5 Mistakes I Made with Industrial Sensors and Testers (And What I Learned)

Why I Started Keeping a Mistake Log

I'm a maintenance engineer handling industrial automation orders for about six years now. I've personally made (and documented) 18 significant mistakes, totaling roughly $8,400 in wasted budget and lost production time. Now I maintain our team's checklist to prevent others from repeating my errors.

This article covers five of the most embarrassing—and expensive—lessons. Some involve SICK components (yes, the brand, not the illness), others involve common test equipment. If you work with sensors, voltage testers, or insulation testers, you'll probably recognize at least one of these.

Mistake #1: Confusing SICK Encoder Models (DBS60E vs DBS60)

In September 2022, I ordered 12 SICK DBS60E incremental encoders for a conveyor line. The specs looked right: 1024 ppr, 10–30 VDC, IP67. I checked the datasheet, approved the PO—$1,850 total.

They arrived. The shaft diameter was 12 mm—our application needed 14 mm. The DBS60E comes with a 12 mm solid shaft; the DBS60 (without 'E') offers a 14 mm shaft option. I had misread the suffix. That error cost $1,850 in redo plus a 2-week delay because of backorder on the correct model.

Lesson: Always verify shaft size, connection type, and mechanical interface against the actual mounting. Datasheets list options—don't assume the default fits.

Mistake #2: Treating 'SICK' Like a Fever Thermometer (It's Not)

When a new tech heard I worked with SICK sensors, he asked, "Oh, do you also use SICK fever thermometers?" No. SICK is a German industrial automation company—they make photoelectric sensors, encoders, flow meters, and safety devices. They do not make medical thermometers.

But the keyword confusion is real. I've seen articles ranking "sick thermometer fever temperature"—that's a total misdirection. If you're looking for industrial temperature measurement, SICK offers non-contact infrared temperature sensors (e.g., the TBS series) for process monitoring, not for human fever screening. Don't confuse the brand with a symptom.

Mistake #3: Using the Wrong Voltage Tester (2AC Alert)

I once grabbed a Fluke 2AC non-contact voltage tester before troubleshooting a 480 V motor starter. It beeped when near the wires—good, said power was present. But the 2AC has a detection range of 90–1000 V AC. It won't reliably detect DC voltage or low voltage (like 24 V DC control circuits).

I assumed the 2AC would catch everything. It didn't. I got a mild shock from a live 24 V DC terminal because the 2AC is AC-only. That mistake cost $0 in direct repair but $450 in lost credibility when the electrician had to rescue me.

Lesson: Keep a multimeter handy for DC circuits. The 2AC Alert is great for quick AC checks, but always read the fine print on its detection limits.

Mistake #4: How Does a Megger Insulation Tester Work? (I Learned the Hard Way)

During a preventive maintenance check in 2021, I used a Fluke 1507 insulation tester (megger) on a motor winding without first disconnecting the VFD drive. The megger applies a high DC voltage—500 V, 1000 V, up to 2500 V—to measure insulation resistance. Standard test voltage for motor windings is 500 V or 1000 V, depending on motor rating.

I selected 1000 V and pressed test. The megger output fried the input filter capacitors in the VFD. The repair cost $2,300 plus 8 hours downtime.

Here's how a megger works: it applies a known DC voltage between the conductor and ground (or between phases) and measures the current leakage. Insulation resistance (MΩ) = voltage ÷ leakage current. Good insulation shows >1 MΩ per kV of rated voltage—typically >100 MΩ for new motors. But if you test while the VFD is connected, you're also testing the electronics' insulation, which is not designed for high voltage.

Lesson: Always isolate the equipment from any electronics before megger testing. Verify with a wiring diagram first.

Mistake #5: Assuming 'Operating Microscope' Means Anything to a Sensor Engineer

During a supplier audit, a colleague asked if we had an "operating microscope" to inspect surface finish on encoder shafts. I thought he meant a surgical microscope—those are used in operating rooms. Nope. In quality inspection, an operating microscope is a stereomicroscope for assembly and inspection tasks, typically with magnification 10× to 40×.

We didn't have one. We'd been using a handheld magnifier. After that, we bought a proper stereomicroscope (from a brand like Olympus or Leica, not SICK). The $1,200 investment caught 3 shaft surface defects in the first month—saved us from sending out faulty encoders.

Takeaway: You don't need a full CMM for every check. A good stereo microscope is a cheap insurance policy for mechanical quality.

Summary: What I'd Do Differently

Looking back, most of my mistakes came from two things: assuming a component would work without double-checking the context, and ignoring the boundaries of each tool.

• For SICK encoders: verify shaft size, connection type, and options—suffixes matter.
• For temperature measurement: know the brand's actual products.
• For voltage testers: AC-only testers can't detect DC.
• For insulation testers: isolate VFDs and electronics before testing.
• For inspection: a stereo microscope is a must for fine features.

I can only speak to my experience in a mid-size automation facility. If you're in high-volume manufacturing or cleanroom environments, your mileage may vary. But these basic points should help you avoid the same costly lessons I went through.