Masses (also known as weights) are usually made of three basic materials - Cast Iron, Brass or Stainless Steel. Some masses have been previously made from Brass which are chromed or nickel plated, to improved the stability of the mass.
As the material the mass is manufactured from determines the daily and long term stability, you should select a base material that's suitable for your application. We do not recommend the adjustment of unsuitable masses to finer tolerances, as the mass will soon drift out of tolerance.
When selecting a mass try to find the appropriate tolerance suitable to your application. This is usually about one half of the balance or scale readability. Where it is not possible to select one with a small enough tolerance then you should choose the best tolerance (E2).
If you need to know the exact value of the mass or need traceability to the National Standard, then you should order a NATA certificate when you order your masses. Remember that the lower the grade of material the shorter the recalibration period.
Cast iron masses will vary in true value due to moisture, rust and wear. Cast iron masses are highly magnetic and will be affected by magnetic fields from electric motors and balance force motors.
Cast iron masses should be stored in a dry environment and re-calibrated annually. Cast iron masses usually have a lead adjustment pot for fine adjustment.
Brass masses are softer but have better stability characteristics than cast iron are less affected by magnetic fields or atmospheric air buoyancy. Brass or brass alloy masses will wear and will corrode with use if gloves are not worn. Most brass masses are provided with a lead adjustment pot. Brass masses should be stored in a dry environment and re-calibrated annually.
Stainless steel masses are the preferred mass for use in analytical and reference applications. Stainless steel masses are high polished to improve their wear resistance and corrosion ability. Stainless steel masses are manufactured from an non magnetic grade of material and density of 8000 kg/m3.
Two types of grade are available - the economy series and the reference standard grades . The economy series have a lead adjustment pot for fine adjustment. This affects the air buoyancy, so that in applications where high stability requirements are needed i.e. reference standards then the fully stainless steel masses should be used.
As there is no adjustment on these masses the utmost care is required to maintain the stability and tolerance of these masses. Stainless steel masses should be re-calibrated every 3 years for reference sets or annually for frequently used masses.
PCS have a NATA Laboratory that can perform a NATA calibration and issue a NATA Report as well as a Regulation 13 report. PCS offer a free* visit by our staff to discuss mass calibration requirements which will provide an opportunity for your company to ask any questions they have about masses or report requirements.