Communication · radio
LoRa for water and heat meters
Where there is no cabling or the meters are widely spread out, the H2O and DELTA III send their values by radio. Here is what you need and where the limits lie.
How it works
From the meter via the gateway to the application
- M-Bus: one cable, many metersThe master supplies the two-wire line with about 40 V. All meters are connected in parallel; polarity does not matter.
- M-Bus: readingThe master selects a meter by its secondary address. Only that meter replies, by modulating its current draw.
- RS-485: line with terminationA twisted pair A/B runs as a line from device to device, with 120 Ω at both ends. RS-485 is the physical interface.
- Modbus RTU: request and responseThe protocol layer: the master polls a slave address (1–247) with a function code; the meter replies with a CRC-16 checksum.
- LoRa: radio to the gatewayThe meter sends short uplinks on 868 MHz. Every gateway in range receives them, with no cable to the metering point.
- LoRa: server and applicationGateways forward the data to the network server, which passes it on to the application. Range and transmission interval limit data volume and timeliness.
How LoRa works
LoRa is the radio technology: a modulation scheme that transmits over long distances using little energy. In Europe, it uses the licence-free 868 MHz band.
The network protocol built on it is called LoRaWAN. It defines how devices join a network, how data is encrypted and how gateways and servers work together. Helvatron meters join the network via OTAA (over-the-air activation); new session keys are derived on each join and are not stored permanently in the device.
The building blocks of a LoRa network
- End device
- H2O or DELTA III with LoRa interface, sends short uplinks
- Gateway
- receives transmissions from all devices in range and forwards the packets via the internet
- Network server
- checks and decrypts packets, and removes duplicates when several gateways receive the same packet
- Application
- decodes the payload and makes it available, for example in Joulio-Web or the control system
Limits of radio transmission
- Range depends heavily on the building, the pit and the gateway position. Meters in basements and pits often need a gateway nearby.
- Duty-cycle limits apply in the 868 MHz band. LoRa is suited to meter readings and interval values, not to second-by-second values.
- Every transmission draws on the battery. For the DELTA III, this means 10 + 1 years for daily transmission and 11 + 1 years for transmission every other day.
- Check reception at the installation location before installing the meter.
Alternative: NB-IoT
For individual sites without a LoRa network, both meters can also transmit via NB-IoT over the mobile network.
Questions about LoRa
Do I need my own LoRa network?
Not necessarily. The meters work with your own gateways and network server or with an existing public or private network. What matters is gateway coverage at the installation location.
How does the data get into Joulio-Web?
The application receives the packets from the network server and decodes them. Joulio-Web offers a dedicated licence for EMU and Helvatron meters.
How often does a meter transmit?
The transmission interval is set during configuration. Shorter intervals reduce battery life.
For details of the LoRa data path and payload decoder, see the pages of our sister company EMU on emuag.com.