19/05/2023

6 Easy Ways to Calibrate a Digital Thermometer

Accurate temperature measurements are crucial for ensuring optimal performance, reliable data, and, most importantly, the well-being and safety of individuals. However, over time, thermometers can experience deviations in accuracy due to various factors, including regular usage, environmental conditions, or even mechanical wear.

This guide will explore various calibration equipment options available in the market today. We will cover a range of tools, from simple and cost-effective solutions suitable for home use to more advanced and specialised equipment utilised in professional settings. Each type of equipment serves a unique purpose, catering to different calibration needs and budgets.

Whether you’re a professional in a scientific laboratory, a healthcare provider, or simply someone who wants to ensure the accuracy of their everyday thermometers, this guide is here to help you make informed decisions about the best temperature calibration equipment you can purchase.

How often must food temperature probes be calibrated?

The frequency of calibrating food temperature probes depends on several factors, including industry standards, regulatory requirements, and frequency of use.

In many industries, including food service, the general recommendation is to calibrate food temperature probes at least once a month. This frequency helps to ensure that the thermometer remains accurate and reliable for temperature measurements. However, certain situations may require more frequent calibration, such as HACCP plans, high-volume usage and regulatory requirements.

It’s essential to keep a record of calibration dates and results to demonstrate compliance with regulatory requirements and to ensure proper monitoring of your thermometer’s accuracy. Regular calibration not only promotes food safety but also supports quality control and helps prevent potential issues that may arise from inaccurate temperature measurements.

What to do after calibrating a thermometer?

If you have verified the accuracy of your thermometer and found it to be out of range, you’ll need to send it to a laboratory to be recalibrated. At ETI, we have eight in-house calibration laboratories, including three UKAS laboratories and one specifically designed for infrared calibration.

Learn more about our calibration services here.

Best temperature equipment for calibration

Temperature calibration equipment explained.

Ice bath mug

Best for: economic probe thermometer checks

An ice bath is the cheapest and easiest way to carry out a temperature probe calibration check. However, creating an accurate ice bath that is 0 °C in temperature is pretty tricky, so using this ice bath mug printed with measurements for your ice water and step-by-step instructions makes things a bit simpler. Once you’ve created the ice bath, you can use it to check the temperature on your probe thermometer. It’s ideal to also use a high-accuracy reference thermometer as well so you can get a more accurate reading of the ice water and compare temperatures.

The limitations of this method are that it can be inaccurate if the ice bath isn’t made carefully. In addition, preparing the ice bath takes time and won’t stay accurate for long, which makes it only ideal for checking a couple of thermometers at a time. However, if you aren’t required to check your thermometers regularly and you only have a small number of thermometers, this could be the best option for you.

Shop the Ice Bath Mug.

Comparator cups and black body calibrators

Best for: infrared thermometer calibration

Infrared thermometers need to be used carefully to get accurate readings and even more carefully to carry out an accurate thermometer calibration test. There are two options you can choose for your infrared device: a comparator cup or a black body calibrator.

The comparator cup is a budget option, ideal for calibrating smaller numbers of infrared devices on a less frequent basis. You simply insert a high-accuracy probe into the base of the cup to use as your reference point whilst taking a reading inside the cup using your infrared device. Then compare the two readings. The limitation of this is that it is difficult to use the cup to calibrate your IR thermometer at various temperatures, particularly high and low ones. Factors such as steam and condensation need to be taken into consideration when using infrared thermometers. However, with care, it is possible to use the comparator cup at low temperatures by storing it in a fridge or freezer so it can acclimatise.

In contrast, the IR-500 Black Body Calibrator creates stable temperatures of 50 to 500 °C for infrared instrument calibration. Suitable for checking multiple IR thermometers regularly, this is an easier and more accurate method of calibrating thermometers. Again, this device is best used alongside a calibration thermometer for maximum confidence in the accuracy of your tests.

Shop the Comparator Cup or the Black Body Calibrator.

High-accuracy reference thermometers

Best for: all types of calibration tests

When carrying out a calibration process, it’s often useful to have a highly accurate reference or calibration thermometer to compare the thermometer under test with. It enables you to be confident in measuring your stable temperature source, particularly if using a less reliable method such as an ice bath.

We have two different high-accuracy thermometers for this: the Reference Thermometer and the Reference Thermapen. Both have 0.01 °C resolutions and come with a 5-point UKAS calibration certificate. The Reference Thermometer has an accuracy of ±0.03 °C and a wired probe for two-handed operation. In contrast, the Reference Thermapen has an accuracy of ±0.05 °C and a folding probe for single-hand operation. Both are accurate and reliable choices for comparison points in your accuracy checks. Please note that these thermometers have slow response times and delicate sensors, therefore they are only appropriate for using on calibration tests.

Shop the Reference Thermometer or Reference Thermapen.

Thermometer test caps

Best for: thermistor and PT100 instruments

If you use a thermistor or PT100 temperature sensor with interchangeable probes, there’s a very easy way to check the accuracy of the thermometer: test caps. Available in a range of temperatures, these simple devices screw onto your thermometer connector, where you can take a reading to compare to that of the one set on the test cap. Excellent for quickly and easily checking the accuracy of your thermometer at any time, test caps are economical choices for thermistor or PT100 users.

The only limitation of these, however is that they only confirm the accuracy of your thermometer, not your probes. Your probes will have to be calibrated separately using one of the other methods described in this blog.

Shop the Thermistor or the PT100 test caps.

Microcal calibrators

Best for: thermocouple instruments

Similarly to thermistor and PT100 test caps, MicroCal calibrators enable quick and easy validation of thermocouple thermometers. Compatible with type K, J, T, R, N, S and E thermocouple thermometers, the MicroCal 1 calibrator has 12 adjustable temperature points, making it easy to calibrate your equipment at multiple temperature points very quickly.

Like the test caps, the MicroCal calibrators only test the accuracy of your instruments, not your probes. Therefore, probes must be checked separately.

Shop the MicroCal 1 calibrator.

Dry block calibrators

Best for: accurate testing of multiple probe thermometers

Dry block calibrators, also known as dry wells, create a stable temperature source for testing thermometer probes. These portable devices are a more accurate and reliable alternative to ice baths, enabling users to check large quantities of probes quickly and at desired checkpoints.

At ETI, we stock a cool source calibrator with a temperature range of -10 to 110 °C and a heat source calibrator with a range of 33 to 250 °C. In addition, both accept a wide variety of thermometers, including thermocouple, thermistor and PT100 probes, and are available with different sized holes for compatibility with varying probe diameters.

Shop the cool or hot dry well calibrators.

Summary

The calibration method you choose depends on how many thermometers you need to calibrate, how often you need to calibrate them, and the time and budget you have allocated to this process. Whichever one you go for, the most important thing to remember is to carry out each test with care and precision so that results are accurate and you can continue using your instruments with confidence.