Electrical Troubleshooting Quiz

A complex gearbox system has a left and a right main drive gear. Because of an outdated controller, every six months or so one of these gears gets overloaded and strips out. It takes three hours to change the gear, but only 25 minutes to pull and replace the gearbox. Downtime runs about $400,000 an hour in revenue. You are fairly sure that a more responsive controller would keep the left and right side loads balanced, thus preventing the damage. But the production superintendent won’t sign off on that or a spare assembly.

To solve this problem, what should you do?

This is a twist on our usual quiz concept. In this case, you're troubleshooting the organization rather than the equipment. If you lobby for a replacement controller, you weaken your credibility by also arguing for a post-incident solution. So focus on the preventive. Be more than fairly sure about that controller. The drive gear overload happens only once every six months, so measuring the unbalances is problematic. Because of the failures, you can assume these occur.

You need the controller to limit output whenever the delta between the two output channels is greater than some number. Find out from the gearbox manufacturer what that number is. If the controller can't sense and control that variable, you'll need to replace it with one that can. This is the technical basis for your case for a replacement controller; cost basis is controller cost versus downtime cost.

Finally, do a complete control loop tuning so your repair does what it's intended to do. Leave nothing to chance.

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