How To Calibrate A Bi-metal Thermometer

by Shawn S.

Why Calibration Is Important

bimetal thermometer in calibrator

Proper calibration provides confidence in knowing the temperature you are reading is correct. Depending on your application, this can be extremely important for procedures that require precise control. Thermometers should read within 2° of the actual temperature to be considered accurate. (+/- 1.1° C)

Know Before Go

Please Note: If you have a Liquid-in-Glass Thermometer, GIVE IT TO A PROFESSIONAL. If there is NO adjustment nut or calibration screw, GIVE IT TO A PROFESSIONAL. Typically the calibration screw can be found on the back of your unit. Although applications vary, when in doubt, play it safe.

Bimetal Calibration Equipment Options

  • Constant Temperature Bath
  • Dry Block Calibrator- This is the method we will be using in our example. As a general rule of thumb, the dry block or other source of accuracy should be four times better than the device under test. This is typical for most calibrations.


  • Prerequisites

    • 1 Hour Warm-up Time for Proper Stabilization
    • Temperature: 23 +/- 5 deg C
    • Humidity: 50 +/- 30%
    • Perform 3 Trials for Each Point or Range
    • Measurement Data Sheet (MDS)

    Required Equipment

    Calibration Procedure

    1. Take proper care and precautions, temperature calibrators generate extreme temperatures, which can be dangerous and potentially cause burns.
    2. Look for any visual defects that may affect the accuracy. Do not proceed if you find errors.
    3. Clean thermometer to the best of your ability
    4. Prep the measurement data sheet with the necessary information to identify the unit. (Brand, Product, Serial #)
    5. Determine the range of the thermometer, equally divide the range based on the scale, choose at least three or more test points based on the user's needs.
    6. Power on your Temperature Calibrator and set the desired temperature. Once it is fully stabilized, going from low to high heat, insert the probe into the holes of your calibrator.
      • Note: There are different sized holes for different size probes; choosing the correct one ensures maximum heat absorption and accuracy.
    7. Wait for display to stabilize (typically takes 15 min.), after tapping the face once, record the reading in the MDS.
    8. Wait two more minutes and get another reading. Repeat this process three times.
    9. Continue steps 7 and 8 until all setpoints are complete.
    10. Cross-reference level of accuracy provided by the manufacturer and your readings. (ie. accuracy = +/-1.5 % of Full Scale)
    11. Readings within limits can be labeled, sealed, and issued to its owner. If NOT within the listed limits, perform necessary repairs or adjustments.
    12. End of Verification

    To achieve the best accuracy, follow the recommended stabilization time, and ensure a proper immersion of stem or probes by tapping the face while taking a reading.

    For further assistance, or any questions, comments, or concerns, visit Instrumart.com or call at 1-800-884-4967 to speak with an application engineer. We offer free full tech support with every product we sell.