Digitally Connected Variable Speed Drives

Whether controlling pumps, fans, blowers, conveyors, compressors, extruders, mixers, agitators, chippers, etc., AC variable speed drives can be found in most plants and mills. Emerson’s Jonas Berge, whom you may recall from earlier digital communications-related posts, recently had an article published in Control Engineering Asia magazine. The article, The Digital Drive, highlights the operating and diagnostic information, configuration, and integration of these variable speed drive units that incorporate electronic device description language (EDDL). EDDL, an IEC 61804-3 global standard, allows automation engineers to connect control systems and motor controls independently from different manufacturers, and enjoy the benefits of tight integration.

Jonas notes that these drives were traditionally connected with control system with wiring. He wrote:

Drives have many control signals from the DCS as well as discrete and analog status feedback signals to the DCS (see Table 1). Hardwiring all of these individual signals can be very expensive.

Besides this large amount of wiring, such traditionally hardwired systems typically require many analog and discrete input and output cards, and many system tags for each drive. Lots of engineering work is required to size and plan the I/O and labor for installation and testing. Changes late in the project often require major rework and cause delays.

Bus technologies allow these digital communications to occur over a single pair of wires. Jonas highlights some of these digital communications technologies found in plants and mills:

…typical installation may use Foundation fieldbus for process control and alarms, hardwired Hart for instruments on safety systems, WirelessHart for indication, and Profibus-DP for motor controls.

Jonas explains how the EDDL standard helps with user interactions with these various digital communications technologies:

Electronic device description language is the only device integration technology which is an integral part of the Hart, Foundation fieldbus, Profibus, and WirelessHart standards. EDDL (www.eddl.org) enables all devices using these protocols to be managed from the same intelligent device management software throughout their life-cycle. That is, the same universal software that manages the drive over Profibus-DP also manages instrumentation on Foundation fieldbus, Hart, and WirelessHart.

The benefit is commissioning, configuration, and diagnostics can be done with common software–reducing learning curves and streamlining work practices.

He contrasts the text-based file approach used with EDDL devices to others that require installation–much like printer drivers. The EDDL text file approach also avoids issues with operating system flavors and versions to help protect the investment of EDDL-based devices and control and asset management systems.

In the article, Jonas also shares examples and images showing the common look & feel of application screens displaying device diagnostics and wizards, which provide step-by-step device configuration, and commissioning.

Jonas sums of the advantages of this digital communications-based approach:

Bus technology in combination with EDDL offers a number of advantages over individually hardwired signals. These advantages range from lower installation cost, shorter commissioning, and greater flexibility to accommodate late changes, to setup and diagnostics from the control room.

If you have or are planning to have variable speed drives in your plant, and you want to understand the types of information that can be connected with your control and asset management systems, then Jonas’ digital drive article may be worth a read.

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