# Reliability calculation

I am an expert in the reliability of space technology. At some point I wondered if there are any online services that allow you to make a simple calculation of reliability. I decided to fix that and made my simple online reliability calculator.

Reliability is a property of an object to keep in time within the established limits the values of all parameters characterizing the ability to perform the required functions in the given modes and conditions of application, maintenance, storage and transportation. Reliability is one of the most important qualities of any object.

Reliability calculation is the procedure for determining the values of reliability indicators of an object using methods based on their calculation based on reference data on the reliability of the elements of the object, from data on the reliability of analogical objects, data on the properties of materials and other information available at the time of calculation. As a result of the calculation, quantitative values of reliability indicators are determined.

*Attention! If you have opened a site from a smartphone — make a horizontal orientation of the screen.*

**1. Calculation of reliability for cascade connection of elements**.

Example for data entry: PNF1 engine = 0.995. PNF2 gearbox = 0.996.

PNF enter with a dot, not a comma. 0,992 — incorrect format. 0.992 is the correct one.

PNF — probability of no-failure operation of the element, unit or system. The probability of failure-free operation is the probability that within a given operating time or a specified time interval the object will not fail.

**2. Reliability calculation for parallel connection of elements**

Example for data entry: PNFO1 engine = 0.995. PNF2 gearbox = 0.996.

PNF enter with a dot, not a comma. 0,992 — incorrect format. 0.992 is the correct one.

PNF — probability of no-failure operation of the element, unit or system. The probability of failure-free operation is the probability that within a given operating time or a specified time interval the object will not fail.

**3. Element reliability calculation ** in case the failure rate is known. Pay attention, the intensity of failures, it is a lambda is usually a tabular value, given in a dimension of 10 to minus 6 degrees. For example, the intensity of the manometer failure is 1.3 by 10 in minus 6 degrees. For calculation, take the value exactly 1.3, you do not need to enter the level, the calculator will automatically translate into the desired dimension.

**4. The calculation of the average uptime ** (MTBF — mean time between failures) in the event that the failure rate of the element is known. Pay attention, the intensity of failures, it’s lambda is usually a tabular value, in my calculator is given in a dimension of 10 to minus 6 degrees. For example, the intensity of the manometer failure is 1.3 by 10 in minus 6 degrees. For calculation, take the value exactly 1.3, you do not need to enter the level, the calculator will automatically translate into the desired dimension. Here the result is obtained in years.

**5. The calculation of the average uptime ** (MTBF — mean time between failures) in the event that the failure rate of the element is known. Pay attention, the intensity of failures, it’s lambda is usually a tabular value, in my calculator is given in a dimension of 10 to minus 6 degrees. For example, the intensity of the manometer failure is 1.3 by 10 in minus 6 degrees. For calculation, take the value exactly 1.3, you do not need to enter the level, the calculator will automatically translate into the desired dimension. Here the result is obtained in hours.

6. Sometimes it is necessary and important to do a reverse calculation — to calculate the ** failure rate ** in the event that the PNF (probability of no-failure operation) and the operating time of the element are known. PNF enter with a dot, not a comma. 0,992 — incorrect format. 0.992 is the correct one.

7.7. In real world, sometimes the following calculation is important. We have **MTBF**, issued to us by the equipment manufacturer, taken from the product catalog or reference book. We need to calculate the **PNF** (probability of no-failure operation) for a given operation time.

**8. Availability calculation (availability ratio) **. Indicates the probability that the facility will be operational at an arbitrary point in time, except for planned periods during which the use of the facility for its intended purpose is not foreseen. For calculation, it is necessary to know the mean time before failure (MTBF) and the mean time to repair (MTTR), which is often determined by the method of expert evaluation (taken from the head), for example 1 hour.

**9. Calculation of average idle time for the year**. Displays the idle time of the object for the year. To calculate, you need to know the availability factor.

From me, greetings to all «trustees», fighters for reliability in various design bureaux and organisations. Save your health, take care of your time. I would be happy for comments. Alexey Glazachev.

## Leave a Reply