CEMP-E
TI 810-11
30 November 1998
7. DDC VERSUS SLDC.
a. Background. "Single-loop" digital controls are currently the Army standard, but there are
situations where direct digital control is a better choice. DDC is a more sophisticated technology and its
use may be warranted in complex applications such as laboratory or medical facilities. A complex
application may loosely be defined as one where numerous points must be remotely monitored and
controlled. In this type of application the DDC system will likely include a dedicated operator work station
(front-end or supervisory computer) which is staffed by an operator up to 24 hours per day. Waiver
requests for the use of DDC systems may be approved by the District Commander or at the Division on a
project by project basis, as with other Corps criteria. The design agent or district shall ensure that the
customer understands the problems as well as the benefits of a DDC system and supports its use on the
project. The district/division shall also ensure that proprietary DDC procurement is only included in a
contract package when fully justified with strong, clear and accurate documentation.
b. Comparisons. Prior to making a decision on whether to use DDC as opposed to the SLDC
technology, the designer is advised to consider the impact and ramifications of the decision.
Comparisons include:
MULTI-LOOP DDC
SINGLE-LOOP
DIGITAL CONTROLS
Commercial DDC systems are software-
The single-loop controller is industrial-grade
based with terminal connections, setpoints,
and firmware-based, with relatively simple,
calibration parameters, and calculations all
straightforward configuration requirements
handled by proprietary programs.
and does not require programming
Software operation, diagnostics and
capability. Army installations currently
modification requirements vary by
have personnel with the skills required to
manufacturer.
support the single-loop controller approach
with minimal training.
With present DDC systems,
The single-loop controller market is well
software/hardware maintenance and repair
established in the process controls industry.
or system expansion is vendor-dependent,
Single-loop controllers and other
resulting in sole source requirements that
components of an SLDC-based system are
can potentially increase costs. This
interchangeable between manufacturers
dependence on a single vendor for each
and are not dependent on any single
DDC system is further complicated if the
vendor. SLDC systems' configurations are
vendor drops support for older equipment or
nonproprietary for maintenance, repair, and
withdraws from the market. Historically,
expansion. This nonproprietary
changes in the DDC market have been
arrangement can significantly reduce spare
frequent .
parts requirements.
Open competition and the low bid
SLDC-based systems should present fewer
procurement environment could result in
special training or maintenance problems as
numerous proprietary DDC system
all replacement parts could be provided by a
manufacturers on an installation. Since
single manufacturer.
each system would have different
hardware, software, and maintenance
requirements, in-house forces would have
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