Calibrating a thermometer seems straightforward on its surface, but in industries where precision matters and thermometers are more sophisticated to handle these demands, the stakes are high. Whether you’re using thermometers in pharmaceuticals, aerospace, or food safety, reliable calibration ensures accurate temperature measurements and compliance with critical standards.
While simple methods like the ice water or boiling point techniques can help for some basic calibration applications, they aren’t enough for professional-grade accuracy or traceability to international standards.
In this article, we’ll cover why calibration is critical, review some of the most commonly used thermometers for industrial applications, and walk through some of the most popular ways to calibrate those thermometers.
Why Do Thermometers Need Calibration?
Like all measurement tools, the accuracy of a thermometer’s measurements can drift over time, usually due to wear, environmental factors, or regular or rough usage. And inaccurate temperature readings can lead to costly mistakes, safety risks, and non-compliance in critical industries. For example:
- Regulatory requirements for a pharmaceutical lab might mandate that any digital thermometer that staff use for research or manufacturing needs an accuracy within 0.01°C (32.018 °F), which requires careful calibration.
- In food manufacturing and storage, a properly calibrated dial thermometer ensures a facility’s ability to consistently adhere to health codes.
- An infrared thermometer used in manufacturing might require traceability to confirm its readings during critical quality checks.
By regularly calibrating your thermometer, you can ensure it remains accurate and trustworthy, avoiding costly mistakes like ruined batches in pharmaceutical production, spoilage in food manufacturing, or equipment failure in aerospace applications.
While basic methods like ice point calibration are helpful for quick checks, they don’t offer the level of accuracy or traceability that these industrial scenarios require. Now, before diving into how to calibrate, let’s explore the common thermometer types.
What Are the Most Common Types of Thermometers?
There are many different types of thermometers designed for an array of different situations and applications, and understanding these differences is key to choosing the right calibration method for your needs.
Digital Stem Thermometers
Digital stem thermometers are compact and commonly used in medical and industrial applications. As their name suggests, these thermometers consist of a simple design: a stem/temperature probe that you insert into whatever medium, substance, or object you need to measure and a digital display. Near the tip of the stem or probe is a digital temperature sensor that collects and transfers the relevant temperature data to the display.
Sometimes, the display of a digital stem thermometer attaches directly to the probe. Other times, there might be a flexible cord that houses a wire that runs from the stem and the display; these are helpful for situations where you might not want to or cannot have the display near whatever you’re measuring.
While digital stem thermometers are easy to use — simply insert the stem or probe into whatever you’re measuring and look at the display for the reading — they rely on temperature sensors that can drift over time.
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Dial Gauge Thermometers
Often found in commercial kitchens or industrial environments, dial thermometers can look similar to digital stem thermometers, but there are some key differences. One such difference is that the display on a dial gauge thermometer is an analog, clock-like dial rather than a digital display. The dial display attaches directly to a stem or probe.
There are different types of dial gauge thermometers, but the most common is a bimetallic thermometer. Bimetallic thermometers rely on a strip of two different types of metal — each with different thermal expansion rates — that are fused together; this bimetallic strip runs through the stem of the thermometer. The thermal expansion of the metals deforms the strip, rotating a coil that then moves the pointer on the display dial.
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Industrial Thermometers: Thermocouples and Infrared Thermometers
Thermocouples and infrared thermometers dominate industrial applications, so it makes sense to discuss them together.
Thermocouples
Thermocouples are temperature sensors that have two electrical-conducting prongs — each prong made of a different type of metal — that are joined together at a base to form an electrical junction. Relying on the Seebeck effect, a voltage is created between the two prongs when the temperature changes. Then, generally speaking, whatever instrument that’s connected to the thermocouple interprets the electrical signal, transmits that information, and displays the corresponding temperature.
While they’re not technically thermometers, thermocouples are a crucial component of many industrial thermometers, are highly versatile, and can measure a wide range of temperatures depending on which two metals are used for the prongs.
Infrared Thermometers
Infrared (IR) thermometers — also called laser thermometers, temperatures guns, and non-contact thermometers — take temperature measurements by relying on the infrared radiation that nearly all objects emit. In simple terms, the hotter an object gets, the more quickly its atoms move, and the more quickly those atoms move, the more infrared radiation an object emits. The IR thermometer uses specific internal components to focus, absorb and measure that surface radiation before converting it to a temperature reading.
This contactless temperature measurement is ideal in many industrial settings. For instance, users can simply point their IR thermometer at whatever surface they need to, helping them measure hard-to-reach areas, surfaces that are too hot to safely approach, or equipment that emits dangerous fumes. Despite their convenience, calibrating IR thermometers is difficult given their complex measurement mechanisms.
