电子天平最小称样量

gongzi

节选自USP37<1251>使用分析天平称量（中英文）
Minimum Weight 最小称样量

The minimum net sample weight, mmin, of a balance can be expressed by the equation:

天平的最小称样净重，mmin，可以用以下等式表达：

mmin = k × s/required weighing tolerance

mmin = K X s/所要求的称样误差

where k is the coverage factor (usually 2 or larger) and s is the standard deviation (in a mass unit, e.g., in mg) of not fewer than 10 replicate measurements of a test weight. The minimum weight describes the lower limit of the balance below which the required weighing tolerance is not adhered to. The equation above takes into account that the performance of laboratory balances at the lower end of the measurement range is limited by the finite repeatability.

这里，K是包含因子（一般取2或更大），s是对一个测试用砝码进行不少于10次重复称量所得的标准偏差（质量单位，例如mg）。最小称样量描述的是天平可以用于称量的低限，如果样品量低于该限度，则不能满足要求的允差。上述公式考虑了化验室天平的称量范围内较低称样量的性能，其采用的是有限重复性方法。

For materials that must be accurately weighed, 41 stipulates that repeatability is satisfactory if two times the standard deviation of the weighed value, divided by the nominal value of the weight used, does not exceed 0.10%. For this criterion the equation above simplifies to:

对于必须精密称定的物质，<41>中说明了如果所称数值的标准偏差乘以2，除以所用砝码的名义质量，不超过0.10%，则认为重复性满足要求。对此标准，上述公式简化为：

mmin = 2000 × s

If not subject to the requirements of 41 , the minimum weight value may vary depending on the required weighing tolerance and the specific use of the balance.

如果不需要满足<41>的要求，则最小称量值可能会依据所要求的称重允差不同和天平用途不同而不同。

To facilitate handling, the test weight that is used for the repeatability test does not need to be at the minimum weight value but can be larger because the standard deviation of repeatability is only a weak function of the test weight value.

为便于操作，用于重复性测试的砝码重要不需要是最小重复值，可以更大，因为重复性的标准偏差只是所测试重量值的一个很弱的功能。

In order to satisfy the required weighing tolerance, when samples are weighed the amount of sample mass (i.e., the net weight) must be equal to or larger than the minimum weight. The minimum weight applies to the sample weight, not to the tare or gross weight.

为了满足所要求的称重误差，样品称重量（即净重）必须等于或大于最小称重量。最小重量是指样品净重，不是指皮重或毛重。

Factors that can influence repeatability while the balance is in use include:

在天平使用中可能影响重复性的因素包括：

1. The performance of the balance and thus the minimum weight can vary over time because of changing environmental conditions.

天平性能，因为环境条件变化在不同时间可能会变化的最小重量

2. Different operators may weigh differently on the balance—i.e., the minimum weight determined by different operators may be different.

不同操作人员在天平上操作可能会不同-----即，最小称样量由不同操作者来测试可能会有不同结果

3. The standard deviation of a finite number of replicate weighings is only an estimation of the true standard deviation, which is unknown.

有限次数重复称量的标准偏差仅是真实标准偏差的估计，而真实标准偏差是不可知的

4. The determination of the minimum weight with a test weight may not be completely representative for the weighing application.

一个测试砝码进行最小称样量的测试可能不能完全代替实际称量应用

5. The tare vessel also may influence minimum weight because of the interaction of the environment with the surface of the tare vessel.

盛装样品容器也可能会对最小称样量形成影响，因为环境与样品容器的表面可能会有相互作用

For these reasons, when possible, weighings should be made at larger values than the minimum weight.

由于这些原因，如果可能，称样量应尽可能大于最小称样量。

黑夜之月

越来越糊涂了

wuyxwuyx

按照USP的进行就是了，绝对没问题

jorsen_viasa

你的最小称样量是怎么计算出来的？如果误差这么大的话，你的天平就有问题了，你们每天内校吗？有发现问题吗？

huicheche

似乎USP上有标准吧 我记得 是公式计算的

87L01

参照USP38-1251章节，上面有详细的说明怎么来确定一台精密天平的最小精密称定量！
通常选取天平量程的5%砝码做重复性测试10次，计算10次的标准偏差值SD与0.41d(d为天平分度值)；如果SD大于0.41d，不确定度（U） =2*SD/目标最小称量值；如果SD小于0.41d，则将0.41d替代SD代入以上公式计算，不确定度（U）= 2*0.41d/目标最小精密称量值。
根据不确定度不大于0. 10%。
计算最小精密称量值=2*SD(0.41d)/0.0010=你所需要的最小精密称量值。