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Bi-Color Level Gauges: A Vision of Innovation

Indicatore di Livello Bicolore

Bicolor level gauges are a variant of glass indicators and are used to measure the level of steam and water inside a boiler. These instruments consist of a carbon steel body with a trapezoid cross-section, machined to create a longitudinal chamber and frontal holes evenly distributed on the two non-parallel faces. An illuminator colours the fluid (water) and steam with two distinct colours.

Principle of Operation: The Refractive Index

Bicolor level gauges are in principle transparent gauges in which the center piece has a wedge-shaped section. This design makes bicolor indication possible: there is an illuminator on the back with two colored filters positioned in front of the light source, one red and one green.

When viewed from the front, the red filter should always be placed on the left, in the narrowest part of the indicator section.

The optical separation between the space occupied by steam and that occupied by water is based on the different refraction of light in the two fluids.

The bicolor indication is produced by the red and green light rays:

  • When entering the water, the red light rays are deflected sideways and totally absorbed, whereas when passing through the steam, there is no deflection and the light rays arrive unobstructed and appear in the front indication as red.  
  • In contrast, when passing through water, green light rays can freely travel, making the liquid indication appear as green, while they are completely absorbed when passing through steam.

This phenomenon occurs due to the different speed at which the red and green light rays travel. As they pass from one optically different medium to another, the speed at which the light waves propagate varies, causing the two colors to refract at different angles.

Benefits and Applications.

Bicolour level gauges find application in industries where the measurement of steam at medium and high pressures is necessary. They are mainly employed when accurate monitoring of water and steam levels is critical to ensure process safety and efficiency.

These indicators provide a clear visual indication of the level, with green representing the liquid (water) zone and red representing the vapor zone. This colour distinction greatly simplifies monitoring for operators.

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