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Now that we’ve reviewed some common thermometer types, let’s examine how to calibrate them effectively.
What Are the Most Common Ways To Calibrate a Thermometer?
There are three main methods to calibrate a thermometer: the ice water method, the boiling point method, and the use of thermometer standards. Each method has its place, but the choice depends on the thermometer type and the level of accuracy you need for your application.
Ice Water Method
The ice water method is a popular, straightforward calibration method that’s best for quick accuracy checks — particularly for digital stem and dial thermometers. However, factors like the purity of the water and ice you use, the ambient temperature of the calibration environment, and how those factors impact melt rate can all affect the accuracy and precision of test results. Because of these variables, the ice water method isn’t precise enough to use in traceable calibrations in industrial or scientific settings.
How To Calibrate Using the Ice Water Method
- Fill a glass with crushed ice and add enough distilled water to cover the ice. Stir the mixture to create a slushy consistency.
- Insert the thermometer probe into the ice water, ensuring it does not touch the sides or bottom of the container.
- Wait for the thermometer reading to stabilize, which should be 0°C (32°F).
- If the reading deviates, adjust the thermometer if necessary or note the error for correction.
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Critical note: This method is not sufficient for calibrating thermometers used in environments that require high degrees of precision or require compliance to regulations. Professional calibration tools, like Fluke Calibration's temperature baths, offer a superior alternative.
Boiling Point Method
The boiling point calibration method is similar to the ice point method, but it relies instead on the thermometer reading at the boiling point of water. Similar to the ice water method, many environmental factors — such as water purity and the altitude of the testing location — can affect water’s boiling point and thus the accuracy of this calibration method. That said, it’s still a popular calibration method for thermometers that you don’t expect to use in any applications that require precise measurement.
How To Calibrate Using the Boiling Point Method
- Boil distilled water in a container.
- Insert the thermometer probe into the boiling water, ensuring it does not touch the sides or bottom.
- Wait for the thermometer reading to stabilize at the boiling point (100°C or 212°F at sea level). Adjust for altitude if necessary.
- Note any discrepancies and adjust or correct the thermometer accordingly.
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Critical note: This method is not appropriate for industrial thermometers like thermocouples or infrared thermometers. Fluke Calibration’s precision temperature standards and calibration baths and standards provide better accuracy and repeatability.
Using Thermometer Standards
Calibrating a thermometer using thermometer reference standards ensures traceability and accuracy, especially for the thermometers that experts in critical, industrial industries use. Fluke Calibration offers tools like triple point cells and precision baths, which are the gold standard for professional calibration.
What Are Thermometer Standards?
Thermometer standards are specialty, high-quality measurement devices or substances with well-defined temperature values, such as triple point cells (0.01°C, 32.018 °F) or fixed-point baths. Because standards are specialized equipment, they can be expensive, and the process of calibrating a device with standards isn’t always as straightforward as with other methods. As such, you would typically find them in independent calibration laboratories staffed with highly trained technicians. (Though large organizations may utilize them in in-house calibration labs.) These standards ensure calibration traceability of the device being tested — also called the device under test (DUT) — to international standards, such as ITS-90.
How To Calibrate Using Thermometer Standards
- Set up the thermometer and the standard device (e.g., a triple point cell or calibration bath).
- Place the thermometer probe in the calibration medium, ensuring immersion conditions align with the standard’s requirements.
- Allow the system to stabilize.
- Record the thermometer reading and compare it with the standard’s reference temperature.
- Adjust the thermometer or record the correction factor.
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Critical Note: Fluke Calibration’s solutions, such as triple point cells and dry block calibrators, streamline this process, ensuring reliable results for high-precision applications.
Ensure Your Thermometer’s Calibration Is Accurate
While basic calibration methods like the ice water and boiling point techniques are helpful for quick checks, they’re inadequate for professional or high-stakes applications. Factors like environmental conditions, operator error, and equipment drift make traceable calibration critical in industries where precision is paramount.
Fluke Calibration’s calibration tools provide the accuracy, repeatability, and traceability required to ensure your thermometers meet the highest standards. For example, Fluke’s Triple Point of Water Cells offer unmatched precision, achieving uncertainties as low as 0.00005 °C (32.00009 °F), making them indispensable in applications ranging from cryogenics to pharmaceuticals.
Why Choose Fluke Calibration?
- Precision Tools: From dry block calibrators to fixed-point baths, Fluke Calibration ensures unparalleled accuracy.
- Traceability: All products comply with international standards, ensuring confidence in your measurements.
- Expertise: Trusted by industries worldwide, Fluke Calibration sets the benchmark for quality and reliability.
For the most reliable thermometer calibration solutions, explore Fluke Calibration’s full range of temperature calibration products.