M-Bus meters with the M-Center in Node-RED

Route 1: Modbus TCP

1. In the M-Center, enter the OBIS code for the required registers. The import tariff 1 reading (1-0:1.8.1) is then at register 1030.
2. In Node-RED, add a «Modbus Read» node. Server: IP of the M-Center, port 502, type TCP.
3. Unit ID: the Modbus device address of the meter in the M-Center.
4. FC 3 (Read Holding Registers), address 1029 for register 1030, quantity 2, poll rate for example 15 minutes.
5. Attach a function node that combines the two registers into a floating-point number.

// Two 16-bit registers (big endian, high word first) -> float32
const buf = Buffer.alloc(4);
buf.writeUInt16BE(msg.payload[0], 0);
buf.writeUInt16BE(msg.payload[1], 2);
msg.payload = buf.readFloatBE(0);
msg.topic = "apartment1/import_t1";
return msg;

The manual counts registers from 1, node-red-contrib-modbus expects the address from 0. Hence 1029 for register 1030. Compare the first value with the meter reading in the M-Center.

For several meters, create one read node per meter with its own unit ID. The addresses stay the same as long as the OBIS codes are entered.

Route 2: MQTT

With the MQTT licence, the M-Center publishes every value under its own topic. An «mqtt in» node with a wildcard subscription receives all values of an M-Center:

<prefix>/emu/mcenter/<MAC>/meterreading/#

First attach a debug node and look at the topics and the content of the messages. Then separate the values by topic with a switch node, for example by the OBIS code at the end of the path.

Which route?