These devices are considered appropriate for measurement of level in boilers since the glasses used in their construction are carefully guarded against the wet steam generated in a boiler drum. This steam protection is provided by putting in high quality mica sheets. Detection of level in bi-color level gauges depends upon the distinction in index of refraction between steam and water. They can work with temperatures as high as 120kg/cm2 and well suited for saturated steam applications.
“Bi-colour gauge is in fact a transparent gauge with its liquid chamber in a wedge shape section and fitted on a rear side with an illuminator.” Two color filters, one red in color and the other green in color are positioned directly facing the light source in the illuminator, hence the name bi-color gauge. In cases where red color light radiations hit upon the water, they gets averted in one side and then absorbed whereas when they encounter the steam region, they tends to pass through without any constrictions and emerges red in color. On the other hand, reverse action takes place for light radiations passing via green filters.