Is Temperature Really Important During Calibration?
It’s all too easy to take for granted just how important scales, gages and electronic testing equipment are in our daily lives. They work to keep the roads safe and make sure we get a fair shake at the supermarket when buying our favorite fruits and veggies. They even help make sure our medications are exactly as they should be. Because of this, all devices must be regularly calibrated to ensure they measure objects with a degree of accuracy.
Calibration needs to be done very carefully, as several variables can affect it. If calibration is done incorrectly, the electronic equipment can give skewed results, or a scale can give a false weight — either too much or too little — which can affect the device’s performance until the next calibration.
But what about temperature? Can it really affect the outcome of a calibration? In a word, yes. Maintaining an even temperature is crucial during calibration, whether you need electronic calibration, physical dimensional calibration or even some instances of pressure calibration, and here’s why.
How Temperature Affects Calibration
Several factors can affect the overall accuracy of a measuring device. Temperature is one factor that affects all devices, causing their measurements to deviate or drift over time. This is why many devices need a temperature controlled-environment for calibration.
General Requirements for Calibration
Environmental conditions affect all reference standards and test equipment used in calibration. As required in ISO 17025:2017, the calibration laboratory must monitor and control environmental conditions such as temperature according to relevant specifications. We need to monitor, control and record the temperature throughout calibration to reduce its influence on the validity of measurement results.
Calibration laboratories can operate outside the specified temperature as long as they compensate for any environmental contributors to correct their measurement results and uncertainty values. However, this process is time-consuming, and working in a temperature-controlled laboratory can save a lot of resources.
The Goldilocks Zone
Remember the story of Goldilocks? Everything had to be just right, not too hot and not too cold. Well, calibration works very similarly. The issue is that metal doesn’t exist at a set volume or size but can swell or shrink due to the temperature of its environment.
In pressure calibration, temperature changes the density of metal. Higher temperatures cause it to expand, and lower temperatures cause it to shrink. When this happens to the metal parts used in calibration instruments, it can lead to inaccurate measurements and decreased sensitivity.
Looking at it on an atomic level, all of the atoms that make matter (those not subjected to absolute zero) are in a constant state of motion. As the metal heats up, the atoms become more active, buzzing and vibrating faster. This atomic buzz means the atoms occupy more space, which in turn causes the metal to expand. Conversely, when it becomes cold, metal contracts due to the atoms slowing down and vibrating less violently.
This expansion and contraction can make a huge difference in accuracy when it comes to the calibration of many measuring instruments. Some physical/mechanical and electronics are so sensitive that a temperature difference of 2 degrees Fahrenheit in either direction can affect the measurements.
Drifting out of Balance
Most calibration instruments have manufacturer-defined ambient temperature limits that make it easier to ensure accurate readings. However, instruments can vary widely in how they perform outside of those limits, and while some manufacturers provide a residual ambient temperature coefficient for their products, some do not.
Once the ambient temperature in the calibration environment has varied beyond an instrument’s limit range, the metal parts of the instrument begin to swell or shrink. This alteration manifests differently depending on the type of instrument, but decreased accuracy is the consistent result.
Calibration relies on knowing whether or not an instrument’s readings are accurate and how much they need to be corrected. Temperature regulation is essential to maintain consistently accurate evaluations.
Physical Dimensional Calibration
All dimensional equipment must receive routine testing and calibration to measure the physical size of objects accurately. Dimensional measurements are significantly affected by temperature variations and require a stable temperature environment to obtain a high level of accuracy. The temperature requirement for a dimensional calibration laboratory is referenced to 68 degrees Fahrenheit (20 Celsius), but it may change based on the instrument specifications.
Physical mechanical gages that contain steel gage blocks as a measuring medium require temperature control — this is due to the changes in size that occur as metal heats up and cools down. We need to prevent any expansion or contraction from affecting measurement results generated from dimensional calibration, so a temperature-controlled environment is crucial for sensitive instruments such as high-resolution dial gages.
The electronics used in an instrument may be affected by temperature variations. Environmental conditions, such as the ambient temperature, can introduce errors to electronic equipment that affect the validity of measurement results. When testing samples with unknown values, these errors may not be readily apparent.
If electronic measuring equipment is calibrated at one temperature but operated at a significantly different temperature, its tolerances will drift and degrade the result’s accuracy. Rusted metals or corrosion can create a leakage path for current and voltage, leading to equipment malfunction or inaccurate results.
The temperature requirement for electrical or electronic calibration is typically about 73 degrees Fahrenheit (23 Celsius). However, electrical measurements can handle a broader temperature range than dimensional specifications. While temperature fluctuations are more tolerant for electronic calibration, strict temperature control is still vital to perform measurements accurately.
Temperature Controlled Calibration
Garber Metrology has earned several certifications, including an ISO/IEC 17025 Accreditation from the American National Standards Institute (ANSI) National Accreditation Board (ANAB). This certification confirms our commitment to accurate calibration. Our lab is fitted with thermodynamic instruments to measure temperature and regulate the environment, such as:
Temperature and humidity data loggers.
With these measures in place, we can monitor both the temperature and humidity in the testing environment. By controlling those environmental factors, we ensure that every reading and calibration we perform is as accurate as possible.
The Practice of Metrology
Many different businesses rely on having an accurate ability to measure and weigh. Some perform numerous stress tests to ensure that a product will be safe and functional in even the harshest conditions. Because of this, Garber Metrology has been in the business of calibrating scales, transducers, and other measurement devices throughout the Mid Atlantic region for more than 40 years. Our goal is to ensure the accuracy and peace of mind that companies need. If you need accuracy, Garber handles sales, service, installations and even regular calibrations for all things measured.