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Expressing results in ppm is the standard for high-precision balances. It allows for direct comparison independent of the load according to Euramet cg-18.
1 ppm = 1 mg/kg — Deviation in ppm = (Deviation in g / Load in g) × 10⁶
1. Environmental Conditions
- Temperature: 20°C ± 2°C — acclimatization 2 hours after power-on
- Humidity: 45–65% RH
- Absence of vibrations, drafts, and magnetic fields
- Level balance checked (bubble centered)
2. Control Points | MPE in ppm (Euramet cg-18)
| Load | Average (g) | Deviation (ppm) | MPE (ppm) | Status |
|---|---|---|---|---|
| 500 g | 500.023 | +46 ppm | ±100 ppm | ✅ COMPLIANT |
| 1,000 g | 1000.033 | +33 ppm | ±50 ppm | ✅ COMPLIANT |
| 2,000 g | 2000.037 | +18.5 ppm | ±25 ppm | ✅ COMPLIANT |
| 4,000 g | 4000.043 | +10.8 ppm | ±25 ppm | ✅ COMPLIANT |
| 6,000 g | 6000.063 | +10.5 ppm | ±16.7 ppm | ✅ COMPLIANT |
3. Thermal Correction in ppm
u_therm = TC × ΔT / √3 = 2 ppm/°C × 2°C / √3 = 2.3 ppm
4. Archimedes' Buoyancy Correction in ppm
| Scenario | Correction (ppm) | Impact |
|---|---|---|
| Steel vs steel | 0 ppm | Negligible |
| Steel vs aluminum | +310 ppm | ⚠️ Significant |
| Steel vs plastic | +950 ppm | 🔴 Correction mandatory |
5. Uncertainty Budget in ppm
| Source | Value (k=1) |
|---|---|
| u_rep | 1.0 ppm |
| u_res | 0.5 ppm |
| u_mass (F1) | 0.8 ppm |
| u_therm | 2.3 ppm |
| u_eccentricity | 1.7 ppm |
| Expanded U (k=2) | 6.6 ppm |
ILAC-G8 at 500 g point: |46| + 6.6 = 52.6 ppm < MPE 100 ppm → ✅ COMPLIANT
6. ISO 17025 Compliance
- Traceability: Class F1 standard weights with COFRAC certificate traceable to LNE
- §7.6: Expanded uncertainty U stated in ppm on the test report
- §7.8.6: ILAC-G8 rule applied — compliance if |Deviation| + U ≤ MPE (in ppm)
- Periodicity: 12 months — extendable to 24 months via OIML D10