If abnormal resistance readings are detected at the hot runner communication terminal resistor or the SRS1-T module, immediately shut down the system to inspect physical connections and wiring conditions. A deviation in resistance from the nominal ≈60Ω (or ≈60.5Ω for the SRS1-T) indicates an open circuit, a short circuit, or a poor connection; troubleshooting and repairs must be performed according to the following steps.
1. Common Symptoms of Abnormal Resistance and Corresponding Remedies
|
Measurement Result |
Possible Cause |
Remedial Action |
|
∞ (Open Circuit) |
Module burnt out, module not installed, broken solder joint, disconnected cable |
Verify that terminal modules are installed at both ends; use a multimeter to check the continuity of the communication line segment by segment. |
|
≈120Ω (or ≈121Ω) |
Terminal installed at only one end; the other end is missing |
Install the missing terminal resistor or SRS1-T module at the unequipped end. |
|
<50Ω or >75Ω |
Poor contact, cold solder joint, oxidation, incorrect connection at an intermediate node |
Clean terminal contacts and tighten screws; check if a terminal resistor has been incorrectly installed at a non-terminal (intermediate) station. |
|
Unstable/Fluctuating Resistance |
Aging solder joints, internal component damage/cracks, humid environment |
Replace the module with a new one, and implement appropriate measures for moisture and vibration protection. |
Note: The SRS1-T module has a nominal resistance of 121Ω. When two modules are connected in parallel, the theoretical combined resistance is 60.5Ω; therefore, actual measured values within the range of 58–63Ω are considered normal.
2. Systematic Troubleshooting and Resolution Process
① Power-Off Safety Preparations
Shut down the system and cut off power; execute the LOTO (Lockout/Tagout) procedure; wait 5 minutes to allow for residual discharge.
Wear an anti-static wrist strap to prevent electrostatic discharge damage to communication interfaces.
② Inspect Installation Locations
Verify that terminal resistors or SRS1-T modules are installed only at the first and last stations of the bus network.
Strictly prohibit connecting these components to intermediate slave devices; doing so will lower the equivalent resistance value and trigger communication anomalies.
③ Remove and Inspect Module Condition
Remove the SRS1-T module or resistor; visually inspect for signs of carbonization, bulging, or cracked solder joints.
If using a surface-mount resistor, use a magnifying glass to check for the presence of micro-cracks.
④ Cleaning and Re-testing
Use an isopropyl alcohol-dampened cotton swab to clean the contacts on the terminal block and the module interface.
After re-installation, measure the resistance between the A and B lines again to confirm that normal values have been restored.
⑤ Emergency Alternative Solution
If the SRS1-T module is out of stock, a metal film resistor with a value of *120Ω ±1%* and a power rating of *0.25W or higher* may be temporarily soldered in place as an equivalent substitute.
The use of a 1210 package size is recommended to enhance heat dissipation and prevent thermal drift.
Practical Tip: In workshops characterized by high temperatures and high humidity, prioritize the use of integrated terminal modules with IP67 protection ratings to enhance long-term reliability.
3. Mandatory Three-Step Verification After Resolution
① Measure Resistance (Power Off)
Re-measure the equivalent resistance between the A and B lines → It should stabilize at ≈60Ω.
② Check Waveforms (Power On)
Connect an oscilloscope to observe the differential signals → They should appear as clean square waves, free of ringing or overshoot.
③ Monitor Logs (System Running)
Allow the system to run for at least 4 hours → Verify that no error messages (e.g., "Communication Timeout," "CRC Error") are reported.
Acceptance Criteria: The fault is deemed resolved only if all three verification steps are successfully passed.
