Two types of measurement methods are used for tank gauge LTD (Level-Temperature- Density) mass custody transfer: 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. Varec, therefore, recommends level (volume) based measurement systems.
Float and Tape Tank Gauge LTD (Level-Temperature- Density) Mass Custody Transfer
These instruments have been the liquid level measurement technique of the petroleum tank gauging market for over 90 years due to their simplicity, reliability and cost.
Float and tape tank gauge LTD (Level-Temperature- Density) mass custody transfer solution consists of a ATG selected for the appropriate tank type. The instrument provides a measurement to +/- 4 mm accuracy and tank side display that is suitable for inventory management to API specifications. If control room integration and volumetric calculations are required, a tank gauge LTD mass custody transfer transmitter is recommended with a STS for spot temperature measurement. The selection of the transmitter often depends on the required or existing field communications and protocols.