In contact-type temperature sensors such as thermocouples and resistance thermometer, heat is transferred from the object being measured to the temperature-sensing part, and the temperature change of the temperature-sensing part is detected as an electrical signal.

Therefore, simply fixing a temperature sensor to the equipment does not necessarily guarantee that you are measuring the desired temperature.

Consider what temperature the temperature-sensing element is at.

For example, even when measuring the fluid inside a pipe, the heat conditions the sensor experiences will change depending on whether the temperature-sensing element is located close to the pipe wall or is embedded in the fluid.

Similarly, multiple heat sources and heat paths exist: the atmosphere and the workpiece in a furnace, the liquid and the wall in a tank, and the object being measured and the surrounding air in surface measurements.

When installing a temperature sensor, the basic principle is to think not about "where to attach the sensor," but rather "what temperature do you want the temperature sensing element to be at?"​

Sensor selection and installation are separate decisions.

Sensor accuracy, temperature range, and responsiveness are important, but they are only useful for measurement if they are properly installed.

The differences between thermocouples and resistance thermometer, and how to select the appropriate sensor for your application, are explained in the Temperature Sensor Guide | Differences between Thermocouples and resistance thermometer and Selection Points FAQ.

Temperature is not necessarily the same everywhere in the equipment or the object being measured. When deciding on the mounting location, first clarify "what this measurement will be used for."

Clearly define the temperature you want to control during process.

The required measurement points vary depending on the application, such as quality control, equipment monitoring, temperature control, and safety monitoring.

For example, the temperature required to monitor equipment malfunctions may not be the same as the temperature required to judge product quality.

Don't determine the measurement location based solely on ease of installation.

Choosing a measurement location solely based on factors like ease of wiring, ease of work, or the presence of existing mounting holes can result in the measured temperature not matching the actual temperature you want to know.

When determining the measurement location, we check not only the equipment structure but also the temperature distribution, flow, and the positional relationship with the heat source.

Make it possible to explain what the measured values represent.

Especially when it comes to temperature control used for quality control and process control, it's crucial to be able to explain "why the measurement is being taken at this particular location."

For more information on the concept of temperature measurement itself, please also see "What is Temperature Measurement? Differences from Measurement, Mechanism, and How to Measure Correctly."

When inserting a temperature sensor into pipes, tanks, furnaces, etc., it's not always sufficient to insert only the temperature-sensing element into the object being measured. Insufficient insertion depth can make the sensor more susceptible to the effects of heat conduction through the mounting area.

Heat is transferred between the mounting part and the surrounding area.

The sheath or protective tube of a temperature sensor connects the object being measured to the outside of the equipment. If there is a temperature difference between the object being measured and the outside, heat will transfer through that part.

If the sensor is inserted too shallowly, the temperature near the temperature-sensing element may be affected by this heat transfer, making it difficult to match the temperature of the object being measured.

A good guideline for thermocouples is that the outer diameter should be 15 to 20 times or more.

Chino's comprehensive temperature sensor catalog indicates that the insertion length of a thermocouple should be 15 to 20 times or more the outer diameter as a general guideline.

A general guideline resistance thermometer is that the outer diameter should be 20 to 30 times or more.

For resistance thermometer, a general guideline is that the outer diameter should be 20 to 30 times or more.

*The above is a general guideline. The required insertion length will vary depending on the object being measured, its material, the sensor's outer diameter, etc. Meeting the magnification requirement does not guarantee accurate measurement.

Don't judge solely on insertion length.

In actual measurements, the way heat is transferred varies depending on the outer diameter and material of the sensor and protective tube, the condition of the object being measured, the flow, and the temperature difference with the surroundings.

Especially in equipment where it is difficult to secure a sufficient insertion length, such as small-diameter piping, the decision should not be based solely on magnification, but should also be made considering the sensor structure and mounting method.

The proper way to install a temperature sensor varies depending on what you are measuring. Here, we will summarize the key considerations for typical measurement targets.

When measuring the temperature of pipes and fluids

In piping systems, we check the pipe diameter, measurement location, and fluid state to determine the optimal position for the temperature-sensing element.

Since temperature conditions may differ between the area near the pipe wall and the inside of the fluid, we will consider the installation method, including whether sufficient insertion depth can be ensured.

