Thermometer Calibration FAQ

  • Why do brand new digital thermometers need calibrating?

    An assumption could be made that because the thermometer is brand new that the accuracy is within the specifications. This assumption may turn out to be true a lot of the time, but often it doesn’t.


    The only way to be sure is to have the thermometer calibrated.


    In addition, (depending on what industry you are in), a fully traceable calibration certificate may be a requirement of your auditors and/or clients.


    Thermometer manufacturers generally do not provide a fully traceable calibration certificate with the thermometer as standard.


    Some manufacturers provide a ‘statement of accuracy’ or similar statement which states that the thermometer has been manufactured according to the specifications.


    Some manufacturers provide a ‘factory calibration certificate’ however such certificates contain limited information and are not fully traceable to the international standards. These certificates are often out of date by the time they reach the end user.


    The calibration points on these certificates may not be very close to the actual temperature range the unit will be used over.

  • How often do digital thermometers need calibrating?

    In general, most digital thermometers used in the food & beverage and manufacturing industries are calibrated every 12 months.


    This 12 month frequency is specified in most of the thermometer manufacturers specifications for the types of thermometers that are typically used for measuring product or air temperatures.


    Our recommendation is to start with 12 months as the default period and then review as required.


    For more information, please refer to Guide to thermometer calibration and frequency of calibration.

Prior to first use

After an instrument has been repaired or modified

When a specified time period has elapsed

Whenever observations appear questionable or instrument indications do not match other instruments

As specified by a requirement, e.g. customer specification, instrument manufacturer recommendation, auditor requirement.​

The appropriate calibration frequency for your device needs to be determined by several factors such as quality assurance requirements, regulatory requirements and operating environment.​

Guide to thermometer calibration and frequency of calibration.

Thermometers should be calibrated:

Recommended best practice:

Have your thermometer calibrated or obtain a new thermometer with a IANZ endorsed calibration certificate. This calibration certificate needs to include calibration points that cover the temperature range over which the thermometer will be used.


Carry out your own basic single point check frequently. This can be a simple comparison with another thermometer or a check using a container of finely crushed wet ice that has had the excess water drained off. (Thermometer should read 0.0 °C). Compare result to the ice point reading on the latest calibration certificate.


Have the thermometer calibrated every 12 months and a new IANZ endorsed certificate issued.

Common problems with thermometers:

Thermometers used in food processing, food service and manufacturing environments are subject to knocks, drops, moisture, calibration drift and general wear and tear from multiple users.


The most common causes of reading errors in digital thermometers used in these environments are from moisture ingress, physical damage and calibration drifting. 


Obvious physical damage can easily be identified by visual inspection but often the damage can be internal and therefore not visible to the user.

  • Moisture

    Even tiny cracks in the instrument case can result in moisture being drawn in and damaging internal components. This also happens to ‘water proof’ thermometers. Water proof thermometers are only water proof when they are not damaged and are used within the parameters of their IP rating (ingress protection rating).

  • Physical damage

    Drops or knocks can cause internal damage to the temperature sensing element in the form of tiny cracks.  The circuitry inside most digital thermometers* measures the electrical resistance of the temperature sensing element which is proportional to the value of the measured temperature.


    If this sensing element is cracked it can result in the resistance of the sensing wire within the element to change due to stress applied as it is heated or cooled.  This can add or subtract resistance to the output of the element resulting in incorrect readings.


    *The exception to this is thermocouple based intruments. However, the accuracy and design of most thermocouple based instruments is better suited for less accurate readings and readings required above 200 ºC

  • Analog signal errors (calibration drift)

    Digital thermometers are actually not fully digital. The temperature sensor inside is analogue!  So rather than either 'working or not working'  as in digital signals, analogue signals are subject to errors related to changes (drift) in their eletrical properties over time.


    Regular calibration is the only way to determine that the thermometer is still within the required accuracy tolerance.


    Ultimately, the calibration frequency is up to you after considering things like product quality, food safety and regulatory requirements.

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