What is a Level Gauge or Level Indicator?
Level gauges or level indicators are instrument devices that are installed in plants for determining the liquid level in process equipment like drums, vessels, tanks, etc. The level gauge instrument has several parts like head, float, measuring tape, bottom anchored bracket, guide wires, elbows, anchors, coupling, pipe support brackets, and pipework. To suit the requirement of the industry, various types of level gauges (Fig. 1) are available.
How many types of Level Gauges are there?
Depending upon application and level measuring techniques, the following types of Level gauges are found:
- Transparent level gauge
- Reflex level gauges
- Magnetic level gauges
- Tubular level gauge
- Bi-color level gauge
Transparent Level Gauges
They are made of two transparent glass plates which are fitted with the liquid cavities on both sides. By detecting the dissimilarity of transparent characteristics of two media, Transparent Level gauges determine the fluid level. In some applications, an illuminator from which rays emit is used to make the liquid level easier to see. Such level indicators can be used for almost all installations.
What is Reflex Type Level Gauge?
The reflex type level gauge operates by detecting the dissimilarity in the refraction index between fluids and vapors. They are frequently used in vessels or containers. They are durable, can sustain high temperature and pressure and normally, made of carbon steel or stainless steel. In the gas or steam phase, the light is reflected by the prismatic grooves of the glass, which therefore gives a clear appearance. In the liquid phase, the light is absorbed, thus providing a dark indication of the level on the sight glass which is a transparent tube, clamped to the gauge body. Reflex Level gauges are frequently used as they have low initial cost, low operating cost, easy level reading.
Magnetic Level Gauges
Magnetic level indicators are used to control the fluid level. Operating based on Archimedes Buoyancy Principle, such level gauges are highly durable and finds its application for high-pressure temperature and highly toxic or corrosive environments. These gauges are able to detect the inter-phase level.
Tubular Level Indicators
The tubular Level indicator is the simplest form of Level indication. Used in a low pressure, non-toxic services, Tubular level gauges detect and report the process fluid level through the direct reading of level in tanks or vessels. It consists of a Glass tube, Packing Material, end blocks, Vent plug, Drain valve, isolation valve, etc.
Bi-Color Level Gauges
Bi-color level gauges are basically a transparent gauge having a liquid chamber in a wedge-shaped section. The illuminator on the backside of the device is fitted with two color filters; red and green. When red color light radiations hit the water, they get alerted to one side and absorbed. When the same light hits the steam, the light passes through and shows up as a red color. The reverse happens for light passing through green filters. This allows users to tell how much of each media is in the system.
These are specifically used to measure the media level in a boiler and detect level by distinguishing the index of refraction between the steam and water. The gauge uses high-quality mica sheets to guard against the wet steam generated in a boiler drum.
Measuring Range of Level Indicators
The measuring range is the level range that the devices can measure and the range is determined by the maximum and minimum media levels. While choosing a level gauge, this parameter must be examined accounting for anticipated media-level fluctuations.
How to Order a Level Indicator?
While selecting and placing an order the following points need to be mentioned:
- Process conditions with Temperature range, Maximum operating pressure, Fluid Density
- Center to center distance
- End connections (flanged or screwed)
- Device Medium
- Mounting Options and
- Application of the instrument
Few more Resources for you..
What is FMS or Flow Metering Skid?
Types of Flowmeters and their Applications
Overview of Piping – Instrument Interface: An article
An article on Temperature Measurement by Filled Thermal Systems
An article on Conductivity Analyzers
The safe way to install restriction orifices
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