Chapter 5 ________________________________________________________________ Operation
VAISALA ______________________________________________________________________ 179
Message 7 - MITRAS Emulation
For compatibility on the system level, LT31 also supports the message
format, frames, and polling format of Vaisala MITRAS
Transmissometer. The MITRAS polling format is accepted only when
the MITRAS message emulation is selected with the
SET MESSAGE
TYPE MITRAS
command.
The MITRAS polling format is the following:
P<Space><ID>
-*
.
The emulated Vaisala MITRAS Transmissometer message is presented
below:
"
ID 1 V 4550 B ///// S010101
-*#
----
-
---
------
---
-----
--
----
--------
¦ ¦ ¦ ¦ ¦ ¦ ¦¦ ¦ ¦___
receiver 2 status (fixed to 01)
¦ ¦ ¦ ¦ ¦ ¦ ¦¦ ¦___
receiver 1 status
¦ ¦ ¦ ¦ ¦ ¦ ¦¦___
transmitter status
¦ ¦ ¦ ¦ ¦ ¦ ¦____
S, status heading
¦ ¦ ¦ ¦ ¦ background luminance value
¦ ¦ ¦ ¦ ¦___B,background luminance heading
¦ ¦ ¦ ¦_____ visibility m, 1 min average
¦ ¦ ¦________V, visibility heading
¦ ¦________unit ID (one character only)
¦_________ID, start indicator
The total amount of characters in the message is 35. The transmission
times are: 1.2 s at 300 bps (10-bit char), 0.15 s at 2400 bps, 0.04 s at
9600 bps.
The binary status is in hexadecimal notation. The status bits emulate the
MITRAS status as follows.
The transmitter status correspondence between MITRAS and LT31 is the
following:
BIT MITRAS
LT31
BIT.0=1
MEAS
MODE
ON
II BIT.1=2
CONT/OTHER
OFF
BIT.2=4
OPTICAL
SURFACE Window
contamination
BIT.3=8 POWER SUPPLY
Power supply failure
BIT.4=1
HEATING
OFF
I
BIT.5=2 FLASH LAMP
LED failure
BIT.6=4 BL METER
BL sensor status (ON/OFF)
BIT.7=8
MEASUREM.
LOOP
SIGNAL
OFF