Temperature sensors monitor the most common quality metric in the manufacturing industry: temperature. These temperature measurement devices play a key role in ensuring temperature conditions are constantly kept at an optimal level during production, storage, and transportation of temperature-sensitive goods. Regular calibration of temperature sensors ensures the long-term accuracy of measurements and eventually, product quality and safety.
What is temperature calibration?
Temperature calibration is the process of comparing the measurements of a certain temperature instrument, such as a data logger, wireless sensor or simply a thermometer, to a reference device to establish the accuracy of the temperature instrument.
Any measurement deviances of the device to be calibrated are adjusted to the parameters of the reference device. The aim of calibrating temperature instruments is to minimise any uncertainty in temperature readings by ensuring their accuracy.
Calibration schemes are not only relevant in terms of product quality and safety, but also regarding compliance. Industry standards, such as the Good Distribution Practice (GDP) for pharmaceutical manufacturers, often require the use of only calibrated sensors for storing and transporting goods.
How to calibrate a temperature sensor?
As temperature sensors measure environmental temperature, their calibration involves exposing the sensor to a specific temperature in this stable temperature environment. Figure 1 outlines the most common method of temperature sensor calibration in form of submerging the sensor into a liquid bath or dry block. These temperature sources can be heated or cooled to the desired temperature for calibrating the device.
A separate reference sensor with a high level of accuracy is usually immersed together with the sensor that needs to be calibrated. The reference sensor itself should be calibrated to international standards to guarantee its accuracy. The readings of both devices are then compared, and potential deviances of the instrument to be calibrated are adjusted to the parameters of the reference device.
Figure 1: Most common method of temperature sensor calibration
During the calibration process, both sensors should be immersed to the same depth to ensure the same temperature readings. Another key factor of correct calibration is the length of the calibration process. As environmental temperature sensors need time to adjust to environmental temperature, it is important to schedule enough time for the calibration process.
High accuracy of iMonitor’s temperature monitoring devices
Exact temperature readings are essential for our customers in the food and pharmaceutical manufacturing, logistics, hospitality, and food retail industries. We take calibration very seriously and calibrate all our devices once a year to ensure that our customers can rely on the accuracy and consistency of the recorded data.
iMonitor works together with calibration provider Entec to calibrate all our devices. In 2019 and 2020, Entec calibrated roughly 1,400 iMonitor devices, ranging from high-temperature probes through wireless temperature sensors to hand-held Bluetooth probes.
The data of our calibration corrections during the last two years (see Figure 2) shows that the large majority of our devices measure very precisely. Only slight corrections needed to be undertaken during the calibration processes.
Figure 2: Calibration corrections for iMonitor’s temperature measurement devices
According to international standards, measurement deviances of up to 5 percentage points are tolerable in terms of the devices’ accuracy. All calibrations of iMonitor devices lay within these tolerances. The standard deviation for the IoT monitoring device SeRa 3, for example, was only 0.23 (See Figure 3). The accuracy of iMonitor’s temperature measurement devices combined with a thorough calibration policy guarantees that customers can measure temperature reliably and accurately.
|SeRa 3||SeRa 1||Probes||Probe 60°C||Probe 20°C|
Figure 3: Standard deviation for iMonitor’s temperature measurement devices