What Is EDDL in HART Device Integration?
Behind every HART device description file is a language, and understanding that language explains why a DD works on any conforming host and outlives the hardware it describes. This page explains EDDL, the Electronic Device Description Language, what makes it a description rather than a program, and why that distinction has practical consequences for long-lived plants. It is for engineers who maintain device-description libraries and want to know why EDDL was chosen over shipping executable drivers.
EDDL in one line: EDDL, the Electronic Device Description Language, is the standardized text-based language HART device descriptions are written in. It describes a device's variables, commands, menus, and procedures declaratively rather than as executable code, so one description runs on any conforming host and remains usable for the life of the device, independent of operating systems and host software generations.
A Description, Not a Program
EDDL is a language for describing what a field device is and how to interact with it, not for programming how to do so. A device description written in EDDL declares the device's variables and their units, names its commands, lays out the menu structure an engineer navigates, and specifies the sequence of steps for procedures like a calibration. Crucially it does all this declaratively: it states what the host should present and what steps a procedure involves, and leaves the host to actually render the interface and execute the interaction.
This declarative nature is the whole point. Because an EDDL description contains no executable code, it cannot depend on a particular operating system, cannot carry a driver's compatibility quirks, and cannot crash the host. The host reads the description and builds the appropriate user experience itself, whether that host is a rugged handheld, a plant asset-management workstation, or a configuration tool from a different vendor. One description, many hosts, because the description says what to do and the host decides how. The HART device description page covers the DD file this language produces.
The contrast with the FDT/DTM approach is instructive. A DTM is executable software that carries its own interface and plugs into an FDT frame, which buys a richer, vendor-controlled experience at the cost of being tied to a platform and behaving like installed software. EDDL trades that richness for durability and universality. The DTM page covers that alternative; the two coexist precisely because they make opposite trade-offs, and a device may ship a description in both forms.
Why the Distinction Matters for Long-Lived Plants
Industrial plants keep instruments in service for a very long time, and the tools that manage them change far faster than the devices themselves. An executable driver written for one generation of host software can stop working when the operating system moves on, stranding the ability to fully configure a device that is still perfectly good in the field. A text description in EDDL does not have that fragility: as long as a host can read the description language, it can present the old device, so the device outlives many generations of host software.
This durability is why EDDL is valued in industries that plan in decades. The device description is a stable, human-and-machine-readable record of how to work with an instrument, tied to a standardized language rather than to any vendor's software product. When a plant modernizes its asset-management system, the EDDL descriptions for its installed base continue to work on the new conforming host, so the modernization does not orphan the field devices. That continuity is worth a great deal when the field devices represent an enormous installed investment.
For the practicing engineer the takeaway is to treat the EDDL description library as a durable asset in its own right, kept current with device revisions the same way the physical spares are. When a monitoring platform such as Merobix surfaces a device's live values from a gateway or multiplexer, it does so through the portable command set rather than needing every EDDL description, but the deep configuration work that keeps the fleet healthy over its life leans on those descriptions - and their host-independence is what keeps that work possible across decades of changing tools.
Frequently Asked Questions
What is EDDL used for in HART?
EDDL, the Electronic Device Description Language, is the language HART device description files are written in. It describes a device's variables, commands, menus, and procedures declaratively so that any conforming host can render the device's interface and run its procedures. It is what lets a generic host fully configure a device it has never seen, using the device's DD.
Why is EDDL host-independent?
Because an EDDL description contains no executable code - it declares what a host should present and what steps a procedure involves, and the host decides how to render and execute it. With no dependence on an operating system or a particular software generation, the same description runs on any conforming host, from a handheld to a workstation, and keeps working as host software changes.
How is EDDL different from a DTM?
EDDL produces a declarative text description the host renders, so it is portable and durable across host generations. A DTM is executable software that carries its own interface and plugs into an FDT frame, giving a richer vendor-controlled experience but tied to a platform. EDDL trades richness for universality and longevity; the two coexist because they make opposite trade-offs.
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