Forward/reverse conveyor

What you will build

Work order NP-2602. Northfield Packing, Transfer conveyor CV-04.

Northfield Packing (packaging) needs a controller program for Transfer conveyor CV-04. Run a conveyor both ways from two contactors that must never close together, with a dead time before the motor may be reversed.

A transfer conveyor on our packing line has to run both ways. Two contactors drive its motor: Fwd_K for forward and Rev_K for reverse. They swap two phases, so if both are ever on together we get a phase to phase short circuit; that must never happen, not even for one scan. Fwd_PB and Rev_PB are momentary push buttons, and Stop_PB is wired normally closed (1 is healthy, 0 is pressed). Pressing Fwd_PB runs the conveyor forward and pressing Rev_PB runs it in reverse; either direction keeps running after the button is released, until Stop is pressed. While the conveyor runs one way, the other direction's button does nothing: the operator stops first. The motor needs time to coast down before it is reversed, so the opposite direction must not start until ms have passed since the running contactor dropped out. A press during that time must not start the motor early. Whether a restart in the same direction also waits is up to you. If both buttons are pressed together, at most one direction may start.

What you will learn

• Electrical and software interlocks
• TON timers
• Seal-in circuits
• Reversing starters
• Read a short user requirement specification (URS) and turn it into ladder logic
• Prove your program against a numbered factory acceptance test (FAT)

How it goes

1. Read the work order and the URS.
2. Build the ladder program against the tag table.
3. Run the plant and watch it respond.
4. Run the FAT and fix whatever fails.

Tools

• Ladder editor in the browser

  Draw contacts, coils, timers and counters, then run the program.

• A working simulated plant

  Watch the machine respond as your logic runs.

• A tag table

  3 inputs and 2 outputs: Fwd_PB, Rev_PB, Stop_PB, Fwd_K, Rev_K.

• URS and FAT documents

  The paperwork a real project starts from, with numbered tests.

Questions

Is it free?

Yes. The lab is free to use with a free account. There is nothing to buy to open this scenario.

Do I need to install anything?

No. It runs in your browser with the ladder editor and a simulated plant.

What will I do in PLC-02 Forward/reverse conveyor?

You build and test a program, then check your work against an acceptance test.

How long does it take?

A first attempt takes about 60 minutes.

Do I need experience?

No. Each work order says what to do step by step, and hints are there if you get stuck.