Principle of Radar Tank Gauging
Radar tank gauges are "downward-looking" measuring system installed on the tank roof. Operating on the time-of-flight method, they measure the distance from the reference point (process connection) to the product surface. Radar impulses (FMCW principle) are emitted by an antenna, reflected off the product surface and received again by the radar system. The distance to the product surface is proportional to the travel time of the impulse. Due to the nature of the microwave, radar tank gauges need to be equipped with functions to suppress interference echoes (e.g. from edges and weld seams) in the tank so they are not interpreted as level measurement. Radar technology is suitable for measuring a wide range of petroleum products.
Process Conditions
Radar gauge measurement is independent of the process conditions inside the tank. Temperature, pressure and gas vapors have minimal affect on "radar beams". The dielectric constant of the liquid being measured is a critical factor when considering a radar tank gauging solution.
Radar Antennae
It is essential for specific application and installation requirements to be evaluated and the correct antenna type selected. The Varec range of radar antenna include:
- Horn and Parabolic antennae - suited for free space applications
- Planar antenna - specifically suited for stilling well applications
- Small horn antenna - suitable for installation on existing tank fittings
Radar Tank Gauging Solution
Varec's 7200 and 7500 Radar Tank Gauges are suitable for most bulk storage tank applications to provide inventory management level (+/- 3-10 mm) measurement accuracy or NMi approved high accuracy (+/- 1 mm) respectfully. A 4590 TSM is required to integrate a temperature device. A 4532 ATC, 4539 ATC, 3-wire RTD or 4-wire RTD can be selected for temperature measurement suitable for inventory management applications. The 4590 TSM also provides power to the radar tank gauge and additional functionality, such as I/O, tank calculations, pressure (HART®) sensor integration and the appropriate field communications protocols for data transfer to the control room system.
