Lufft CHM 15k, User Manual

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Operating Manual CHM 15k R13 / 07-2019
Communication via RS485 & Ethernet 38
For the stated standard deviations of the individual quantities, the same exception values "NODET /
NODT / ---" apply as for the corresponding basic quantities (see
0
Standard data telegram).
Further system parameters
The system parameters for data evaluation, including penetration depth, are explained
in section 9 Data Evaluation / Sky Condition Algorithm (SCA).
Designation Description
Outside temperature The outer temperature is measured at the bottom of the unit.
Display in Kelvin x10, tolerance ±5 K
Inside temperature Measured temperature at the sensor:
Display in Kelvin x10, tolerance ±2 K
Detector temperature Measured temperature at the sensor:
Display in Kelvin x10, tolerance ±2 K
NN1 unassigned
NN2 unassigned
Laser operating hours (h) Operating time of the laser in hours
Window status Degree of contamination of the glass window in percent
100 = clear view, 0 = opaque
Laser frequency Number of laser pulses in the measuring interval (7-digit)
Receiver status Evaluation of the status of the optical path and receiver
100 = maximum sensitivity
0 = no sensitivity
Light source status Evaluation of the stability and ageing process of the light source
100 = start value (good), 0 = bad
Table 10 Designations in the extended data telegram.
8.3.5 Raw data telegram
The raw data is output in NetCDF format (for a description see 8.4 Structure of the NetCDF format).
NetCDF is a binary format. For transmission via RS485 / RS232, a transformation in a 7-bit ASCII code
(range 21 to 60 HEX) with UUencode is required to be able to handle none printable characters such as
<STX> or <EOT>.
The size of the NetCDF file of a raw data set is approximately 14 kilobytes. The UUencode conversion
produces 20 kilobytes of ASCII data that has to be transferred. At a baud rate of 9,600, the transmission
takes about 16 seconds. The automatic output of the raw data telegram is restricted to specific logging
time / Baud rate combinations, as set out in Table 11 below.
Baud rate no. Baud rate [bit/s] Logging time interval [dt(s)]
0 1,200
Not possible
1 2,400
Not possible
2 4,800
≥ 40 s
3 9,600
≥ 20 s
4 19,200
≥ 10 s