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Interface · EMU Professional II

LoRa on the EMU Professional II: LoRaWAN, TTN and payload decoder

Radio in the licence-free EU868 band, range instead of data rate, meters that transmit of their own accord. This page explains how LoRa and LoRaWAN fit together, why the duty cycle determines the timing, and how the TTN template and our decoder give you readable values without any programming of your own.

Switch interface

M-BusRemote meter reading over two wires RS-485 / Modbus RTUFieldbus for control systems TCP/IPModbus TCP and MQTT on the network LoRaRadio without cabling of its own KNXFrom Q1 2027

The principle

How does LoRa work?

Two terms are constantly mixed up. LoRa is the radio technique – a spread-spectrum modulation that fans a narrow signal out so widely that it is still detected below the noise. That buys range at the cost of data rate. LoRaWAN is the network protocol on top of it: gateways, network server, encryption, join procedure.

The logic differs from M-Bus or Modbus: no master polls the meter. The meter sends a small packet of its own accord at a fixed rhythm, and a gateway within radio range picks it up and forwards it to the network server. After each transmission the device briefly opens two receive windows – that is Class A, the most economical operating mode.

In Europe this runs in the licence-free EU868 band. Licence-free does not mean rule-free: a duty cycle limit applies, restricting transmission time per device and hour. That is why LoRa is made for quarter-hour or hourly values and not for per-second values.

Terms

LoRa

The radio technique. Spread-spectrum modulation, range at the cost of data rate.

LoRaWAN

The network protocol: gateways, network server, keys, join.

Spreading factor

SF7 to SF12. Higher means further and more robust, but slower and with more transmission time.

Duty cycle

Statutory limit on transmission time per device in the licence-free band.

Class A

The device transmits, then two short receive windows. The most economical mode.

OTAA

Joining over the air with DevEUI, JoinEUI and AppKey. The recommended route.

ABP

Permanently programmed session keys. Simpler, but less secure.

Payload

The useful data of the packet – compactly packed bytes, not readable text.

Data path

How do the readings of a LoRa meter reach the target system securely?

Whether with your own network server or straight into Joulio-Web: the meter joins via OTAA, and all readings travel end-to-end encrypted. This applies to the EMU Professional II LoRa as well as to the Helvatron H2O and DELTA III meters. The gateways only forward.

Use case 1: external network server with API

Radio EU868BackhaulAPIDuplicate discardedProfessional II LoRaElectricity · EMUHelvatron H2OWaterHelvatron DELTA IIIHeatGateway 1SIM modem (LTE)Gateway 2LANNetwork serverLNS + join serverPayload decoderControl systemBillingCloud / BIIn the meterDevEUIJoinEUIAppKeyDevAddrNwkSKeyAppSKeySession keys follow after the joinIn the gatewaysno keysonly forward packetsIn the network serverDevEUIJoinEUIAppKeyDevAddrNwkSKeyAppSKeySession keys follow after the join
  1. Keys in placeEach meter knows its DevEUI, the JoinEUI and the secret AppKey. The same three values are registered in the network server. The AppKey is never sent over the air.
  2. Join requestThe meter joins with its DevEUI, the JoinEUI and a random number. The message is signed with the AppKey. Every gateway in range receives it – here, both.
  3. Forwarding over LTE and LANGateway 1 sends via its built-in SIM modem, gateway 2 via LAN. The gateways open nothing. The network server recognises the packet received twice and discards the copy.
  4. Join acceptThe network server checks the signature, assigns a network address (DevAddr) and replies, encrypted with the AppKey, via the gateway with the best reception.
  5. Session keysThe meter and the network server each derive the same session keys independently: NwkSKey for integrity, AppSKey for the readings. Neither key is transmitted.
  6. Sending readingsThe electricity, water and heat meters send their values at a fixed interval, encrypted with the AppSKey. The gateways cannot read the content.
  7. Check and decodeThe network server checks the signature, discards duplicates, decrypts with the AppSKey and uses the payload decoder to turn the bytes into kWh, m³ and heat quantity.
  8. Passing on via APIThe decoded values go to the control system, billing or the cloud via the network server’s API, for example REST, webhook or MQTT.

Use case 2: Joulio-Web with integrated network server

Radio EU868BackhaulUseDuplicate discardedProfessional II LoRaElectricity · EMUHelvatron H2OWaterHelvatron DELTA IIIHeatGateway 1SIM modem (LTE)Gateway 2LANJoulio-Webintegrated LNSDecoder + analysisDashboardsUtility costsAPI (optional)In the meterDevEUIJoinEUIAppKeyDevAddrNwkSKeyAppSKeySession keys follow after the joinIn the gatewaysno keysonly forward packetsIn Joulio-WebDevEUIJoinEUIAppKeyDevAddrNwkSKeyAppSKeySession keys follow after the join
  1. Keys in placeEach meter knows its DevEUI, the JoinEUI and the secret AppKey. The same three values are registered in Joulio-Web. The AppKey is never sent over the air.
  2. Join requestThe meter joins with its DevEUI, the JoinEUI and a random number. The message is signed with the AppKey. Every gateway in range receives it – here, both.
  3. Forwarding over LTE and LANGateway 1 sends via its built-in SIM modem, gateway 2 via LAN. The gateways open nothing. Joulio-Web recognises the packet received twice and discards the copy.
  4. Join acceptJoulio-Web checks the signature, assigns a network address (DevAddr) and replies, encrypted with the AppKey, via the gateway with the best reception.
  5. Session keysThe meter and Joulio-Web each derive the same session keys independently: NwkSKey for integrity, AppSKey for the readings. Neither key is transmitted.
  6. Sending readingsThe electricity, water and heat meters send their values at a fixed interval, encrypted with the AppSKey. The gateways cannot read the content.
  7. Check and decodeJoulio-Web checks the signature, discards duplicates, decrypts with the AppSKey and uses the payload decoder to turn the bytes into kWh, m³ and heat quantity.
  8. Straight into Joulio-WebJoulio-Web holds the keys itself and uses the values directly for dashboards, load profiles and utility cost statements. Third-party systems can connect via the Joulio-Web API.

