Operating Manual CHM 8k
R1.7 / 01-2020
Communication via RS485 & Ethernet
25
8
Communication via RS485 & Ethernet
The
CHM 8k supports the interfaces RS485 (see section 8.2) and Ethernet (see section 8.7) for
communication with the device. Both offer the possibility of data transfer of the measured values and the
configuration of the device and can be used at the same time.
A web interface is part of the device for the communication via the Ethernet interface. Regardless of the
operating system, the ceilometer can be accessed through various web browsers.
The web interface can also be used to manually download the measured data stored in NetCDF daily
files on a built-in SD card (see section 8.4). Also implemented on the system is an AFD (ftp) service (see
section 8.8) which, for example, allows data in the form of 5-minute blocks of NetCDF files to be
transferred to an external FTP server.
RS485 communication requires a terminal program.
Transmit and receive with RS485
The RS485 interface does not allow simultaneous send and receive operation (half
duplex mode). Accordingly, the interface is automatically switched internally. Hence,
while receiving an automatically transmitted data telegram (see sections 8.3.3 to
8.3.5), it is not possible to send other commands (as described in 8.1). The incoming
start and end flags <STX> and <EOT> indicate a current receive transmission.
8.1 List of configurable parameters
Table 4 lists the most important settings. These are explained in the following sections. To prevent
unwanted effects on the functioning of the device, some options can only be set in service mode (RS485)
or in super user or service user mode (Ethernet), such as the device name. Table 5
shows a list of other
parameters (read-only properties). These parameters are stored in part on the EEPROM on the
measuring unit and affect data evaluation and the basic system settings. The tables contain the
permissible value range for each parameter and the default value on delivery of the device. They also
contain an indication when the service mode is required or when the parameter availability is different
between RS485 and web-interface.
Parameter
Short
cmd
RS485
Default
value
Range / short description
AfdMode*
AFD
0
0; 1, switch on (s)ftp data transfer
Altitude(m)
ALT
0
0
– 9999, unit is always in meters!
ApdControlMode*
ACM
2
0
– 2, APD mode, change only if function is
known in detail
Azimuth
AZT
0
0-360 degrees (x 100)
Web
(e.g. 12.25
RS485
and 1225
Web
)
Baud
BAU
3
2
– 7 (4,800 – 115,200 baud)
BaudAfterError*
BAE
3
2
– 7 (4,800 – 115,200 baud)
BlowerMode
BLM
0
0
– 4
ChmTest*
CHT
0
0; 1
CloudDetectionMode
CDM
3
0
– 3, switch between variants of algorithm
(bit 1 = HLC, bit 2 = BLC)
Comment
COM
Comment; also stored in the NetCDF file
Comment 1
RS485
CM1
Additional comment field (31 characters)
Comment 2
RS485
CM2
Additional comment field (31 characters)
Comment 3
RS485
CM3
Additional comment field (31 characters)
Comment 4
RS485
CM4
Additional comment field (31 characters)