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Operating Manual CHM 8k
R1.7 / 01-2020
Commissioning and Decommissioning 22
7
Commissioning and Decommissioning
7.1 Starting up with the RS485 connection
Requirements:
•
The
CHM 8k ceilometer must be installed correctly
•
Control cable (RS485), grounding cable and mains cable (115 VAC or 230 VAC) must be
connected
•
A terminal program, e.g., HyperTerminal
or Bray’s terminal, can be used under Windows for
monitoring communication. It has to be configured for communication as follows:
- Baud rate: 9,600
- Data bits: 8
- Parity: none
- Stop bits: 1
- Flow control: none
CAUTION
After switching on the power supply, the CHM 8k emits Class 1M invisible laser
radiation through the opening at the top of the sensor. When viewed with optical
instruments, Class 1M radiation can lead to serious eye injuries.

Never view the laser beam with optical instruments, especially binoculars

Avoid looking directly into the laser beam
After connecting the supply voltage, the CHM 8k will start up by itself. During the start-up process an
internal self-check is done, e.g. the fans start for a few seconds. Communication with the device is
possible within 1 minute. The CHM 8k will be fully operational after a temperature adjustment phase of
varying length depending on outdoor temperature conditions. The time until measurement data are
available in high quality, can be between 2 minutes (warm start) and one hour (cold start at -40 °C).
The CHM 8k automatically sends out standard data telegrams when the start-up procedure has been
completed. It is part of the default setup and might differ for user specific CHM 8k start settings. The
automatic output every 15 s is helpful to check if the communication works correctly without entering any
command.
To change the start-up behavior like polling vs automode or the telegram that should be used at start see
chapter 8 Communication via RS485 & Ethernet.
Test commands for RS485 communication
To test the communication, use the command (RS485Number = 16 (default value)):
set<SPACE><RS485Number>:Transfermode=0<CR><LF>
This command changes the settings from auto to polling mode. Testing in polling mode is helpful to avoid
interruptions by automatically sent telegrams while typing. 9 telegram types are available:
•
Standard data telegram (short name: 1 or s)
•
Extended data telegram (short name: 2 or l)
•
Raw data telegram (short name: 3 or a)
•
User telegrams (short name: 4, 5, ..., 9)
Section 8 describes the possible commands and their effects in detail. Some commands for functional
testing required in routine operation or to setup the system in the beginning are listed in Table 3
.