Material Density
The reference standards manufactured from non-magnetic alloys of iron, chromium, nickel and carbon provide the stable physical weights required for high-accuracy force and pressure calibrations. These stainless steel masses are preferred because their density is highly consistent and well-documented in international standards. In a deadweight tester, the density of the weights must be known to calculate the correction for air buoyancy.
The stability of this density ensures that the generated pressure remains traceable over long periods of use.
Corrosion Resistance
Surface oxidation on weight sets increases their mass. Using stainless steel masses prevents this corrosion, maintaining the certified mass value. Even a microgram of oxide invalidates a calibration certificate.
Metrological Drift
Over time, handling and wear can cause minor scratches or deposit oils on the surface of the weights, leading to changes in mass. High-quality stainless steel masses exhibit very low drift compared to brass or cast iron alternatives. Regular cleaning and recalibration in a controlled laboratory are required to monitor this drift.
The weights are handled exclusively with specialized tweezers or gloves to prevent contamination.
Force Calibration
The precise mass of the weights is used to calculate the downward force applied to a piston or load cell during calibration. When using stainless steel masses, the calculation must include both the local acceleration of gravity and the air buoyancy correction. The air density is measured during the test to ensure that the buoyancy correction is accurate.
This process is necessary to achieve the low measurement uncertainties required by national calibration laboratories.
