What is meant by DDCS?

With the involvement of computers in almost every aspect, large-scale manufacturing industries have already made a major shift from manual working towards a fully automated manufacturing process. This shift has replaced the man with machines. Automating manufacturing processes reduces dependency on human labor to a greater extent as result unnecessary labor charges are removed. Automation also leads to superior product finishes with extreme accuracy. The material processing time is reduced with reduced output delay. An interconnection between machines and electronic systems automates a manufacturing process. A variety of sensors pick the inputs and feed them into a device, which is a microcontroller-based computer system. This system indeed operates the machinery. An example of such a system is the DDCS, which stands for direct digital control systems. DDCS means an automated control of a condition or a process by the use of a variety of digital devices, mostly computer systems or workstations.

The DDCS uses centralized network connectivity where different instrumentation systems involving digital and analog systems connected to a centralized microcontroller through a network of wirings. The signals acquired by these instrumentation systems of the DDCS are transferred to the microcontroller. The microcontroller has the flexibility to be programmed by simple programming languages. In the DDCS, the programming of the controller is such that it follows the required operation according to the necessity of the function. The processor of the computer then processes these inputs and sends output signals to control various devices such as valves, hydraulic actuators, motors, pneumatic actuators, conveyor lines, LEDs, and so on. One of the most popular examples of DDCS is the programmable logic controller (PLC).

Basic elements of DDCS

In this section, the different elements of DDCS are outlined.

Direct digital control points or DDCP

The term DDCP represents the storage locations of data in the DDCS. The data collection comes from various sources, such as sensors and software. The sensors are also known as DDCRS (direct digital control receivers). These receivers take in real-time data and convert them into digital signals, which form the input to the DDCS. Each data collected is stored in a unique location bearing unique identification addresses. The data collection is the primary process in DDCS operation.

Programming language

Programming languages are the set of codes given to the controller that instruct it to do specific tasks with the received signal, from the DDCRS. There are three classifications of programming languages used, they are:

• Line programming language: The line programming language uses FORTRAN based programming language to control devices.
• Manu-based programming language: Manu-based languages use inbuilt templates or logical functional blocks to frame the set of instructions. The interconnection of different blocks generates such instructions.
• Graphical programming: The functions and logic in this category use graphical symbols connected by data flow lines to form the set of instructions. All mechanical and electrical elements have their own set of unique symbols.

Direct digital control mapping (DDCM)

The DDCM is also known as the architecture or the layout of DDCS. It refers to the local area network (LAN) of the DDC architecture. It enables the operator to communicate with the system. These LANs interconnect all the instrumentations with the DDCS and permit the flow of information back and forth.

Direct digital control microprocessor (DDCMP)

The DDCMP is the brain of the DDCS and is also known as the controller. It accepts data from input sources, processes them, performs calculations, and executes the instructions. Direct digital control transmission (DDCT) modules handle the execution of the instructions. DDCT consists of output ports controlled by relay switches. It is directly connected to the devices to be operated.

Classification of controllers

There are generally two kinds of controllers used in the DDCS, they are outlined below.

Building controllers

The building controllers are the key controllers in the DDCS. They provide graphics to the operator, are programmable multiple times, schedule/reschedule operations, and operate control loops. These controllers do not have inbuilt input/output (I/O) modules but have a plugin to attach external I/O modules.

Custom application controller

The custom controllers generally have a mechanical subsystem that is coupled to the devices at the site. These controllers do not have an open system interface and are intended to control only subsystems.

Application-specific controller

The functions of the application-specific controllers are rather constrained than their other counterparts, and can only handle single equipment. These controllers are specifically known as DDCVA (direct digital control for variable air volume) controllers and DDCU (direct digital control for rooftop units) controllers, as these are specifically meant for the control and operation of variable air volume devices and rooftop units.

DCS vs SCADA

The full form of DCS is distributed control system. It is a collection of several modules such as sensors, systems, and computers which are distributed throughout a unit or plant. All these systems are connected to a centralized workstation through a network of cables called the control network. The DCS functions as the central brain of the whole plant. It performs the task to automate the plant's operations based on the inputs it receives from the sensors. DDCS can handle only specific equipment whereas DCS is meant to automate and handle the entire plant and its associated equipment.

The full form of SCADA is a supervisory control and data acquisition, it is similar to DCS architecture and consists of computers and cable networks. The main characteristic that differentiates SCADA from DCS is the sense that it uses high-level graphical interfaces for user interfaces (UI). This allows for high degree supervision and control of machinery and processes. The architecture of SCADA covers sensors and even PLCs.

The human-machine interface or HMI is the main component of a SCADA system. The HMI is the unique graphical window presented before the operator in charge of the plant. The interface mimics the whole plant and its associated devices in a single computer window with accurate simulations. The HMI is linked with the SCADA computer units which are further linked with the actual devices in the plant, this allows to drive and represent the process such as alarm, operating pumps, compressors, fluid flows, and graphs on a single screen.

Context and Applications

This topic is widely used in many undergraduate and postgraduate degree courses of:

• Bachelors of Technology (Instrumentations Engineering)
• Bachelors of Technology (Electronics Engineering)
• Master of Technology (Control Systems)
• Master of Technology (Automation technology)

Practice Problems

Q1. What is the function of DDCR or sensors in a DDCS?

1.  Conversion of real-time signals to digital signals
2. Conversion of decimal to digital signals
3. Conversion of real-time to decimal signals
4. Conversion of digital to real-time signal

Answer: Option a

Explanation: The function of DDCR or sensors is to convert real-time signals acquired from field devices into digital signals, which can be processed by the DDCS's controller.

Q2. Which of the following is also known as the architecture or layout of DDCS?

1. Direct digital control mapping (DDCM)
2. Direct digital control and numerical control (DDCNC)
3. Direct digital control zonal mapping (DDCZ)
4. Direct digital control transmission (DDCT)

Answer: Option a

Explanation: Direct digital control mapping (DDCM) is also known as the architecture or layout of DDCS.

Q3. Which of the following is known as the brain of DDCS?

1. Direct digital control and numerical control (DDCNC)
2. Direct digital control zonal mapping (DDCZ)
3. Direct digital control microprocessor (DDCMP)
4. Direct digital control for rooftop units (DDCU)

Answer: Option c

Explanation: The DDCMP is also known as the brain of DDCS.

Q4. What is the full form of DDCVA?

1. Direct digital control and valve actuation
2. Direct digital control variable actuation
3. Direct digital control by vacuum actuation
4. Direct digital control for variable air volume

Answer: Option d

Explanation: The acronym of DDCVA is direct digital control for variable air volume.

Q5. What is the main component of SCADA?

1. HMI
2. Variable frequency drives (VFD)
3. DCS
4. Both a and c

Answer: Option a

Explanation: The human-machine interface or HMI is the main component of SCADA.