Guided Wave Radar TransmitterFigure 2. This two-wire unit can handle challenging measurements on liquids, slurries and solids.
Source: Emerson Process Management.
For example, in September E+H, Kildare, Ireland, completed a major overspill protection project for Apollo Adhesives in Tamworth, U.K. that solved a persistent problem. Apollo, whose core products are a range of solvent-based adhesives, was having trouble measuring very-low-dielectric-value mixed and chlorinated solvents with stored in underground vessels. The manual measurement method used was time-consuming and not precise enough. The company required an accurate and reliable automated system that would provide real-time data and give low-level alerts to avoid running out of stock as well as high-level alerts to avoid overspill. It also had to be electrically suitable for a zoned explosive area.
The low-level alarms were particularly important as Apollo wanted to ensure that raw materials always were readily available to meet customer demand and to facilitate ordering in bulk from suppliers to reduce delivery costs. The high-level alarms, meanwhile, would help protect the environment and employees from danger.
E+H supplied eight Levelflex M FMP40 coaxial guided-wave-radar (GWR) devices that accurately measure low dielectric materials and also comply with the necessary electrical requirements. Additionally, E+H installed eight RIA261 loop-powered field displays in the hazardous area for use by tanker drivers during filling operations. A separate panel next to the hazardous area incorporates all hardware to generate the high- and low-level alarms as well as a siren and beacon — and provides signals to an additional panel situated inside the main office building.
This system provides Apollo with direct access to real-time data about the level of raw materials and thus plenty of time to replenish stocks when levels get low.
As a result, the company now saves on transportation costs by avoiding repeat deliveries by suppliers, and frees staff from having to take the manual measurements. More importantly, Apollo reduced the risk of running low on stock or completely running out of stock, which would lead to manufacturing downtime and incur great costs.
Emerson also sees a strong role for GWR at process plants. “We estimate growth of around 14% from 2008–2013 compared to 4.1% for continuous level measurement in general,” says Chettle.
With GWR, a pulse of microwave energy is transmitted down a probe rather than through the air. The devices are an easy fit to many applications, eliminating concerns associated with in-tank issues such as obstructions, foaming and turbulence. Software allows detecting and tracking the interface between two liquids, for example in a separator, giving users a reliable measurement to optimize control. However, one potential problem with GWR is that the instruments are contacting devices and may not work well in some applications involving hydrocarbons where very low dielectrics and dirty product coating the probe can significantly reduce the reflected signal.
Plants increasingly are relying on radar level measurement technology to generate tank graphs — effectively maps of tank echoes. By analyzing and comparing such graphs over time, users can identify trends that may help in planning maintenance or making long-term improvements.
“The market for microwave [radar] and ultrasonic level transmitters continues its rapid growth across an expanding application base, thanks to their proven reliability and low maintenance requirements. Meanwhile, differential transmitter level systems benefit from better system construction, sizing and installation practices, giving increased installed reliability, while point level switches are widely used to meet safety standards for high/overfill and low level measurements,” notes Chettle. He expects further developments in enhanced instrument diagnostics to enable remote interrogation of instrument condition and advance warning of potential problems.