Turck Sensors for Centrifuges: A 7-Step Checklist From a Maintenance Engineer Who Learned the Hard Way

If you're the person who has to specify sensors for centrifuges, this is the checklist I wish someone had handed me in 2014. It's not a 50-page spec guide. It's seven steps. Seven. And every one of them came from a mistake I made or watched a coworker make in the field.

Background on why I get to have an opinion: I'm an electrical maintenance lead handling sensor selection orders for 12 years. I've personally made (and documented) 28 significant mistakes, totaling roughly $41,000 in wasted budget—wrong sensors, wrong cable lengths, wrong connectors, wrong assumptions. Now I maintain our team's pre-order checklist so that nobody else has to repeat that tuition.

Who Should Use This Checklist

Use this when you are ordering Turck sensors for a centrifuge, a centrifuge package skid, or the auxiliary equipment around it—feed pumps, lubrication systems, discharge valves. It also works for standard rotating packages.

My experience is based on about 300 sensor selections on decanter and disc-stack centrifuges in wastewater and dairy. If you're working on high-speed chemical separators with solvent cleaning, your constraints might be different. In those cases, use this checklist as a starting point, not the final word.

The Checklist

1. Define the environment before you open the catalog

Seriously. Do this first. I skipped it once and paid for it twice.

Ask four questions:

• How is the machine washed? High-pressure hot water, caustic foam, steam?
• What chemicals contact the sensor body and cable?
• What is the ambient temperature range around the mounting point?
• Is there vibration? Most centrifuges: yes.

If the sensor is on the machine housing and gets a regular caustic washdown, IP67 is not enough. I look for IP69K-rated connectors and housings, per ISO 20653. That's the rating for high-pressure, high-temperature washdown. In 2016, I ordered standard M18 inductive sensors with IP67 for a dairy centrifuge. The first one died in three weeks. The corrosion wasn't visible on the outside—it got into the connector under the cap. Replacing it meant a production stop during a wash cycle.

I'm not a materials engineer, so I can't tell you exactly which stainless alloy works with every chemical. What I can tell you is to check the sensor body material and the connector material separately. And check the cable jacket, too. No one checks the cable jacket.

2. Confirm the target metal and sensing distance

Inductive Turck sensors detect metal—but not all metals the same way. Standard inductive sensors have a factor that varies based on the target. A standard sensor rated for 15mm on mild steel might give you only 7.5mm on aluminum or copper.

This is where Turck's uprox technology earns its keep. Uprox sensors are factor 1, which means the sensing range is the same for all metals. If you're aiming at a stainless steel bearing housing or an aluminum spacer ring, you don't have to derate the distance.

I almost approved a standard M18 sensor for a speed wheel on a decanter. It looked fine on paper. But the target was stainless, and the mounting distance was tight. The standard version wouldn't have been reliable. So glad I double-checked the sensing range before approving. We were one click away from a costly mounting redesign.

Refer to IEC 60947-5-2 for the standard definitions of rated operating distance and repeatability. It's the common language between sensor catalogs and panel drawings.

3. Choose the output type and wiring before you get to the connector

PNP or NPN? This causes more trouble than almost any other specification.

Many modern PLC inputs use PNP (sourcing) sensors. If you have an older PLC or a specific input card, check it. In 2019, we replaced a whole set of sensors on a centrifuge lube skid and ordered NPN out of habit. The PLC waited for PNP. We didn't have adapters, so we sat with a machine that couldn't see its oil level. Nightmare.

If you're not sure, do a quick continuity test with a multimeter before you install 20 sensors. I use the 88 multimeter I carry in my bag—it's not the fanciest, but it has a continuity beep and a stable DC voltage setting. That's enough to confirm whether a sensor is sourcing or sinking.

4. Do not guess the connector and cable length

I once ordered 24 inductive sensors with 5-meter PVC cables. The machine was pre-wired with 2-meter drop cables and M12 connectors. I should have ordered sensors with M12 connectors and a short pigtail. Instead, I had to add junction boxes and coil the extra cable. Not ideal, but workable.

