How to Know if a Professional Infrared Thermometer is Calibrated Correctly

During the COVID-19 emergency, we have witnessed an exponential increase in the requirement to measure body temperature at the entrances to public and private facilities, with the aim of identifying any altered states and thus being able to carry out a preliminary screening between those at risk and those not.

As a result, infrared thermometers and thermal imaging cameras of various types and, above all, various qualities are spreading rapidly on the market.

For this type of test, FDM offers its climatic chambers for environmental tests, designed and produced in Italy since 1949.

The accuracy of a thermometer can depend on the heat of the operator's hand, on any incorrect aiming, but above all on:

• the build quality of the thermometer itself
• the temperature of the environment in which the measurement is taken
• the quality and frequency of its calibration

Is the Infrared Thermometer Reliable?

The digital thermometer remains a fundamental device due to the speed with which it detects the temperature compared to a simple thermometer of a different type.

Speed ​​is, in general, but especially in this historical moment, a necessary requirement , given the number of measurements that need to be taken in a very short time .

In light of the current situation, however, an unreliable measurement is a risk no operator can take, for both ethical and direct liability reasons.

what happens if a digital thermometer doesn't work? 

On the other hand, on the contrary, the danger is:

• Overcrowding hospital facilities, already in great difficulty, without real need
• Administering drugs that are useless and/or, in the worst cases, harmful to people's health.

How can we make sure it's working? 

The solution to making sure an IR thermometer is measuring correctly is the ITeR.

FDM ITeR – Professional Reliability Indicator of an Infrared Thermometer, directly on site 

The FDM R&D Team has studied an innovative solution for Scientific Research, obtaining a tool capable of combining, in a single form, safety, speed and simplicity of testing.

ITeR allows the operator to always have a professional, yet portable, control tool for infrared thermometers at hand

This solution ensures greater security in airports, hospitals, and access points to public places, where rigorous health monitoring is required.

What is ITeR and how does it work?

ITeR is a compact, portable, high-precisionthat periodically checks in real time. With a temperature range from chamber temperature to 45°C, ITeR generates a reliable and consistent reference over time.

Thanks to ITeR, the operator can check, at any time, in the workplace, the functioning of his measuring device, minimizing the risk of reading errors and therefore the occurrence of results that are not faithful to reality.

ITeR is a smart and easy-to-use device: it has no display and connects via Bluetooth to the Android or iOS app for smartphones and tablets. Through the app, you can set the setpoint and receive notifications of any alarms for very high/very low temperatures and/or anomalies.

Thanks to the system's integrated PID algorithm, maximum source stability. The effectiveness of using a distributed source allows for excellent uniformity in heat distribution. 

Let's briefly explore this fundamental point.

The sensors used for an IR thermometerhave a thermopile inside them that converts the infrared rays into an electrical signal and therefore makes the temperature measurement available.

Due to the high dependence on ambient temperature, there is also a reference sensor inside the case, often an NTC, which has a curve like the one in the following image:

The image curve shows how, as the ambient temperature increases, the variability of the sensor's response decreases. Specifically, in the range between 25 and 30 degrees, the resolution is increasingly lower than in the range between 10 and 20 degrees. This means that, at operating temperatures (between 20 and 30 degrees), the reference accuracy degrades exponentially.

Therefore, pointing the IR thermometer at a heat source of known temperature can make it possible to compensate for the error due to variations in ambient temperature.

ITeR moves in this precise direction, offering a large surface that allows you to have a target with a known and settable temperature to be able to continuously compare the result of the infrared thermometer with the value set in ITeR.

Why ITeR

ITeR is a device with unique features on the market. 

There are, of course, tools for calibrating thermometers and IR cameras, but these are devices positioned differently in terms of pricing, which calibration laboratories purchase to provide a service to third parties and which require an investment of time and money.

ITeR can be easily placed on a desk, mounted on a stand or on the wall, depending on the configuration most comfortable for the operator.

Reference Standards

• ASTM E1256 — Standard Test Methods for Radiation Thermometers (Single Waveband Type). Main standard for metrological characterization of IR thermometers.
• ASTM E2758 — Standard Guide for Selection and Use of Wideband, Low Temperature Infrared Thermometers.
• VIM (JCGM 200:2012) — International Vocabulary of Metrology, reference terminology for calibration and uncertainty.
• ISO/IEC 17025 — General requirements for the competence of testing and calibration laboratories, required for issuing an ACCREDIA LAT certificate.
• JCGM 100 (GUM) — Evaluation of measurement data – Guide to the expression of uncertainty in measurement.
• IEC 60584-1 — Thermocouples – Reference tables (reference for indirect calibration via reference thermocouples).
• ITS-90 — International Temperature Scale of 1990, reference scale for metrological fixed points.

