7. Timing of Temperature Measurement and Its Impact

in Introduction to Temperature Measurement

INDEX

7.1 Factors of Temperature Fluctuation and Their Impact
7.2 Summary

To improve the accuracy of temperature measurement, selecting the appropriate measurement timing is extremely important. Even for the same object, different temperatures may be observed due to factors such as the progress of heating or cooling, changes in the surrounding environment, and the thermal inertia of the measured object. If measurements are not taken at the correct timing, it may be impossible to accurately grasp the actual temperature, leading to discrepancies between the measurement results and the intended purpose.
For example, in a process where a halogen heater is used to heat a thick metal object, the surface temperature rises rapidly, but it takes time for the internal temperature to catch up. Additionally, in environments such as outdoor areas or factories, measurement values may fluctuate depending on the time of measurement and surrounding temperature changes, requiring careful timing management.

This chapter provides a detailed explanation of how the following three key factors influence measurement timing:
1. Temperature fluctuations due to heating and cooling progress
2. Effects of environmental temperature changes
3. Effects of the thermal inertia of the measured object

7.1 Factors of Temperature Fluctuation and Their Impact

Temperature is never constant and changes over time. If the measurement timing is incorrect, the obtained results may differ from the actual temperature, reducing the reliability of measurement data. The following sections explain in detail how measurement timing affects temperature fluctuations.

7.1.1 Temperature Fluctuations Due to Heating and Cooling Progress

In the heating and cooling process, different temperatures are observed depending on the measurement timing. Particularly when using infrared heating, such as with halogen heaters, temperature differences occur between areas directly exposed to heat and those that are not. If measurement timing and location are not appropriately selected, accurate temperature readings cannot be obtained.

Example: Temperature Fluctuation in a Heating Process Using a Halogen Heater
Immediately after heating starts: The surface temperature rises rapidly, but the internal temperature changes much more slowly.
During continued heating: The internal temperature gradually increases, reducing the difference between surface and internal temperatures.
After heating is completed and stabilized: The internal and surface temperatures become nearly uniform, making stable temperature measurement possible.

Appropriate Measurement Timing:
1. Wait until heating or cooling is complete and the internal temperature has become uniform before measuring.
2. Consider not only the surface temperature but also the internal temperature when conducting measurements.
3. During rapid temperature changes, take multiple measurements over time to improve data accuracy.

7.1.2 Effects of Environmental Temperature Changes

Measurement results are influenced not only by the object being measured but also by changes in the surrounding environmental temperature. Especially in outdoor measurements or indoor environments affected by air conditioning, temperature variations due to measurement time cannot be ignored.

1. Effects in Outdoor Environments
Temperature differs significantly between morning, afternoon, and night, making comparison difficult when measurements are taken at different times.
Example: In summer, asphalt can reach over 60°C during the daytime but drop below 30°C at night.

2. Effects in Indoor Environments
Room temperature changes due to air conditioning operation and human movement throughout the day.
Example: In a factory, room temperature rises due to machine operation, causing measurement results to vary depending on the time of measurement.

Countermeasures:
1.Standardize measurement times to ensure comparability under the same conditions.
2.Conduct measurements in locations and at times that are less affected by environmental temperature fluctuations.
3.Perform continuous measurements and use the average value to reduce the impact of fluctuations.

7.1.3 Effects of Thermal Inertia of the Measured Object

Thermal inertia refers to the delay in an object’s response to temperature changes, which is mainly determined by heat capacity and thermal conductivity. Objects with high heat capacity experience slower temperature changes, and when heat transfer speed is low, temperature distribution changes more gradually. This can result in different measured values depending on the timing of measurement.

Examples of How Thermal Inertia Affects Measurement:

1. Heating of a Metal Block
Immediately after heating starts: The surface temperature rises rapidly, but the internal temperature remains mostly unchanged.
After several hours: Heat penetrates internally, allowing for a uniform and accurate temperature measurement.

2. Thick Plastic Parts
During rapid heating: The surface heats up quickly, but the internal temperature takes time to rise.
After a period of time: Heat fully penetrates, allowing for a stable temperature measurement.

Appropriate Measurement Timing:
Wait until the internal temperature of the object stabilizes before measuring.
Perform multiple measurements to improve measurement accuracy.
For thick objects, consider both surface and internal temperatures.

7.2 Summary

If the timing of temperature measurement is incorrect, the obtained values may differ from the actual temperature. By selecting an appropriate measurement timing, more reliable data can be obtained.

Key Points for Selecting the Right Measurement Timing:
✅ Ensure that heating or cooling is completed and temperatures are stable before measurement.
✅ Consider both surface and internal temperatures to obtain accurate data.
✅ Standardize measurement timing to minimize the influence of environmental factors.
✅ Take multiple measurements over time for improved accuracy in rapidly changing conditions.

Selecting the proper measurement timing is the key to accurate temperature management.