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Maintenance
You and IR, Part 1
In the previous five issues, we discussed insulation resistance (IR) testing. However, there is more than one kind of IR.

This abbreviation also stands for infrared radiation, which forms the basis for infrared thermography. The word “thermography” is similar to the word “photography,” except we substitute thermo (meaning heat) for photo (meaning light). Thermography is basically a matter of working with pictures of heat.

In the early 1990s, thermography was expensive and cumbersome. Although moving the carts of equipment required for a single scan didn't take a village, it did take a crew. Few facilities could afford thermography for maintenance.

Today, there are light, handheld thermographic cameras. Technological advances have reduced prices and lowered the training requirements for effective use. Nevertheless, just adding infrared scans to your PM schedule doesn't provide you with an effective thermography program.

The deeper your understanding of how to correctly take and interpret those "heat pictures," the more effective your thermography work becomes. Learn more in the next issue of MRO Insider.

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Electrical Troubleshooting Quiz
The conveyor on a PLC-controlled packaging machine occasionally stops for no reason, and operators are unable to restart it. This problem has occurred on four occasions. Each time, the tech has gone through the PLC logic, found nothing wrong, and simply restarted it.

Is the process of just checking the control logic really solving this problem each time? Nobody can come up with a better explanation, yet nobody can say why this seems to work. How can you determine what's really going wrong?

Visit EC&M's Web site to see the answer.


Conquering PLC Gremlins
In our previous issue, we noted that, for PLC-controlled systems, problems rarely occur inside the PLC. However, what if:

1. You have the proper incoming signals for your control loop, and
2. You can simulate outputs at the field terminations and get the correct control action?

This means the problem is in the input module, PLC, or output module.

In the previous newsletter, we discussed how to use the divide-and-conquer method to troubleshoot a PLC system. Now, use this method to determine if the problem is in the I/O modules (the most likely place).

To read more on this story, visit EC&M's Web site.

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Operation
NEC in the Facility
How big do your feeder and branch conductors really need to be? You may be undersizing conductors by using the ampacity tables in Art. 315, if you ignore 90.1(B) and the FPN in 315(A)(1). That FPN says the tables don't consider voltage drop. As noted in 90.1(B), following NEC requirements makes installations essentially free from hazard but not necessarily efficient.

Voltage drop is just one issue to consider when designing for efficiency. For example, if the loads have low power factor, high harmonics, and/or high wave distortion, they'll draw more current to do the same work. You can correct power factor and harmonics only so much before further correction is impractical. Thus, conductors will carry some “bad power.”

To read more on this story, visit EC&M's Web site.


Safety
Each year, OSHA reports on the types of injuries that happen on the job. Every year, injuries from improper ladder use are high up on the list. Follow these general tips:

• Use only insulated (fiberglass) ladders.
• Before you use a ladder, inspect it. If it's damaged (e.g., bent rung), remove it from the work area immediately. Put an “Out of Service” or similar tag on it.
• Keep the area around the ladder clear of tools and materials.
• Ensure the ladder is level and standing on something that won't give way.
• Rather than carry tools when climbing a ladder, use a rope and bucket to raise and lower tools.
• Allow only one person at a time on a ladder.
• If you must work from a ladder, face the ladder when doing so. Also face the ladder when going up or down.
• Use ladders only for purposes they're designed for. Propping one end of a scaffolding board, for example, isn't such a purpose.