Design, Build With Trouble in Mind

Designers Can Provide Critical Information That Is Often Hard to Find, or Is Misleading

Jack ChopperBy Jack Chopper

Some efficiency experts argue that we spend too much time looking for things. They argue that by organizing, discarding unneeded clutter and categorizing what remains, the time we spend looking for things can be reduced significantly.

We can apply those same ideas to machine controls. With very little additional effort as designers, we can provide the critical information that is often so hard to find, or worse yet, is misleading or incomplete. Penalties for this lack of organization include mistakes during original construction and additional time required for commissioning and troubleshooting events. No big deal? Maybe so, but if we include damaged equipment in the list of penalties, most would agree that we need to look no further for incentive.

The points that follow can be done in addition to a minimum set of requirements as outlined in specifications. This additional information is intended to provide quick, on-the-spot reference for the individual responsible.

  • Cross-reference the high-target items, solenoid valves and motor starters, and show the drawing number and grid location on that cross-reference. For example, provide a chart that shows the drawing location for the coils for every relay used in the panel. When troubleshooting, the technician won't have to scan drawings incessantly. Ditto that for analog sources, proximity switches and motor brakes. Provide this cross-reference for every type of device, and list the components in alphabetical order.
  • Mount the devices most likely to require interaction while troubleshooting in a convenient location. Resist the urge to mount the PLC at the very top of the enclosure, if that puts it out of the normal field of view for the average person.
  • Label the wireway covers (on the back of the cover), especially if several different lengths are used. It will encourage technicians to re-install them after removal for a troubleshooting event. Show the locations on the layout drawing to save time when reinstalling.
  • Consider printing drawings on adhesive-backed stock and affixing them to the inside of the control cabinet doors. This ensures a set of drawings always will be in the cabinet. A duplicate (mobile) set can reside in the print pocket.
  • Keep similar things together, and use meaningful names to identify those components. The names "VFD-1" and "VFD-2" are definitive, but I often witness technicians referencing drawings several times to make sure they are testing the correct components. Instead, try "VFD-1, Infeed Conveyor" or "VFD-2, Outfeed Conveyor" or whatever applies to your particular situation.
  • When similar components are used more than once, locate them in the panel in the same order as they serve in machine operation. This helps reduce confusion and, as a result, reduces troubleshooting time.
  • Neatness counts. Provide sufficient space to make connections neatly and properly. Lack of space, especially near terminal strips, encourages less-than-optimal connections. This ultimately invites intermittent, hard-to-find problems.
  • Similarly, arrange terminal connections in logically sensible groups. Keep the PLC inputs together and keep them in order. Ditto that for PLC outputs, safety interlocks and analog test points. Clearly mark terminal locations that serve as test or calibration points, referencing the appropriate documentation pages so there's no question regarding safe and appropriate test procedures.
  • Show 2-D face views for components with multiple connectors. Bubble the locations, clearly defining each connector and its purpose. Use this same face view for line diagrams, so the troubleshooter won't need to search and question whether the proper connector is being tested. It also will help the shop when it builds the panel.
  • Consider installing some lighting in every control panel you build. Good lighting encourages neatness and saves time while servicing the panel.

A well-lit, well-marked, well-documented control panel, although perhaps the most inviting, is the one that technicians will spend the least time inside. Ultimately, that means increased uptime for your machine.
Jack Chopper is chief electrical engineer at Filamatic (www.filamatic.com) in Baltimore.

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