A burned-out terminating resistor in hot runner communication directly disrupts bus signal integrity, leading to serious malfunctions such as communication interruption and device disconnection. A three-step method-measuring resistance, observing waveforms, and checking logs-can systematically determine if a terminating resistor is burned out.
1. Measuring Resistance: Power Off and Checking Physical Connection Status
Operating Steps:
Stop the machine and disconnect the main power supply, ensuring the communication line is de-energized.
Use a multimeter in resistance mode to measure the equivalent resistance between bus lines A and B.
Judgment Criteria:
Normal Value: ≈60Ω (120Ω each in parallel)
Abnormal Performance: ∞ (open circuit) or close to 120Ω → Indicates at least one terminating resistor is burned out or not connected.
Key Inspection Locations:
The two furthest communication nodes (first and last)
Observe the resistor body for signs of burning such as carbonization, cracking, or discoloration.
Tip: If the measured resistance is unstable or fluctuates, it may indicate poor internal contact and the resistor is in a critical damage state.
2. Observe the waveform: Use an oscilloscope to capture abnormal signal characteristics
Operation steps:
Restart the system and connect the oscilloscope online to the A/B differential signal lines.
Observe the signal waveform during communication.
Typical waveform anomalies after burnout:
Ringing: Continuous oscillation at the signal edges, due to reflections not being absorbed.
Overshoot: Voltage peaks far exceed standard levels (e.g., >6V).
Edge distortion, eye diagram closure: The receiver has difficulty accurately identifying logic "0" and "1".
Key judgment: If the waveform is normal at the beginning of communication but deteriorates after a period of operation, it is very likely caused by the resistor burning out due to heat.
3. Log Review: Analyze the temporal and environmental correlation of faults
Retrieve communication logs from the PLC/SCADA system and pay attention to the following characteristics:
Faults tend to occur when equipment runs for extended periods or when workshop temperatures rise. Error types include "Communication Timeout," "CRC Check Failure," and "Equipment Offline." Temporary recovery occurs after restarting, but the same fault recurs after several hours.
Typical Pattern:
The fault exhibits thermal accumulation and intermittent nature. After ruling out loose cables or interference, a burnt-out terminating resistor should be highly suspected.
Empirical Evidence: In industrial settings, over 70% of intermittent communication faults ultimately trace back to a failed terminating resistor.
