PLC and SCADA Training Together: Why the Combination Matters and How to Learn Both Free

PLC SCADA training teaches the two halves of most automation projects together: the PLC program that controls the machine, and the SCADA system that lets operators watch and command it. Learning both matters because the difficult problems sit at the interface between them. You can learn both free, using vendor trial software and simulators instead of hardware.

In this lesson by Jitendra Anne, PLC, DCS and SCADA are compared side by side. It is used in the opening module of the free ABB System 800xA DCS course, where learners place a DCS against a PLC-plus-SCADA design. Watch it for the big picture, then read on for how the two halves meet in practice.

Who does what

The division of work between PLC and SCADA is simple to state and easy to blur:

• The PLC controls. Interlocks, sequences, timers, PID loops and everything the plant needs to stay safe and running.
• SCADA supervises. Screens, alarms, history, trends, reports and the setpoints and commands operators send.

A useful test: if the SCADA server fails, does the plant stay safe and carry on (or stop cleanly)? If the answer depends on a SCADA script, logic is in the wrong place.

Why employers want both

Automation teams are often small. The engineer who writes the PLC program is frequently the one who builds the screens, and on site the same person commissions both. Fault finding crosses the boundary all the time: the screen shows a pump running, the pump is not running, and the answer could be in the PLC logic, the tag mapping, the driver or the screen. Someone who can read both sides finds it in minutes; someone who knows only one side has to wait for a colleague.

There is a second reason. SCADA work teaches you what operators need to see, which makes you write PLC code that is easier to supervise: clear status bits, fault codes and modes instead of hidden internal states.

The interface is where projects go wrong

Most PLC and SCADA problems come from the handful of tags that pass between them. These rules prevent the common ones:

• Pulsed commands. If SCADA holds a Start bit on and the network drops, the command can stay set. Let SCADA set a command bit and have the PLC act on it and reset it.
• Clamped setpoints. Limit setpoints in the PLC as well as on the screen, so a typing mistake or a script cannot push a value outside the safe range.
• Heartbeat. A counter or toggling bit in each direction lets the PLC know SCADA is alive, and lets SCADA show stale data as stale.
• Status from feedback. Show a motor as running from its contactor feedback or drive status, not from the command that was sent.

Faults that cross the boundary

These are the faults you will meet in your first months of commissioning, and each one needs both skills to find:

1. The screen shows a value that never changes. The tag may point at the wrong address, the driver may have lost the connection and be showing the last good value, or the PLC may not be writing that tag at all. Check the tag quality first, then the PLC program's cross-references.
2. A button does nothing. The command reaches the PLC, but an interlock in the program blocks it, and nothing on the screen says why. The fix is on both sides: a status or permissive bit in the PLC and an indicator on the screen.
3. Values are ten or a hundred times out. Scaling was done twice, once in the PLC and once in SCADA, or not at all. Decide where scaling happens and write it down.
4. An alarm floods every morning. A limit set too close to normal operation, or an alarm on a normal state such as a pump stopped by its sequence. Fix it in the alarm configuration and, where the logic is wrong, in the PLC.

Each of these takes minutes when one person can look at the program and the screen together, which is why commissioning engineers are expected to read both.

What a combined course should cover

On the PLC side: hardware configuration, ladder and structured text, timers and counters, analog scaling, function blocks, and a small sequence. On the SCADA side: tags and drivers, screens and navigation, alarms, history and trends, users and security. Between them: industrial Ethernet, Modbus TCP and OPC UA, tag naming and interface blocks, plus the network segmentation that NIST's OT security guide (SP 800-82 Rev. 3) describes. Our 12-week free automation curriculum puts these in order across several courses.

One project that proves both

Employers ask to see what you have built. A single small project covering both halves is worth more than two unrelated exercises:

A tank fill station or a short conveyor with a reject gate is enough. Keep the functional description to one page, keep the I/O list honest, and record a two-minute screen video of the running system, including one alarm being raised and acknowledged.

A free PLC SCADA training route

1. PLC: Siemens TIA Portal, from zero to a simulated S7-1200 with an HMI. The free PLC training page lists other brands.
2. Networks: Industrial Communication, for Modbus, PROFINET and OPC UA.
3. SCADA: Ignition SCADA, which connects to almost any PLC, or Siemens WinCC SCADA if you are targeting Siemens plants. For practice at home, Inductive Automation offers Ignition Maker Edition free for personal, non-commercial use. Our free SCADA courses comparison covers the other platforms and the vendors' own free training, and the SCADA training guide explains the architecture and protocols in more depth. If SCADA is the job you want, how to become a SCADA engineer sets out the skills in order.

The PLC foundations path and the SCADA specialist path group the courses for each half. Hands-on time with real hardware is still worth arranging later, through an employer, an apprenticeship or a local technical college.

What it costs

Every course is free in full: credited video lessons from independent YouTube creators, written notes, a practice task per module and one 15-question final assessment (60% to pass, three attempts, then a 24-hour wait and a fresh paper). Create a free account so progress is saved. No card.

The optional EDWartens Certificate of Completion is a small one-off fee per course: US$8.99 for beginner courses such as Siemens TIA Portal and Ignition, and a little more for intermediate courses such as Industrial Communication and WinCC SCADA. Each certificate has a code anyone can check at edwartens.com/verification. None is a vendor certification or an accredited qualification.

Take the free course

Free

PLC programming · Beginner · Free

Siemens TIA Portal

Free

SCADA · Beginner · Free

Ignition SCADA by Inductive Automation

Free

Industrial networks · Intermediate · Free

Industrial Communication: Serial, Fieldbus, Ethernet, Modbus, PROFINET and OPC UA

Free

SCADA · Intermediate · Free

Siemens WinCC SCADA: V7, Unified and Advanced