Mass
The unit of mass is the kilogram which is defined as the mass of the International Prototype Kilogram maintained at the International Bureau of Weights and Measures (BIPM) in France. A copy of the Prototype, no. 75, being of the same form and material, is being kept by this Laboratory as the reference measurement standard of mass for Hong Kong and for the dissemination of the unit of mass.
The Laboratory can provide calibration services for standard weights of accuracy class E 2 and lower in the range from 1 mg to 10 kg, and standard weights of accuracy class F1 and lower from 20 kg to 50 kg. The classification of weights depends on their maximum permissible measurement errors (refer to the following table), shape, material, construction and surface finish, as described in the International Recommendation R111 - (Weights of accuracy classes E1 , E2, F1, F2, M1, M2, M3 ) of the International Organisation of Legal Metrology (OIML).
|
Nominal Values of Mass |
Accuracy Class E2 (±mg) |
Accuracy Class F1 (±mg) |
Accuracy Class F2 (±mg) |
Accuracy Class M1 (±mg) |
Accuracy Class M2 (±mg) |
Accuracy Class M3 (±mg) |
|---|---|---|---|---|---|---|
|
50 kg |
75 |
250 |
750 |
2 500 |
7 500 |
25 000 |
|
20 kg |
30 |
100 |
300 |
1 000 |
3 000 |
10 000 |
|
10 kg |
15 |
50 |
150 |
500 |
1 500 |
5 000 |
|
5 kg |
7.5 |
25 |
75 |
250 |
750 |
2 500 |
|
2 kg |
3.0 |
10 |
30 |
100 |
300 |
1 000 |
|
1 kg |
1.5 |
5 |
15 |
50 |
150 |
500 |
|
500 g |
0.75 |
2.5 |
7.5 |
25 |
75 |
250 |
|
200 g |
0.30 |
1.0 |
3.0 |
10 |
30 |
100 |
|
100 g |
0.15 |
0.5 |
1.5 |
5 |
15 |
50 |
|
50 g |
0.10 |
0.30 |
1.0 |
3.0 |
10 |
30 |
|
20 g |
0.080 |
0.25 |
0.8 |
2.5 |
8 |
25 |
|
10 g |
0.060 |
0.20 |
0.6 |
2.0 |
6 |
20 |
|
5 g |
0.050 |
0.15 |
0.5 |
1.5 |
5 |
15 |
|
2 g |
0.040 |
0.12 |
0.4 |
1.2 |
4 |
12 |
|
1 g |
0.030 |
0.10 |
0.3 |
1.0 |
3 |
10 |
|
500 mg |
0.025 |
0.08 |
0.25 |
0.8 |
2.5 |
- |
|
200 mg |
0.020 |
0.06 |
0.20 |
0.6 |
2.0 |
- |
|
100 mg |
0.015 |
0.05 |
0.15 |
0.5 |
1.5 |
- |
|
50 mg |
0.012 |
0.04 |
0.12 |
0.4 |
- |
- |
|
20 mg |
0.010 |
0.03 |
0.10 |
0.3 |
- |
- |
|
10 mg |
0.008 |
0.025 |
0.08 |
0.25 |
- |
- |
|
5 mg |
0.006 |
0.020 |
0.06 |
0.20 |
- |
- |
|
2 mg |
0.006 |
0.020 |
0.06 |
0.20 |
- |
- |
|
1 mg |
0.006 |
0.020 |
0.06 |
0.20 |
- |
- |
The submitted weights should be in a clean condition and housed in a suitable container or containers.
During calibration test weights are compared with appropriate measurement standards. As weights of higher accuracy class require use of measurement standards of higher accuracy and more elaborate calibration procedures, calibration charge will be higher. The customers are therefore urged to apply for calibration accuracy appropriate to their usages (see following paragraph for reference) and specifications of their weights. For example, owing to their brittle property and inferior resistance to wear and corrosion, cast iron weights will only be used as weights of accuracy class M1 and lower.
For calibration of weighing machines, normally the measurement uncertainties of the weights used will be less than the resolution of the machine to be calibrated. The following table serves as a general guideline:
Recommended lowest accuracy class of weights required for calibration of weighing machines
| Capacity | Resolution of weighing machine |
|||||||
|
100 g |
10 g |
1 g |
100 mg |
10 mg |
1 mg |
0.1 mg |
0.01 mg or less |
|
|---|---|---|---|---|---|---|---|---|
|
Up to 200 g |
|
|
|
M1 |
M1 |
F2 |
F1 |
E2 |
|
200 g to 1 kg |
|
|
M1 |
M1 |
F2 |
F1/E2 |
E2 |
E2 |
|
1 kg to 30 kg |
M2 |
M2 |
M1 |
F2 |
E2 |
E2 |
E2 |
|
|
30 kg to 100 kg |
M2 |
M1 |
F2 |
F1 |
E2 |
|
|
|
|
Above 100 kg |
M2 |
M1/F2 |
F1 |
E2 |
|
|
|
|
The measured value for the test weight will be the mass of a hypothetical weight of density 8000 kg/m3 which, at 20 ¢J and in air of density 1.2 kg/m3 , would balance the test weight. The basis is taken by convention and accords with OIML No. 33.
The measurement uncertainty quoted will normally relate to the accuracy class of the submitted weight, such that the measurement uncertainties for accuracy class E2 weights and weights of accuracy class F1 or lower will be about 1/3 and 1/5 of the prescribed maximum permissible measurement errors respectively.
Calibration charges
| Fee in HK$ | |
|---|---|
| Accuracy Class E2 standard weight, per piece. | $1680 |
| Accuracy Class F1 standard weight, per piece. | $660 |
| Accuracy Class F2 (or below) standard weight, per piece. | $430 |
| Minimum charge per issue of certificate/report. | $1020 |
Enquiry Telephone: (852) 2829 4835
e-mail: tkchan@itc.gov.hk
