A high-performance version of the Rosemount™ 3308 Guided Wave Radar (GWR) Wireless Level Transmitter has been introduced by Emerson. It the first standalone wireless radar level device to comply with the API 18.2 standard that provides guidance for crude oil custody transfer from small lease tanks. The transmitter – part of Emerson’s Plantweb™ digital ecosystem portfolio of transformational technologies, software and services – delivers enhanced accuracy which can be verified without having to open a tank’s thief hatch, thereby increasing safety.“The API 18.2 standard places strict accuracy demands on level measurement instrumentation because high levels of uncertainty during custody transfer can have significant financial implications,” said Christoffer Widahl, product management lead with Emerson’s measurement and analytical business. “Measurement precision is therefore essential in these applications, and the enhanced performance of the Rosemount 3308 delivers the high accuracy required to reduce uncertainty and comply with API 18.2.”
An upgraded microwave module has made the Rosemount 3308 more tolerant to difficult process conditions and therefore able to deliver a more sensitive and repeatable measurement and higher accuracy. API 18.2 requires level transmitters to operate with 1/8” (3mm) resolution and 3/16” (4.7mm) measurement accuracy, which the Rosemount 3308 achieves when set up in high-performance mode. This then enables it to achieve the installed accuracy of 1/4” (6.3mm) required to comply with API 18.2. In standard mode, the accuracy of the device has been improved to 1/5” (5mm).
Accuracy can be easily verified in just a few minutes using the Rosemount VeriCase mobile verification tool. This straightforward procedure does not require a tank’s thief hatch to be opened or any product to be transferred. Opening the thief hatch can cause high concentrations of hydrocarbon gases and vapours to be released, putting worker health at risk, so eliminating this requirement is an important safety improvement.
In addition to providing the accuracy required for custody transfer applications, the Rosemount 3308 also delivers reliability in continuous level and interface monitoring applications in refineries, oil fields, offshore platforms and chemical plants, thereby providing a cost-effective standardised solution across an entire facility. The Rosemount 3308 is a top-mounted device that is virtually unaffected by changing process conditions such as density, conductivity, temperature and pressure, and because it does not have moving parts, no calibration is required, and maintenance is minimised. A wide range of process connections, probe styles and accessories ensure application flexibility.
For applications involving interfaces, the high accuracy of the Rosemount 3308 helps to maintain product separation by issuing an early warning if an interface is identified where there should be only one liquid. By reducing uncertainty and optimising product quality it helps to produce significant savings for end users.
Wireless technology significantly reduces installation and configuration time for level measurement applications and can typically reduce costs by at least 30 percent compared with a wired solution. The Rosemount 3308 can be installed and operating in less than an hour – reliably transmitting data via a wireless gateway to a control system or data historian. Status information and device diagnostics are easily accessible from the control room, reducing maintenance requirements and enhancing operator safety by eliminating unnecessary field trips.
• Radar level measurement best practice. by Sarah Parker, Applications Manager, Emerson Process Management, Rosemount division (Sept 2010)
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