The core method for determining whether a platinum resistance thermometer requires repair is to use a multimeter to measure its resistance value-checking if it meets standard specifications and if the resistance changes in response to temperature variations-as well as to inspect its physical appearance and insulation integrity. If an open circuit, short circuit, significant deviation in resistance value, or insulation failure is detected, the device requires either repair or replacement.
I. Basic Assessment: Measuring Resistance Value with a Multimeter (Most Common Method)
Establishing an Ambient Temperature Reference
Record the current ambient temperature (e.g., 25°C) and cross-reference it with a standard resistance value table:
0°C → 100.00Ω
20°C → 107.79Ω
25°C → 109.73Ω
If the measured resistance value falls within a range of ±0.5Ω of the standard value, it is considered normal.
Measurement Procedure and Anomaly Identification
3-Wire Platinum Resistance Thermometer (Most Common):
Disconnect the wiring and measure the resistance values between terminals A-B, A-C, and B-C individually.
Normal: A-B ≈ A-C (matching the temperature-corresponding standard value), B-C ≈ 0Ω (indicating the compensation wire).
Abnormal:
A-B or A-C reads "OL" (infinite resistance) → Open circuit (broken platinum wire); requires repair.
A-B or A-C resistance value is significantly lower than the standard → Internal short circuit or moisture ingress.
B-C resistance value is significantly high → Open circuit in the compensation wire.
2-Wire Platinum Resistance Thermometer: Directly measure the resistance across the two terminals; the assessment criteria are the same as above.
Dynamic Heating Test
Hold the sensing head in your hand or apply gentle heat to it, and observe whether the resistance value rises steadily.
If the resistance value remains unchanged or changes very minimally → The platinum wire is likely contaminated or aged, resulting in reduced sensitivity; replacement is recommended.
II. Auxiliary Assessment: Visual and Insulation Inspection
Visual Inspection
Check the protective tube for damage, the lead wires for breaks, and the interior of the junction box for signs of water ingress or corrosion.
If obvious physical damage is present, it can typically be determined immediately that the device requires repair or replacement. Insulation Resistance Testing
Using an insulation resistance tester, connect one lead to the sensor's output wire and the other to its protective sheath.
Typically, the insulation resistance is required to be ≥ 20 MΩ (at 25°C).
Insufficient insulation resistance can lead to signal interference; therefore, it is necessary to inspect the device for moisture ingress or damage to the insulating material.
III. Should You Choose "Repair" Over "Replacement"?
|
Condition |
Recommendation |
|
Broken Platinum Wire (Component Otherwise Intact) |
Can be repaired using arc welding (6–8 V); this method is low-cost and highly reliable. |
|
Broken Lead Wire |
Easy to repair; simply solder the connection and trim away any excess material. |
|
Internal Short Circuit or Contaminated Platinum Wire |
Typically difficult to repair; replacement is recommended. |
|
Long-Term Use / Declining Accuracy |
Even if repairable, replacement is recommended to ensure measurement accuracy. |
|
Critical Operating Conditions / High-Precision Applications |
Prioritize replacement to ensure stability and compliance with calibration standards. |
Professional Tip: A repaired platinum resistance thermometer must undergo successful verification before being put back into service-particularly in demanding environments such as industrial metrology and medical applications.
