ice point and boiling point methods microbica laboratory partners, inc. © 2011 1
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Thermometer Calibration
Ice Point and Boiling Point Methods
Microbica Laboratory Partners, inc. © 2011
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Why calibrate a thermometer? Directives or standards such as ISO 9000 or ISO 17025 require organizations to
provide accurate temperature measurements traceable to national or international standards. It is an important part of quality assurance in industry - for example in manufacturing to guarantee the quality of a product- and also to ensure effective testing or calibration by laboratories.
Temperature is a critical measurement for ensuring the safety and quality of many food products. Whether monitoring temperatures at receiving, throughout production or final product storage and distribution, thermometer calibration is essential. The validation, verification reassessment section of the Hazard Analysis and Critical Control Point system stated in the Code of Federal Regulations (9CFR 3:417.4) specifies that instruments used for monitoring critical control points must be calibrated.
Choosing a thermometer: If your thermometer is not accurate within +/- 2°F of 32°F., adjust the
thermometer accordingly. The ice point method permits calibration to within 0.1°F.
If your thermometer is not accurate within +/- 2°F of 212°F., adjust thermometer accordingly. The boiling point method permits calibration to within 1.0°F.
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Regulations
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Use an insulated Cup for thermal stability◦ We recommend a thermos
over Styrofoam cups Measure the cup height
against your thermometer probe◦ Probe should be at least
one inch shorter than the cup
Place hole in center of thermos lid.
Microbica Laboratory Partners, inc. (c) 2011
Ice Point Calibration 32F +/-2F
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Add ½ crushed ice and ½ tap water (distilled preferred)
Allow to set for couple minutes
Place Thermometer probe in center hole
Slosh Ice-water to verify stability.
Readings 32oF +/- 2oF =Ok◦ 32oF = 0oC
Prefer 32oF +/- 0.1oF
Microbica Laboratory Partners, inc. (c) 2011
Ice Point Calibration 32F +/-2F
If the temperature is not at 32oF (0oC), then hold the calibration nut securely with a wrench and rotate the head of the thermometer until it reads 32ºF (0oC). Follow manufacture’s instructions.
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Use a Pyrex cup or flask.◦ Metal pot not preferred
Fill cup 1.5inch below top. Bring water to a slow boil. Then place Probe in center
of cup for 1-2minutes or until stable.
◦ Keep probe off bottom of cup◦ Use a non-metal support
(safety) with vents/slots (keeps steam off dial) for visibility. And prevents loss of probe in hot liquid.
◦ Example: pasta scoop.
Microbica Laboratory Partners, inc. (c) 2011
Boiling Point Calibration 212F +/-2F
• Water boils at 212oF (100oC) at elevations of sea level to 1,000ft.
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Bimetallic Dial thermometers are sensitive only to about 2inches from the tip.
Most have a ‘dimple’ indicator.
Microbica Laboratory Partners, inc. © 2011
Using a Dial Thermometer
The full bimetallic part of this sensor must be immersed in the liquid (soup) or solid (meat) for accurate readings.
Test ‘slim’ cuts or portions from the side for best results.
Cut away view
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Dial: If the temperature is not at 32oF (0oC), Ice Point or 212oF (100oC) Boiling Point, then hold the calibration nut securely with a wrench and rotate the head of the thermometer.
Microbica Laboratory Partners, inc. (c) 2011
Calibration Adjustment
Digital: Follow manufacture’s instructions.
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Calibration Examples -Quiz
Laboratory Calibration
Boiling Flask, glass thermometer supported by clamp and stand
Correct. Note: Thermometer centered and does not touch bottom
9Microbica Laboratory Partners, inc. (c) 2011
Calibration Examples -Quiz
Boiling Point Calibration
Boiling Metal Pot, with clipped thermometers.
Not Preferred. Do not ‘cook’ thermometers during calibration.
•Does tip contact the pot or extend away?
•Metal Pot and water not necessarily same temperatures
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Calibration Examples -Quiz
Boiling Point Calibration
Boiling Metal Pot, With metal tongs.
Not Preferred. Note: Cooking method not good for calibration.
Salad tongs not made to hold thin rods. Thermometer can slip out.
11Microbica Laboratory Partners, inc. (c) 2011
Calibration Examples -Quiz
Ice Point Calibration
Covered insulated cup, glass thermometer with clamp and stand.
Acceptable TechniqueAvoid Styrofoam when possible
Never use glass thermometers with food.
12Microbica Laboratory Partners, inc. (c) 2011
Calibration Examples -Quiz
Ice Point Calibration
Cubed Ice in water glass
Not Preferred. Use crushed ice and insulated cup
13Microbica Laboratory Partners, inc. (c) 2011
Calibration Examples -Quiz
Ice Point Calibration
Glass thermometer in ice
NEVER USE GLASS THERMOMETERS IN FOOD !!!
14Microbica Laboratory Partners, inc. (c) 2011
Calibration Examples -Quiz
CALIBRATION SUMMARY
Avoid Styrofoam cups. Save environment
Pyrex cups work well for both Ice Point and Boiling Point
Insulated Cups with plastic lids best for Ice Point Calibration
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