Page 225 - Dynamics and Control of Nuclear Reactors

224 CHAPTER 16 Nuclear plant instrumentation

Therefore, the differential pressure is proportional to the fluid column height and
provides quantitative height measurement if the fluid density is known.
In level measurement by differential pressure measurement, the fluid is in contact
with the pressure sensor. Therefore, if the fluid is radioactive or otherwise hazardous,
maintenance on or replacement of the pressure sensor is problematical.

16.2.5.2 Bubbler
A bubbler system also provides level measurement capability. See Fig. 16.13.
The figure shows a bubbler system for a tank that is open to the atmosphere. A
regulator maintains constant gas flow. The gas flow induces bubble release at the
bottom of the tank. As the fluid level increases, the flow regulator increases pressure
in order to maintain flow. To maintain bubble flow, the pressure at the bubble outlet
must equal the fluid pressure at the outlet location. Therefore, the gas line pressure
equals the fluid pressure at the location of the bubbler outlet. So, the pressure on the
gas line equals the liquid pressure at the location of the gas outlet.
Bubbler fluid level measurements for a closed tank require a pressure regulator to
maintain constant pressure in the space above the fluid.
Bubbler fluid level measurements are useful in limited-space situations (only the
gas tube must occupy space in and near the tank) and it is applicable in hot or oth-
erwise hostile environments. Only gas is in the sensing line adjacent to the pressure
sensor, thereby facilitating maintenance.

FIG. 16.13
A bubbler level measurement system.