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Electrical Troubleshooting Quiz. August 14, 2012

Recently, the production department began complaining about random control problems

Recently, the production department began complaining about random control problems and, consequently, high rates of scrap. Furthermore, the sales department is complaining that the automated reports they receive show wildly different production levels from what actually happen.

Another tech tried to solve this problem, but it’s now turned over to you. Previous efforts included completely reloading the distributed control system (DCS), rebooting the computers, calibrating all the final control elements, calibrating all of the sensors, and doing complete loop checks on all of the instrumentation and control loops. Yet, the problem persists. What are your first steps?

It's nice that the tech ruled out those problems, but none of them can be a root cause. Your next steps are:

  • Review power quality logs. If you don't have power monitoring for the relevant feeder(s), use a portable power analyzer to look for transients and other random anomalies.
  • Visit the affected areas. Look for smart phones on tables, belt clips, and other places. These radio devices are ubiquitous today, and your system may not be sufficiently hardened to prevent interference.
  • Inspect the control cabinetsfor proper bonding, neutral connections, and green wire power "ground" connections. Deficiencies in such cabinets are common, and correcting them may also solve any radio issues.
  • Walk down each control loopand ensure conformance to IEEE Std 142 and the NEC Art. 250, Part V. The most common violation is a broken metallic bonding path.
  • Test the insulation integrity of all related conductors.
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