Operating Manual CHM 8k
R1.7 / 01-2020
Technical Description
13
4.2.2 Function control and device status
Figure 3 Flow chart - standard measuring cycle.
The functional control of the CHM 8k (measurement and evaluation) is performed by an FPGA and an
OMAP processor. The logging interval (not shown here) consist of multiple measuring cycles calculated
in the OMAP processor, while processes with higher time resolution of up to 1s time intervals are
processed in the FPGA.
Figure 3 shows the internal measurement cycle that takes place every second. The measured data and
the evaluation of the status parameters are checked after each measurement cycle. If the values are
outside the tolerances or there is a hardware error, the standard measurement cycle is reinitialized, and
an error message is generated and output.
However, there are parts that are controlled internally with higher time resolution, such as the temperature
control of the laser and processes that run in the logging interval, such as the evaluation of the window
contamination sensor [153] and the fan controller in case of precipitation. Laser safety is also monitored
by the FPGA and the firmware, independently of the above measurement cycle. In addition, there is a
watchdog circuit that monitors the operating system and relevant voltages, and a software watchdog to
control the firmware processes. Determined values and status values are output in the extended data
telegram and the NetCDF files. The standard message contains rough information about the status code
(see 8.5 Status code).
-
laser diode testing
-
detector testing
-
transmission of status
codes
Measurement 1s
Evaluation
of
temperatures,
signal quality, voltages are
checked, laser safety check
N
O
Y
E
Measurement & system
performance okay?