Before you order, write down:

• Connector type (M8, M12, M12 with IO-Link, pigtail, etc.)
• Connector orientation (straight vs. angled)
• Cable length from sensor to junction box or PLC input
• Cable jacket material (PUR for flex and oil; PVC for general use)

The surprise wasn't the sensor price. It was the connector compatibility. The Turck sensor catalog has an enormous number of connection variants, which is good—but only if you look. The 60 seconds it takes to check the drawing can save you a week of waiting.

5. Consider a Turck radar sensor for the messy measurements

Not every measurement on a centrifuge is a proximity sensor. Liquid levels, feed tank levels, and discharge chute blockages can be brutal on traditional sensors. Steam, foam, condensation, or buildup will fool an ultrasonic sensor and coat a standard level sensor.

That's where I'd look at the Turck radar sensor range. The radar unit sits outside the tank or through a process connection, and the radar beam doesn't care about foam, steam, or temperature gradients. In 2023, we replaced a troublesome ultrasonic unit on a sludge feed tank with a Turck radar sensor. The sensor saw through the steam and didn't need daily cleaning. Worse than expected? No—better than expected.

I'm not saying radar solves everything. It's not cheap, and you need to follow the installation instructions for false echo suppression. But for centrifuges with messy process conditions, radar is one of the first options I consider.

6. Budget for the tools that catch problems early

You can spend a lot of money on the right sensor and then lose it all to a bad setup. Test tools matter.

First, the multimeter. If you're asking whether you need an 88 multimeter, the answer is: maybe. It's a workhorse for 4-20 mA loops and contact closure checks. But an 88 multimeter won't tell you if a sensor is sensing reliably at speed. For that, use a metal flag and a slow jog.

Second, thermal imaging. If you've ever Googled how much is a flir thermal camera, you're not alone. A basic FLIR camera can cost anywhere from roughly $800 to $2,000 depending on the model and features (as of mid-2025). You don't need to buy one immediately—rent or borrow one first. We bought ours after a bearing failure that turned out to be a slow overheating problem. A thermal scan would have caught it weeks earlier. The camera paid for itself with that one avoided outage.

By the way, thermal camera pricing varies widely and changes. Do not use my numbers as a quote. Use them as a rough budget line.

7. Mark the spares and update your maintenance system

This is the step everyone skips, including me. In 2021, I needed a spare sensor for a centrifuge feed pump. The old part number had been superseded. I had no idea what the original sensor was, because no one recorded it. I spent a morning pulling panels, checking part numbers, and comparing catalogs. Eventually I found it, but the machine sat idle for two extra hours.

Now our rule is simple: if you install a sensor, you also write its part number on the terminal label and in the CMMS. It takes two minutes. It saves everyone later.

Common Mistakes I Still See

• Choosing the sensor before checking the environment.
• Assuming all metal targets behave the same—they don't.
• Forgetting that M12 connectors have a gender and a pin count. Check both.
• Ignoring ambient temperature around the sensor head, especially near steam vents.
• Buying one sensor for every location without asking if a Turck radar sensor might be better for the messy spot.
• Thinking a multimeter is enough to check a sensor. You also need a visual inspection and a manual trigger test.

Final Thought (No Pressure, Just Experience)

Look, I'm not saying every sensor needs to be the most expensive one. I'm saying the sensor that fits the environment, wiring, and process is the one that saves money. A poorly specified sensor that fails in service is more expensive than a well-specified Turck sensor that runs for years.

To be fair, I have seen perfectly fine standard sensors running on clean, dry applications. I own that. The checklist isn't about avoiding simplicity—it's about avoiding surprises. The surprise shouldn't be a ruined bearing because a sensor didn't see what it needed to see.

If this checklist helps you avoid one bad order, that's enough. It would have saved me about $41,000.