05-1 Read-out performance
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 not only expect interoperability from DLMS/COSEM, but also superior performance compared to earlier solutions.
By courtesy of Actaris, a leading meter provider, member of the DLMS UA has received test results, in which the performance of meter reading using IEC 62056-21 Mode C (ex IEC 1107) and the DLMS/COSEM based mode E was compared.
The same data from the same meter have been read through the optical port at the most commonly used speed of 9 600 Baud using a read-out API, first using Mode C then using the DLMS/COSEM. The meter has been 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” has been 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 the reception of the result. The test results are shown in the table below:
| Length of profile, 15-minute | Reading time, seconds IEC62056-21 Mode C, R5 command | Reading time, seconds IEC62056-21 Mode E, DLMS/COSEM |
| 1 day 4 channels | 5 | 4 |
| 3 days 4 channels | 14 | 12 |
| 7 days 4 channels | 32 | 29 |
As it can be seen, the DLMS/COSEM mode is faster in all cases by more than 10%.
The superior performance is mainly due to its more efficient data presentation: the given meter presents each value in the load profile for Mode C readout as an 8 byte ASCII string. In the DLMS/COSEM representation, data are sent as type double-long-unsigned, which requires only 5 bytes, one for the tag and four bytes for the value. For one line of load profile data, Mode C requires 42 bytes whereas DLMS/COSEM 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, the reading is even slower;
- With DLMS/COSEM, only the blocks eventually lost have to be repeated, and with the window size the communication can be easily adapted to the quality of the line.
Communication performance expectations were clearly expressed by a major European utility, and were part of their tender specification. Actaris DLMS/COSEM ACE SL7000 meters have successfully passed the communication benchmarks, exceeding customer’s expectations.