an electronic or mechanical system. Generally expressed in hours. The higher the MTBF is better. There is a simple way to calculate it:

 

 

The example is MTBF in its simplest form for us to understand the basics. However, when dealing with various malfunction metrics, these calculations are becoming more complicated. This becomes more apparent when analyzing long periods of time with multiple issues occurring, which obviously necessitates more steps when performing your calculations.
 

In reliability engineering, the MIL-HDBK-217 standard remains one of the most widely used and accepted reliability prediction standards in use today. There is a number of additional reliability prediction standards currently used, including Telcordia (formerly Bellcore), 217Plus, and China’s GJB/z 299. Here is the MTBF of electronics in component-based according to MIL-HDBK-217:

λp = (C1 * πT + C2 * πE) * πQ * πL

What is MTTR?

 

Mean Time To Repair is the arithmetic mean or an average of repair when of course, the system or device is down. Generally expressed in Hours. Lowering the MTTR is better. Generally, when a system or device is down, there would be a device, part or module to change. How long it takes to replace the part is the basis of the MTTR calculation. MTTR is all about when part or system is down. System downtime costs resources.

There are many approaches to reduce down time. Such as;

• Designing devices modular based. It would take less time to replace modules compared to replacing electronic components.

• Choosing or designing system components with internal fault-finding features (Built-in Test).

• Having spare parts close by.

• Training personnel for replacement. Even though periodic maintenance can increase MTBF, it is usually not preferred.

 

MTBF and MTTR in Application

 

It is natural to consider the MTBF as the product life in practice. However, opposite to our simple intuition, mean life does not mean real life equals to the MTBF. Actually, it is not correct if the value of MTBF is considered as the product life for an individual. MTBF is a statistic.

If the manufacturer has an MTBF goal to reach it is important to start from the design phase. Choosing right standards for application, and components, and designing boards with a proper number of conjunctions and expected working temperature are the parameters that affects the outcome. There are analysis software in the market for the job. Although MTBF can be calculated with proper formula when the information is available.

In the aspect of system engineering, choosing high MTBF value device, and components for the system is desired. It allows you to have longer expected working time. Devices with critical roles in the system are advised to be redundant in order to prevent or reduce system downtime. There are many redundancy methods available according to your design.

Reliability and Availability

 

It would be unfair to summarize the whole reliability engineering. However, we’ll try our best to explain it for us to understand. MTBF, or mean time between failure, is a basic measure of a system’s reliability. Here is why the higher the better:

 

MTTR impacts availability and not reliability. The longer the MTTR, the worse off a system is. Simply put, if it takes longer to recover a system from a failure, the system is going to have lower availability.

 

 

This is why MTBF and MTTR are important for Reliability and Availability calculations. These values can be arranged to be their best using some important techniques. However, its heavily depends on the application. Also, these formulas depend upon selected standard and system approach as well.

 

DID YOU KNOW?

 

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