Hydra step level indicator/ electrode drum level


The water column and the connecting pipes generally
are well insulated, but the insulation is not sufficient
to keep the water in the water column as hot as that
inside the drum. Density of the cooler water in the
water column is denser than that in the drum, and
therefore the water level in the water column is lower
than that inside the drum. This phenomenon, known
as the Density Error, could induce as much as
150mm of measurement error in some cases.
However, the error can be limited to about 20mm by
deliberately exposing a part of the hot leg pipe close
to the water column as illustrated in the figure. The
steam inside the exposed portion of the pipe cools
and condenses, releasing the latent heat of
condensation to the water. This results in raising the
temperature of water in the water column appreciably
higher compared to the water without the exposed
section, thereby reducing the density error. For this
method to be effective the connecting pipes must be
installed with proper inclinations and insulated as
shown in the figure.
In cases where the height of the water column
exceeds 1m, water column itself may have to be
thermally insulated.