As a core component of a temperature control system, the condition of the temperature sensing wire directly affects process stability. Determining if a temperature sensing wire is damaged requires a comprehensive analysis combining abnormal electrical parameters, system performance distortion, physical damage, and cross-validation results. The following is a systematic judgment method:
I. Electrical Performance Testing (Basic Criteria)
Abnormal Resistance Measurement
Use a multimeter to measure the resistance at room temperature (25℃). For PT100, the resistance should be approximately 109.6Ω.
If the display shows "OL" or "∞" → Open circuit fault
If the resistance is < 50Ω → Short circuit or internal breakdown
Resistance fluctuating or changing irregularly with temperature → Poor contact or intermittent open circuit
Degraded Insulation Performance
Use a 500V megohmmeter to measure the insulation resistance between the wire core and the shield/ground.
The normal value should be ≥ 500MΩ
If the resistance is below 1MΩ, there may be a risk of leakage, especially in humid environments where false alarms are easily triggered.
Shielding failure leads to interference.
Controller displays drastic temperature fluctuations and periodic jumps.
Check if the shielding wire is broken or not grounded at a single point to prevent electromagnetic interference from entering the signal.
II. Abnormal System Operation (On-site Identification)
Table: Fault Phenomenon | Possible Cause
Display -273.15℃ (Absolute Zero) | Open circuit in the temperature sensing wire, signal interruption
Display Full-scale maximum value (e.g., 999℃) | Open circuit or poor contact
One zone does not heat up, other zones are normal | Corresponding temperature sensing wire is damaged, the system misjudges "set temperature reached"
Temperature continues to drift and cannot stabilize | Aging temperature sensing wire, slow response, or intermittent open circuit
Note: Some hot runner controllers have self-diagnostic functions; "E1" or "Sensor" errors may occur. Alarm codes such as "Open" usually indicate a fault in the temperature sensing wire.
III. Physical Condition Inspection
Protective Sleeve Damage: Check for flattening, excessive bending, corrosion, or mechanical damage.
Connector Burning or Oxidation: Terminals may be blackened, loose, or have poor contact.
Wiring Path Risks: Check for damage caused by mold compression, friction, or proximity to high-temperature heating coils leading to insulation aging.
Excessive Installation Stress: Bending radius less than 6 times the wire diameter can easily lead to internal wire core breakage over long-term use.
IV. Cross-Verification Method (Precise Judgment)
Replacement Test Method
Connect the suspected faulty temperature sensing wire to a normal channel. If the error persists → the temperature sensing wire itself is confirmed to be damaged.
Or connect a normal temperature sensing wire to the faulty channel. If normal operation is restored → Determining if the original temperature sensing wire is damaged:
Standard Source Comparison Method
Use a temperature calibrator to simulate a PT100 standard signal (e.g., 0℃=100Ω, 100℃=138.5Ω).
If the controller can normally recognize the standard signal, the problem lies with the temperature sensing wire itself.
Infrared Thermometry Comparison
Heat to the operating temperature (e.g., 250℃) and use an infrared thermometer to measure the actual temperature of the nozzle surface.
Compare with the value displayed on the controller. If the deviation is > ±3℃ and emissivity setting issues are ruled out, the temperature sensing wire should be suspected of being inaccurate.
V. Preventive Maintenance Recommendations
Regular Inspection: Perform resistance and insulation tests every 3 months.
Lifespan Reference: Generally, a replacement cycle of 3–5 years is recommended. The cycle should be shortened under long-term high temperature and high humidity environments.
Batch Replacement Warning: If multiple temperature sensing wires in the same system have successively failed, it is recommended to also test those in the same batch that are not yet damaged to prevent cascading failures.
✅ Best Practice: Establish a "detection → recording → warning" mechanism, combined with historical data trend analysis, to achieve a shift from passive maintenance to proactive prevention.
