To replace an Omron SRS1-T module, you must follow a four-step process: "Safe Power-off → Precise Removal & Installation → Standardized Wiring → Three-Step Verification." This ensures stable impedance matching on the DeviceNet communication bus and prevents communication anomalies caused by improper handling.
1. Safety Preparation and Power-off Verification
System Shutdown & Power-off: Turn off the main power supply for both the injection molding machine and the hot runner control system. Execute the LOTO (Lockout/Tagout) procedure to prevent accidental power restoration.
Residual Voltage Discharge: Wait 5 minutes after powering off to ensure that any residual voltage in the communication lines and controller has fully dissipated.
Tool Preparation:
Hex key or screwdriver (for securing the module)
Anti-static wrist strap (must be worn and properly grounded)
Multimeter (for measuring resistance values)
New SRS1-T module (verify the model number is correct; alternatively, a spare 120Ω/0.25W metal film resistor may be used)
Safety Warning: Never perform operations while the system is powered on; doing so risks damaging the communication interface or causing electric shock.
2. Removing the Old Module
Locating the Module: The SRS1-T module must be installed at the two outermost nodes (the first and last stations) of the DeviceNet bus.
Removal Steps:
Loosen the securing screws or release the latches, then gently remove the old module.
Inspect the terminal block for any signs of carbonization, deformation, or poor solder joints.
Use an isopropyl alcohol-moistened cotton swab to clean the interface contacts, ensuring a reliable connection.
Note: If the module features a soldered-in package, use a soldering iron (set to 300°C ± 20°C) in conjunction with a desoldering pump to carefully remove it, avoiding damage to the PCB pads.
3. Installing the New Module
Module Selection Confirmation:
Model: SRS1-T
Resistance Value: 121Ω ±1%
Power Rating: 0.25W
Interface Type: Compatible with DeviceNet terminal blocks (typically M8/M12 interfaces)
Installation Procedure:
Align the new SRS1-T module with the terminal block interface, ensuring correct orientation (A and B lines must correspond).
Gently press the module into place by hand, then secure it firmly using screws or clips to prevent loosening due to vibration.
Verify that the A, B, and SHIELD lines are securely connected; note that the shielding layer must be grounded at only one end-specifically on the control room side.
Practical Tip: If the SRS1-T module is out of stock, a 120Ω/0.25W surface-mount resistor may be temporarily soldered directly onto the terminal block as an equivalent substitute.
4. Post-Replacement Verification (Three Steps)
① Measure Resistance (Power Off)
Use a multimeter to measure the equivalent resistance between the A and B lines. The normal value should be ≈60Ω (representing two 121Ω resistors connected in parallel).
② Check Waveforms (Power On)
After powering up the system, connect an oscilloscope to the differential A/B lines.
Observe the waveform to ensure it appears as a clean square wave, free from ringing, overshoot, or edge distortion.
③ Monitor Logs (System Operation)
Run the system for at least 4 hours.
Check the PLC/SCADA logs for any anomalies, such as "Communication Timeout" or "CRC Check Failure" errors.
Acceptance Criteria: All three verification steps must be successfully completed before the replacement can be deemed successful and the system returned to continuous production.
Summary: Although the SRS1-T module is small in size, it serves as the critical "ballast" for ensuring stable DeviceNet communication. It is imperative to ensure that these modules are installed only at the two physical ends of the bus; connecting them at intermediate nodes is strictly prohibited. Following a replacement, it is essential to perform a comprehensive verification using the "Measure Resistance + Check Waveforms + Monitor Logs" three-step method to guarantee the long-term, reliable operation of the hot runner system.
