How to Calibrate a Thermometer

Thermometers are a useful tool. Whether you’re testing a solution, checking the safety of food and drink, or conducting an experiment with moving parts, getting a correct temperature reading is key to making sure you have the most accurate information at hand. 

Calibrating a thermometer regularly will make sure you get a correct reading every time. However, there are lots of different thermometers available. Digital thermometers, infrared thermometers, laser thermometers and probe thermometers all operate slightly differently. This means they each have their own specific calibration process. 

This guide will explain how to calibrate a thermometer, what calibration involves, why it's important and how you can run the process for different thermometers.  

Calibrating a thermometer is a process that makes sure the instrument is taking an accurate temperature reading. By testing a thermometer on a substance with a known temperature and adjusting it, you can make sure the device is reading correctly, meaning there’s as little deviation from the set standard as possible. 

If you don’t have an accurate reading, then you aren’t operating with correct information. This will have different repercussions depending on what you’re using your thermometer for. For example, if you’re conducting an experiment, using an uncalibrated thermometer will throw out your measurements, disrupt your data and lead to incorrect judgments. If you’re using a thermometer to check the temperature of a key piece of equipment, then uncalibrated instruments can lead to problems with safety or the efficiency of operation. 

In short, regularly calibrating your thermometer will ensure you have access to the most accurate information and don’t make incorrect judgments which can lead to significant consequences. Depending on the industry you’re working in, you might also need to meet certain accuracy, traceability and safety standards that require you to calibrate your thermometers at specific intervals or under particular conditions. 

The specific calibration process will be different for each thermometer and each instrument will come with a set of instructions on how to re-establish its accuracy. However, there are two main methods you can follow to calibrate your thermometer: 

• Testing against known temperatures: whether it’s boiling water, ice water, or a substance you regularly test and recognise, taking measurements of materials that you know the temperature of and adjusting the thermometer to the correct reading is the standard method for recalibration
• Verifying with a calibrated thermometer: taking readings of a material alongside another calibrated instrument and adjusting it accordingly will help you ensure your thermometer is within an acceptable degree of accuracy

It’s important to note that the calibration process also differs depending on a thermometer’s specific design. 

Digital thermometers come in all shapes and sizes, from hand-held models to bench and wall-mounted instruments. They can also be used with a range of probe attachments, making them highly flexible instruments suitable for lots of functions. It also means that each device has a unique calibration process, some of which require specialised equipment or a tightly controlled environment. 

However, if you’re looking to run a quick calibration with a basic digital thermometer, then you can use the freezing point method: 

• Fill a container two-thirds full of clean water
• Add ice to the container and leave for a couple of minutes
• Test the digital thermometer with the probe you’re planning to use later, whether it's by inserting or laying the probe on the surface
• The reading should be 0C or 32F. Once you’ve taken two to three readings, you can adjust the thermometer accordingly and retest until it’s reading more accurately
• To adjust the thermometer, you may need to turn a screw or nut, or simply press and hold the reset button

If you’ve been wondering what can be used to calibrate a probe thermometer, then you might be surprised to know that for most standard instruments, all you need is a container of hot water:

• Boil tap water and put it in a heatproof container
• Put the probe into the water, stir and leave it to sit for a couple of minutes
• Check the temperature reading. It should be within 1C of 100C or 2F of 212F
• If the reading isn’t accurate, then the thermometer needs to be adjusted and retested until it’s correct

Certification of calibrated thermometers is an important consideration for many industries, particularly those with strict quality control and regulatory requirements. Calibration certification assures that the thermometer has been calibrated to a specified standard and is accurate within a defined range. This can help to ensure product quality, safety, and compliance with regulations.

Certification of calibrated thermometers is typically provided by a third-party calibration laboratory that has been accredited to perform calibration services. These laboratories have the necessary equipment, expertise, and quality systems in place to provide accurate and reliable calibration services and to issue certification documents that are recognised by regulatory authorities and industry standards bodies.

The certification process typically involves performing a calibration on the thermometer using traceable standards and equipment that have been calibrated to national or international standards. The calibration laboratory will then compare the results of the calibration to the specified accuracy requirements for the thermometer and issue a certification document that includes the calibration results and other relevant information such as the date of calibration, the calibration method used, and the calibration laboratory's accreditation details.

It is important to note that certification of calibrated thermometers is not always required for all applications. The need for certification will depend on the specific requirements of the industry or regulatory body, as well as the intended use of the thermometer. Some applications may require certification for compliance with regulations, while others may not require certification but may still benefit from it as a means of ensuring accuracy and quality.

If certification of calibrated thermometers is required for your industry or application, it is important to choose a reputable calibration laboratory that has the necessary accreditations and expertise to perform accurate and reliable calibrations. In addition, regular recalibration of the thermometer is recommended to ensure ongoing accuracy and compliance with regulations. Here at RS, we can supply certificated thermometers and we also offer a calibration service for recalibration.