Varec's hydrostatic tank gauging solution consists of a temperature sensor and one or more HART® pressure sensor(s) integrated into the 4590 TSM. The 4590 TSM Connects up to 6 HART devices via an intrinsically safe 2-wire loop and a 3-wire RTD, 4-wire RTD 4532 ATC or a 4539 ATC. The 4590 TSM is then able to provide calculations at the tank side and transfer data to the control room.
Hydrostatic tank gauging utilizes up to three pressure sensors and one or more temperature elements. The hydrostatic pressure (liquid head) is measured; as the height increases the pressure increases as well. If a single pressure sensor is used, a manual density measurement is required for an inventory calculation. A second pressure sensor is used to enable automatic density calculations. A third pressure sensor is generally used to measure vapor pressure and increase the overall accuracy of the system. Combined with the tank strapping table, this technique provides an excellent method to measure mass, but liquid level, volume and density are only indirectly inferred. A 0.02% full scale accuracy, which is dependent on the pressure sensors installed, is normally desired to provide reasonable inventory management.