Here are the 2 basic types of level gauges.
Reflex Level Gauge
This type of level gauge is used to easily distinguish the level of liquid, gases or vapours. The basic working principle behind this device is based on reflection and refraction. Essentially, the glass panel is fitted facing the chamber and it has prismatic grooves on it. The liquid is deposited in the lower half of the gauge and the gases are deposited in the upper part. Thus, the fluid levels are known thanks to the brightness reflected by the glass in the two respective zones.
Reflex level gauges can be used in most liquid systems, with the exception of high-pressure steam. For fluids that have high operating pressure, a different kind of gauge is used.
Transparent Level Gauge
As the name suggests, a transparent level gauge can be seen all the way through. Comprising two glass plates, the fluid is held in between these plates. Due to the different levels of transparency of the two glass plates, the level of the fluid can be accurately measure. Moreover, in order to protect the gauge from corrosive fluids, transparent level gauges are offered an extra layer of protection using mica shields.
Due to added protection, these gauges are perfect for corrosive fluids, high-pressure fluids like steam and in cases where the system receives thermal shocks.