Calibration of Temperature Sensors

Customers often ask: "I have located a few thermometers and temperature meters in the same room but they show a different temperature. Which devices or thermometers should we believe? “

There is a certain temperature gradient in any room even without ventilation. Within two meters horizontal temperature gradient may be 2 °C, but a temperature difference between the floor and the ceiling may consist up to 10 °C. Therefore, the difference in a few degrees of the readings within the room is not an indicator of equipment malfunction.

However, if there is any doubt,  you should perform the calibration test or at least checking of measuring instruments.

The calibration is testing of measuring instruments with the purpose to confirm their accuracy. Each instrument should be calibrated before it is shipped out. Usually one year of calibration period is specified in the certificate. So, to be sure in correct measurements, thermometers should be checked in the Regional State Standard laboratory once a year, where specialists will confirm the correctness of metrology measurements or recognize them unusable.

It is clear that all temperature instruments used by customers are hardly possible to calibrate in the State Standard laboratories. We recommend you to select at least one thermometer or temperature indicator (the most accurate of those that you have) and calibrate it every year. Such a standard precision instrument will allow you to check the measurement of all temperature instruments by your own.
 

Measuring instruments can be checked by comparison. You will have to pour water in any container. Then the container, sensors and metallic open thermos should be kept for some time in the place where they will be compared in a few hours. By this time the water and the thermos wall will accept room temperature (picture1). Pour the water in the thermos and immerse the sensors and thermometers into it (picture 2). Keep it for at least half an hour. After that, we can assume that the unevenness of the water temperature in the thermos will be less than 0,2 °C and it can be possible to compare the indications. The indications of devices and thermometers should be compared with the indication of the standard precision thermometer. 

If the difference between the device indications and the standard precision thermometer differ by no more than the sum of errors plus 0,2 ° C, it means that devices and thermometers measure correctly.

If you find that any of the glass thermo- meters indicate incorrectly, it cannot be used anymore. If you find the wrong indicating of any sensor or measuring instrument, it should be calibrated in the State Standard laboratory. The specialists will measure the exact deviation from the true value and amend the device. After that the instrument will once again show correctly.