Level Measurement Instruments
Level measurement instruments are used to provide the exact level of liquids or solids in atmospheric or pressurized vessels, tanks or hoppers that can lead to calculate their weight or volume.
Level measurement instruments could be used for inventory control, custody transfer, leakage monitoring, overfill protection, batch control, dosing systems, mixed liquids separation and many other precise controls.
Level measurement instruments could be categorized as the following:
- Level gauge
- Level Transmitter
- Level Switch
The most common industrial types of level gauges are:
- Sight Glass
- Glass Level Gauge
- Magnetic Level Gauge
- Float Level Gauge
Sight glass is a glass window or tube installed on a vessel or tank that allows the operator to observe the inside of that vessel or tank.
Operator might needs to observe liquid level or check the process inside of the vessel to ensure optimal quality or safety.
Sight glass could be in form of a glass disk with a flanged metal frame which will be installed on the vessel nozzle or could be a vertical tube with flange connections at top and bottom.
Tube sight glasses are similar to contemporary level gauges, but only provides level indication at a specific level or a very small range.
Glass Level Gauge
There are three types of level gauges; Reflex, Transparent and Bi-Color.
Glass Level gauges have three major parts; metal chamber, glass, two cock valves on top and bottom and two valves or plugs for drain and vent.
Tubular is another type of glass level gauge but is not applicable in industrial applications.
Reflex Level Gauge
Reflex Level Gauge works based on light reflection and refraction laws.
In Reflex Level Gauge, front of the metal chamber is covered with a glass that has prismatic grooves with section angle of 90° that forms an angle of 45° with the liquid.
When the liquid enters the chamber, based on communicating vessels principle, its level in the gauge settles at the same level of liquid in the vessel or tank.
The liquid level is distinguished by different brightness of the glass in the liquid and in gas/vapor zones, because of the difference in the refractive indices of liquid and gas/vapor.