DDC (Direct Digital Control)

'As the name specifies itself ;DDC be directly interfaced to thr process to control just with some interfacing hardware i.e. opto coupler,ADC,signal conditioning.It mainly works on position or velocity algorithm.both having some advantages and drawbacks too,so we use it as per requirement.

while DCS is the centralised control system which control the diffrent processes in local loops/unit control operation loops[for dedicated processe with help of a centralised control station.the process may be geographically or functionally distributed.PLC used along with DCS or independently for the sake of emergency rapid action as PLC acts very faster than DCS.

DDC or Direct Digital Control is a term used in the HVAC controls industry. PLC are Programmable Logic Controls they are process controllers used for industry.

PLC controllers are independent controllers that can stand alone without a centralized controller. And yes you can put in a centralized monitoring system for a PLC system.

DDC controls are, and I have to say mostly, all networked together back to a centralized monitoring system and lets you control a building / campus from a central location. In the early days of DDC we had DDC controls that were not centralized and each controller stood alone, but that was in the early days of networking and it was expensive to connect all of your controllers. But now adays I don't know of anyone that doesn't put in a front-end as we call it.

DDC controls came out in the 70's, at least to be best of my knowledge. And they had computers the size of a couple of refrigerators. When I got into it in the 80's computers had come a long way and I had a Compaq that we called a lugable, you didn't want to put one of those in your lap. Those were exciting and fun times.

https://ducon.mailwebconnect.com/exchange/gshine/Inbox/FW:%20CR4%20-%20Thread:%20DDC%20(Direct%20Digital%20Control).EML/Industrial%20Based%20Control%20Systems.pdf/C58EA28C-18C0-4a97-9AF2-036E93DDAFB3/Industrial%20Based%20Control%20Systems.pdf?attach=1

Open this attachment, it explains your question!!!

The term direct digital control needs to be defined for it to convey any meaning.

• PLCs operate digitally.
• So does a thermostat.

Thanx everybody for your help & info.