The company I was working for had moved into a new building. After moving the machine tools in, it was taking quite a while to get everything working correctly.
After several weeks it seemed like I had the computerized machines functioning properly again. Then one of the older machines started shutting itself down every day at 4:15 p.m. It seemed like one of the four power supplies in the electrical cabinet must be shutting down momentarily, but every day when the operator would notify me, I would check, and all the supplies seemed to be working fine. The machine would then run without a problem for the next 10 hours during the night shift.
Nothing different was happening in the plant at 4:15 p.m. to cause the problem. For several days at 4:00 p.m. I went out to the machine and hooked up several meters to watch the four power supply outputs. I would watch them until 5:00 p.m., and everything was fine and the machine ran without a problem the rest of the night.
Then one day I didn't go out to watch and around 4:15 p.m. the machine shut down. As a last resort, I ran wires from the power supplies to outside the cabinet so I could watch without opening the doors. As I checked throughout the next day, one of the supplies started putting out less voltage around 4:00 p.m.
Sure enough at around 4:15 p.m. the supply shut down, until I opened the cabinet door to look, which must have let the built up heat out of the cabinet, causing the supply to spring back to life. The reason the night shift didn't have a problem is because I would vent the cabinet at 4:15 p.m. when I checked things out and then the plant would be cooler at night, so the heat didn't build up. I ended up replacing that power supply. We never had that problem again.
Steve Araujo spent almost 30 years in machining, as a manufacturing engineer doing machine repair, CNC programming, job planning and layout, along with designing and building specialized equipment, working mostly with computerized machine tools. He is presently a design engineer for a company that makes hermetically sealed electrical connectors.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.