What SCADA Was Actually Designed For
SCADA (Supervisory Control and Data Acquisition) emerged in the 1970s and 1980s for large continuous process industries: chemical plants, utilities, water treatment, oil and gas pipelines. These facilities needed centralised visibility across thousands of I/O points, tight closed-loop control integrated with PLCs, and certified safety systems that could shut down processes in milliseconds.
The architecture reflects these origins: SCADA runs on dedicated HMI workstations, communicates with PLCs over proprietary fieldbus protocols (Modbus RTU, Profibus, DNP3), stores data in a dedicated historian database, and is configured - not programmed - using licensed software packages from Siemens, Rockwell, Wonderware (AVEVA), or Ignition.
This architecture delivers real value for its intended use case. For a 500-employee petrochemical plant with certified safety instrumented systems, SCADA is the right tool. For a 30-employee food processing facility trying to get temperature records out of its cold rooms, it is significant overkill.
The SCADA Cost Problem at Small Scale
SCADA costs accumulate at every layer. Software licensing for a mid-tier SCADA package runs R80,000–R500,000 depending on I/O point count and vendor. Hardware - industrial HMI panels, dedicated historian servers, licensed client workstations - adds another R50,000–R200,000. Integration engineering (configuring the PLC driver, building the HMI screens, historian configuration) requires specialist contractors who bill R1,200–R2,500 per hour.
The ongoing cost is equally significant: annual software maintenance and support (typically 18–22% of license cost), dedicated IT infrastructure for the historian server, and vendor lock-in that makes every future change an engineering engagement.
For a plant where the monitoring need is relatively simple - temperature in 8 locations, pressure on 4 pump circuits, motor run status for 12 motors - the SCADA cost model does not fit the problem.
What IIoT Delivers Differently
Industrial IoT monitoring systems built on commodity hardware (ESP32, STM32, Raspberry Pi) and open protocols (MQTT, HTTP, WebSockets) sidestep the licensing and proprietary infrastructure problem entirely. The hardware cost for a 20-point monitoring system is in the range of R8,000–R25,000 for field hardware - an order of magnitude below SCADA infrastructure.
IIoT systems are typically web-based: the dashboard runs in a browser on any device, including the operations manager's phone at 2am when an alert fires. There is no dedicated workstation, no client license, no VPN configuration required to view live data from outside the facility.
Because IIoT systems connect directly to sensors via their own field hardware - not through existing PLCs - they can be deployed at facilities that have no PLC infrastructure at all, or retrofitted alongside existing automation without modifying or interfacing with the existing control system.
Where SCADA Remains the Right Choice
IIoT monitoring systems are monitoring systems. They observe and report. SCADA systems, in their full implementation, can also control - they close the loop back to the PLC to adjust setpoints, start and stop equipment, and execute process changes from the central HMI.
If the facility requires: certified safety instrumented systems (SIL-rated shutdown logic), tight closed-loop control integrated with existing PLC infrastructure, full integration with an existing SCADA historian, or operator workstations with licensed control capabilities - then SCADA remains appropriate.
| Requirement | IIoT monitoring | SCADA |
|---|---|---|
| Real-time sensor visibility | ✓ | ✓ |
| Mobile / remote access | ✓ | Complex, often VPN-only |
| Retrofit without PLC | ✓ | ✗ |
| No software licensing | ✓ | ✗ |
| Closed-loop PLC control | ✗ | ✓ |
| SIL-certified safety logic | ✗ | ✓ |
| Historian integration | Partial | ✓ |
The Practical Decision Framework
For most small-to-medium South African facilities, the decision comes down to three questions: Do you need to control equipment from the monitoring interface (not just observe)? Do you have existing PLC infrastructure that the monitoring system must integrate tightly with? Do you have certified safety system requirements that mandate licensed software?
If the answer to all three is no, IIoT monitoring delivers the visibility you need at a fraction of the cost and in a fraction of the deployment time.
The most common outcome in practice: IIoT for monitoring and alerting alongside existing manual control - operators still start and stop equipment locally. This hybrid approach captures 80% of the monitoring value at 20% of the SCADA cost.
Getting the First System Right
Start with the highest-pain monitoring gap: the equipment or process where an undetected failure has the most expensive consequences. One pressure circuit, one cold room, one critical motor. Deploy, learn what the data tells you, and expand from there.
The incremental cost of adding a monitoring point to an existing IIoT system is low - one additional sensor, one firmware update. This is fundamentally different from SCADA, where adding a monitoring point means an I/O point license increment and an HMI screen change from the integration engineer.