Program Structure
Day 1: Relay Logic -- Understanding Hard-Wired Control by Building It
Students start from first principles and build progressively more complex control circuits by hand. Every concept is wired, tested, broken, and fixed before moving to the next.
Topics covered:
Motivation and scope: most control faults live in the wire, not the program. The control circuit world: 24VDC versus 120VAC. The 24VDC supply including sizing, derating, hold-up time, bus protection, and the case for UPS. Terminal discipline and best practices: screw versus spring clamp, ferrules, and color conventions. Relay anatomy covering coils, contacts, ratings, pilot duty versus power duty, and coil suppression. Relay logic fundamentals: the seal-in circuit, permissive logic, multiple outputs, and the forward/reverse interlock. Timer modes: on-delay, off-delay, one-shot, and timer cascade.
Lab 1: Terminal Reliability. Terminate, torque, loosen, retighten. Understand why terminal connections fail.
Lab 2: Relay Bench Familiarization. Identify contacts, coil ratings, and verify operation.
Lab 3: Progressive Relay Build. Wire the seal-in circuit, add permissive logic, build forward/reverse interlock.
Lab 4: Timer Wiring. All three modes plus cascade. Set, verify, fault, diagnose.
The day ends with a bridge setup: the relay logic students built becomes the foundation for Day 2, where half of it gets replaced with field devices.
Day 2: Field Devices -- Selection, Behavior, and Integration
Students take the working relay logic from Day 1 and integrate real field devices into the circuit. The day builds toward a full-circuit integration lab where students close the loop, verify operation, introduce a fault, and diagnose it.
Topics covered:
Proximity sensors: inductive versus capacitive, sensing distance, and target material effects. Photoelectric sensors: through-beam, retroreflective, and diffuse. Encoders: incremental versus absolute, resolution, and quadrature output. Pushbuttons, selector switches, and pilot devices including contact blocks and operator types. Contactors and full-voltage starters: ratings, utilization categories, and overload classes. Coil suppression in the output circuit: what happens without it and why it is never optional. NPN versus PNP, sourcing versus sinking: the logic of current flow. The 4 to 20mA loop: loop power, signal flow, and shield termination. Cable routing and separation: power versus control versus signal.
Lab 5: Sensor Identification and Bench Test. Identify the device, read the nameplate, determine output type, verify behavior against a live circuit.
Lab 6: Starter Wiring. Pushbutton to contactor to pilot light. Add overload relay. Trip and diagnose.
Lab 7: Full Circuit Integration. Connect a field device to the relay logic built on Day 1. Close the loop, verify operation, introduce a fault, diagnose it.
Closing session: Control circuit troubleshooting philosophy. Field device first, wiring second, card third, program last. The bridge: relay bank to PLC ladder. Every symbol mapped to what you built this week.