Do you know how you calibrate a thermometer? Calibrating a thermometer may be a simple but necessary process.
If you’re anything like me, you’ve probably got a couple of thermometers dancing around your drawer of miscellaneous kitchen tools. But are they accurate?
If you’re roasting a turkey, a degree or two of inaccuracy isn’t going to make a dramatic difference. How do you calibrate a thermometer in general? Keep reading!
But if you’re making caramel, tempering chocolate, cooking sous vide, grilling a steak, or performing any other tasks requiring a particular temperature, having a thermometer you’ll trust is clutch.
Calibrate a Thermometer
Calibrating your thermometer is quick and easy. Many analog and digital thermometers allow you to offset the temperature to regulate the calibrated value.
However, if your thermometer doesn’t offer an offset function, a bit of blue tape with the delta will work fine.
Calibrating a thermometer involves checking and adjusting its accuracy to ensure accurate temperature readings. Over time, thermometers can drift from their original calibration due to wear and tear, exposure to extreme temperatures, or improper handling. Calibration is vital in various settings where temperature accuracy is critical, such as in scientific laboratories, food service establishments, healthcare facilities, and industrial processes.
Calibrating a thermometer typically involves comparing its readings against a known reference temperature, such as a standard thermometer or a calibrated temperature source, and making adjustments if necessary. The specific method for calibrating a thermometer depends on its type and design, but it generally involves the following steps:
Preparing the reference temperature
The reference temperature source or standard thermometer used for comparison should be appropriately calibrated and stabilized to a known temperature.
Comparing readings
Place the reference temperature source and the calibrated thermometer nearby, ensuring they are exposed to the same temperature. Allow them to stabilize for a sufficient period, and then compare the readings of the two thermometers.
Adjusting if necessary
Adjustments may be needed if the readings of the thermometer being calibrated deviate from the known reference temperature. Some thermometers have a calibration screw or knob that can be adjusted to bring the readings in line with the reference temperature. Others may require professional calibration by a qualified technician.
Verification
After making adjustments, recheck the readings of the calibrated thermometer against the reference temperature to ensure that they match within an acceptable tolerance.
Documentation
Record the calibration results in a calibration log or certificate for traceability and quality control purposes, including the date, reference temperature used, and any adjustments made.
Method 1: ICE Water
1. Fill a glass with ice cubes, and then top off with cold water
2. Stir the water and let it sit for 3 minutes
3. Stir again, and then insert your thermometer into the glass, making sure not to touch the sides
4. The temperature should read 32°F (0°C). Record the difference and offset your thermometer as appropriate
Method 2: Boiling Water
1. Boil a pot of distilled water
2. Once the water has reached a rolling boil, insert your thermometer, making sure not to touch the sides or bottom of the pot
3. The temperature should read 212°F (100°C). Record the difference and offset your thermometer as appropriate
Why It’s Important to Calibrate Your Thermometer
Calibration gives you the peace of mind of knowing the temperature you’re reading is the correct temperature of the media you’re measuring.
This can be extremely important for procedures that require precise temperature control, such as industrial chemical processes and food preparation.
Many cities and state health departments have food storage guidelines with strict temperature ranges from which edibles can’t deviate. Beyond the regulations, you don’t want anyone to get sick because your thermometer said your pork ribs were 145° F when they were only 110° F.
That is an extreme example. A thermometer far off the register would likely need to be replaced. To be considered accurate, a thermometer should register within 2° F of the actual temperature, which is 1.1° C.
Testing should be done regularly, depending on the frequency of use and the thermometer’s purpose. Thermometers used for processes that require precise measurements should be tested daily or week ifIf a thermometer goes out of calibration often. The replacement may be necessary.
How do You Calibrate a Thermometer
There are a couple of alternative ways to calibrate digital and bi-metal thermometers.
The most common comparison is boiling and freezing. There are also thermometer calibration services that will do that for a price.
The liquid in glass thermometers should be sold directly by the manufacturer. Feature an adjustment screw on the rear of the dial. Note that if your thermometer doesn’t have an adjusting nut (or calibration screw, etc., usually found on the rear of the thermometer, you’ll need to send it to one of these services for re-calibration.
The duration choice bi-metal thermometers we sell have an optional calibration dial on the rear of the dial case. The first and simplest method is to compare them.
That is, compare the thermometer you think might need recalibration to one that has already been calibrated or has been certified by the National Institute of Standards and Technology (NIST).
This is why a NIST-certified thermometer
This method is often effective; goodbye, as you’re confident that the comparison thermometer is reading correctly. This is why a NIST-certified thermometer, tested annually, is preferable.
