0315 Calibrating the thermometers


This SOP provide instructions on how to calibrate the thermometers at KI biobanks to ensure that they function properly.

1. Purpose

Describe how the thermometers of the KI Biobank should be calibrated. These thermometers can be external, i. e. a movable thermometer inside the fridge, or internal, i. e. a fixed thermometer as for example in low temperature freezers, in which the temperature is displayed on the outside of the freezer. The calibration is performed with an externally calibrated reference thermometer.

2. Scope

All the thermometers in KI Biobank that measure the temperature in fridges, freezers, low temperature freezers, and heating cabinets.

3. Responsibility

The research assistant issuing this instruction is responsible for updating it and to make sure it is being followed.

4. Reference document

Manual: Testo 735-1 temperature sensor, Nordtec Instrument AB

5. Equipment

Calibrated Testo 735-1 instrument with a temperature sensor.

6. Functions of the reference thermometer, Testo 735-1

6.1 Turning on/off the instrument

  1. Connect the temperature sensor to the instrument before starting the measurement.
  2. Start: Press the power button. The instrument will turn into measuring mode.
  3. The measured value is shown as a numeric value or as --- if there is no value to show.
  4. To turn off the instrument: Press the on button for about 2 s until the display turns dark.

6.2 Temperature measurement/Calibration of thermometer

Once per year all the thermometers at KI Biobank should be calibrated.

All calibrations should be documented in the Form 0385 log sheet for calibration of thermometers (Blankett 0385 Loggblad Kalibrering av termometrar) in the logbook Reference thermometers for each thermometer.

Place the temperature sensor of the reference thermometer in the fridge/freezer at least one hour before the measurement. The whole sensor should not be inside, only 2/3 of the flexible metal. The yellow part should always stay outside. In the nitrogen tanks the sensor has to be bended so that it can hang on the edge, pointing downwards. In the low temperature freezers the sensor should be placed on the shelf at the bottom left.

Reading the temperature

1.   Start the instrument as in 6.1 above after at least 1 hour.

2.   Press Medel

3.   Choose Tid and press OK.

4  Press Start to start the measurement.

5.   After 10 min press Stopp to stop measuring.

6.   Read and document the value.

7.   Read the temperature on the thermometer to be calibrated.

8.   Turn off the instrument.

9.   Repeat from step 1 to get two measurements. (You do not have to wait one hour for the second measurement.)

Calculating the temperature deviation: Calculate the average of the two measurements – both the measured and read value.  Then calculate the difference between the measured average of the reference thermometer and the read average on the thermometer to be calibrated – the calibration factor K is calculated as in the example below:

Measured value (average) on the reference thermometer:          8.0°C

Read value (average) on the thermometer to be calibrated:        7.6°C

K is: 8.0 – 7.6 = +0.4

K= +0.4 should then be added each time the temperature is checked.


Print a label to put on the thermometer with the following information:

Date of calibration: (day/month/year)/Sign

Next calibration: (month/year)

K = (see example above)


6.3 Calibration low temperature freezers (-80˚ freezers)

  1. After leaving the thermometer at least 30 min inside the freezer, raise the temperature from -80˚ to -70˚, by pressing MODE until set temperature is shown. Press the arrows to change the temperature to -70˚ and then press ENTER. This is done to turn off the condenser which will make it easier to compare the measured values. The limit for the alarm is automatically set to     -65˚.
  2. After 10 min read and note the temperature on the freezer and on the reference thermometer.
  3. Repeat step 2 again after 10 more min.
  4. Calculate the temperature deviation as in step b above.
  5. Calibrate the freezer by pressing MODE until calibrate is shown. Press the arrows to adjust the temperature according to the calculated K, then press ENTER.
  6. Reset the temperature of the freezer to -80˚ and the limits for the alarm to -70˚ and -90˚ respectively. Do not forget to press ENTER after each adjustment.


6.4 Resetting the memory

When the reference thermometer shows that the memory is full, a resetting of the memory is needed:

  1. Press the button under triangle next to "Undermeny" shows in the display.
  2. Go down to Instr. using the arrows and choose OK.
  3. Go down to Reset using the arrows and choose OK.
  4. When ”Fabriksinställn.?” shows, press OK.
  5. Then choose ESC until back in the measuring mode.


7.    Calibration of reference thermometer

Once per year the reference thermometer with its sensor should be sent for external calibration. This calibration is performed by SP Sveriges Tekniska Forskningsinstitut. See Calibration of reference thermometer (Kalibrering Referenstermometer) in the logbook.

The calibration shall be done at five different temperatures: +65°C, +4°C, -20°C, -80°C och -180°C.

The certificate from the calibration should be saved under the Calibration of reference thermometer (Kalibrering Referenstermometer) in the logbook for the Reference thermometer.




SOP collection, KI Biobank. 0315 Calbrating the thermometers. The Molecular Methods Database. 2016/01/20

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