When measuring the liquid temperature inside a tank

Temperature variations can occur within the tank due to factors such as heating and cooling locations, liquid circulation and stirring, and changes in the liquid level.

We verify that the temperature-sensing element is always in proper contact with the object being measured and that it is positioned to represent the temperature we want to control in process.

When measuring the temperature inside the furnace

Inside a furnace, the ambient temperature and the temperature of the heated workpiece are not necessarily the same. Clearly define what the measurement is intended to control before determining the measurement location.

When measuring the temperature of a solid surface

When measuring a solid surface with a contact-type sensor, the contact condition between the temperature-sensing element and the measurement surface is crucial.

If contact is insufficient or if the device is strongly affected by heat from the surrounding air or fixed parts, a difference may occur between the temperature of the measurement surface and the temperature sensing element.

Industrial temperature sensors utilize protective tubing and various mounting bracket to secure the sensor to equipment and protect it from pressure, fluid, corrosion, and mechanical influences.

While the protective tube protects the sensor, it also affects how heat is transferred.

When a protective tube is used, heat is transferred from the object being measured to the temperature sensing element through the tube. Therefore, the protective tube should be selected considering not only its strength and corrosion resistance, but also the influence of its outer diameter and structure on the response.

The method for adjusting the insertion length varies depending on the mounting method.

Chino temperature sensors offer various mounting options depending on the application, including fixed flanges, sliding flanges, fixed nipples, sliding nipples, and compression fittings.

There are two types of systems: one with a fixed position and another that allows adjustment of the insertion position during installation. Therefore, the selection should be made after checking the required insertion length, equipment structure, pressure, airtightness, and other conditions.

Some sheath-type temperature sensors can be bent to fit the shape of the equipment. However, they cannot be freely bent at any position, including the temperature-sensing element.

Do not bend the temperature-sensing part of resistance thermometer.

With Chino's sheathed resistance thermometer, care is taken not to bend the 100mm tip section containing resistance element.

Since the bending positions and conditions vary depending on the product, please check specifications and instruction manual of the product before actual installation.

Pay attention to the bending radius and repeated bending.

When bending the sheath, ensure you adhere to the bending radius specified in the product specifications. Excessive bending or repeated bending in the same location may lead to disconnection, sheath damage, or insulation failure.

The response of a temperature sensor is not determined solely by the type of sensor. Actual mounting conditions, such as the outer diameter, structure of the temperature-sensing element, the protective tube, and the contact condition with the object being measured, also affect how well it tracks temperature changes.

When strengthening protection, we also need to consider the impact on response time.

In industrial applications, sensors need to be protected from pressure, corrosion, vibration, and other elements. However, adding protective structure also alters how heat is transferred from the object being measured to the temperature-sensing element.

Therefore, configuration is determined not only based on durability, but also on the level of response required during process.

If using it for temperature control, also check the sensor location.

In temperature control, the output to heaters and other components is adjusted based on values detected by sensors. Therefore, it is crucial that the sensors are positioned to accurately capture temperature changes in the object to be control.

For more information on the concept of temperature control itself, please see "What is control? The Concept of Approaching a Target Value and Maintaining a Stable State."

The installation of a temperature sensor is not the end of the process. The condition of the measurement point must be continuously monitored, taking into account changes and degradation due to the operating environment.

If the reliability of the measurement values is required, proceed to calibration.

Simply checking the installation condition does not allow us to determine the deviation of the sensor or instrument 's indicated value. If it is necessary to verify the reliability of the measured values for quality control or audits, calibration is performed according to working conditions and management standards.

The basics of calibration are explained as follows: What is calibration? It's a mechanism for comparing the values of a measuring instrument to a standard and checking the difference.

Before installing the temperature sensor on the equipment, checking the following items will help prevent overlooking the measurement location or installation method.

• It is clear what temperature is being measured.
• It has been decided what those measurements will be used for.
• We confirmed whether the measurement location could represent the target temperature.
• I checked where the temperature-sensing element was located.
• We considered the required insertion depth.
• Checked the sensor's outer diameter and length.
• We confirmed the necessity and material of the protective tube.
• I checked mounting bracket and how to adjust the insertion position.
• I confirmed the required response speed.
• We checked the operating environment, including pressure, flow rate, vibration, and corrosion.
• It is structure to allow for inspection, replacement, and calibration after installation.