Integration

How do I decode the LoRa payload of a power meter?

What arrives at the network server is at first a short block of bytes. To turn that into “active energy import, tariff 1, 128,431 kWh” you need a payload decoder: a small piece of code that takes the bytes apart according to the device’s payload structure.

This is exactly where LoRa projects most often fail – not on the radio link, but because the decoder was written by hand and never documented. That is why we provide it ready-made.

The Things Network

In the TTN network the EMU Professional II LoRa is directly available as a template. Create the device, choose the template, enter the keys – the decoder comes with it. In the most common case, that is all there is to it.

Other network servers

For integration into other systems the decoder is on GitHub. It comes with two tools that run straight in the browser: a payload decoder to check a received packet, and a payload generator to create test packets before the first meter is installed. Both save troubleshooting on site.

Tools

GITLoRa decoderemuag/professional_II_lora WEBPayload decoderCheck a received packet WEBPayload generatorCreate test packets

Test before installation

With the payload generator the whole chain from the network server to the target system can be built and checked before a single meter hangs in the shaft. That moves troubleshooting from the basement to the desk.

Radio planning

What range does LoRa achieve inside buildings?

Spreading factor

A higher spreading factor brings range and robustness, but lengthens transmission time and therefore uses up more of the permitted duty cycle. Meters in the basement often end up at SF11 or SF12, meters with line of sight at SF7.

Structural situation

Reinforced concrete, soil and metal cabinet doors weaken the signal more than any distance figure suggests. A meter 30 m away in the basement is harder to reach than one 2 km away with a clear view of the gateway.

Measure beforehand

A test device at the planned installation point says more than any calculation. For distributed properties a walk-through with measurements pays off before gateways are permanently installed.

Where it fits

When is LoRa the right interface?

In favour

  • Measuring points with no cable route, for instance in existing buildings
  • Distributed properties sharing one gateway
  • Retrofits where no cable can be pulled any more
  • Quarter-hour or hourly values as the target resolution
  • TTN template available, decoder public on GitHub

Against

  • Per-second values or control tasks – the duty cycle rules that out
  • Large amounts of data per reading
  • Guaranteed delivery at a fixed point in time
  • Deep-lying measuring points with no radio path to the outside
  • Installations where an M-Bus or Ethernet is present anyway

View M-Bus · View TCP/IP

Documents

Manuals and data sheets to download

This page explains the principle. Register lists, telegram structure, terminal assignment and the exact parameters of each version are in the interface manual.

PDFLoRa interface manual1490 · payload structure · English GITLoRa decoderemuag/professional_II_lora GITPayload generatorSource on GitHub WEBPayload decoderRuns in the browser WEBPayload generatorRuns in the browser PDFProfessional II data sheet1441 · English

Frequently asked questions

Frequently asked questions about the interface

What is the difference between LoRa and LoRaWAN?

LoRa is the radio technique – a spread-spectrum modulation that trades data rate for range. LoRaWAN is the network protocol on top of it, with gateways, a network server, encryption and a join procedure. In practice you need both.

Is there a ready-made template for The Things Network?

Yes. In the TTN network the EMU Professional II LoRa is directly available as a template. Create the device, choose the template, enter the keys – the payload decoder comes with it.

How do I integrate the meter into another network server?

Through the decoder we provide on GitHub. There is also a payload decoder and a payload generator as web tools: with the decoder you check a received packet, with the generator you create test packets to build the chain before the first meter is installed.

How often does a LoRa meter transmit?

At a fixed rhythm, not on demand. The timing follows the duty cycle in the licence-free EU868 band, which limits transmission time per device and hour. That makes LoRa suitable for quarter-hour and hourly values, not for per-second values or control tasks.

What range will I achieve?

That depends on the location, not on a number in a data sheet. Reinforced concrete, soil and metal cabinet doors weaken the signal far more than distance does. A meter 30 m away in the basement can be harder to reach than one 2 km away with line of sight. A measurement at the planned installation point beats any calculation.

OTAA or ABP?

OTAA, joining over the air with DevEUI, JoinEUI and AppKey, is the recommended route: the session keys are negotiated at join time. ABP works with permanently programmed keys – simpler to set up, but less secure and more awkward when a meter is replaced.

Not sure whether LoRa fits?

Send us the number of measuring points, the distances and the target system. We will tell you which version makes sense – and when another interface would be the better choice.

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