In the field of industrial temperature measurement, connection tube type thermocouples and fixed thread type platinum resistance thermometers are two common types of temperature sensors. They have significant differences in structural design, working principles, performance characteristics, and application scenarios. The following provides a systematic comparison from multiple dimensions to clarify their core differences.
I. Differences in Structural Design and Installation Methods
1. Connection Tube Type Thermocouple
The core feature of a connection tube type thermocouple lies in its connection tube fixing and bimetallic wire structure. It typically uses a metal connection tube (such as stainless steel) to closely fit against the surface of the object being measured. Secure installation is achieved through the mechanical pressure of the connection tube, while the interior consists of two different metal wires (such as nickel-chromium and nickel-silicon) welded together to form the measuring end. The connection tube design allows the probe to form close contact with the equipment surface, improving measurement accuracy and response speed. For example, in mechanical manufacturing or electronic equipment, the connection tube design ensures sufficient contact between the probe and the equipment surface, reducing heat loss during the heat transfer process. Its structural design emphasizes the tightness of the connection tube fixing and the independence of the bimetallic wires. The connection tube design reduces the impact of environmental factors on measurement accuracy and enhances resistance to mechanical shock. However, its installation process requires ensuring that the connection tube is completely in contact with the surface of the object being measured, which increases the complexity of installation. Furthermore, the bimetallic wires may oxidize in high-temperature environments, affecting long-term stability.
2. Fixed Thread Type Platinum Resistance Thermometer
The core feature of a fixed thread type platinum resistance thermometer lies in its fixed thread connection and platinum wire winding structure. It typically uses a fixed thread (such as M20×1.5) to achieve secure installation by screwing it into the surface of the object being measured. The interior consists of platinum wire wound on a ceramic or mica skeleton, forming the temperature-sensing element. The fixed thread design ensures a rigid connection between the probe and the equipment surface, suitable for high-pressure or applications requiring long-term stable measurement. For example, in the chemical or pharmaceutical industries, the fixed thread design ensures that the probe maintains a stable position on high-pressure pipelines, reducing the impact of vibration on measurements. Its structural design emphasizes the rigid connection of the threaded fixing and the stability of the platinum wire. The threaded fixing design reduces the influence of environmental factors on measurement accuracy and enhances resistance to mechanical shock and chemical corrosion. However, its installation process requires ensuring that the threads are completely in contact with the surface of the object being measured, which increases the complexity of installation. Furthermore, the threaded connection may loosen due to vibration during long-term use, affecting measurement accuracy.
II. Differences in Working Principles
1. Working Principle of Thermocouple with Connecting Tube Probe
Thermocouples are based on the Seebeck effect, where two different metal conductors generate a thermoelectric potential difference under a temperature gradient. When two metal conductors are connected to form a closed circuit, and the two junctions have different temperatures, an electromotive force is generated in the circuit. Its magnitude is related to the material properties and the temperature difference between the junctions. By measuring the electromotive force, the temperature value can be indirectly calculated. Thermocouples have high sensitivity; a 1°C temperature change results in an output potential change of approximately 5-40 microvolts. They have a simple structure with no moving parts and are suitable for high-temperature, high-pressure, and highly corrosive environments.
2. Working Principle of Fixed Threaded Probe Platinum Resistance Thermometer
Platinum resistance thermometers are based on the characteristic that metal resistance changes with temperature. Their resistance value has a non-linear relationship with temperature and needs to be determined by consulting a table or using a formula (e.g., Pt100 has a resistance of 100Ω at 0°C, and the resistance value increases linearly with increasing temperature). Platinum resistance thermometers have high sensitivity; a 1°C temperature change results in a significant change in resistance value. They have a simple structure with no moving parts and are suitable for precise measurements in medium and low temperatures (-200°C to 600°C), but strong magnetic fields or mechanical vibrations should be avoided to prevent affecting measurement accuracy.
III. Identification Methods
1. Visual Inspection
Thermocouple with connecting tube probe: The head is usually covered with a metal protective tube, and the inside consists of two different metal wires welded together. The connecting tube part is in close contact with the surface of the object being measured.
Fixed threaded probe platinum resistance thermometer: The head is usually covered with a metal protective tube, and the inside is a temperature-sensing element wound with platinum wire. The threaded part is screwed onto the surface of the object being measured. 2. Wiring Method
Thermocouple with connecting tube type probe: Uses a two-wire system (positive and negative), the terminal box is marked "TC+" and "TC−", and the leads are usually red (positive) and black/blue (negative).
Platinum resistance thermometer with fixed thread type probe: Uses a three-wire system (R1, R2, R3), the terminal box is marked "R1", "R2", "R3", and the leads are usually red, white, and yellow.
3. Multimeter Measurement
Thermocouple with connecting tube type probe: The resistance value is very small, usually only a few ohms.
Platinum resistance thermometer with fixed thread type probe: The resistance value is approximately 100 ohms at room temperature (Pt100).
IV. Differences in Application Scenarios
1. Thermocouple with connecting tube type probe
Scenarios requiring fast response and close contact: For example, in mechanical manufacturing or electronic equipment, the connecting tube design ensures sufficient contact between the probe and the equipment surface, improving measurement accuracy and response speed.
High-temperature or corrosive environments: Suitable for high-temperature, high-pressure, and highly corrosive media environments.
2. Platinum resistance thermometer with fixed thread type probe
Scenarios requiring fast response and close contact: For example, in the chemical or pharmaceutical industry, the fixed thread design ensures sufficient contact between the probe and the equipment surface, improving measurement accuracy and response speed.
Medium and low-temperature environments: Indoor or low-pressure scenarios. For example, in HVAC systems, its fixed thread design facilitates installation and maintenance.
V. Selection Suggestions
1. Selection of Thermocouple with connecting tube type probe
Installation requirements: Select a probe with a connecting tube specification that matches the equipment to ensure a secure connection.
Environmental conditions: Use in scenarios requiring high-temperature or corrosive environment measurement, avoiding strong vibration or impact environments.
2. Selection of Platinum resistance thermometer with fixed thread type probe
Installation requirements: Select a probe with a fixed thread specification that matches the equipment to ensure a secure connection.
Environmental conditions: Use in scenarios requiring precise measurement and fast response at medium and low temperatures, avoiding strong magnetic fields or mechanical vibration environments. VI. Summary and Complementary Relationship
The core difference between the thermocouple with a connecting tube probe and the platinum resistance thermometer with a fixed threaded probe lies in their working principles and applicable environments: the thermocouple with a connecting tube probe utilizes the Seebeck effect to provide flexible temperature measurement, suitable for scenarios requiring fast response and close contact; the platinum resistance thermometer with a fixed threaded probe utilizes resistance change to provide precise measurement in medium and low temperature ranges, also suitable for scenarios requiring fast response and close contact. When selecting a sensor, it is necessary to clarify the core requirements: the thermocouple with a connecting tube probe focuses on response speed and measurement accuracy in high-temperature environments, while the platinum resistance thermometer with a fixed threaded probe focuses on response speed and measurement accuracy in medium and low-temperature environments. Working together, they can meet the temperature measurement needs of different scenarios.