Authoritative Sources

• ACCREDIA. Italy's sole accreditation body, handles the accreditation of LAT calibration laboratories according to ISO/IEC 17025.
• INRIM – National Institute for Metrological Research. Italian institute for the traceability of units of measurement, maintains the ITS-90 fixed points.
• BIPM – International Bureau of Weights and Measures. Defines the ITS-90 temperature scale and coordinates international comparisons.
• ASTM InternationalPublishes the ASTM E series of radiation thermometers.

Frequently Asked Questions about the ACCREDIA Calibrated IR Thermometer

What does "ACCREDIA calibrated" mean and why is it important?

An ACCREDIA LAT calibrated IR thermometer is an instrument accompanied by a calibration certificate issued by an ACCREDIA accredited laboratory according to the ISO/IEC 17025 standard . The certificate attests the metrological traceability of the measurement to SI units through an uninterrupted chain of comparisons up to ITS-90 maintained by INRIM. The difference compared to a non-accredited “commercial calibration” lies in: (1) technical competence verified by ACCREDIA with periodic audits; (2) uncertainty declared according to GUM with a detailed budget; (3) international mutual recognition thanks to the ILAC-MRA agreements; (4) legal validity in industrial disputes and inspections. An ACCREDIA LAT certificate is required for GLP applications, pharmaceutical GMP, ISO 9001 audits, ISO 17025 accreditation of customer laboratories.

What uncertainty does a professionally calibrated IR thermometer reach?

The uncertainty of an ACCREDIA calibrated IR thermometer depends on the range and quality of the instrument. For the physiological range 30-45 °C (medical thermometers): uncertainty U (k=2) ≤ 0.2-0.3 °C. For the industrial range 0-500 °C: U ≈ 0.5-2% of the reading value or ± 1-3 °C. For high temperatures 500-1500 °C (steel and metallurgy, smelting): U ≈ 0.25-0.5% of the reading value or ± 2-5 °C. For low temperatures -40/0 °C (cold chain): U ≈ ± 0.5-1 °C. The main contributions to the uncertainty are: target emissivity (0.95 ± 0.03), ambient reflection temperature, measurement distance, instrument resolution, temporal drift, repeatability. Calibration is performed on reference blackbodies (blackbody calibrator) with certified emissivity ε > 0.99 in the working range of the thermometer.

How often should you recalibrate an IR thermometer and why?

The recommended frequency is annual for GLP/GMP/ISO 17025 applications and for intensive use (> 100 measurements/day); biennial for occasional use and backup instruments. Factors that accelerate drift: (1) repeated thermal shocks (measurement on hot surfaces ≥ 300 °C immediately after cooling); (2) optical contamination on the objective (dust, grease, solvents that alter transmittance); (3) falls and mechanical shocks that misalign optics and sensor; (4) aging of the pyroelectric or bolometric detector (typical 0.1-0.5 °C/year); (5) electronic drift of the spectral filter and signal conditioning. The pre/post calibration comparison allows you to evaluate drift and decide whether the current interval is sustainable or should be reduced. A thermometer with drift > U/3 between two calibrations requires revision or replacement.

How is emissivity handled in real-world measurements?

Emissivityε is the ratio of radiation emitted by a real surface to that of a black body at the same temperature. Typical ranges: shiny metals 0.02-0.1 (IR measurements not recommended without preparation); oxidized metals 0.5-0.9; paints and plastics 0.9-0.97; human skin 0.98; water 0.96-0.98; polished stainless steel 0.14. An error of 0.1 in ε causes an estimated measurement error of ≈ 2-4% of the absolute temperature (e.g. +/- 6-12 °C at 300 K). Corrective methods: (1) apply matte black tape ε=0.95 to the target for 5 minutes of equilibration; (2) high-emissivity paint (Nextel Velvet 811-21 ε=0.97); (3) reference hole in the material (cylindrical cavity L/D ratio > 6 simulates blackbody ε ≥ 0.99); (4) differential measurement with reference contact (calibrated K thermocouple) for in-situ calibration of the effective emissivity.