Pressurizer Level Instruments:

Above Figure display a typical pressurizer level system. A Pressurizer temperature is held fairly constant in during normal operation. The ?P detector for level is calibrated along with the pressurizer hot or the effects of density changes do not occur. A pressurizer would not always be hot. It might be cooled down for non-operating maintenance  conditions,  in  that  case  a  second ?P detector, calibrated for level measurement at low temperatures,  replaces  the normal ?P detector. The density has not actully been compensated for; it has really been aligned out of the instrument through calibration.

Density compensation may also be accomplished through electronic circuitry. A few systems compensate for density changes automatically by the design of the level detection circuitry.  Another application compensate for density through manually adjusting inputs to the circuit as the pressurizer cools down and depressurizes, or in during heatup and pressurization. The Calibration charts are also available to right indications for changes within reference leg temperature.

Figure: Pressurizer Level System