Filter ratings are an often misunderstood area of contamination control. On several recent occasions, I have witnessed someone describing a filter by its nominal rating. A nominal rating is anarbitrary micrometer value given to the filter by the manufacturer. These ratings have little to no value. Tests have shown that particles as large as 200 microns will pass through a nominally rated 10-micron filter. If someone tries to sell you a filter based on an "excellent" nominal rating offive microns, run away.
在杂质控制领域，过滤器的评级常常会被用户误解。*近在一些场合，我看到有人用名义过滤等级（国内常称为：名义精度）来描述过滤器的性能。名义过滤等级事实上是滤清器制造商赋予滤清器产品的一个标称值。这种名义等级基本上没有什么意义。试验表明，即便是尺寸大至200微米的颗粒依旧可以通过一个名义过滤等级为10微米的过滤器。如果有人想卖给一个“上等的”滤清器给你，并告诉你这个产品标称的名义过滤等级为5微米，那么，你可以闪人了。
Absolute Rating
**评级
Another common rating for filters is the absolute rating. An absolute rating gives the size of the largest particle that will pass through the filter or screen. Essentially, this is the size of the largest opening in the filter although no standardized test method to determineits value exists. Still, absolute ratings are better for representing the effectiveness of a filter over nominal ratings.
另一个常见的滤清器评级是所谓的**评级。**评级给出*大能够通过该滤清器的颗粒尺寸。从本质上讲，并没有哪个标准的检测方法是通过评估滤清器*大的通过尺寸进而评判滤清器性能的。不过，**评级在某种程度上来说，与名义过滤等级相比，能更好地描述过滤器的有效性。
Figure 1（图1）
Beta Rating
β 比
The best and most commonly used rating in industry is the beta rating. The beta rating comes from the Multipass Methodfor Evaluating Filtration Performance of a Fine Filter Element (ISO16889:1999).
在工业领域，*好和*常见的评级是用β比（或称β率）。Beta比是来自：“利用多次通过法评估精过滤器过滤性能” 这个标准。（ISO 16889:1999）
Table 1. Effect of Filtration Ratio (Beta Ratio) on Downstream Fluid Cleanliness
表1. 过滤率（β比）对下游燃料清洁度的影响
To test a filter, particle counters accurately measure the size and quantity of upstream particles per known volume of fluid, as well as the size and quantity of particles downstream of thefilter. The ratio is defined as the particle count upstream divided by the particlecount downstream at the rated particle size. Using the beta ratio, afive-micron filter with a beta 10 rating, will have on average 10 particles larger than five microns upstream of the filter for every one particle five microns or greater downstream.
测试滤清器的性能，颗粒计数器可以**地测量滤清器上游已知体积的燃油内还有的颗粒尺寸和数量，同样也对下游进行测量。过滤率的定义是指定尺寸的上游的颗粒物的数量除以下游颗粒物的数量。使用β比，一个5微米β比为10的滤清器，意味着上游平均每10个大于5微米的颗粒物，经过此过滤器过滤，下游还会有1个大于5微米的颗粒物。
The efficiency of the filter can be calculated directly from the beta ratio because the percent capture efficiencyis ((beta-1)/beta) x 100%. A filter with a beta of 10 at five microns is thus said to be 90 percent efficient at removing particles five microns and larger.
滤清器的过滤效率将可以直接用β比换算：(β-1) / β * 100% = 效率。即，如果一个滤清器对5微米的β比是10，也就是说，它对于大于等于5微米的颗粒物的过滤效率是90%。
Caution must be exercised when using beta ratios to compare filters because they do not take into account actual operating conditions such as flow surges and changes in temperature.
当然，在利用β比来对滤清器性能进行比较的时候，必须要注意是否有考虑到实际的操作环境，比如流量和温度的变化。
A filter's beta ratio also does not give any indication of its dirt-holding capacity, the total amount of contaminant that can be trapped by the filter through out its life, nor does it account for its stability or performance over time.
一个过滤器的β比并没有指出其容纳污染物的能力，一个滤清器在其整个有效寿命期间所能捕获的杂质，并没有考虑到其稳定性或者性能随着时间推移而发生的变化。
Nevertheless, beta ratios are an effective way of gauging the expected performance of a filter.
不论如何，β比是一个有效的测量滤清器预期性能的参数。
I hope this knowledge of filter efficiency ratings enables you to make a more informed purchase the next time you buy a filter.
希望这个关于滤清器效率评级的文章能让您在下次购买滤清器的时候更加明智。