Electrical & Logic | Module 220
RS-485 Network Shielding & Ground Audit
Field Status: Modbus RTU communication is highly susceptible to “Signal Reflected Noise.” Because it utilizes a balanced pair, any mismatch in impedance or lack of proper termination will cause high-frequency voltage pulses to bounce back, corrupting incoming data packets.
Always audit the termination resistance. A properly terminated RS-485 bus must have a 120-Ohm resistor installed at the *very first* and *very last* node of the daisy chain. Intermediate nodes must NOT have termination resistors.
SYS AUDIT: Bus Integrity Metrics
NETWORK STATUS: —
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RS-485 Topology
RS-485 is a “Daisy Chain” bus. T-Taps or “Star” wiring configurations create impedance discontinuities that result in signal reflections. Always wire in a continuous serial line.
| Metric | Target Range |
|---|---|
| Bus Resistance | 60-120 Ohms |
| Shield Grounding | Single Point Only |
| Wiring Style | Daisy Chain Only |
Diagnostic Gateway Challenge
You are running new shielded wire to resolve an intermittent 01 error. How should the shielding foil be terminated?