Which OIML weight class do I need for an analytical balance?

For a standard analytical balance reading to 0.1 mg, OIML class F1 is the usual choice, and class E2 is used where the balance reads to 0.01 mg or where the uncertainty budget is tight. The practical rule is that the uncertainty of the test weight should be no more than one third of the tolerance of the balance at that load. Class F2 weights are fine for routine daily checks on 0.1 mg balances and for top-pan balances reading to 1 mg.

How often should calibration weights be recalibrated?

Most laboratories recalibrate working weights every twelve months and reference or master weights every twenty-four months, or sooner if the weight has been dropped, stored badly or used heavily. Accredited calibration against a national standard, with a certificate stating the measured mass and uncertainty, is what makes the result traceable. In Singapore, traceability normally runs back through the National Metrology Centre, and certificates should be kept with the weight set for audit.

Why do calibration weights have to be handled with forceps and gloves?

Skin oils, salts and dust transfer mass. A fingerprint can add tens of micrograms to a small weight, which is larger than the tolerance of an E2 or F1 weight at that nominal value. Handle weights with plastic- or wood-tipped forceps, wear lint-free gloves if you must touch them, and never pick a weight up by the adjustment cavity. Oils also corrode the surface, and a corroded weight can never be brought back to its certificate value.

Does JWRESEARCH supply calibration weights in Singapore?

Yes. JWRESEARCH supplies OIML and ASTM calibration weight sets and single check weights in Singapore, from 1 mg to 20 kg, in classes E1, E2, F1, F2, M1 and M2, with wooden or aluminium cases, forceps, gloves and desiccant. We also supply certificate-ready sets for ISO/IEC 17025 laboratories and can quote recalibration and replacement schedules for multi-site customers.

Calibration Weights Singapore — OIML and ASTM Test Weights

Published: {{NEW_ARTICLE_DATE}} | By JWRESEARCH | Category: Laboratory Equipment

Every weighing result a laboratory reports rests on a chain that starts at a piece of metal in a case. If that metal has drifted, been touched with bare fingers, or was never the class it claimed to be, the balance is still perfectly linear and still perfectly wrong. Calibration weights are small, cheap and easy to neglect — which is exactly why they cause so many quiet failures.

JW RESEARCH SUPPLY supplies OIML and ASTM calibration weights, check weights and handling accessories to laboratories across Singapore. This guide explains the classes, the tolerances, how to match a weight to a balance, and how to keep a set in certification condition.

Why a Balance Needs Reference Masses

A balance only compares; it needs a known mass to anchor what its sensor sees. Two activities use weights and are often confused. Calibration establishes the relationship between indicated value and true mass, normally by an accredited provider with reference weights and an uncertainty budget. Verification, the daily check, confirms the balance still agrees with a check weight within a stated limit. The check weight calibrates nothing, but it catches drift, a damaged pan or a new draught before a batch of samples is weighed.

Between annual calibrations, a documented check at a load close to your working range is the cheapest quality control available. If it fails, stop weighing and call for service.

OIML and ASTM Weight Classes

OIML R 111 defines classes E1, E2, F1, F2, M1, M2 and M3, running from highest to lowest accuracy. ASTM E617 defines Classes 1 to 7 in a similar progression. The two systems are not identical, but for procurement purposes Class 1 corresponds roughly to E2, Class 2 to F1, Class 3 to F2 and Class 4 to M1.

OIML Class	Approx. Tolerance at 100 g	Typical Balance	Typical Use
E1	± 0.05 mg	Micro and ultra-micro balances	Reference standard in a metrology laboratory
E2	± 0.16 mg	Analytical balances reading 0.01 mg	Master weights for in-house calibration
F1	± 0.5 mg	Analytical balances reading 0.1 mg	Routine calibration and drift checks
F2	± 1.6 mg	Analytical and semi-micro balances	Daily verification, teaching laboratories
M1	± 5 mg	Top-pan and precision balances to 1 mg	General weighing, production checks
M2 / M3	± 16 mg / ± 50 mg	Platform and industrial scales	Rough checks, bulk receiving

Tolerances scale with nominal value, so read the certificate for the size you are buying. At 1 mg the gap between an F1 and an M1 weight is the gap between a usable and a meaningless check.

Common Set Configurations

Set	Nominal Range	Pieces	Best For
Analytical set, E2 or F1	1 mg – 100 g	21 – 24	0.1 mg and 0.01 mg balances, linearity checks
Precision set, F1 or F2	1 g – 1 kg	12 – 13	Top-pan balances, 0.001 g to 1 mg readability
Industrial set, M1	10 g – 5 kg	10 – 12	Platform scales, receiving and dispatch
Single check weight	50 g, 100 g or 200 g	1	Daily verification at the working load
Handling kit	—	—	Forceps, gloves, brush, desiccant, certificate folder

Choose the working load first. A laboratory that routinely weighs 20 to 50 mg on a 0.1 mg balance should verify near that load, not only at 100 g, because eccentricity and linearity errors behave differently across the range. Two check weights — one near the tare and one near the working load — catch far more faults than a single 100 g piece.

Handling Rules That Protect the Certificate

Conventional mass is defined against a density of 8000 kg/m³, which is why most weights are stainless steel, polished and slightly adjusted underneath. Anything that changes the surface changes the mass. Handle weights only with plastic- or wood-tipped forceps, wear lint-free gloves when gloves are needed, and never lift a weight by the adjustment cavity or the knob of a larger piece. A fingerprint on a 100 g E2 weight can exceed its entire tolerance.

Keep weights away from magnets, motors and speakers: magnetised steel interacts with the balance's force motor and the reading drifts each time the weight is placed. Store the set closed with fresh desiccant, or Singapore's humidity will film and corrode the polished surfaces. Let a weight that has been in a cold room come to room temperature inside its closed case before use, or condensation will form on it.

Recalibration, Records and Audit

Working weights are normally recalibrated every twelve months and master weights every twenty-four months, or immediately after a drop or a failed check. An accredited certificate should state the measured mass, the conventional mass, the uncertainty and the class, and it should be traceable to a national standard. Keep certificates with the set, record the check weight results in the balance log, and note the weight's serial number so a drifted set can be traced to the batches it verified.

If a set fails, do not adjust it in-house and continue. Demote it to a lower class for rough work, or retire it. An unrecorded adjustment turns a known error into an unknown one.

Ordering Checklist

Balance readability and maximum capacity for each instrument
Working load range you actually weigh, not just the capacity
Required class: E2, F1, F2 or M1, and whether ASTM class is specified
Nominal sizes needed, and whether a full set or single check weights suit
Certificate type required by your quality system
Case, forceps, gloves and desiccant as one line item
Recalibration interval and who will hold the schedule

Tell us the balances on your bench and the load you weigh most often, and we will propose a weight set and check-weight pair that match them, with certificates and local delivery in Singapore.

Contact JWRESEARCH

JW RESEARCH SUPPLY — laboratory equipment and consumables, Singapore.
Telephone / WhatsApp: +65 8039 3660
Email: SINGAPORE@JWSHY.COM
Website: www.jwresearch.cn