Operating Manual CHM 15k
R13 / 07-2019
Communication via RS485 & Ethernet
40
8.3.6 Additional data telegrams
The structure of the data telegrams is defined in a file "telegram.xml". This can be downloaded via the
web interface in superuser mode, modified and uploaded again in service user mode.
Some user telegrams are already pre-defined in the firmware:
Telegram 4: Telegram 2 + fan and heating status and the 8 comment fields (COM to CM7). The length
of the telegram is variable, because the comments only take up the space that their length requires.
Telegram 5: Telegram 1 + different display of
“altitude(m)” + fan and heating status
Telegram 8: CT25k data telegram 1 from Vaisala
Telegram 9: CT25k data telegram 6 from Vaisala
A separate description is available for the predefined user telegrams. These telegrams can change.
8.4 Structure of the NetCDF format
8.4.1 General
The ceilometer saves all measured backscatter profiles in a day file in the NetCDF format (Network
Common Data File). The storage capacity of the internal 8 GB SD card allows files to be kept on record
for approximately one year. The files can be accessed via web interface (LAN connection). In a
“Communication interrupted” service case, affected data can be inspected and traced back. In addition,
the raw data of a single measurement can be called up as a raw data telegram via the RS485 or LAN
interface. The operation does not include the transmission of more than a single measurement via RS485,
since this would negatively influence the time sequencing in this mode. Because the transmission rate
depends on the time resolution of the measured data and the RS485 interface settings, this transmission
would take too long. A one-day NetCDF file with dt(s)=30s measurement time intervals will be
approximately 12 MB in size. Switching to 15s time resolution 24 MB daily file sizes are generated. For
the LAN interface a direct access to the daily files, to 5 min files (AFD (ftp) mode) and single files via
request is possible.
8.4.2 Basic principles
NetCDF provides a computer platform-independent interface for storing and reading scientific data. It
was
developed
by
Unidata,
a
project
funded
by
the
National
Science
Foundation
). Each record contains explanations of the stored content.
The ceilometer stores all the data for one day in a file and in case the ftp mode is switched on in 5 min
files. The time used is UTC. In the standard mode (RS485), the CHM 15k transmits a raw data telegram
with a single backscatter profile and all descriptive variables and attributes in the NetCDF format. The
raw data telegrams for one day can be merged into a day file.
8.4.3 File names
Day file:
YYYYMMDD_[Location]_[DeviceID]_[Index].nc
Raw data in RS485
telegram:
YYYYMMDDhhmmss_[Location]_[DeviceID].nc
Raw data with 5-minute
time resolution for
ftp mode (AFD)
YYYYMMDDhhmmss_[Location]_[DeviceID]_hhmm_Index.nc
Length of data file names
For problem-free file transfer, the ISO standards should be complied with in their extended
form. The file length should not exceed 31 characters. For the structure of the day files
with [Date]_[Location]_[DeviceID]_[Index].nc (8_5_9_3.2=31 characters), this means that
the
variable “location” has less than 5 characters.
Summary of Contents for CHM 15k
Page 1: ...General Information 1 Titelseite...
Page 73: ...Index of Tables 73...
