PLC Programming from Zero: The Visual Guide to Ladder Logic

Unit 1: Meet the PLC

1. What a PLC does: Sense, decide, and control
2. Find the PLC in a generic control panel
3. Before you touch a panel: Lockout/tagout and electrical safe work practices
4. Follow the scan: Read inputs, execute logic, update outputs
5. Scan timing, startup, and I/O updates: Check your controller's behavior
6. Tags, addresses, and data types: Give each signal a clear name
7. Your first simulator project: Create, run, stop, and save

Unit 2: Connect Inputs and Outputs

1. Trace a 24 VDC control circuit and its return path
2. Discrete inputs: Push buttons, limit switches, and sensors
3. Normally open and normally closed describe physical contacts
4. Sinking and sourcing: Follow conventional current
5. PNP and NPN sensors: Match the sensor to the input module
6. Relay and transistor outputs: Match the load and check the datasheet
7. Contactors, interposing relays, and inductive load suppression
8. Build an I/O map: Device, terminal, tag, and expected state

Unit 3: Read and Build Ladder Logic

1. Read IEC 61131-3 ladder: Rails, rungs, contacts, and coils
2. Test a Boolean tag: Contact instructions do not show physical wiring
3. Series contacts: Require every condition with AND
4. Parallel branches: Accept alternative conditions with OR
5. Output coils: Follow rung results and avoid duplicate writers
6. Internal bits and rung order: Trace changes within a scan
7. Set and reset latches: Define priority and check power-up retention
8. Rising and falling edges: Turn a signal change into a single event

Unit 4: Add Time, Counts, and Decisions

1. TON: Delay an action while the input stays true
2. TOF: Keep an output true after the input goes false
3. Retentive timing: RTO-style behavior, reset, and platform differences
4. Read timing charts: Input, elapsed time, and timer output
5. Count up and down: Events, limits, and reset conditions
6. Count one part once: Scan edges, sensor chatter, and missed pulses
7. Compare values: Equal, greater than, less than, and within range
8. Move and calculate values: Types, rounding, overflow, and division checks

Unit 5: Control Motors and Sequences

1. Build a motor start/stop seal-in circuit: Wiring, ladder, and scan trace
2. Overloads and contactor feedback: Separate command from actual state
3. Emergency stops and safety circuits: Understand the limits of ordinary PLC logic
4. Forward and reverse: Understand electrical, mechanical, and logic interlocks
5. Plan a sequence: Steps, transitions, and output conditions
6. Build a state-based sequence with timeouts and fault handling
7. Stop, reset, and restart: Prevent an unintended automatic restart

Unit 6: Use Analog Signals and HMIs

1. Follow a 4–20 mA loop: Transmitter, supply, and analog input
2. Scale raw input data into engineering units
3. Handle noisy signals, out-of-range readings, and loop faults
4. Read an HMI screen: Tags, values, status, and communication loss
5. HMI commands and setpoints: Validate requests in the PLC
6. Alarms and trends: Separate acknowledgment, reset, and fault clearance

Unit 7: Troubleshoot and Practice

1. Read and document a program: Cross-references, comments, backups, and revisions
2. Monitor online: Confirm the controller, project version, and live tag states
3. Trace a fault from symptom to signal: Diagnose in simulation without forces
4. Conveyor simulator lab: Part counting, jam timeout, worked solution, and fault tests
5. Tank fill simulator lab: Level control, fill timeout, worked solution, and fault tests
6. Traffic light simulator lab: Timed states, conflict checks, and worked solution

Glossary: Shop terms and instruction names

Appendix: 33 wiring diagrams, drawn to spec