SOP for Calibration of Glass Thermometer

Objective

To provide a standard operating procedure for calibrating a filled glass thermometer.

Scope

This procedure applies to all thermometers used in plants.

Responsibility

Doing: Technical Assistant/Executive

Checking: Executive /Manager

Accountability

Head of the Department

Procedure

Frequency: Once in a six-month

• Assign a Q.C Report No to each thermometer as per the following logic TPL/0000 

        Where,

        TPL= Abbreviation of Company 

        0000 = serial number.

• Keep the thermometer which is to be calibrated at room temperature till room temperature is achieved.
• Inspect the thermometer for cracks, gaps, clear correct markings, chipped or distorted glass, and separation in the mercury column.
• If separation in the mercury (liquid) column, is found then take the following corrective action.

1. Immerse the bulb portion of the thermometer in a block of dry ice until the meniscus has stopped moving. Ensure not to freeze the mercury (liquid) in the bulb.
2. If the separation remains, gently tap the bulb on a soft object and swing the thermometer in a small arch until the mercury (liquid) is united.

• Thermometers with measurement ranges above 50℃ are calibrated by a third party.
• Calibration Procedure for thermometer having measuring range up to 50℃.

1. First, keep all 50 range thermometers at room temperature till room temperature is achieved.
2. After achieving room temperature, keep all thermometers with reference thermometers in an ice bath.
3. Ensure the thermometer is immersed to the proper immersion depth.
4. When the meniscus has stopped moving gently tap the thermometer, as some amount of the meniscus may adhere to the wall of the thermometer.
5. View the 0℃ mark and compare the test thermometer with the reference thermometer.
6. Record the value of the test and reference thermometer in Annexure-I.
7. Use low low-temperature water bath for calibration.

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• For the first temperature point use the following procedure.

1. Set the water bath at 10℃ + 1℃ temperature. After achieving the temperature of 10℃ + 1 ℃, keep the reference calibrated thermometer and test thermometer inside the water bath.
2. After 5 minutes observe the temperature of the reference and test the thermometer.
3. Record the value of the test and reference thermometer in Annexure-I.

• For the second temperature point use the following procedure.

1. Set the water bath at 25℃ + 1 ℃. After achieving the temperature of 25℃ + 1 ℃, keep the reference calibrated thermometer and test thermometer inside the water bath.
2. After 5 minutes observe the temperature of the reference and test the thermometer.
3. Record the value of the test and reference thermometer in Annexure-I.

• For the third temperature point use the following procedure.

1. Set the water bath at 40℃ + 1 ℃. After achieving the temperature 40℃ + 1 ℃, keep the reference calibrated thermometer and test thermometer inside the water bath.
2. After 5 minutes observe the temperature of the reference and test thermometer.
3. Record the value of the test and reference thermometer in Annexure-I.

• Ensure the results are within the tolerance limit.
• If values are out of tolerance, keep the thermometer for 72 hrs. For stabilization and then recalibrate it.
• If it is out of the limit, remove it from the services and destroy the thermometer.
• Maintain the issue record of the thermometer as per Annexure-II.

Annexure

Abbreviations

℃: Degree centigrade

Revision History

Nil

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