Operation

Before being able to transmit data over a LoRaWAN® network, the device must be personalized and activated. This can be done in two ways: 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 device joins the LoRaWAN® network. In contrast, for ABP, all keys are set manually and stay constant over time. The tables below list the required information depending on the activation mode.

CMi4160 is configured via the Elvaco OTC App. It uses NFC to transfer settings to the module. Downlink may also be used for some applications.

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 10 and 1440 minutes (i.e. from 10 minutes to once per day). It is possible to fix the transmit interval, but for battery-operated devices where battery lifetime is critical, Elvaco recommends using the EcoMode feature, which adapts the transmit interval depending on prevailing radio conditions.

ADR is part of the LoRaWAN® standard where the network server determines the optimal rate 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.

The module relies on the meter’s clock to keep time. The meter time is assumed to be 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 use 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.

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 the configuration lock has been enabled, a device-specific Product Access Key (PAK) will be needed to access the device. Keys are managed securely using Elvaco’s OTC solution which includes the mobile application for configuration.

Payloads using M-Bus encoded data use 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 the meter, bits 4–5 of the DIF code (first byte of each index field) will be set to 11b.