Regular Maintenance Cycle and Inspection Items
Monthly Inspection: Visually inspect the surface of the protective tube for corrosion, scratches, and deposits; confirm that the junction box sealing ring is not aged or cracked, and that the terminal connections are not loose or oxidized.
Every 6 Months Inspection:
Measure the insulation resistance between the lead wires and the protective tube using a megohmmeter (500V DC), ensuring it is ≥100 MΩ (ideal value ≥200 MΩ);
Check for loose threaded connections and retighten to the recommended value using a torque wrench (M12×1.5: 15–20 N·m);
Clean the outer surface of the probe, using a soft brush and lint-free cloth to remove dust and oil stains. High-pressure water guns or corrosive solvents are strictly prohibited.
Annual Calibration:
According to the "JJG 229-2010 Industrial Platinum and Copper Resistance Thermometer Verification Regulations," perform multi-point calibration (0℃, 100℃, 300℃) in a constant temperature bath (ice point bath or dry well furnace);
If the accuracy deviation exceeds Class A ±(0.15 + 0.002|t|)℃ or the resistance value deviates from the nominal value by ±0.5 Ω, calibration or replacement is required;
After calibration, issue a certificate compliant with ISO/IEC 17025, archive it for future reference, and meet GMP, FDA, and other compliance requirements.
Common Fault Diagnosis and Troubleshooting Measures
|
Fault Phenomenon |
Possible Cause |
Solution |
|
Insulation resistance decrease (<100 MΩ) |
Junction box dampness, seal failure, lead wire insulation aging, dust contamination |
1. Disconnect the power and open the junction box, clean the inside with anhydrous ethanol;2. Dry in a 40℃ drying oven for 30 minutes;3. Replace the PTFE sealing ring or reseal with high-temperature silicone;4. Reassemble after the insulation resistance test meets the standard. |
|
Temperature Signal Drift (Unstable or Deviating Readings) |
Platinum wire thermal cycling fatigue, poor lead contact, carbon buildup on the inner wall of the protective tube |
1. Measure the resistance value at room temperature using a high-precision bridge and compare it to the nominal value;2. Check if the three-wire/four-wire connection is correct and if the terminals are oxidized;3. If the resistance value continuously deviates by >±0.5 Ω, replace the probe; self-repair of the platinum wire is prohibited. |
|
Threaded Seal Leakage |
Seal material carbonization, thread damage, failure to use high-temperature sealant |
1. Shut down and depressurize before removing the probe;2. Remove the old sealant and reapply high-temperature thread sealant (such as Loctite 577);3. The use of PTFE tape is strictly prohibited (>200℃ failure);4. Reinstall and perform a pressure test (1.25 times the working pressure, hold for 10 minutes). |
|
Slow Response Time |
Scaling on the inner wall of the protective tube, drying of thermal conductive grease, insufficient insertion depth |
1. After shutdown, remove the probe and clean the inner wall with a neutral cleaning agent and a soft brush;2. Reapply a small amount of high-conductivity thermal grease (≤0.1 mL);3. Ensure the sensing end insertion depth is ≥10 mm, away from the wall thermal interference zone. |
Industry-Specific Maintenance Requirements
Pharmaceutical and Food (CIP/SIP):
Use pure steam or compliant cleaning agents at ≤135℃ during cleaning, avoiding mechanical scraping;
The junction box must be an IP67 waterproof sealed structure to prevent cleaning fluid from entering;
All maintenance operations must be recorded in the electronic batch record system, complying with GMP traceability requirements.
Chemical and Petrochemical:
Intergranular corrosion and stress cracking of the protective tube (316L/Hastelloy) must be checked during each major overhaul;
In high-pressure environments (>5 MPa), online disassembly is prohibited; operations must be performed after shutdown and depressurization.
Power and Energy:
In steam pipeline environments, special attention must be paid to preventing thermal shock, avoiding inserting the probe directly from a high-temperature environment into a cold medium;
Annual calibration must be performed according to the mandatory standard "JJG 229-2010" and cannot be delayed.
Maintenance Taboos and Safety Regulations
Prohibited:
Using power tools to forcibly screw in/out;
Disassembling under pressure or high temperature;
Touching the platinum wire or bending the leads directly with hands;
Cleaning the temperature sensing end with organic solvents such as ethanol or acetone;
Using ordinary tape or non-high-temperature sealing materials in the junction box.
Required:
Operators must wear anti-static gloves;
Perform static resistance testing and pressure sealing testing after maintenance;
Establish equipment maintenance records, documenting the date, operator, torque value, calibration results, and batch number of replaced parts.
The maintenance of fixed-thread platinum resistance thermometers is essentially a systematic protection of material integrity, electrical insulation, and heat conduction paths. Every cleaning, every tightening, and every calibration is a silent promise of process safety and product quality.
