The Perfect Match: How to Choose a Temperature Calibrator

Estimated reading time:10 minutes 

Imagine this: a batch of life-saving vaccines hangs in the balance, jeopardized by a mere dip or rise in storage temperature. It's a powerful illustration of how important accurate temperature measurement is in our lives. Whether it's protecting pharmaceuticals or keeping food fresh, precise temperature control is absolutely vital. But how do you guarantee the accuracy of your temperature readings? The answer is simple: Prioritizing regular calibration using a temperature calibrator. Choosing the right calibrator, however, can be a complex task. This guide will help you navigate essential steps and features to find the best fit for your specific needs. 

What is a Temperature Calibrator? 

A temperature calibrator is a device used to verify and adjust the accuracy of temperature-measuring instruments, such as thermometers, thermocouples, and RTDs (Resistance Temperature Detectors). It creates a stable and controlled temperature environment, enabling you to compare the reading of your device under test with a known reference temperature. Regular calibration ensures reliable measurements, maintains product quality, complies with industry regulations, and helps prevent costly errors. 

Step 1: Define Your Application Requirements

Before diving into specific calibrator models, it's important to clearly define your application requirements. This will form the basis for all subsequent decisions.  

Ask yourself the following questions: 

• A. Temperature Range: What are the minimum and maximum temperatures you need to calibrate? This will determine the required temperature range of your calibrator. Make sure the calibrator's specified temperature range encompasses all the temperatures you need to calibrate. Some calibrators offer a wider range than others, so choose one that fits your specific needs. 

• B. Accuracy: Accuracy describes how close the calibrator's displayed temperature is to the true temperature, and is often expressed as a tolerance (e.g., ± a certain value). How accurate do your temperature measurements need to be, considering tolerances and acceptable deviations? 

• C. Measurement Uncertainty Requirements:  Uncertainty provides a more complete picture of the possible error in a calibration. It encompasses accuracy but also accounts for other factors like stability, resolution, and the influence of environmental conditions. Uncertainty is typically expressed with a confidence level (e.g., 95%), indicating the probability that the true temperature lies within the stated range. 

Tip: Think of accuracy as a snapshot of a single measurement, while uncertainty is a range of possible values around that measurement, reflecting the inherent limitations of the measuring process. 

•  Ratio of the test uncertainty to the calibrator uncertainty is also important. Your calibrator's uncertainty ratio should be significantly smaller than the uncertainty of the devices you are calibrating. A common rule of thumb is a 4:1 ratio (or better), meaning the calibrator's uncertainty should be at least four times smaller than the device under test's uncertainty. 

• D. Stability Requirements: How stable does the temperature need to be during calibration? High-precision applications require extremely stable temperature sources. Look for stability specifications, often expressed as a drift rate (e.g., °C/hour). A lower drift rate indicates better stability. Consider the stability over the entire temperature range you plan to use, as some calibrators may exhibit different stability characteristics at different temperatures. Also, consider the effect of external factors, such as ambient temperature fluctuations and air currents, on stability. If you're using a liquid bath, the type of fluid and its stirring mechanism will also influence stability. 

The following example from Mensor’s CTD9350 Dry-Well Calibrator datasheet illustrates key characteristics to look for. 

Other considerations include: 

• Types of Sensors/Probes Used: What types of temperature probes do you use (thermocouples, RTDs, thermistors)? This directly impacts the choice of readout and the compatibility with the temperature source. Consider also the sensor response time and potential for sensor drift. 

• Connection Type: How are the sensors connected to the calibrator? Make sure the connections are compatible. Does it have the right number and type of input channels if you are doing comparison calibrations? 

• Calibration Frequency: How often do you need to calibrate your instruments? Frequent calibrations suggest a need for more robust or portable equipment. 

Need help defining your application requirements? Our experts can guide you through the process. Schedule a free consultation today. 

Step 2: Select the Appropriate Temperature Source

Once you define your application requirements, you can choose the temperature source that meets your application's technical demands and operational conditions.  

Remember: The temperature source is the stable temperature environment, while a calibrator combines the source with a highly accurate reference measurement to compare your temperature device.  

When to choose: When portability is key, fast heating or cooling is needed, and moderate accuracy is sufficient. 

These devices allow for quick temperature adjustments in a controlled environment and are commonly used for field calibrations, on-site checks, and industrial process control where portability is important. When choosing a dry-block calibrator, consider its temperature range, stability, well size and depth, as well as the axial and radial uniformity within the block. Additionally, be cautious of possible loading effects when calibrating multiple probes simultaneously. Considering a dry-block calibrator? Explore our range of high-performance dry blocks here. 

When to choose: When high accuracy and stability are paramount, when calibrating irregularly shaped probes, or when wide temperature ranges are needed. 

