MTBF和MTTR到底要如何運用

MTBF和MTTR到底要如何運用

1. mtbf——全称是mean time between failure，即平均失效间隔。就是从新的产品在规定的工作环境条件下开始工作到出现第一个故障的时间的平均值。mtbf越长表示可靠性越高正确工作能力越强 。

2. mttr——全称是mean time to repair，即平均恢复时间。就是从出现故障到恢复中间的这段时间。mttr越短表示易恢复性越好。

3. mttf——全称是mean time to failure，即平均无故障时间。系统平均能够正常运行多长时间，才发生一次故障。系统的可靠性越高，平均无故障时间越长。(mttf=mtbf+mttr)

不过，MTBF的统计与运用在管理上是属于不同的境界，如果光有数字，却没有善加利用，就太可惜了。 首先针对MTBF这个名词稍微做说明，常用的定义摘录如下：Mean Time Between Failure[English]MTBF is an abbreviation for Mean Time Between Failures.MTBF is a measure of how reliable a product is. MTBF is usually given in units of hours; the higher the MTBF, the more reliable the product is.For electronic products, it is commonly assumed that during the useful operating life period the parts have constant failure rates, and part failure rates follow an exponential law of distribution. In this case, the MTBF of the product can be calculated as:MTBF = 1/(sum of all the part failure rates)and the probability that the product will work for some time T without failure is given by:R(T) = exp(-T/MTBF)Thus, for a product with an MTBF of 250,000 hours, and an operating time of interest of 5 years (43,800 hours):R = exp(-43800/250000) = 0.839289which says that there is an 83.9% probability that the product will operate for the 5 years without a failure, or that 83.9% of the units in the field will still be working at the 5 year point. 在TPM的设备保养中，MTBF的概念就是一种可靠度、信赖度的概念，因此，运用方面可以从了解设备的信赖度着眼，换句话说，MTBF的数值愈大，则表示设备较没有故障，若MTBF数值下降，则表示设备故障的状况较为严重，有些企业将所有的设备状态以一个MTBF值来表示，这虽然可以看到整体的状态，但是若没有更细部得数据，则对于改善没有太大帮助，因此，理想上，MTBF应该要以单一设备来管理，甚至更理想的话，以一个 failure causes或 equipment components来管理，这样对于改善的方向会更明确些。 MTTR这个名词，对于推动TPM的企业，或者在设备管理方面进行绩效衡量者，应该是一个不陌生的名词，不过，MTTR的统计与运用在管理上是属于不同的境界。 首先针对MTTR这个名词稍微做说明，常用的定义摘录如下：Mean Time To Repair[English]Mean Time To Repair (MTTR) is the most common measure of maintainability. It is the average time required to perform corrective maintenance on all of the removable items in a product or system. This kind of maintainability prediction analyzes how long repairs and maintenance tasks will take in the event of a system failure.MTTR also factors in to other reliability and maintainability predictions and analyses. MTTR can be used in a reliability prediction in order to calculate the availability of a product or system. Availability is the probability that an item is in an operable state at any time, and is based on a combination of MTBF and MTTR.在TPM的设备管理中，MTTR的概念基本上是作为衡量设备修理的相关指标，它主要应用在三个方向，第一是作为设备故障维修时间的参考（类似于停机时间），第二则是衡量设备本身维修的难易度（设备是否容易维修，与设备设计具有某些关连，因此，应列为设备采购时的参考），第三个作用则是作为维修技术人员的技能纯熟度指标（用来进行技能训练的参考），透过MTTR，可以依据管理上的需求，与MTBF进行关连分析。