What is a Device Description?
A Device Description or DD is an electronic data file prepared in
accordance with Device Description Language specifications that describes
specific features and functions of a device including details of menus
and graphic display features to be used by host applications (including
handheld devices) to access all parameters and data in the corresponding
device.
What
DD's Really Do?
The HART Protocol operates in a host/slave environment where an instrument
is queried and responds to a host. HART has a command structure that
allows device manufacturers a great deal of latitude on designing
a device. All HART devices must have a minimum command set to be compliant
called Universal commands. Devices may also have a number of optional
commands called Common Practice Commands, Many devices implement manufacturer
specific commands called Device Specific Commands. The DD allows access
to all commands. DD aware host systems can then use the data and display
it as the user desires.
How DDs are distributed
The HCF requires that all DD's be registered with the foundation
to test for compliance with established HART protocol guidelines.
The HCF manages a library of registered device descriptions. The
library is distributed to host manufacturers on a quarterly basis
for inclusion with their products. The DD Library Distribution CD
is available to HCF members only. The HCF
Product Catalog also allows anyone to download DD's one at a
time. However, please review the following paragraph to determine
if you will be able to use the DD once it is downloaded. A complete
listing of DDs in the library is available on the HCF
web site.
Using DD's
HART Handheld Communicators are available
from major instrumentation suppliers around the globe and are supported
by HCF member companies. Using Device Description (DD) files, the
communicator can fully configure any HART device for which it has
a DD installed. If the communicator does not have the DD for a specific
device, it will still communicate and configure the device using
the HART Universal and Common Practice commands.
Newer models may give you the ability to add DD’s to the
handheld. There are also PC-based software configuration applications
that allow DD updates. Contact your device suppliers for their solution
but be sure to ask if you can update the DD on your own.
Not all software applications and handhelds use DD files in the
same manner. Some device and software manufacturers use their own
binary files that are created from the DD source . Others, like
the 275 handheld, require special
programming. Before you download a DD file, make sure that you
can use the DD file provided by the HCF in your handheld or software
application. Please feel free to contact
the HCF if you need help.
Once you have a DD, you will need to place it where the software
application or handheld can access it. Before you download a DD
file please take note of the Manufacturer ID and Device Type listed
on the download page. Most manufacturers store the DD files using
these two numbers. The downloaded files should be placed in a folder
named with the manufacturer ID number and then a child folder created
using the device type number. The folder should then be copied to
the directory where DD files are stored. If the folders are already
there they may contain a previous revision of the DD. The new files
simply replace the old and work with all revisions of the same device.
|
