The hot runner temperature sensing wire is a core component of the temperature control system, and its condition directly affects the stability of the injection molding process. Determining whether replacement is necessary requires a comprehensive assessment considering factors such as abnormal resistance, distorted temperature display, physical damage, and the wire's lifespan.
I. Abnormal Electrical Performance (Core Indicators)
Resistance Value Out of Range or Unstable
Measure the resistance value at room temperature (25℃) using a multimeter. The standard resistance for PT100 should be approximately 109.6Ω.
If the resistance value is < 50Ω (short circuit) or displays "OL"/"∞" (open circuit), replace immediately.
Uneven resistance fluctuations and irregular temperature changes indicate poor internal contact.
Degraded Insulation Performance
Measure the insulation resistance of the temperature sensing wire to ground using a megohmmeter.
The normal value should be ≥ 500MΩ (reference).
If it is below 1MΩ, there may be a risk of leakage, especially in humid environments where false alarms are likely.
Shielding Layer Failure
The controller displays drastic temperature fluctuations or interference.
Check if the shielding wire is broken or not grounded, causing electromagnetic interference to enter the signal.
II. Abnormal System Operation
Table: Fault Phenomenon Possible Cause
Display -273.15℃ (Absolute Zero) Temperature sensing wire open circuit, signal interruption
Display Full-Scale Maximum Value (e.g., 999℃) Open circuit or poor contact: One zone fails to heat up while others operate normally. The corresponding temperature sensor is damaged, causing the system to mistakenly register "set temperature reached."
Temperature continues to drift and cannot stabilize. The temperature sensor is aging, has a slow response, or has intermittent open circuits.
Note: Some hot runner controllers have self-diagnostic functions. Alarm codes such as "E1" or "Sensor Open" usually indicate a temperature sensor fault.
III. Physical Condition and Installation Inspection
Protective Sleeve Damage: Check for flattening, excessive bending, corrosion, or mechanical damage.
Joint Erosion or Oxidation: Terminals may be blackened, loose, or have poor contact.
Wiring Path Risks: Check for damage from mold compression or 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 core breakage with prolonged use.
IV. Service Life and Preventive Replacement
Generally Recommended Replacement Cycle: 3–5 years. Temperature sensing cables operating in high-temperature, high-humidity, and vibration environments for extended periods may have a shortened lifespan. Referring to temperature sensing cable equipment, the aging process accelerates around 8 years (reference), although not absolute. Applicable, but can be used as a reference trend.
If multiple temperature sensing wires in the same system have been replaced successively, it is recommended to also test those in the same batch that are not faulty to prevent batch failure.
V. Verification and Replacement Test Methods
Cross-substitution method
Connect the suspected faulty temperature sensing wire to the normal channel and observe whether it still reports an error.
Or connect the normal temperature sensing wire to the faulty channel to verify whether it returns to normal.
Standard source comparison method
Use a temperature calibrator to simulate a standard PT100 signal to verify whether the controller response is accurate.
If the controller can normally recognize the standard signal, the problem lies with the temperature sensing wire itself.
Infrared temperature measurement comparison
Measure the actual temperature of the nozzle surface with an infrared thermometer and compare it with the value displayed by the controller.
If the deviation is > ±3℃ and emissivity setting issues are ruled out, the temperature sensing wire should be suspected of being inaccurate.
Recommendation: Establish a regular inspection system and conduct resistance and insulation tests every 3 months to detect potential problems in advance.
