Operation

Before being able to transmit data over a LoRaWAN® network, the module must be personalized and activated. This can be done in two different ways for LoRaWAN®, Over-the-air activation (OTAA) or Activation by Personalization (ABP). For security reasons, Elvaco strongly recommends using OTAA, where all network keys are generated each time the module joins the LoRaWAN® network. In contrast, for ABP, all keys are set manually and stay constant over time.

The transmit interval is used to set how frequently the module should transmit data on the LoRaWAN® network. The parameter can be set to a value between 5 and 1440 minutes (i.e. between 5 minute values and daily values). It is possible to fix the transmit interval, but for battery operated devices where battery lifetime is critical, Elvaco recommends using the EcoMode feature, adapting the transmit interval depending on prevailing radio conditions.

The module relies on the meter’s clock for keeping time. Time in the meter is assumed to be in standard local time (no DST). When synchronizing time in the meter using the Elvaco OTC App, local standard time is always used, even if DST is in effect. The timestamped meter data sent from the module can be adjusted to be sent in UTC by specifying the “UTC offset” configuration parameter. The UTC offset will be subtracted from the timestamp prior to transmission. If the meter is in Sweden, which uses CET (Central European Time), it should have UTC offset set to +60 (+1h). In this case at time 12.00 a telegram is sent with timestamp 11.00 as this is the corresponding UTC time. A meter in New York (USA) should have a UTC offset of "-300" (-5h) etc. A UTC offset of "0" means the meter time is used as-is.

If the meter is set to used DST this is ignored by the module and the standard time is used. Thus, the time on the meter’s display may not match the time in the telegram or in the Elvaco OTC App.

ADR is part of the LoRaWAN® standard where the network server determines the optimal rate of communication for the module based on current signal conditions. In the best radio conditions, the module will use its highest data rate (DR5) in order to be as energy-efficient as possible. When signal conditions are poor, the network server will incrementally lower the data rate until it is able to receive the message. When the data rate is low, the energy consumption per telegram will increase.

All message formats encoded to M-Bus standard will have the following structure. Each telegram begins with one byte specifying the message format. Then follows a sequence of data information blocks (DIBs). The data and structure of the DIBs depends on the message type set. Each DIB contains a data information field (DIF), a value information field (VIF) and a data field (DATA), where the actual payload is stored.

M-Bus message structure

The product has a configuration lock feature, which prevents unauthorized access to the module. When configuration lock has been enabled, a device-specific Product Access Key (PAK) will be needed to access the device. Keys are managed in a secure way using Elvaco’s OTC solution which includes the mobile application for configuration.

The payloads using M-Bus encoded data uses the Function field of the DIF to indicate errors. In this case it is set to “value during error state” (M-Bus standard EN 13757-3:2013) and the value sent should not be used. A typical case for this is when the module is unable to communicate with the meter and retrieve meter values, in which case all the fields in the payload have the DIF indicating “value during error state”. In case of erroneous data or if the module is unable to communicate with meter, bit 4-5 of the bit of the DIF code (first byte of each index field) will be set to 11b.