M-Bus meter read faults — address, baud, bus load

M-Bus (Meter-Bus) reads electricity/water/heat/gas meters in buildings & plants (energy metering). When a gateway/converter can't read a meter, the cause is usually address, baud, unit load or polarity/wiring — rarely a faulty meter.

Common causes

1. Wrong/duplicate address — duplicate primary, or mixing up primary vs secondary.
2. Baud mismatch — master and meter at different speeds (usually 2400).
3. Bus overload — meter count exceeds the M-Bus master/converter unit load.
4. Polarity / wiring — M-Bus is non-polarized, but breaks/shorts/poor connectors still cause faults.
5. Converter — M-Bus ↔ Modbus/RS-232 with wrong mapping config.

Step-by-step diagnosis

1. Scan addresses Try scanning primary (1–250) and secondary (serial); see if a meter replies.
2. Match baud Set the same baud (usually 2400); try 300/9600 if unsure.
3. Compute unit load Count meters versus the master's capacity; split the bus / add a repeater if overloaded.
4. Check wiring Look for breaks/shorts, connectors; M-Bus is non-polarized but still needs good contact.
5. Point-to-point Wire one meter ↔ master alone to rule out the bus.
6. Converter config If via M-Bus ↔ Modbus: check register mapping and the read cycle.

When to call an expert

Large M-Bus systems (many meters, via converters) get tangled at unit load and mapping. DeepDebug helps localize and configure M-Bus ↔ Modbus/SCADA gateways remotely.