Supervisory control and data acquisition (SCADA) and the distributed control system (DCS) are two modern standards widely employed to control industrial machines electronically. Although they share many similarities, you’ll find that SCADA is used more often in discrete manufacturing and may be spread over wide geographic regions, whereas DCS works best on a common local network where control is continuous and tightly managed.
TL;DR (Too Long; Didn't Read)
With SCADA, the emphasis is on data-gathering and analysis from industrial operations; staff may oversee the system remotely at a separate location. DCS is geared towards real-time control of continuous manufacturing processes on a tightly-managed local data network.
Industrial Processes and Electronic Controls
Most industrial systems including manufacturing, chemical processing and power generation have been under electronic control for several decades. Specialized computers and programmable electronic modules monitor and adjust machinery and processes in real time, and allow supervision and control from remote locations. The advent of data networks and the internet made communication between manufacturing systems and people faster and easier.
In the Loop
The control loop is a key concept for industrial systems such as SCADA and DCS. An electronic module, such as a temperature sensor, monitors a machine or process. The module sends information over a network to a control system, which automatically adjusts the process. If the machine becomes too hot, for example, the control system makes adjustments to cool it off. The actions of sensing, decision-making and adjustment form a continuous loop of control that may or may not involve a person, though people are involved in scheduling and overall management.
DCS in a Nutshell
In DCS, many electronic control units are connected together in a data network, but no one unit plays a central role. This allows the whole system to keep working if trouble develops in one part. DCS is typically focused on the localized control of machinery in a plant or building. Though managed by people, the computerized automation in the DCS does most of the low-level work.
SCADA – A Bird’s Eye View
SCADA, like DCS, is a computerized system that includes sensors, control units and displays. As its name implies, data acquisition and the electronic recording and reporting of system conditions play a strong role in SCADA. It may entail a combination of display panels near the equipment and remote monitoring via the internet. In addition to real-time displays, the system may save information in a database for long-term analysis. SCADA includes alarm settings to automatically alert operations staff; this helps people manage emergencies when system conditions fall outside normal limits.
Many electronic hardware and software vendors offer products that work with the DCS and SCADA standards; no one company owns the rules by which these systems work. Control systems made by one vendor work with sensors made by another, allowing the end user to custom tailor a solution that fits their own needs.
Difference Between SCADA and DCS
DCS and SCADA technologies have a lot of overlap in how they work; differences largely lie in who uses them and how they’re used. Discrete manufacturers – companies that produce individual items such as auto parts, consumer electronics and furniture – tend to go with SCADA-type systems. Large-scale heating and air conditioning systems also use SCADA. DCS typically finds favor with continuous, tightly-controlled processes such as water treatment, electric power generation, refining and food processing.
Difference Between DCS and PLC
A programmable logic controller (PLC) is a device used to control equipment. You can program it to follow simple rules to automatically adjust industrial equipment based on sensor data. In this sense, it’s a small standalone version of a DCS, much like the relationship between a solo musician and an orchestra.
Distinguish Between SCADA and DCS
SCADA and DCS evolved from a need to automatically manage large, complex industrial systems safely and efficiently. Both are vendor-independent standards that entail the use of specialized electronic measuring and control devices, computers and data networks including the internet. SCADA emphasizes reporting and analysis of data gathered during industrial operations; DCS is geared towards real-time monitoring and control of continuous processes.
- Pipes and tubes and chimney at a power plant image by Andrei Merkulov from Fotolia.com