Updated: Jun 23
Every process control operator carries a flashlight, typically operating plants are not well lit and since plants typically run 24/7 it is dark much of the time. However often it is due to the operator not being able to see the level through the sight glass. Calling it a sight glass is a little funny in most cases. These work great with clean liquids. However very quickly be covered.
Our answer is a magnetic level gage; while the initial capital cost is higher, in the long run, it is far superior. This comes down to a few key reasons:
First is safety, in a pressure vessel, glass is a risk. A magnetic level gage has glass; but it isn't exposed to the high pressure.
Second is maintenance, sight glasses need constant, expensive, and difficult maintenance to even have a chance of being visible. Although the typical experience is operators are unable to see the level only days after the maintenance is completed.
Finally visibility, a magnetic level gage is visible from long distances, however not all mag gages are equal, some look like the one below after only a few years of service. A gage like this is not helpful at all.
Compare that to a PLT mag-gage in service for over 15 years, still working perfectly and visibly from long distances.
This is much easier to see and has minimal maintenance.