Two types of measurement methods are used for tank gauging: volume or mass based.
In a volume based system, level is measured. In a mass based system, the measurement of the hydrostatic pressure of the liquid column is used. The users choice should, therefore, be based on how product inventory is calculated and accounted via volume or weight.
Both methods provide a direct measurement of one factor in the inventory equation, level or pressure. However, bulk storage tanks tend to have large diameters, store products with varying densities that can stratify, and require consideration for high tank levels and overfill protection. A small change in level can make a big difference in accountable volumes (level x diameter), while stratification can lead to level changes that are undetectable by mass based systems. Vendors, therefore, recommends level (volume) based measurement systems.
Float & Tape Tank Gauging
Changes in the liquid level inside the tank raise or lower a large stainless steel float. The float is attached to a powerful negator spring via a perforated tape. The negator spring provides constant tension, which balances the float on the liquid level. The perforated tape engages pins on a sprocket wheel that, in turn, drives the counter assembly.
When a gauge board is used to display level in a float & tape system, the negator spring is replaced by a counter weight system. The liquid level in feet and inches or meters and decimeters is displayed on the gauge counter or indicated on a gauge board. This simple design and operation allows the gauge to perform with negligible maintenance throughout its working life.
A range of analog and digital tank gauge transmitters are available that mount directly to mechanical tank gauges. Level measurement data is encoded by the transmitter and output via industry standard communications to the control room.
Some transmitters also offer spot temperature measurement integration that can be used for inventory control applications. When a tank gauge transmitter is used, communications and power are required at the gauge head. Varec transmitters do not require an adaptor flange. When connecting third party equipment, a specific adaptor flange, depending on the transmitter, is often required.
Simplify the process of negator motor replacement and improve the performance of your mechanical tank gauge with a removable Negator Cassette with the negator motor enclosed.
Hydrostatic Tank Gauging