背景

This chapter states the requirements for balances used for materials that must be accurately weighed (see General Notices and Requirements, 8.20). Unless otherwise specified, when substances must be “accurately weighed,” the weighing shall be performed using a balance that is calibrated over the operating range and meets the requirements defined for repeatability and accuracy. For balances used for other applications, the balance repeatability and accuracy should be commensurate with therequirements for its use.

本章節的要求適用于必須“準確稱量”樣品的天平要求（見通用條款和要求，8.20），除非另有規定，否則當被要求準確稱量時，必須使用稱量范圍經校正且符合重復性及準確性要求的天平。其他使用目的的天平，重復性及準確性必須與其使用要求相適應。

For a discussion of the theoretical basis of these requirements, see Weighing on an Analytical Balance ?1251?, which may be a helpful—but not mandatory—resource.

這些要求的理論基礎的討論詳見<1251分析天平的稱量>章節，該章節不是強制性要求。

Repeatability重復性

Repeatability is assessed by weighing one test weight NLT 10 times. [Note—The test weight must be within the balance's operating range, but the weight need not be calibrated. Because the standard deviation is virtually independent of sample mass within the balance's capacity, use of a small test weight, which may be difficult to handle, is not required.]

重復性是通過稱取一個測試砝碼不少于10次（備注：該測試砝碼必須在天平的稱量范圍內，但該砝碼可不需校正，因為這標準偏差實際上是獨立于樣品的質量而存在于天平，使用小重量測試砝碼將更難達到，不做要求。）

Repeatability is satisfactory if two times the standard deviation of the weighed value, divided by the desired smallest net weight (i.e., smallest net weight that the users plan to use on that balance), does not exceed 0.10%. If the standard deviation obtained is less than 0.41d, where d is the scale interval, replace this standard deviation with 0.41d. In this case, repeatability is satisfactory if 2 × 0.41d, divided by the desired smallest net weight, does not exceed 0.10%.

如果兩倍的稱量值的標準偏差(S)除以期望的最小準確凈重不超過0.10%，則重復性被認為是符合要求的。（最小準確凈重m：是使用者計劃在該天平上稱取的最小重量）。

如果計算的標準偏差小于0.41d,這里的d為顯示增量，用0.41d來代替測得的標準偏差，這種情況下，如果兩倍的0.41d除以想要設定的最小準確凈重不超過0.10%，則重復性被認為是符合要求的。

實例分析：因為使用小重量測試砝碼，重現性將更難達到，故選用小砝碼，例如10 g砝碼，連續測定10次，結果分別為

該臺天平的d為0.01mg，0.41d為0.0000041g，故標準偏差大于0.41d，故將S=0.000004g帶入計算

故最小準確凈重m=2000×0.000004g=0.00843g。

由于進行上述測試時，一般情況下，實驗室處于最佳條件狀態，真實的稱量條件下，可能達不到上述條件，故應乘以相應的系數，建議1.5~2的系數來制定天平最終的最小準確凈值。

The accuracy of a balance is satisfactory if its weighing value, when tested with a suitable weight(s), is within 0.10% of the test weight value.

當使用一個或數個合適的砝碼進行測試時，稱量結果在測試值的0.10%的允許范圍內，則表明該天平符合準確性的要求。

A test weight is suitable if it has a mass between 5% and 100% of the balance's capacity. The test weight's maximum permissible error (mpe), or alternatively its calibration uncertainty, shall be NMT one-third of the applied test limit of the accuracy test. [Note—Applicable standards are the following: ASTM E617 (available fromhttp://www.astm.org) and OIML R 111 (available from http://www.oiml.org).]

測試砝碼的要求：測試砝碼應處于天平量程范圍的5%~100%的范圍內是合適的，測試砝碼的最大允許誤差（mpe）或者校正不確定度應該不超過準確性測試限值的三分之一。

實例分析：砝碼應處于天平量程范圍的5%~100%的范圍內，且測試砝碼的最大允許誤差（mpe）或者校正不確定度應該不超過準確性測試值的三分之一，故應選用大砝碼，例如選用200g砝碼具體數值如下表：

故稱量結果在測試值的0.10%的允許范圍內。