  Pressure calibration for most diamond-anvil cell (DAC) experiments is mainly
based on the ruby scale, which is key to implement this powerful tool for
high-pressure study. However, the ruby scale can often hardly be used for
programmably-controlled DAC devices, especially the piezoelectric-driving
cells, where a continuous pressure calibration is required. In this work, we
present an effective pressure gauge for DACs made of manganin metal, based on
the four-probe resistivity measurements. Pressure dependence of its resistivity
is well established and shows excellent linear relations in the 0 - 30 GPa
pressure range with a slope of 23.4 (9) GPa for the first-cycle compression, in
contrast to that of multiple-cycle compression and decompression having a
nearly identical slope of 33.7 (4) GPa likely due to the strain effect. In
addition, such-established manganin scale can be used for continuously
monitoring the cell pressure of piezoelectric-driving DACs, and the reliability
of this method is also verified by the fixed-point method with a Bi pressure
standard. Realization of continuous pressure calibration for
programmably-controlled DACs would offer many opportunities for study of
dynamics, kinetics, and critical behaviors of pressure-induced phase
transitions.
