- Direct digital control
A very early example of a DDC system meeting the above requirements was completed by the Australian business Midac in 1981-1982 using R-Tec Australian designed hardware. The system installed at the University of Melbourne used a serial communications network, connecting campus buildings back to a control room "front end" system in the basement of the Old Geology building. Each remote or Satellite Intelligence Unit (SIU) ran 2 Z80 microprocessors whilst the front end ran 11 in a Parallel Processing configuration with paged common memory. The z80 microprocessors shared the load by passing tasks to each other via the common memory and the communications network. This was possibly the first successful implementation of a distributed processing direct digital control system.
Central controllers and most terminal unit controllers are programmable, meaning the direct digital control program code may be customized for the intended use. The program features include time schedules, setpoints, controllers, logic, timers, trend logs, and alarms.
The unit controllers typically have analog and digital inputs, that allow measurement of the variable (temperature, humidity, or pressure) and analog and digital outputs for control of the medium (hot/cold water and/or steam). Digital inputs are typically (dry) contacts from a control device, and analog inputs are typically a voltage or current measurement from a variable (temperature, humidity, velocity, or pressure) sensing device. Digital outputs are typically relay contacts used to start and stop equipment, and analog outputs are typically voltage or current signals to control the movement of the medium (air/water/steam) control devices. Usually abbreviated as "DDC".
When DDC controllers are networked together they can share information through a data bus. The control system may speak 'proprietary' or 'open protocol' language to communicate on the data bus. Examples of open protocol language are BACnet (Building Automation Control Network), LON (Echelon), Modbus.
When different DDC data networks are linked together they can be controlled from a shared platform. This platform can then share information from one language to another. For example, a LON controller could share a temperature value with a BACnet controller. The integration platform can not only make information shareable, but can interact with all the devices.
Most of the integration platforms are either a PC or a network appliance. In many cases, the HMI (human machine interface) or SCADA (Supervisory Control And Data Acquisition) are part of it. Integration platform examples, to name only a few, are the Tridium Niagara AX, Johnson FX40,TAC Vista and the Unified Architecture i.e. OPC (Open Connectivity) server technology used when direct connectivity is not possible.
DDC is often used to control HVAC (heating, ventilating, and air conditioning) devices such as valves via microprocessors using software to perform the control logic. Such systems receive analog and digital inputs from the sensors and devices installed in the HVAC system and, according to the control logic, provide analog or digital outputs to control the HVAC system devices.
These systems may be mated with a software package that graphically allows operators to monitor, control, alarm and diagnose building equipment remotely.
- Building Automation
- GE FANUC GE Fanuc Intelligent Platforms
- Safety instrumented system, (SIS)
- Industrial control systems
- Industrial safety systems
- ^ a b Samuel C. Sugarman (2004). HVAC Fundamentals. The Fairmont Press. ISBN 0881734896. http://books.google.com/books?id=N23gDS3wrDUC&pg=PA199&dq=%22direct+digital+control%22&lr=&as_brr=0&ei=5ro8SdjCHpOIkASioeD9Cg.
- ^ James R. Leigh (1987). Applied Control Theory. IET. ISBN 0863410898. http://books.google.com/books?id=QWY4SXNe4DIC&pg=PA41&dq=%22direct+digital+control%22&lr=&as_brr=0&ei=5ro8SdjCHpOIkASioeD9Cg.
Wikimedia Foundation. 2010.
Look at other dictionaries:
Direct Digital Control — (DDC) refers to the ability to control HVAC (Heating, Ventilating, and Air Conditioning) devices via microprocessors containing a software performing the control logic. DDC receive analog and digital inputs from the sensors and devices installed… … Wikipedia
Direct Digital Control — DDC GA Komponente Draufsicht Eine Komponente der Direct Digital Control Gebäudeautomation, kurz DDC GA, ist eine einem Computer ähnliche elektronische Baugruppe, die für Steuerungs und Regelungsaufgaben in der Gebäudeautomatisierung eingesetzt… … Deutsch Wikipedia
direct digital control — tiesioginis skaitmeninis valdymas statusas T sritis automatika atitikmenys: angl. direct digital control vok. direkte digitale Regelung, f rus. прямое цифровое управление, n pranc. commande numérique directe, f … Automatikos terminų žodynas
direct digital control — (DDC) Use of digital computer to perform required automatic control operations in a total energy management system … Dictionary of automotive terms
Direct Digital Control (Regelungstechnisches Verfahren) — Direct Digital Control (abgekürzt DDC) ist ein Verfahren, Regelkreise mit darin teilweise enthaltenen Übertragungsgliedern von digitalen Prozessorsystemen (inklusive AD und DA Wandler modellierende Glieder) zu konstruieren und ihre Eigenschaften… … Deutsch Wikipedia
Direct torque control — (DTC) is one method used in variable frequency drives to control the torque (and thus finally the speed) of three phase AC electric motors. This involves calculating an estimate of the motor s magnetic flux and torque based on the measured… … Wikipedia
Digital Control — Digital Control, engl. für digitale Steuerung/Regelung, bezeichnet in der Elektrotechnik die Verwendung von digitalen Halbleiterbausteinen, wie Mikrocontroller, oder Logikgatter zum Steuern und Regeln von Prozessen, Anlagen und Schaltungen. Die… … Deutsch Wikipedia
Direct digital synthesis — (DDS) is an electronic method for digitally creating arbitrary waveforms and frequencies from a single, fixed source frequency. OverviewA basic DDS circuit consists of an electronic controller, a random access memory, a frequency reference… … Wikipedia
Direct digital synthesizer — A DDS function generator. Direct Digital Synthesizer (DDS) is a type of frequency synthesizer used for creating arbitrary waveforms from a single, fixed frequency reference clock. Applications of DDS include: signal generation, local oscillators… … Wikipedia
control system — Means by which a set of variable quantities is held constant or caused to vary in a prescribed way. Control systems are intimately related to the concept of automation but have an ancient history. Roman engineers maintained water levels in… … Universalium