Metrological Comparison
Calibration of dual deadweight testers through direct hydraulic or pneumatic interconnection establishes a precise ratio between two effective areas. Metrologists use cross floating to determine the effective area and pressure-dependent distortion coefficients of the secondary piston.
Pressure Equilibrium
Alignment of the floating pistons requires systematic adjustment of mass loads until both assemblies hover without vertical acceleration. In this balanced state, the pressure generated by the master standard equals the pressure generated by the test unit. Any difference in their calculated pressures reveals the deviation of the instrument under test.
Uncertainty Traceability
Traceability to national metrology institutes relies on the certified values of the reference assembly. Environmental variables such as local gravity, ambient temperature, and air density must be measured and corrected to minimize systematic error. These corrections ensure that the calculated pressure remains accurate to within the specified tolerance.
Industrial Boundary
Operating conditions like fluid contamination or physical wear on the piston surface can degrade the measurement during the process. The method remains invalid if the system suffers from microscopic leaks or if the piston axes deviate from a true vertical alignment. National laboratories verify the integrity of the reference weights before and after every sequence.
This verification prevents drift and guarantees that the calibration remains within the designated limits.
