PLC Control Box

During my Fall Semester 2021 Co-op with Magnum Shielding Corp I had the opportunity to rebuild a control box for one of the production cells. I was tasked with researching the parts and pieces required, then the complete disassembly and reconstruction of the box. While the cell was offline, the old box was mapped, deconstructed, and rewired into the new enclosure. The task took just under two weeks and had zero errors.

The Original Box

This is the original box, or at least most of it. In the image on the left below the frame is a 12" square board with pneumatic components screwed to it. It's just hanging by the air hoses, and is also where the main building air is connected.

The original creator of the box had left no wiring diagrams or explanation of how it worked when they left the company. The only knowledge remaining was how it was intended to operate, or what buttons to push to get a desired output. It was also open to the environment, susceptible to water, and a general hazard if people stuck their fingers in it.

After spending a little time researching hardware and a properly sized fiberglass enclosure, the pieces were ordered. The production cell was scheduled to be taken offline at 9am the following Monday.

Disassembly and Diagrams

After taking over the conference room table and marking the external connections (to avoid bringing in all the machines as well), the long process of creating wiring diagrams began.

The obvious place to start was the pneumatics. That sub-system wasn't the most interconnected and only linked to a few locations. Getting rid of the large wood block was also nice. The whole process followed the same basic pattern:

Pick a component. If it has no identifying number, give it one
Draw every connection to that component, and the connected components
Remove those connections

Using this process it was only a matter of time before everything was mapped and disassembled.

Organization

With so many components, organization was critical to the success of the project. Components were kept in one corner, tools in another, a third was the main work area, and the fourth became the obligatory pile of scrap (much of which was reused).

Layout

The time finally came to reassemble the box into its new enclosure. On the left is an early image of this process. Each component is placed in a location that minimizes wire length, especially for wires that extend to outside the box. Relative to the original enclosure, the lower DIN rail is actually upside down so the wires from the DC transformer can insert directly into the components rather than wrap around to the top. The blue tape on the walls of the box indicate approximately where holes need to be drilled, though the exact sizes and locations were yet to be determined.

Wiring

By far the most time consuming aspect of reassembly. Wires of the correct color and gage were measured, cut, had new ends crimped on, and then installed. When this was done, it was time for the air subsystem. Pneumatic hose is a lot less flexible than wires, so there was a little trial and error to get lengths right and ensure the door would close properly. After solving that puzzle, the box was completed and ready for installation and testing.

Cutting, stripping, crimping, and installing wires

The pneumatic tubes installed where the door could still close

The front panel, with easy access to the regulators

Installation and Testing

Before the project can be done, the box must be installed and tested. Friday morning it was installed in the cell and the operator called over. After a few short tests we determined there were zero errors during the reconstruction process and everything was in good working order. Labels for exactly what the regulators controlled (with help from the diagrams) were added, among others. A solid wood base was created and everything was tightened down one last time.

Testing the first function of the box

Testing the second function of the box

The Finished Product

This is the finished box installed in the production cell with all applicable labels. Unfortunately, this new enclosure is only a temporary measure as the company is looking to upgrade the whole production line to be more automated in the next year or two. However, until that date, this new enclosure has everything put together the way it should have been done originally. It is also much more accessible, making it much easier to fix in the future should something go wrong.

Feel free to click or scroll through all the photos.

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