System Build, Wiring, and PLC/HMI Programming

System Build, Wiring, and PLC/HMI Programming

This lab brings every skill from the program together into one working system. You will mount hardware, pull and label wire, write production-quality PLC code in two IEC 61131-3 languages, configure an HMI, and commission the system using the same documented process used on real industrial floors.

Safety Before You Touch Anything

No energized work begins until all lockout/tagout (LOTO) requirements under OSHA 29 CFR 1910.147 are met and documented. Each team member applies a personal padlock to the hasp at the energy-isolation point. Tags are filled out completely — no blank fields. The group's LOTO log is signed before the instructor witnesses first power-up.

Before energizing, perform a pre-energization checklist:

• Continuity check on every home run to confirm correct termination.
• Spot-check insulation resistance with a megohmmeter between conductors and between phase and ground.
• Visually verify every wire is landed on the terminal called out in the schematic.
• Any deviation from the approved schematic must be redlined on the drawing — pencil changes that are not documented are wiring errors, not corrections.

Machine guarding follows OSHA 1910.212, and robot safeguarding follows ANSI/RIA R15.06 / ISO 10218. Guards must be physically installed and verified before the robot or any actuator is allowed to move under power. Electrical safety during wiring follows NFPA 70E: verify absence of voltage at the work point with a calibrated meter, even after LOTO is applied — test before you touch. Refer to NFPA 79 for acceptable wire types, routing, and marking requirements for industrial machinery.

Mounting and Wiring the Panel

Mount all components — PLC, I/O modules, power supply, terminal blocks, and drives — on DIN rail inside the enclosure or on the work panel per the approved layout drawing. Route conductors in wire duct; keep AC power wiring separated from low-voltage DC signal wiring to reduce noise. Strip conductors to the depth shown on the terminal data sheet, crimp a wire ferrule on each stranded end before landing it in a cage-clamp or screw terminal, and pull-test each termination. Label both ends of every conductor with the wire number shown on the schematic. A wire with one unlabeled end is an unfinished wire.

Sensor wiring follows the color code on the device data sheet. For a 4–20 mA two-wire loop-powered transmitter, the PLC analog input module supplies 24 V DC; the transmitter sits in series and modulates current. For a 0–10 V device, the module provides the reference voltage and reads the signal lead directly. Land shield drain wires at one end only — typically at the panel ground bus — to prevent ground loops.

Writing the PLC Program

The program must use at least two IEC 61131-3 languages. Use ladder diagram (LD) for the main sequential logic — conveyor start/stop, robot cell enable, safety interlock rungs — because LD is easy to trace during I/O checkout. Add at least one routine in function block diagram (FBD) or structured text (ST) for analog scaling, timer/counter logic, or drive speed reference, where those language styles offer clarity or reuse.

Analog scaling (4–20 mA example): A pressure transducer with a range of 0–150 psi outputs 4 mA at 0 psi and 20 mA at 150 psi. The PLC analog input converts the signal to a raw integer — confirm the module's count range from the hardware manual (commonly 0–32767 or 6242–31208 for 4–20 mA spans). Use a linear scaling instruction or write a ST expression:

```

Eng_Value := ((Raw - Raw_Min) / (Raw_Max - Raw_Min)) * (EU_Max - EU_Min) + EU_Min;

```

Tag every variable with a descriptive name and a comment. Unnamed tags are a maintenance hazard.

Configure the industrial network (EtherNet/IP, PROFINET, or Modbus per lab availability) to connect the PLC to the robot controller or variable-frequency drive. In the software, add the target device by its IP address, set the correct I/O data sizes, and verify the connection status tag goes to "Connected" before forcing any outputs. Map robot I/O registers to PLC tags in the network configuration table and record the mapping in the documentation package.

Configuring the HMI

The HMI must include at minimum:

1. A Run / Stop / Reset control screen with hardwired-style button objects linked to PLC output coils.

2. A real-time numeric display of at least one analog engineering-unit value (pressure, temperature, flow, or position).

3. A fault indicator for each major alarm, color-coded (green = normal, red = fault) and linked to the corresponding PLC alarm bit.

4. A manual jog screen for maintenance mode that is only accessible when the physical key-switch or software mode tag is in Manual — never allow jog commands when the system is in Auto.

Set the HMI polling rate fast enough to show process changes in real time, but do not poll faster than the network and PLC scan can support — 100–500 ms is typical for status displays.

I/O Checkout and Commissioning

Conduct the structured I/O checkout with a partner: one person forces each input or output in the PLC software; the other physically confirms the field device responds correctly. Log every point in the commissioning sheet as Pass or Fail. A failed point is corrected and retested before you move on — do not skip and come back. The completed, signed commissioning sheet becomes part of the project documentation package alongside the redlined schematic, the tag database export, and the HMI screen printouts.

The instructor witnesses the live checkout and signs the sheet. Zero unresolved wiring errors, zero missing guards, and 100% of I/O points verified are the pass criteria. Anything less is corrected in the same session.