How to Calibrate Your Fluke 568 Infrared Thermometer in a Pinch: A 7-Step Checklist

When You Need a Calibration—and You Need It Yesterday

I'm a calibration specialist at an ISO 17025 accredited lab. In the last five years, I've handled over 200 rush calibrations for pharmaceutical, aerospace, and industrial clients. Same-day turnarounds, weekend emergencies, audit deadlines—I've seen all of them.

When I first started this role, I assumed that any calibration was better than none. That if you just did a quick check against a known temperature source, you'd be fine. Three client rejections and one recall later, I realized the opposite: a half-done calibration can cost you more than skipping it entirely. The rework, the shipping, the lost credibility—it adds up fast. That's when I adopted a strict checklist approach, and it's saved my clients thousands in hidden costs.

This checklist is for anyone who needs to calibrate a Fluke 568 infrared thermometer under pressure—whether it's for an upcoming audit, a customer deadline, or an unexpected quality hold. It's also relevant if you're calibrating other instruments (like a Mettler Toledo pH meter or an Efector vision sensor), because the foundational steps are surprisingly similar. But we'll stick with the Fluke 568 for this walkthrough.

Here are the seven steps that I've refined after 200+ rush jobs. Follow them in order, and don't skip any—even the one that seems optional.

Step 1: Confirm Your Reference Source is Valid

Before you touch the thermometer, verify that your blackbody calibrator or other reference source has a current calibration certificate. I know it sounds obvious, but I've seen engineers grab the first blackbody they find, only to discover its calibration expired six months ago. The worst part? They already took measurements. Total wasted time: three hours. Cost of redoing everything with a valid reference: about $500 in labor and fees.

Quick tip: keep a list of all reference sources with their calibration due dates. When I'm triaging a rush order, the first thing I check is that list.

Step 2: Inspect the Fluke 568 for Physical Damage

Give the thermometer a once-over. Cracks in the lens, scratches, loose battery cover—these affect accuracy. I once had a Fluke 568 that looked fine but had a hairline crack in the IR window. The readings were off by 4°C at 100°C. We didn't catch it until Step 5. (Should mention: that was a $1,200 redo because the client had already shipped the unit back to their production line.)

Ignore this step if you're calibrating a clamp meter—obviously different inspection criteria. But for IR thermometers, lens condition is critical.

Step 3: Set the Emissivity Correctly

This is the step most people mess up. The Fluke 568 has adjustable emissivity from 0.10 to 1.00. If you're measuring a shiny metal surface, the emissivity might be 0.3; for a matte black surface, closer to 0.95. Get it wrong and your calibration can be off by 10% or more. Yet I've seen engineers just leave it at the default 0.95 because they're in a hurry.

The fix: determine the emissivity of the surface you're using as a measurement target. If you're using a blackbody, set it to 0.95 (the standard for most blackbodies). If you're using a surrogate target, look up the material's emissivity from a credible table, or measure it with a contact probe.

Step 4: Allow Full Stabilization

Place the Fluke 568 and the reference source in the same environment—preferably a temperature-controlled lab at 23±2°C. Let them stabilize for at least 30 minutes. Why 30? Because thermal shock takes time. I used to do 15 minutes until a calibration failed because the sensor hadn't fully settled. That failure meant rebooking a slot two weeks later. The total cost of that one shortcut? Lost production time for the client and a $400 rush fee on top of the original calibration price.

Now I set a timer. No exceptions.

Step 5: Take Measurements at Three Temperature Points

Typical calibration points for the Fluke 568 are 0°C, 100°C, and 300°C (or whatever range your blackbody supports). Record the reference temperature and the displayed temperature. Do three measurements at each point, averaging the results. Why three? Because a single reading can be an outlier due to operator movement or draft. I learned this the hard way when a single spike made me think the thermometer was out of spec—I almost condemned a perfectly good unit.

Oh, and record the environmental conditions too (temp, humidity). That's often overlooked for simple calibrations, but it's required for traceability. According to ISO 17025 (clause 7.8), measurement records must include environmental conditions. Not doing so can invalidate the certificate.

Step 6: Evaluate Error and Adjust (or Determine Pass/Fail)

Compare the average displayed temperature to the reference. The Fluke 568 specification is typically ±1% of reading or ±1°C, whichever is greater. If the error is within spec, great—document it. If it's out, you have options:

• Send it to a calibration lab for adjustment (never try to adjust the 568 yourself—it requires factory tools)
• Use a correction factor (if the error is stable and documented)
• Flag it for repair before next use

Here's the total cost trap: many people think they'll save money by using an out-of-spec instrument since the immediate cost of adjustment or repair seems high. But the cost of a failed audit or a manufacturing defect traced back to your measurements can be orders of magnitude larger. One of my clients spent $3,000 on a rush repair for a Fluke 568, but that avoided a $50,000 production shutdown. Worth every cent.

Step 7: Document Everything and Apply a Label

Create a calibration report with: instrument details, reference source info, measurement data, pass/fail decision, and technician name. Then attach a calibration sticker or hang tag to the instrument. The sticker should show the due date (typically one year from today, or per your company's policy).

I can't tell you how many times I've seen a newly calibrated thermometer with no label. The next engineer picks it up, doesn't know if it's calibrated, and either wastes time checking or uses it unverified. The uncertainty cost: at least 30 minutes of someone's time, plus the risk of using an uncalibrated tool.

Common Mistakes to Avoid

Mistake #1: Calibrating in the field against an uncertain source. Yes, you can do a quick check with a cup of ice water for a contact thermometer. But for an infrared thermometer, you need a proper blackbody. I've seen people try using a hot plate—don't. The emissivity and stability aren't controlled.

Mistake #2: Forgetting to account for the size-of-source effect. The Fluke 568 has a spot size ratio of 50:1. If you're too close or too far, the measurement area might be larger than your reference blackbody cavity. That introduces error.

Mistake #3: Assuming the same procedure works for a clamp meter. While this checklist is for IR thermometers, I often get rush requests for clamp meter calibration as well. The process for a Fluke clamp meter is entirely different—you need a current source and a known load. Don't try to use a temperature calibration procedure for current measurements.

Mistake #4: Skipping the pre- and post-stabilization. I already mentioned stabilization, but I'll say it again: 30 minutes minimum. I don't have hard data on industry-wide failure due to inadequate stabilization, but based on my 200+ rush calibrations, I'd estimate 15% of failures are caused by insufficient soak time.

"The value of guaranteed turnaround isn't the speed—it's the certainty. For instrument calibration, knowing the certificate will be valid and accepted is often worth more than a cheaper alternative with questionable traceability."

If you're in a real emergency and don't have the resources to calibrate in-house, consider sending it to a lab that offers express service. Prices vary widely—rush fees for a Fluke 568 calibration range from $75 to $200 (based on quotes from three accredited labs, January 2025). Factor that into your total cost calculation: a $200 rush fee can save you a $2,000 audit non-conformance or a $10,000 scrap event.

Bottom line: a rushed calibration done right is better than a perfect calibration done too late. Follow this checklist, and you'll minimize both your time risk and your total cost of ownership.