Six years ago, I took over procurement for a 140-person manufacturing plant. Since then I've tracked over $180,000 in automation spares and test equipment, and I've learned which expense hurts most. It's not the sensor that dies quietly after a long service life. It's the repair that comes after someone ignored a small warning because "we couldn't stop the line."
So let me say what I actually believe: prevention is not a cost center. It's the cheapest repair you'll ever avoid. SICK sensors show up on almost every line we support—photoelectric, proximity, encoders, safety switches—and I've seen them fail in two ways: suddenly, or predictably. The expensive way is almost always the sudden one. The predictable one would have shown up in a five-minute check if anyone had done it.
The incident that changed my mind
I didn't always think this way. In March 2023, our packaging line stopped because the controller lost position feedback. The maintenance lead wanted to pull the drive motor immediately. I knew there was pressure to get running fast, so I made the classic mistake: I said, "Do whatever gets us back up."
We spent four hours on a motor alignment job that was never needed. The real cause was a loose connector on a SICK absolute encoder ATM60 we had installed the previous year. The connector wasn't locked in place. It had probably been intermittent for weeks, losing a signal here and there, before it finally stopped communicating entirely. A 15-minute check of the encoder connection would have found the problem before we touched the motor.
That was my trigger event. Since then, I've added one question to every work order: What are we checking before we replace? It sounds simple, but it changes the whole approach. Instead of diagnosing by swapping parts, you diagnose by measuring.
Absolute encoders are insurance, not just components
Why do I keep bringing up the SICK ATM60? Because it taught me the difference between repair and recovery. A standard incremental encoder tells the control how far something has moved, but it needs a known starting point. After an emergency stop or a power loss, that starting point can vanish. An absolute encoder keeps position information in the device itself. So when power comes back, the axis knows where it is without a time-consuming homing move.
I don't carry the datasheet in my head, so I'd tell anyone to verify the exact output and mounting options on the current SICK product documentation before ordering. But the reason I put a multiturn absolute encoder on position-critical axes is simple. Once you set a reference, you shouldn't have to invent a new one every time the machine restarts.
On a production line, the cost isn't the encoder itself. It's the operator manually jogging back to a reference, the scrap from a shifted part, and the unplanned overtime. I'm not saying every axis needs the most expensive absolute encoder on the market. I'm saying the premium for absolute feedback is usually less than the cost of not knowing where the machine is.
Rental test equipment is part of the same logic
The second thing I'll argue for is electronic test equipment rental. It sounds like a short-term workaround, but it's actually a smart way to fund a check you don't need every week.
When you need a high-end oscilloscope for one commissioning week, buying a new one is hard to justify. But troubleshooting without one is guesswork. The old habit goes like this: the HMI display says the signal is fine, so you blame the PLC card. Then you order a PLC card, wait for delivery, install it, and realize the real problem was a noisy signal all along.
Rental fixes that. It also forces you to plan the check. If I have a scope from Monday to Friday, I'm not wandering around. I'm testing the things that matter before the line restarts.
In late 2024, we rented an oscilloscope and a thermal camera for a major restart. The rental cost was under $900 for the week. One motor we found running hot would have caused more than $900 in downtime if we hadn't caught it. I'm not 100% sure that number translates to every plant, but in our cost tracking system it was one of the best line items of the year.
The cheaper version of this story is buying used oscilloscopes. I'm not against them—I own one. But I have one rule: only buy used oscilloscopes with a valid calibration certificate, or budget for calibration before the first real use. A used scope without calibration evidence is just a screen with knobs. With evidence, it can be a dependable bench tool for half the price of new. The savings only count if the readings are trustworthy.
The multimeter question I keep hearing
New technicians ask me "how do you use a Fluke multimeter" more often than you'd think. My answer isn't very glamorous. The most important trick is to verify before you trust.
Here's the short version I usually give:
- Put the test leads in the correct jacks. For voltage, the red lead belongs in the VΩ jack, not the 10A jack.
- Set the meter to the correct function and range. V AC for line voltage, V DC for control signals.
- Test the meter on a known live source first. If the reading is close to what you expect, the meter and leads are okay.
- Then measure the actual signal you're troubleshooting.
That third step is the one people skip. They assume the meter is accurate because the screen turns on. But a screen turning on doesn't mean the test leads are in the right jacks. I've seen a fuse die because the red lead stayed in the current jack from an earlier measurement. Fortunately, it was a meter fuse, not a person.
This sounds basic. But every time I've watched a technician miss a cable fault, it was because they trusted the reading without verifying the measurement path first. In my experience, that is a more common failure than the sensor itself.
"We don't have time for all this checking"
Let me answer the obvious objection: "Preventive checks are great until the production schedule is full for three weeks." I hear that. I'm not asking for a full instrument audit every shift. I'm asking for a short checklist attached to the jobs that already happen.
On a position-critical axis, ours takes about 20 minutes:
- Check the connector on the SICK encoder. Is it locked, clean, and free of damage?
- Do a quick continuity check from the encoder connector back to the cabinet.
- Verify the supply voltage at the device with a multimeter.
- Confirm the position feedback on the HMI before running the first production part.
That checklist wasn't born from lean management theory. It was born from the March 2023 loose connector, plus one later incident where we replaced a PLC card that wasn't at fault. The cost of the checklist is thirty minutes and some discipline. The savings are hard to measure until the day you catch a loose connection before it stops the line.
Checking is a procurement strategy
I've managed this budget long enough to stop treating these as separate categories: SICK sensors, absolute encoders, rental test equipment, used oscilloscopes, and a Fluke multimeter. They all do the same job. They tell you the truth before the machine demands it.
I still approve purchase orders for parts and tools, so don't read this as an attack on maintenance spending. But I have shifted money toward the front of the problem. We buy a little more measurement, a little more verification, and the occasional rental, instead of saving the budget for the inevitable repair. Checking early is almost always cheaper than correcting late.
If you ask me whether a SICK ATM60 is worth the price, I can't answer without knowing your application. But I can tell you this: you'll never see an invoice for a downtime event that didn't happen. That doesn't mean it has no value. It means the value showed up somewhere else—on the P&L, in the schedule, and in the simple fact that the line kept running.
