Inmetro’s Participation in the Second Run of SIM Kilogram Dissemination Project (SKDP) - Mass Stability Assessment of SIM21 1 kg

Aug 29, 2026

Inmetro’s mass metrology laboratory (Lamas) participated in the SIM Kilogram Dissemination Project (SKDP) second measurement run. The mass stability of the SIM21 1 kg stainless-steel mass standard was assessed with measurements carried out from 2018 to 2021, followed by a second run in progress starting with new measurements agreed in 2022. Results indicate typical weighing-system variability without a clear trend, supporting the conclusion that no mass drift for SIM21 was observed across 2018–2023. Measurement corrections, uncertainties, and environmental conditions are analyzed.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages8

Reading Time20 min

AccessFree to download

Introduction

Participation and SKDP framework

S21 assignment and measurement timeline

Framework for Mass Measurements

Measurement setup and corrections

Environmental conditions

Results

Mass measurement outcomes (2018–2023)

Inmetro’s participation in the second run of SIM kilogram dissemination project (SKDP) F L Cacais1, V M Loayza1, A Beatrici1 , D Quintão1 and A S Rebelo1 1 Laboratório de Metrologia de Massa, Instituto Nacional de Metrologia, Qualidade e Tecnologia (Inmetro), Duque de Caxias/Xerém, RJ 25250-020,BR Email:facacais@inmetro.gov.br Abstract. Inmetro’s metrology mass laboratory (Lamas) participated in SIM Kilogram Dissemination Project (SKDP) . The assessment of mass stability of the SIM21 1 kg stainless steel mass standard was carried out between 2018 and 2021 and a second run of measurements is in progress. The new results show a typical variability for a weighing system but not clear trend in measurements. Therefore one can say no mass drift for SIM21 mass standard was observed along the period between 2018 and 2023. 1. Introduction In the SIM meeting in Montevideo Uruguay (2018), the SIM kilogram dissemination project (SKDP) was introduced to the participant, National Metrology Institutes (NMIs), and the Brazil's participation was agreed. The (SKDP) is a research project involving a set of highly correlated stainless steel mass artifacts standards provided to the participating NMIs across the SIM region aiming to assess their stability in use. Each mass standard is made of the same material and has similar surface, magnetic and density properties. The cylindrical mass standards were manufactured from one of two stainless steel rods with each artifact numbered based on the position within the rod from which it was cut. The S21 standard was assigned to Inmetro and the mass measurements were performed between 2018 and 2021 [1] when it was returned to NIST (USA) for new mass measurements. In 2022 a 2nd run of mass measurements for the S21 standard was agreed and the results of this study are shown here. 2. Framework for mass measurements The setup for mass measurements is the same shown in [2] . Data of S21 characterization with new mass measurement from NIST are shown in tables 1 – 3 [3] . Figure 1 shows the receipt of the SIM21 mass standard. Table 1. Volume, Density and Coefficient of Volumetric Expansion. Mass Identification Volume [cm3] at 20 °C Volume Uncertainty [cm3] (k = 1) Density [g/cm3] at 20 °C Density Uncertainty [g/cm3](k = 1) Volumetric Coef. of Exp. [°C-1] SIM2 1 124.4236 0.0037 803.706 0.00024 0.000045 Table 2. Mass Corrections and Uncertainties. | Date | Nominal
[g] | True Mass
Correction
[mg] | True Mass
Uncertainty
mg
(k = 1) | Conventional
Mass
Correction
[mg] | Conventional
Mass
Uncertainty
[mg]
(k = 1) | | --- | --- | --- | --- | --- | --- | | 20 May 2019 | 1000 | 0.4675 | 0.0158 | 1.1592 | 0.0152 | | 17 Jan 2022 | 1000 | 0.4549 | 0.0277 | 1.1467 | 0.0273 | A 13 􀁐g mass variation in the mass correction can be a result of the standard transport between NIST – Inmetro – NIST. Thus, the increased uncertainty for 2022 measurements [4] should be due to the addition of an uncertainty component for transport which was not accounted for in the 1st run of measurements. Table 3. Measurement Environmental Conditions. | Temperature [°C] | Humidity [%RH] | Pressure [kPa] | Computed Air Density
[mg/cm3] | | --- | --- | --- | --- | | Average 20.270 | 45.5 | 100.425 | 1.1879 | Figure 1. Receipt, storage and placing upon the weight handler of AT1006 mass comparator of S21 standard. Weighings performed in a 1 kg automatic mass comparator Mettler Toledo AT1006 with the aid of a climate station Klimet A30 were corrected for buoyancy effect where air density were determined by CIPM equation [5] . The 1 kg mass standards used to check the stability of SIM/NIST S21 standard in mass and conventional mass are shown in Inmetro’s traceability chain in figure 2 [6] . Figure 2. Inmetro’s traceability chain The typical environmental conditions in a period of a week (May 26th to June 4th 2021) in Module 1 of Lamas are shown in figures 3, 4

FAQs

What is the SIM Kilogram Dissemination Project (SKDP) and what was Inmetro’s role?

SKDP is a research project using highly correlated stainless-steel mass standards distributed to participating national metrology institutes. Inmetro’s mass metrology laboratory participated by assessing the stability of the assigned SIM21 1 kg standard in the second run.

How were the SIM21 mass measurements conducted in the second run?

Measurements were performed using a 1 kg automatic mass comparator (Mettler Toledo AT1006) with buoyancy corrections based on air density determined from CIPM equation. Environmental variables such as temperature, humidity, and pressure were used to compute air density.

Did the results show any mass drift for the SIM21 1 kg standard from 2018 to 2023?

No clear trend was observed; the variability matches typical weighing-system behavior. The study concludes that no mass drift for the SIM21 mass standard was observed over the 2018–2023 period.

Aug 29, 2026

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