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Partial Case Malfunction in Multi-Case Serial Network — Common Control Line

Likely causes

Bus cable mid-break — all cases beyond break point lose communication

Check: Measure bus cable continuity with multimeter — 0Ω end-to-end = normal; OL = open. Use divide-and-conquer: disconnect mid-point and test each half to locate break

What to do: Replace cable in broken segment. After replacement, sequentially verify communication status of all cases

Duplicate address settings — communication conflict between cases with same address

Check: Check address parameter on each case controller — must be set sequentially from 1 with no duplicates. If two or more cases share the same address, communication conflict occurs

What to do: Reassign duplicate address cases with unique numbers (1, 2, 3…) and restart the entire system

Voltage drop at end cases — insufficient control voltage due to wiring resistance

Check: Compare control voltage at first and last case — if drop exceeds 10% of rated voltage, rewire or upgrade cable

What to do: Upgrade cable cross-section (e.g. 0.75mm² → 1.5mm²); or add booster relay power supply mid-run

Termination resistor (120Ω) missing or incorrectly positioned

Check: Check if 120Ω resistors are installed at both ends of bus. Total bus termination resistance should be 60Ω (two 120Ω in parallel); reading 120Ω = one resistor missing

What to do: Install 120Ω resistors at the two end cases of the bus; if installed in the middle, move to the ends

Solenoid coil noise — interference on communication line

Check: Check if communication errors coincide with solenoid valve open/close timing. Use oscilloscope to check bus line voltage waveform — look for voltage spikes

What to do: Add surge absorption diode or snubber (RC) circuit across solenoid coil; route communication cable separately from power cables

Ground potential difference — potential imbalance between cases causing communication errors

Check: Measure potential difference between each case ground terminal and common ground — normal <1V; above 1V = poor grounding or ground loop

What to do: Consolidate all cases to a single common ground point; measure ground resistance and confirm below 10Ω

Field tip

First step in multi-case communication diagnostics: disconnect bus cable at the midpoint — test each half separately to narrow down cable break or address conflict to half the network

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