What’s the difference between PLC and DDC?

Programmable logic controllers (PLCs) and direct digital controls (DDCs) are integral in many automated plant and process control systems, making them function the way you want them to.

PLCs and DDCs are similar in that they both make decisions based on data gathered from sensors to write outputs. However, PLCs often hold the edge over DDCs because they are quicker, more reliable and more accurate in completing their activities.

They also tend to be better suited to more sophisticated automated systems and can be adapted to provide the level of industrial hardening required in mission-critical environments.

Here, we take a look at the differences between PLCs and DDCs and some of the key things you need to consider before choosing which to use…

What are PLCs and DDCs?

A PLC is a hardware device with a dedicated internal CPU and operating system. They are widely used in industrial and manufacturing settings to automate machine functions, processes or production lines.

PLCs read and process data collected from sensors placed across an industrial process. They use that data to trigger actions based on a pre-programmed framework of activities.

PLCs are highly customisable and can be adapted to provide an automated control solution for many purposes. They are used widely in Industry 4.0 and Internet of Things (IoT) applications across various sectors, including manufacturing & engineering, HVAC, oil & gas.

They can communicate data using standard messaging protocols, including SQL when connecting to databases and MQTT when communicating with the cloud.

A DDC, meanwhile, is a control process in which a computer acts as a controller. DDCs continually monitor sensor information and record it in an internal database. They then automatically produce corrective output commands in response to changing control conditions.

DDCs provide a similar function to more traditional control systems, but produce quicker, more accurate corrective outputs. They also enable remote control monitoring.

Because DDCs provide real-time data, operators can adjust their settings from any internet-connected device. Real-time system interruption or service failure alerts allow for quicker response, meaning minor running issues can be resolved remotely before they become significant maintenance issues.

Many automated control systems use DDCs to read and process sensor data and control outputs, and they can be implemented on a PLC, a distributed network or a standalone computer.

While PLC and DDC-based systems provide some common functions, their unique differences make each a better pick for specific jobs.

PLC or DDC – which is best?

When it comes to deciding whether a PLC or a DDC is the best choice solution, there are many things to consider. Often, though, the best way forward will boil down to what you want your control system to do and the environment you’ll be using it in.

PLCs are often the best choice for high performance, 24/7 365 or mission-critical operations because they offer an extended ‘mean time between failure’ (MTBF) when compared with DDC-based systems.

They are also usually more robust than DDCs, with their ruggedness being better suited to heavy industrial environments and manufacturing facilities.

And because PLCs can help reduce the costs associated with unscheduled downtime and risk to human life, this can also bring down their total cost of ownership.

On the other hand, DDC controls are more suited to automating non-mission-critical facilities, where a shorter MTBF is acceptable. Commercial environments like office buildings, shopping centres, light industrial and non-critical processes are well-suited for DDC-based monitoring and control systems.

DDCs aren’t really suitable for high availability environments. You can’t ‘hot’ swap DDC components without first powering down the controller, resulting in system downtime, whereas you can with a PLC.

And while most DDC systems can easily integrate with many application programming interfaces (APIs), they don’t offer open-source resources.

PLCs are much more flexible and adaptable. Many offer open-source coding options to allow users to customise their control outputs based on actual need rather than estimations of that need. This allows for additional usability and plays a vital role in enhancing overall process efficiency.

So, in general, PLCs are a better choice than DDC controls in high-availability, high-performance environments.

While DDC-based systems are usually cheaper than PLCs, more low-cost PLC solutions are available than ever before, with innovation continuing to drive the market and make PLC systems more accessible.

How can Banelec help?

Banelec is a world leader in creating electrical control solutions.
We’ve integrated PLCs and robotics into electrical control systems for some of the world’s biggest manufacturing brands.

Our PLC engineers have the knowledge and capability to program numerous SCADA, HMI or PLC systems, including Siemens, Allen Bradley, Mitsubishi, Schneider and many others.

We’ll work with you to assess what you need from your system and the technology required to achieve it.

Our automation services include complete systems, electrical controls, robotics and conveyor controls. Whatever you do, if you want to do it better, get in touch.