Calibrating Bimetallic Stemmed Thermometers

Transcription

1 L E S S O N 3 Calibrating Bimetallic Stemmed Thermometers Lesson Objectives Getting Ready 1. Explain the importance of thermometer calibration. 2. Demonstrate the ice water method for calibrating thermometers. 3. Demonstrate the boiling water method for calibrating thermometers. 4. Document calibration of thermometers. Materials VCR and monitor Videotape, Your Guide to Thermometers in Foodservice Thermometer Toolkit Copies of Handouts 4, 5, and 6 for each participant (pages 33, 34 and 35) Bimetallic stemmed thermometers (one for each participant, if available) 2 quart liquid measure Ice, crushed Cold water Sauce pan Boiling water Calibration tool or wrench Pot holders Paper towels Note to Trainer All employees may not need all components. The trainer can select sections most appropriate for individuals being trained. This lesson requires some preparation. Ice and cold water are needed to demonstrate the ice water method of thermometer calibration and boiling water is needed to demonstrate the boiling water method of thermometer calibration. Lesson Format Lesson 3 can be taught as one lesson or as three shorter lessons. If all material and activities in the lesson are covered, the lesson will take about 40 minutes to complete. If time is limited, the lesson could be broken down into smaller units. Possible divisions for shorter lessons: Importance of Calibration, Key Point minutes Methods of Calibration, Key Point minutes Documenting Calibration, Key Point minutes Lesson 3 Calibrating Bimetallic Stemmed Thermometers 29

2 Lesson Content Importance of Calibration Key Point 1 Weekly calibration of thermometers is needed to ensure accuracy of temperatures taken. Estimated time: 10 minutes Tools used for various tasks should be accurate. What would happen if you were putting up a shelf and your level was off plumb? What happens when you weigh yourself on scales that are not accurate? What results do you get when you take temperatures with thermometers that are not calibrated? Temperatures taken in foodservice should be accurate. Proper temperatures ensure food safety. For example, a thermometer might measure temperatures 4 F too low a hamburger cooked to only 151 F would appear to be cooked to 155 F. Calibration of thermometers is the process used to ensure that thermometers record temperatures within ±2 F of the actual temperatures. A C T I V I T Y I D E A Ask participants to brainstorm problems that might occur if thermometers are not calibrated. Note: Possible answers may include undercooked and potentially unsafe food, or overcooked food with compromised food quality. Some digital stemmed thermometers (thermistors) can not be calibrated. These thermometers should be checked regularly to determine accuracy. Batteries also need to be changed regularly. Some thermometers, such as thermocouples and infrared, may need to be calibrated by the manufacturer. When is calibration needed? Thermometers are sensitive. The shock of extreme temperatures or jolting that occurs if they are dropped can cause thermometers to lose accuracy. Some food safety experts recommend calibrating thermometers daily. At a minimum, thermometers should be calibrated weekly. 30 Thermometer Information Resource

3 Methods of Calibration Key Point 2 Two methods for calibrating bimetallic stemmed thermometers are ice water method and boiling water method. Estimated time: minutes Two methods of calibrating thermometers used in foodservice are ice water method and boiling water method. The ice water method is preferred to the boiling water method unless the thermometer is not designed to measure 32 F. Refer to the manufacturer s instructions for specific thermometers. The boiling water method is less reliable because of variations in factors such as altitude and atmospheric pressure. There also is a safety concern because it would be easy for an individual to get a water or steam burn if the process is not done carefully. A C T I V I T Y I D E A Show the third segment of the videotape, Your Guide to Thermometers in Foodservice. A C T I V I T Y I D E A Provide each participant a copy of Handout 4, Ice Water Method for Thermometer Calibration. Demonstrate the ice water method of calibration using a bimetallic stemmed thermometer. Give each participant a bimetallic stemmed thermometer, if available, and have them practice calibrating a thermometer. If you use digital stemmed thermometers (thermistors), distribute one to each participant and have them check the accuracy of the thermometer. If they can be calibrated, have participants calibrate. O P T I O N A L A C T I V I T Y I D E A Give each participant a copy of Handout 5, Boiling Water Method for Thermometer Calibration. Demonstrate the boiling water method for thermometer calibration using a bimetallic stemmed thermometer. Give each participant a bimetallic stemmed thermometer, if available, and have them practice calibrating a thermometer. If you use digital stemmed thermometers (thermistors), distribute one to each participant and have them check the accuracy of the thermometer. If they can be calibrated, have participants calibrate. Lesson 3 Calibrating Bimetallic Stemmed Thermometers 31