Just compare the two and adjust the thermometer you’re calibrating to match the “correct” thermometer’s temperature.
This should be done with distilled water, as tap water contains compounds that could affect the freezing or melting points of water and skew the process.
A calibration ice water or “Freezing” thermometer is best for thermometers used to measure low temperatures.
Add crushed ice to a bowl or cup of water to make a slushy mix at least 2” deep. Insert the thermometer stem into the slushy mix for at least one minute.
Make sure the stem does not contact the sides or bottom of the container. The thermometer should read between 30 and 34° F. If it doesn’t, adjust the dial to 32° F.
A thermometer won’t measure higher temperatures, so to calibrate, you might prefer the boiling method. Again, use distilled water and bring it to a rolling boil in a pot or kettle if you have one handy.
Insert the thermometer’s stem a minimum of 2” into the water for a few minutes, taking care not to burn yourself. Do not let the stem touch the edges or bottom of the container.
The thermometer should read between 210 and 214; if it does not, adjust the dial to 212°F.
That boiling point is at sea level. However, since the boiling point changes at different altitudes, you must consult a chart like this one to determine the correct boiling point for your elevation. You can find your elevation here.
(FAQs)
Q: What does it mean to calibrate a thermometer?
A: Calibrating a thermometer means adjusting it to ensure that it measures temperature accurately and provides reliable readings. It involves comparing the thermometer’s readings to a known standard or reference thermometer and making necessary adjustments.
Q: Why is it important to calibrate a thermometer?
A: Calibrating a thermometer is essential to ensure accurate temperature measurements. Temperature is critical in various applications, such as food safety, medical care, scientific research, and industrial processes. An inaccurate thermometer can lead to incorrect results, which can have serious consequences, such as foodborne illnesses or compromised scientific experiments.
Q: How often should I calibrate my thermometer?
A: The calibration frequency depends on the type of thermometer and its intended use. As a general guideline, thermometers used for critical applications, such as food service or medical care, should be calibrated more frequently, ideally before each use or at least once a month.
Other thermometers used for less critical applications may require calibration at regular intervals, such as every 3-6 months or annually. For specific recommendations, it is important to refer to the manufacturer’s instructions and industry guidelines.
Q: How can I calibrate a thermometer?
A: The calibration method depends on the type of thermometer. Here are some standard methods:
Ice bath method: Fill a container with crushed ice and add a small amount of water. Stir the mixture to create a slurry. Insert the thermometer probe into the slurry, avoiding contact with the container, and wait for the reading to stabilize. The temperature should read 0°C (32°F), which is the freezing point of water.
Boiling water method: Bring a pot to a rolling boil and insert the thermometer probe into the water, avoiding contact with the pot. Wait for the reading to stabilize. The temperature should read 100°C (212°F) at sea level or adjust for altitude if necessary.
Comparison method: If you can access a calibrated reference thermometer, you can compare its readings with the calibrated thermometer. If there is a discrepancy, you may need to adjust the calibration of the calibrated thermometer based on the difference between the two readings.
Q: What should I do if my thermometer is not calibrated or is consistently inaccurate?
A: If your thermometer cannot be calibrated or is consistently inaccurate, it may need to be replaced or repaired. Some thermometers, especially digital ones, have a limited lifespan and may need to be replaced periodically. Contact the manufacturer or a qualified technician for further assistance.
Q: Are there any additional tips for calibrating a thermometer?
A: Yes, here are some additional tips for calibrating a thermometer:
1. Allow the thermometer to stabilize in the calibration environment for a few minutes before taking a reading.
2. Avoid touching the probe or the thermometer housing with your hands, as it can affect the temperature reading.
3. Keep the thermometer probe clean and debris-free to ensure accurate measurements.
4. Store the thermometer properly when not in use, following the manufacturer’s recommendations.
5. Record calibration dates, results, and adjustments for documentation and traceability.
Final Thoughts
Calibrating a thermometer is a critical step in ensuring accurate temperature measurements. For the most reliable results, refer to the manufacturer’s instructions and use a certified reference thermometer. Regular calibration, proper handling, and following best practices will help you maintain accurate temperature readings and ensure the safety and well-being of those relying on your thermometer measurements.
When a change of this type occurs, the thermometer’s indication will also change. Re-calibration of the certified thermometer updates the indications and thus allows the user to maintain accurate, reliable, and consistent results when making temperature measurements.
Even if your thermometer can’t be calibrated, you can – and should – use these methods to check its accuracy and ensure that you’re getting a proper temperature read on your food. Follow the manufacturer’s instructions for taking temperatures. Always calibrate a new thermometer that has been dropped on a hard surface.
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