What is the purpose of the management logical dev?
What is the purpose of the management logical device?
Simply speaking, the management logical device is the logical device, which must always be present in the physical device, and for which the upper HDLC address 0x01 is reserved.
Today it is very common that a single physical metering equipment handles multiple metering tasks. A simple example is a heat meter with a pulse input for a water-metering device. A more complex example would be a concentrator handling data for a number of meters.
According to the DLMS/COSEM meter model, each set of metering data is handled by a logical device implemented in a physical device.
The question is now how to know how many logical devices are inside the physical device? We need a ‘porter’ or ‘concierge’ to ask. This is the task of the management logical device.
The management logical device must have a SAP assignment object, which contains the list of all logical devices and their SAP addresses within the physical device. The management logical device must support an application association to a public client, with the lowest security level. The client address 0x10 is reserved for the public client. In case of LN referencing, the SAP assignment object has a predefined logical name. In case of SN referencing, the base_name of the SAP assignment is pre-defined as 0xFC00.
As the only mandatory logical device is the management logical device, it is possible that this is the only logical device in the meter and it contains the metering data as well. However, this would be a hack violating the spirit of COSEM. A much better approach would be to ”mirror” the management logical device on another upper HDLC address as the metering logical device. The overhead of such a solution is very small.