Dual-Sheath Installation Junction Box Type Platinum Resistance Thermometer Installation Guide
In the field of industrial temperature measurement, the dual-sheath installation junction box type platinum resistance thermometer, with its double-layer protective tube structure and modular design, is an ideal choice for high-temperature, high-pressure, and highly corrosive fluid environments. Its installation process must strictly follow specifications to ensure measurement accuracy and equipment safety. The following are detailed installation steps and precautions.
I. Pre-installation Preparation: Safety Assessment and Tool Preparation
Before installation, a comprehensive safety assessment and environmental check must be conducted to ensure that operations comply with safety regulations. First, confirm that the installation environment is free of explosive gases or dust, and check that the equipment is de-energized, the medium is drained, and the temperature has dropped to ambient temperature. In explosion-proof areas, verify that the junction box explosion-proof rating (e.g., Ex d II C T6) matches the hazardous area. Also, assess the installation location, avoiding high-temperature, high-pressure, or high-vibration areas, and ensuring that the sensor is easily accessible for maintenance.
Tools and materials required include:
Flange installation tools: Flange bolts, nuts, gaskets (graphite or metal-wound gaskets), torque wrench (matching flange specifications, such as DN25 PN1.6).
Sealing materials: PTFE tape or thread sealant to ensure the sealing of threaded connections.
Electrical tools: Multimeter, electrical tape, wire stripper.
Protective equipment: Safety helmet, safety gloves, safety glasses.
Sensor inspection includes verifying the model, calibration type (e.g., Pt100), accuracy class (Class A or Class B), insertion depth, protective tube material (e.g., 316L stainless steel), and flange specifications. Check the appearance for scratches, dents, or corrosion, ensure the junction box is properly sealed, and that the terminals are not loose.
II. Installation Steps: From Flange Connection to Electrical Wiring
Dual-sheath connection preparation:
Weld or install the dual-sheath connector on the equipment or pipeline, ensuring that the inner and outer protective tube flange surfaces are flat and free from deformation. The flange connector must match the sensor flange specifications, such as DN25 PN1.6.
When installing the flange connector, clean the flange surface to prevent oil or impurities from affecting the seal. Sensor Mounting:
Secure the sensor to the connector using flange bolts. After manually pre-tightening, tighten the bolts with a torque wrench. The torque value must comply with the flange specifications (e.g., DN25 PN1.6 flange torque is 80–120 N·m) to avoid deformation of the flange or sensor due to excessive force.
Ensure the sensor insertion depth meets process requirements, for example, an insertion depth of at least 100mm in the pipeline, to reduce fluid resistance and prevent breakage.
Junction Box Installation and Wiring:
The junction box is usually integrated into the protective tube, with an IP65 protection rating. It features ceramic or mica insulated terminals and supports three-wire or four-wire connections. A grounding bolt provides a Faraday cage effect to shield against electromagnetic interference.
Wiring method selection:
Three-wire system: Most commonly used in industrial process control, it cancels the influence of lead resistance through a bridge circuit and is suitable for medium-precision measurements. When wiring, connect wire A to the positive terminal of the power supply, wire B to the measuring instrument, and wire C (compensation wire) to a fixed resistor, ensuring that all three wires have the same specifications.
Four-wire system: Used for high-precision measurements, it completely eliminates the influence of lead resistance. Two leads provide a constant current source to the RTD, and the other two leads are connected to a potentiometer to measure the voltage drop.
Wiring operation: Open the junction box, connect the wires according to the color coding, and ensure that the shielding layer is grounded at a single point to prevent electromagnetic interference. Multiple grounding points are strictly prohibited.
Pre-power-on check:
Measure the sensor resistance with a multimeter (at room temperature, Pt100 should be 100±0.1Ω) to confirm there are no short circuits or open circuits.
Check that all connections are secure and that the shielding layer is grounded at a single point.
Confirm that the junction box is properly sealed and there is no risk of water ingress.
III. Post-Installation Inspection and Commissioning
Power-on commissioning:
Connect to the display instrument or control system and observe whether the temperature reading is stable.
If the reading is abnormal (e.g., fluctuating, large deviation), check the wiring, shielding ground connection, and sensor resistance value.
IV. Safety Precautions
Power-off operation: Before installation, be sure to cut off the power to the equipment to prevent electric shock. Protective Equipment: Wear insulating gloves and safety glasses, especially when working on high-temperature and high-pressure pipelines.
Prohibitions: Welding or striking the protective tube is strictly prohibited; avoid scratching the sheath with metal tools; do not install under pressure when the medium has not been drained.
Special Environments: In explosion-proof areas, explosion-proof junction boxes must be used, and explosion-proof installation specifications must be strictly followed.
V. Maintenance and Troubleshooting
Regular Calibration: It is recommended to calibrate every 6–12 months. Compare the measurement with a standard temperature source (such as an ice-water mixture). If the error exceeds ±0.5℃, adjustment or replacement is required.
Fault Diagnosis: If the resistance value is abnormal or the response is sluggish, annealing treatment (heating at 260℃ for 2 hours followed by slow cooling) can be attempted to restore performance.
Record Keeping: After each maintenance, record the inspection results, calibration data, and replaced parts for traceability and analysis.
VI. Summary
The installation of the double-sheath junction box type platinum resistance thermometer requires strict adherence to safety regulations. Every step, from flange connection to wiring, requires precise operation. By reasonably selecting the wiring method (three-wire or four-wire system) and ensuring shielded grounding, measurement accuracy can be significantly improved. Post-installation inspection and debugging are crucial for ensuring stable system operation, while regular maintenance can extend the sensor's lifespan. Understanding these steps ensures long-term reliable temperature monitoring in high-temperature, high-pressure, and high-vibration environments, while also reducing maintenance costs.
