Temperature calibration: Guidelines and best practices

• What is temperature calibration?
• And why is it needed?
• The 7 key terms of temperature calibration
• How temperature calibration is typically performed
• Who handles calibration? And can you do it yourself?
• The difference between accredited and traceable calibration
• Choosing the right calibration type for you
• Common calibration challenges and their solutions

Calibration of temperature and humidity measurement devices is necessary to ensure the accuracy of the data logger sensors used for monitoring. In other words, temperature calibration is about ensuring that measurements are performed correctly so you can rely on the data. With a well-executed data logger calibration, it is ensured that your data loggers measure the same values as all other devices.

In highly-regulated industries, this process is crucial for:

• Product quality: Maintaining the correct temperature prevents the degradation of pharmaceuticals and other temperature-sensitive products.
• Compliance: Adhering to standards and regulations set by bodies like the FDA and EMA.
• Operational efficiency and reputation: Avoiding costly recalls and maintaining trust with customers and other stakeholders.

Calibrations can be required by regulations or customers and is a key part of maintaining a high quality, whether working with medicine, medical samples or food.

Calibration is performed by comparing a value, e.g. temperatures, read by a data logger with a reference. By reading the difference between what the data logger measures and what the reference measures, you can calculate whether the data logger has measured correctly and how close to the true value the data logger has measured.

1. What is the reference temperature and sensor?

The reference temperature is the temperature measured by a reference sensor, which is more precise than the sensor under calibration. The reference temperature is used as a benchmark during the calibration. It ensures the accuracy and traceability of measurements by providing a fixed point of comparison.

2. What is calibration uncertainty?

During calibration, the measured temperature of the data logger is calibrated against a reference, but the comparison that is made will always have a certain degree of uncertainty. The measurement uncertainty describes how precise the two measured temperatures are when compared, thus giving a picture of how close to the “true value” a calibration can be expected to be.

This uncertainty, refering to the inherent error that cannot be eliminated when comparing the output from a data logger sensor to a reference temperature, is a recognized part of the calibration process and a fixed part of a given [calibration method](/temperature-calibration/whatkindoftemperaturecalibrationshouldichoose/.

The measurement uncertainty should always be shown in the calibration certificate.

3. What is Maximum Permissible Errors (MPE)?

Governmental and industry standards typically set forth Maximum Permissible Errors (MPE), which defines the extent of deviation, including calibration uncertainty, that can be tolerated for a sensor’s operation.

4. What is acceptable deviation in temperature calibration?

Acceptable deviation refers to the maximum allowable error limit during the calibration process that a temperature sensor can exhibit while still being considered accurate within its operational specifications. This term is crucial as it helps define the practical boundaries of sensor performance after calibration. Acceptable deviations are often noted on calibration certificates, indicating that the measured values are within the tolerable limits of error promised by the calibration provider. The acceptance level on a calibration certificate indicates whether any deviations from the true value are within a defined limit and if you can rely on the uncertainty that the supplier has promised.

5. What does accuracy mean within temperature calibration?

Accuracy refers to the closeness of a temperature measurement to the true value – the actual, precise temperature being measured. It indicates how correct the measurement is. While uncertainty quantifies the range within which the measurement is expected to lie, accuracy indicates how close the measurement is to this true value.

6. What is traceability in temperature calibration?

Traceability is a vital concept of calibration. Traceability in temperature calibration refers to the ability to link measurement results back to national or international standards through an unbroken chain of comparisons. This ensures that measurements are accurate and consistent across different contexts and locations. In other words, it guarantees that the data loggers provide the same result as any other traceable data logger. For instance, it means that 0 degrees should be the same in any country. Each step in the chain is documented, which allows the calibration to be verified and validated, providing confidence in the accuracy and reliability of the temperature data logger's readings.

7. What are temperature calibration standards?

Temperature calibration standards are benchmark temperatures that provide fixed reference points to ensure the accuracy and traceability of measurements.

Examples of temperature calibration standards are:

• Triple point of water (0.01°C): A primary calibration standard known for its precise and reproducible temperature point.
• Melting point of gallium (29.7646°C): Used in laboratories for calibrating thermometers and other temperature measurement devices.
• Boiling point of water (100°C at 1 atm): A widely recognized standard for basic calibration.
• Fixed points in the International Temperature Scale of 1990 (ITS-90): Includes freezing points of metals like tin (231.928°C), zinc (419.527°C), and aluminum (660.323°C) for high-precision calibration.
• NIST traceable standards: These standards are provided by the National Institute of Standards and Technology to ensure traceability and accuracy in measurements.
• Ice point (0°C): A basic calibration point for verifying the accuracy of temperature sensors at the freezing point.

