With a growing population of DLMS/COSEM-based meters and data collection systems the issue of performance becomes important, as trading on the liberalised markets is based on the daily reading and processing of load profiles, which requires efficient handling of large amounts of data. Customers expect interoperability from DLMS/COSEM and also superior performance.
By courtesy of meter provider Actaris, the DLMS UA has received test results comparing the performance of meter reading using IEC 62056-21 Mode C (ex IEC 1107) and the DLMS/COSEM based mode E. The same data from the same meter was read through the optical port at the most commonly used speed of 9 600 Baud using a read-out API, first using Mode C and then DLMS/COSEM. The meter was configured with a load profile containing four channels of measurement values in 15-minute intervals.
In Mode C, the R5 command, as specified by the German VDEW specification “Static load-profile meters” was used. The meter responds to this command by sending the data in a single frame. In the DLMS/COSEM mode, the meter sends the data in blocks. Window size = 7 was set, meaning that good reception is acknowledged after each seventh block. The time was measured from sending the request until receipt of the result. The test results are shown in the table. As can be seen, the DLMS/COSEM mode is faster in all cases by more than 10%.
The superior perform-ance is mainly due to its more efficient data presentation – the meter presents each value in the load profile for Mode C readout as an 8 byte ASCII string. In the DLMS/COSEM representation, data is sent as type double-long-unsigned, which requires only 5 bytes. For one line of load profile data, Mode C requires 42 bytes, whereas DLMS/COSEM needs only 24 bytes. Efficiency can be further increased by grouping various data in Profile generic objects.
DLMS/COSEM is also more robust. With the R5 command, if a transmission error occurs, the reading needs to be restarted. VDEW also specifies block transfer using the R6 command, making the reading even slower. With DLMS/COSEM, only the blocks eventually lost have to be repeated.
Communication performance expectations were clearly expressed by a major European utility. Actaris DLMS/COSEM ACE SL7000 meters have successfully passed the communication benchmarks, exceeding customer expectations.