What is the Difference Between PLC and DDC [Updated 2022]

Many automated plant control systems rely on programable logic controllers (PLCs) or direct digital controls (DDCs) to perform as required.

For example, building control systems use DDCs or PLCs to control the output of HVAC systems in commercial buildings.

While both systems collect data from sensors and write outputs, there are some differences in how they perform.

What is a Programable Logic Controller?

Table of Contents

PLCs are hardware devices that automate machine functions or work according to pre-programmed actions like production lines. A PLC has a programmable memory where store instructions. PLCs are highly customizable and controllable. They are widely use in Industry 4.0 and Internet of Things applications in manufacturing, engineering, HVAC, and oil and gas. Data can transfer using standard messaging protocols like SQL to connect to databases and MQTT to connect to the cloud. PLCs are widely used in traffic control systems, lifts, burglar alarms, automatic parking systems, automatic tank filling systems, and home automation.

What is Direct Digital Control?

DDC allows for centralized control of a building’s systems. DDCs are commonly used in HVAC, lighting, alarm systems, and other building automation systems. DDC systems can help buildings run more smoothly. Building operators can pre-program DDCs to meet specific criteria, increasing efficiency while maintaining occupant comfort.

DDC technology enables remote facility control. DDC provides real-time data allows facility managers to adjust HVAC settings remotely from any internet-connected location. Actualized equipment failure and service interruption notifications allow for faster resolution of minor issues before they become major. Building managers no longer need to visit the site to start repairs physically.

What is the Difference Between PLCs and DDCs?

PLCs have a longer MTBF than DDCs, making them ideal for 24/7 or mission-critical operations. Moreover, the ruggedness of these devices makes them a better match for heavy industrial environments, such as manufacturing facilities. PLCs can also reduce downtime and human safety risks, lowering the total cost of ownership.

However, DDC controls are better suitable to automate non-mission-critical facilities with shorter MTBF. DDC monitoring and control systems are well suitable for monitoring and controlling non-critical processes in commercial environments such as office buildings, shopping malls, and light industries. DDCs should not be used in high-availability environments.

Unlike a PLC, it cannot swap DDC components without first powering down the controller, which results in downtime. In addition, even though they can integrate with many APIs, DDC systems do not provide open-source resources.

You can modify open-source code to make PLCs that meet your exact requirements. PLCs with more customization and flexibility increase overall building efficiency and usability.

PLCs outperform DDC controls in terms of accuracy, speed, and reliability. It can provide the industrial hardening that DDCs cannot. DDCs have fewer safety features. Less expensive than PLCs, DDC systems are.

Check out our low-cost programmable logic controllers and other industrial computing devices. Other types exist besides mounting, programming interfaces, languages, and networks.

Commercial Vs Industrial

PLCs are generally considered better for high-performance situations because of their extended mean-time-between-failure (MTBF) over DDC systems. In addition to emergency power supply systems, PLCs are a popular choice for environments requiring 24/7 performance (EPSS).

DDC controls are typically use in commercial, i.e., non-mission-critical facilities, where their MTBF is generally acceptable.

For mission-critical facilities like hospitals, the associated costs of unscheduled downtime or human life can lower PLC’s total cost of ownership (TCO).

Because of their ruggedness, PLCs are use in mission-critical environments such as critical care, data centers, and manufacturing.

These systems are ideal for non-mission-critical commercial settings like office buildings, malls, and other non-critical settings.