Wireless Level Switches and Interoperability

Emerson’s Jonas Berge shares how level switches have joined the ranks of wireless devices in a recent Control Engineering Asia article, Switching to Wireless. He notes how this enables:

…an easy and cost-effective solution for level monitoring without laying cable or associated risk of damaging the existing installation, and enable configuration and troubleshooting from a central location.

Many existing plants minimized the number of instruments and relied on operators to take manual, periodic readings. He notes some of the business drivers changing this approach:

…increased focus on quality, throughput, availability/reliability, shorter shutdown periods, energy efficiency, and new environmental regulations is driving change in how plants are maintained and operated. This monitoring now has to be automated.

These wireless level switches can share the existing WirelessHART (IEC 62591) instrumentation network infrastructure as:

…wireless transmitters (e.g. pressure, temperature, pH, vibration, conductivity, level, valve position feedback, etc.), and all of the information is transmitted via the same gateway. One gateway can support up to a hundred IEC 62591 transmitters.

The wireless level switches are based on vibrating fork technology. Jonas describes the principle of operation:

A vibrating fork level switch operates on the principle of a tuning fork. An internal piezoelectric crystal oscillates the external fork at its natural frequency. The frequency changes depending on the medium in which it is immersed. The denser the liquid, the lower the frequency. Thus, the frequency is different depending on if the fork is immersed or dry.

Diagnostics can also be provided from these wireless level switches back to the operators:

…changes in frequency are used to detect not only high or low level, but also media build-up on the fork, external damage to the fork, internal damage to the piezo, and excessive corrosion.

The underlying technology to communicate these diagnostics in a visual way is Electronic Device Description Language (EDDL). Jonas notes that [hyperlinks added]:

EDDL enables IEC 62591 level switches to be set up and checked using the same intelligent device management software as the other devices in the plant. The information from level switches is displayed side-by-side with information from wireless transmitters for pressure, temperature, and other process parameters. They are also displayed the same way as Foundation fieldbus and Profibus devices.

Jonas concludes the article highlighting the technology’s interoperability:

And using EDDL technology, device manufacturers can use human centered design principles to develop wizards which guide setup of intelligent devices around the plant, thus making management of a mixture of simple and sophisticated device types from different manufacturers using different protocols easier.

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