Local level gauge is an important measurement for many process control applications. It provides a reliable way to confirm the level gauge height. It allows a way to check and calibrate level transmitters. It can be used to temporarily and manually control the liquid level gauge when the normal control systems are down. And it offers a redundant technology to measure level gauge.
Two technologies typically used for local indication are armored sight glass and magnetic level gauge.
Armored sight glass usually consists of two armored castings that sandwich a piece of glass, allowing direct visibility of the liquid level gauge. A magnetic level gauge is typically made up of a float containing a magnet that follows the liquid level gauge inside of a chamber. The position of the float inside the chamber is indicated outside by dual-colored flappers embedded with magnets. As the magnet inside the float interacts with the magnets on the flapper outside of the chamber, the flapper turns and changes color to indicate level gauge.
When deciding which technology to use, it is important to look at the long-term cost of ownership rather than just the upfront cost of the unit. Sight glass technology typically has a lower upfront cost than an MLI; however, an MLI has many benefits during installation and normal operations that result in a lower total cost of ownership in the long run.
The four key ways — enhanced safety, maintenance, increased visibility and simplified installation — in which an MLI will actually reduce overall cost over time and improve functionality are discussed in this article. We will also go through an example of comparing the total cost of ownership of a sight glass to that of an MLI over a five-year period. A lot of these values are estimates and will vary greatly on changing applications and from plant to plant. In this example, we will use a 3’ indication length and assume our initial upfront cost of the sight glass is $450 while our MLI has a starting cost of $2,200.
This article comes from process-heating edit released