8. What is a calibration certificate?

A calibration certificate is an official document issued by a calibration laboratory that verifies a temperature and humidity sensor has been calibrated according to specific standards. It details the calibration procedure, the measurement results, etc. The certificate serves as proof that the device has been accurately calibrated and meets the required specifications. It also indicates whether a performed calibration was accredited.

A temperature calibration procedure is a systematic process used to carry out the calibration. Unlike calibration standards, which are the fixed reference points, and calibration methods, which are the techniques used, a calibration procedure outlines the specific steps and protocol followed to ensure the device is accurately calibrated.

This will often look something like this:

Step-by-step guide to the temperature calibration procedure

1. Preparation and setup:

• Ensure the calibration environment is stable and free from temperature fluctuations.
• Gather all necessary equipment, including the sensor and calibration reference.

2. Initial check:

• Compare the sensor readings against the calibration standard without making adjustments.
• Document any deviations.

3. Adjustment:

• Adjust the data logger settings to match the calibration standard.
• Repeat the measurements to confirm accuracy.

4. Verification:

• Verify that the data logger maintains accuracy across the specified range.
• Perform additional tests if necessary to ensure consistency.

5. Documentation:

• Record the calibration process, results, and any adjustments made.
• Provide calibration certificates as proof of compliance.

6. Post-calibration review:

• Review the calibration certificate to ensure it meets all internal and regulatory requirements.
• Store the certificate and related documentation for future reference and audits.

Psst... With Eupry’s temperature and humidity monitoring solution you won’t have to worry about keeping track of or carrying out calibration.

It includes automated – ISO17025-accredited or traceable – calibration and the most efficient (patented) process you will find:

1. When due, we provide you with newly calibrated, external sensors.
2. You switch them in only seconds.

Your data stream is automatically maintained without gaps, and certificates are stored digitally. Handle all calibrations in seconds, directly at your location, and without changing data loggers.

When it comes to calibration services, the terms "accredited" and "traceable" are helpful in understanding the level of assurance and compliance offered by different calibration processes.

Here is a breakdown of each term to clarify their differences:

Accredited calibration:

• Certification: Accredited calibration means that the service is performed by a laboratory that has been formally recognized by an accreditation body. This recognition is based on the laboratory's adherence to international standards, such as ISO 17025.

Psst.. Did you know that, at Eupry, we have our own ISO17025-accredited calibration lab?

• Audit and oversight: Accredited laboratories undergo regular audits to ensure they meet stringent standards for their technical competence and quality management systems.
• Higher assurance: This type of calibration provides a higher level of assurance in the accuracy and reliability of the equipment calibration, along with detailed reporting that aids in regulatory compliance.

Traceable calibration:

• Standard compliance: Traceable calibration refers to a calibration service that can directly relate its measurements back to recognized standards through an unbroken chain of comparisons. This is typically documented to demonstrate that the measurements are consistent with national or international standards.
• Documentation: Traceability requires detailed records that document each step of the calibration process and the corresponding results.
• Broad applicability: While it ensures accuracy and consistency, traceable calibration does not imply the rigorous oversight or formal quality system compliance that comes with accreditation.

Is traceable and NIST calibration the same?

No, traceable and NIST calibration are not the same. Traceable calibration means that the calibration can be traced back to a recognized standard, which can be either national or international. This ensures that measurements are consistent with others that follow the same standards.

NIST calibration specifically refers to calibration that is traceable to standards maintained by the National Institute of Standards and Technology (NIST) in the United States. This type of calibration provides a direct assurance of accuracy and compliance with NIST standards, often required in specific regulatory environments within the U.S.

So, while all NIST calibrations are traceable, not all traceable calibrations meet the specific standards set by NIST.

Choosing the right calibration type for you

The choice between accredited and traceable calibration often depends on your regulatory requirements and the specific needs of your business.

• Accredited calibration is essential for industries such as pharmaceuticals and biotechnology, where compliance with standards is strictly monitored.
• Traceable calibration might suffice for internal standards and less regulated tasks where formal accreditation is not a necessity. Typically, you would opt for NIST calibration if your industry requires traceable calibration in adherence to U.S. standards.