Thermocouple and thermal resistance selection and installation - Database & Sql Blog Articles

Thermocouple and Thermal Resistance Selection

Thermocouples are essential instruments used for temperature measurement. Choosing the right thermocouple or RTD (Resistance Temperature Detector) ensures accurate readings, safety, and reliability. Here’s a quick guide to help you understand these components better.

1. For objects with normal temperatures below 300°C, thermal resistors (RTDs) are typically the best choice due to their high accuracy and stability.

2. When the measured object operates at higher temperatures above 300°C, thermocouples are more suitable because of their wide temperature range and durability.

Installation Methods for Thermocouples and RTDs

1. First, measure the size of the thermocouple or RTD flange or threaded screw, and machine the corresponding flange or threaded base.

2. Drill holes in the pipe according to the size of the flange or threaded base.

3. Weld the flange or threaded base into the hole, ensuring it is securely attached to the pipe.

4. Tighten or screw the thermocouple or RTD into the welded base.

5. Connect the junction box of the thermocouple or RTD based on the wiring diagram and link it to the display instrument. Make sure the junction box does not touch the pipe wall to prevent overheating (temperature should not exceed 100°C). Also, ensure the outlet hole is sealed properly to avoid short circuits caused by moisture or dust.

6. Choose an installation location that allows for easy maintenance and inspection.

Installation Requirements for Thermocouples and RTDs

Proper installation of thermocouples and RTDs is crucial for accurate measurements, safety, and ease of maintenance. It should not interfere with the operation of the equipment. To achieve this, consider the following:

1. Thermocouples and RTDs with protective sleeves can cause heat loss and transfer errors. To minimize this, they should be inserted deeply enough. For example: - If the insertion depth exceeds 1 meter, install it vertically or use a support frame. - In flue gas applications, even with a 1000mm diameter, the sensor can be inserted up to 500mm. - For fluid temperature measurement in the center of a pipe, insert the sensor to the center (vertically or at an angle). If the pipe is 100mm in diameter, the insertion depth should be between 50–100mm. - For high-temperature, high-pressure, or high-speed fluids, use shallow-insertion or sleeve-type thermocouples to reduce resistance and prevent damage.

2. Ensure the measuring end has sufficient contact with the medium. Avoid placing sensors near valves, elbows, or other dead zones where the flow might not be uniform.