SMI

DDC

Direct Digital Control Systems (DDC)

DDC control systems use microprocessor-based controllers for typical use in commercial buildings.  These controllers measure signals from sensors, perform control routines in software programs, and take corrective action in the form of output signals to actuators.  Since the programs are in digital form, the controllers perform what is known as direct digital control (DDC).  Microprocessor-based controllers can be used as stand-alone controllers or they can be incorporated into a building management system utilizing a minicomputer or a personal computer (PC) as a host to provide additional functions.  Digital control offers many advantages:

 

Key Benefits

Lower Cost Per Function...
Microprocessor and memory costs keep coming down while inherently functionality keeps going up.  Digital control allows more sophisticated and energy efficient control sequences to be applied at a lower cost than with conventional controls.


Application Flexibility...
Since microprocessor-based controllers are software based, application flexibility is an inherent feature.  Changes in control sequences can easily be accommodated through software whether dictated by system performance or by changes in the owner's use of the facility.  Also, controllers can perform energy management and other building functions.


Multifunction Capability...
Although basic environmental control and energy management operate as independent programs, it is best to have them incorporated as an integrated program in order to provide more efficient control sequences.


Precise & Accurate Control...
Proportional control has the inherent problem of offset.  The wider the throttling range is set for control stability, the greater the offset.  With the microprocessor-based controller, the temperature offset can easily be corrected by the simple addition of integral action.