Liquid baths maintain a very consistent temperature throughout the liquid. These are commonly found in laboratory calibrations, metrology, and pharmaceutical/biotech applications. When choosing a liquid bath, look at its temperature range, stability, uniformity, fluid type, and bath volume. 

When to choose: When calibrating smaller sensors or dealing with limited sample sizes. 

Micro-baths are frequently used in electronics manufacturing and small sensor calibration. When selecting a micro-bath, consider its temperature range, stability, and bath volume. 

Step 3: Choose Compatible Temperature Probes and Readouts

While you might already have temperature probes, there are several reasons why choosing compatible probes and readouts is important when purchasing a temperature calibrator. Compatibility with the calibrator's readout and required accuracy are key considerations. 

How to choose: Based on the temperature range, required measurement uncertainty, compatibility with the selected temperature source and readout, sensor response time, potential sensor drift, and the environment in which the probe will be used. 

When selecting a probe, consider its type, temperature range, accuracy (measurement uncertainty), sheath material, and connection type (2, 3, or 4-wire for RTDs). 

How to choose: Based on compatibility with the selected probe type and the required accuracy and features (e.g., data logging). 

For thermocouples, confirm the readout has cold junction compensation (CJC). Handheld thermometers are commonly used in fieldwork, while resistance bridges are used in high-accuracy lab work. When selecting a readout, look at its input types (thermocouple, RTD, etc.), accuracy (measurement uncertainty), resolution, features (data logging, connectivity), and input impedance. 

Step 4: Consider Environmental Factors and Other Practicalities

Beyond the core components of the calibrator, other practical and environmental factors should be considered before making your decision.  

A. Portability and Power Requirements: Determine if you need a portable calibrator for field use or if it will be used primarily in a laboratory setting. Portable calibrators often prioritize smaller size and battery operation, while lab-based instruments may offer greater accuracy and stability but require mains power. Consider battery life for portable units and the availability of appropriate power sources in your working environment.

B. Calibration Software, Automation, and Documentation: Evaluate the available software and documentation options. Modern calibrators often offer software for data logging, automated calibration routines, and the generation of calibration certificates. This automation can significantly reduce calibration time and minimize human error. Ensure the software is compatible with your existing systems and that the generated certificates meet your industry's traceability and accreditation requirements (e.g., ISO/IEC 17025).

C. Traceability and Accreditation: Traceability verifies the validity and acceptance of your calibration results. Therefore, it's important to confirm that the calibrator itself is calibrated and traceable to national or international standards. Look for calibration certificates that clearly outline the traceability chain and associated uncertainties.

D. Environmental Influences: The ambient environment can significantly impact calibration results. Consider the following:

• Ambient Temperature Fluctuations: Rapid changes in ambient temperature can affect the stability of dry-block calibrators. 
  
• Humidity: High humidity can affect the performance of some sensors and readouts.

• Air Currents: Drafts and air currents can cause temperature gradients around the calibrator, especially with dry-blocks.

E. Calibration Procedures and Best Practices:  How you intend to calibrate directly influences the type of calibrator you need. It's not just about the calibrator's specifications; it's about how those specifications align with your practical calibration process. Here's a breakdown:

• Immersion Depth (for liquid baths and some dry-blocks): If you're calibrating long probes or probes with specific immersion requirements, you'll need a liquid bath or a dry-block with sufficiently deep wells. A shallow dry-block won't be suitable. 

• Stabilization Time:  Calibrators with faster heating and cooling rates (like many dry-blocks) can reduce stabilization time. However, if your application requires exceptionally high accuracy, you might prioritize the superior stability of a liquid bath, even if it takes longer to stabilize. 

• Comparison Methods: Understand the different comparison methods used in calibration (e.g., direct comparison, substitution method) and choose the appropriate method for your application. 

F. Budget and Total Cost of Ownership: While the initial purchase price is important, consider the total cost of ownership, including:

• Calibration Costs: The cost of recalibrating the calibrator itself. 

• Maintenance and Repairs: Potential maintenance and repair costs. 

• Training: Costs associated with training personnel on proper calibration procedures. 

Get a personalized quote for your temperature calibration solution. Request a quote today.

G. Supplier Support, Service, and Expertise: Choose a reputable supplier like Mensor ;) that offers excellent technical support, calibration services, and readily available expertise. This can be invaluable in troubleshooting issues and ensuring the long-term reliability of your calibration equipment.

Navigating the complexities of temperature calibration can be challenging. Choosing the right calibrator requires a thorough understanding of your application, calibration procedures, and the capabilities of different calibration technologies. By following the steps outlined in this guide, you’ll be well-equipped to make an informed decision. 

However, expert guidance can be invaluable. At Mensor, our team of experienced professionals is ready to assist you in selecting the ideal temperature calibration solution for your specific requirements. Don't leave accurate temperature measurement to chance.  Contact us today for a free consultation and personalized recommendation tailored to your needs. Leverage our expertise for accurate, reliable, and compliant temperature measurements.