PLC Programming & Industrial Automation: Zero to Hero

This opening lesson introduces the Automatic Control System (ACS) & Programmable Logic Controller (PLC) online course, taught by Engineer Ahmed El Saadany. It explains how the course is organized into three sections:

1. Main components: what each part of an automatic control system does

2. Industrial control circuits: how control circuits work and how to read their schematic diagrams

3. Troubleshooting: tracing control voltage to find and fix common faults in ACS and PLC systems

By the end of the course, you will be able to read and follow control circuit schematics, troubleshoot real faults, and program a PLC for any control circuit.

A simple first look at the two ways to control a load. In the hard-wired version, a switch is wired directly to a lamp. In the PLC version, the switch goes to a PLC input and the lamp is driven by a PLC output. Animated simulations show a start/stop lamp circuit done the classic way, then the same job on a PLC without a timer and with an on-delay timer. Adding a time delay takes only a programming change, with no rewiring, which shows why PLCs replaced relay logic.

Key topics: control system concept · inputs and outputs · PLC wiring basics · first ladder rung · TON timer demo

A practical tour of every device in a motor control panel:

• Power supply, control voltage and the control transformer.

• MCCB: main protection for the motor feeder.

• MCB: trip curves B (3–5×), C (5–10×), D (10–20×), Z (2–3×) and K, plus single-, double- and three-pole types, with a demonstration video.

• Contactor: how it switches L1/L2/L3 to T1/T2/T3 when its coil goes from 0 to 220 VAC, and how to test one.

• Thermal overload relay.

• Three-phase induction motors: terminal box layout (U1/V1/W1, U2/V2/W2, PE) and how to check the windings with a multimeter.

Key topics: MCCB · MCB trip curves · fuses · contactors · overload relays · motor testing

Compares a personal computer with a PLC part by part. On the PC side are the motherboard, CPU, RAM, hard drive, power supply and fans. On the PLC side is a modular rack with power supply, CPU and I/O cards. A block diagram shows how a PLC is laid out: input sensing devices feed the input module, which passes through optical isolation to the CPU and its program and data memory. The CPU drives the output module, which runs the output loads, and a programming device connects to the CPU. The lecture explains why PLCs suit harsh industrial environments.

Key topics: PLC architecture · optical isolation · PLC vs PC · modular rack

Defines the PLC as a programmable device with three core jobs: Monitor, Record and Control. Animated examples show a PLC receiving start/stop push buttons and driving a contactor, a motor and a stack light. It logs time-stamped events, such as motor start, motor stop and a bearing temperature alarm with operator acknowledgement, and it trends process signals such as vibration.

Key topics: PLC definition · monitoring · event and alarm logging · trending · control

Explains the PLC scan cycle. The organizational block starts the cycle, then the PLC monitors cycle time, reads the input module, runs the user program, writes to the output module and handles other tasks, over and over. A timing diagram gives a 10 ms scan as an example: about 1 ms reading inputs, 8 ms running the program and 1 ms updating outputs. This explains why scan time matters in real-time control.

Key topics: scan cycle · organization block · input image and output image · scan time

A roadmap of the main PLC hardware blocks, each covered in its own lecture later:

• Power Supply

• CPU and Memory

• Digital Input modules

• Digital Output modules

• Analog Input modules

• Analog Output modules

Key topics: PLC hardware overview · module types

A detailed look at the PLC power supply module, the CPU and memory technology:

• RAM, SRAM vs DRAM: speed, refresh, cost, size, power use, and SRAM’s use as cache.

• ROM: permanent and non-volatile.

• PROM: can be programmed once.

• EPROM: erased with UV light and reprogrammable, holding data for 10+ years without power.

• EEPROM: erased and reprogrammed electrically.

The lecture explains where each type is used inside a PLC.

Key topics: PLC power supply · CPU · volatile vs non-volatile memory · RAM, ROM, PROM, EPROM, EEPROM

Covers digital input modules and the field devices wired to them. A 16-channel 24 VDC input card is shown with switches and sensors connected. Device types include push buttons, key switches, emergency stop mushroom buttons and limit switches. The lecture explains how a push button is built (button, threaded neck, base, NO/NC contact blocks) and the contact configurations: SPST, DPST, SPDT and DPDT, single break and double break.

Key topics: DI module wiring · push buttons · E-stops · key switches · limit switches · NO/NC contacts

Explains the difference between PNP (sourcing) and NPN (sinking) proximity and photoelectric sensors. It shows how each switches the load to +V or to 0 V, and how to wire 3-wire PNP and NPN sensors to sinking and sourcing PLC input cards. These wiring mistakes are among the most common in the field.

Key topics: PNP vs NPN · sourcing vs sinking · 3-wire sensor wiring

Covers digital output module technologies:

• Relay outputs.

• Solid-state transistor outputs.

• TRIAC outputs with optocoupler isolation, shown driving a relay coil and a lamp on AC.

It also shows the typical output devices: contactors, interposing relays, solenoid valves and stack lights. It discusses when to choose relay outputs and when to choose solid-state outputs.

Key topics: relay vs transistor vs TRIAC outputs · optocoupler isolation · output field devices

Introduces analog signals from transducers for flow, humidity, load cells, potentiometers, pressure, vibration and temperature. It covers the standard signal ranges: 4–20 mA, 0–1 V, 0–5 V, 0–10 V, 1–5 V, ±5 V and ±10 V. It traces the signal chain from the process through the sensor and transmitter into the analog input module. A worked scaling example converts 100–600 °C to 1–5 VDC and then to 0–4095 counts. The lecture ends with single-ended and differential wiring, using shielded twisted-pair cable.

Key topics: analog signals · 4–20 mA · transmitters · scaling to raw counts · single-ended vs differential

Explains how the PLC turns a digital value into a voltage or current that controls a process. The example is an analog output driving a transducer that sets the pressure of a hydraulic proportional valve, from 100 to 800 psi. Wiring diagrams show single-ended and differential analog outputs to transducers and output devices.

Key topics: analog output · digital-to-analog conversion · proportional control · AO wiring

An overview of the five standard PLC languages: Ladder Diagram (LD), Function Block Diagram (FBD), Instruction List (IL), Structured Text (ST) and Sequential Function Chart (SFC). Two comparison examples write the same logic in every language next to the equivalent electrical diagram:

• Series logic (AND): S1 and S2 drive P1 and P2.

• Parallel logic (OR): S1 or S2 drives P1 and P2.

This makes the differences between the languages easy to see.

Key topics: LD · FBD · IL · ST · SFC · series vs parallel logic

The first hands-on ladder lesson. It links physical wiring (push buttons and a limit switch on a 24 VDC input card, a pilot lamp on an output) to the four basic ladder instructions: NO contact, NC contact, coil and negated coil. Simulations show how NO and NC field switches change the state of each rung and output lamp. This explains the classic confusion between a field NC contact and a program NC contact.

Key topics: contacts and coils · NO/NC logic · negated coil · DI/DO in the program

Builds the AND, OR and XOR logic gates three ways each: as a truth table, as an equivalent electrical circuit and as a PLC ladder rung. It ends with a summary truth table for all the logic gates.

Key topics: binary logic · AND / OR / XOR · truth tables · gates in ladder

Covers the three main PLC timers with timing diagrams and ladder examples: on-delay (TON), off-delay (TOF) and pulse (TP). It explains preset, accumulated value and the enable and done bits. Then it covers counters: count-up (CTU), count-down (CTD) and up/down (CTUD), including the preset value, reset and practical counting uses.

Key topics: TON · TOF · TP · CTU · CTD · CTUD · preset and accumulated values