4 Documenting Calibration Key Point 3 Documenting calibration of thermometers shows that temperature readings are accurate. Estimated time: 10 minutes Each time thermometers are calibrated, it is important to document that calibration was completed. This provides a clear documentation trail for co-workers, as well as for the health department in the event there is a question about food safety or cooking to appropriate temperatures. A Thermometer Calibration Record is used to record information such as: Date and time that thermometer was calibrated Identification number for the thermometer (assigned by facility) Use of the thermometer (for example, for hot or cold foods) Reference temperature at which the thermometer was calibrated (either 32 F or 212 F) Initials of the individual who did the calibration The calibration process should be verified by a supervisor weekly, and that person should date and initial the Thermometer Calibration Record. Verification is done to ensure that thermometers are being calibrated as outlined in the standard operating procedures. This verification also emphasizes the importance of calibration to employees. If calibration has not been done, the supervisor should follow up with employees. A C T I V I T Y I D E A Distribute a copy of Handout 6, Thermometer Calibration Record, to each participant. Review the information that must be recorded on the form. Have each participant calibrate a thermometer and document the calibration process on the form. 32 Thermometer Information Resource

5 H A N D O U T 4 Ice Water Method for Thermometer Calibration (for bimetallic stemmed and digital thermometers that can be calibrated) Equipment/Ingredients Quantity Directions 2-quart measure Ice, crushed Cold water 1 to fill container to fill container 1. Fill a 2-quart measure with ice. 2. Add water to within 1 in. of top of container. 3. Stir mixture well. 4. Let sit for one minute. Thermometer 1 per participant, if available 5. Place thermometer in container so that the sensing area of stem or probe is completely submerged (over the dimple). 6. Do NOT let the thermometer stem/probe touch sides or bottom of container. 7. Let thermometer stay in the ice water for 30 seconds or until the dial stops moving. Calibration tool or wrench 1 per participant (or 2 participants could share) 8. Place the calibration tool on the hex adjusting nut and rotate until the thermometer dial reads 32 F (while in ice water). 9. Some digital stemmed (thermistors) and thermocouples have a reset button, which should be pushed. 10. Repeat process with each thermometer. Stem Head Hex Adjusting Nut Ice Water (32 F, 0 C) 2 in. (5 cm) Minimum Lesson 3 Calibrating Bimetallic Stemmed Thermometers 33

6 H A N D O U T 5 Boiling Water Method for Thermometer Calibration (for bimetallic stemmed and digital thermometers that can be calibrated) Equipment/Ingredients Quantity Directions Deep saucepan or stockpot Water Potholders Thermometer Calibration tool or wrench 1 to fill container 2 1 per participant, if available 1 per participant (or 2 participants could share) 1. Fill the saucepan or stockpot with water. 2. Bring water to a rolling boil. 3. Place thermometer in container so that the sensing area of stem or probe is completely submerged (over the dimple). 4. Do NOT let the thermometer stem/probe touch sides or bottom of container. 5. Let thermometer stay in the boiling water for 30 seconds or until the dial stops moving. Note: Take safety precautions by properly using pot holders with boiling water and being careful not to let steam come in contact with body. 6. Place the calibration tool on the hex adjusting nut and rotate until the thermometer dial reads 212 F (while in boiling water). 7. Some digital stemmed (thermistors) and thermocouples have a reset button, which should be pushed. 8. Repeat process with each thermometer. Note: The boiling point of water is about 1 F lower for every 550 feet above sea level. If you are in high altitude areas, the temperature for calibration should be adjusted. For example, if you were at 1100 feet above sea level, the boiling point of water would be 210 F. NOTE: Be extremely careful to avoid water and steam burns when using the boiling water method. Boiling Water (212 F, 100 C) Stem Head Hex Adjusting Nut 2 in. (5 cm) Minimum 34 Thermometer Information Resource

7 H A N D O U T 6 Thermometer Calibration Record School Date Time Thermometer Identification Use Reference temp. ( F) Calibrated by Date of Verification Verified by Example: 1/10/05 10:30 am B2 Meats 212 B. Smith 1/12/05 J. Brown Example: 1/17/05 8:00 am B2 Meats 212 B. Smith 1/24/05 J. Brown Lesson 3 Calibrating Bimetallic Stemmed Thermometers 35

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