Ceilometer CT25K
CT25K-U059en-2.1 User’s Guide
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5.4 Sky Condition Algorithm
5.4.1 General
The CT25K sky condition algorithm uses a time series of ceilometer data to
calculate the cloud cover and the heights of different cloud layers. The
algorithm is based on so-called Larsson algorithm, developed by Swedish Air
Force and Swedish Hydrological Institute (SMHI), but further modified at
Vaisala. The sky condition information is included in data messages 6 and 7.
The algorithm updates sky condition information every five minutes, based on
data gathered during the last 30 minutes. The algorithm reports up to four
different cloud layers below 25000 feet.
Sky condition information can be displayed with the DD50 Digital Display.
NOTE
The CTC21 Controller Unit, DR21 Data Recorder and
the CT-VIEW software version 1.05 or earlier, can
NOT display the sky condition information.
5.4.2 Option code
The sky condition algorithm is included in the 2.01 software. The user
activates the algorithm by giving an option code number to the ceilometer.
The option code number is based on the DMC50B Processor Board serial
number. If the CT25K ceilometer is purchased with the sky condition
activated, then this is done at the factory. In case the sky condition option is
purchased afterwards, the user can find out the processor board serial number
by giving the following commands:
CT:open
CEILO>advanced
PASSWORD ACCEPTED !
CEILO>get dmc_sn
DMC SERIAL NO.: 850509 (example)
CEILO>close
The processor board serial number is also written on top of the
microprocessor circuit, with a letter as the year code. Forward the DMC50B
serial number to Vaisala. In response, Vaisala will send the option code
needed, for the example below: 48612.
5.4.3 Activation
The sky condition option code is set into the ceilometer with commands:
CT:open
CEILO>advanced
PASSWORD ACCEPTED!
CEILO>set option sky_cond on 48612 (example)
Code OK. Sky Condition option activated.
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