Vaisala LT31 - Replacing Measurement Cpu;Window Receiver LTC112

Chapter 6 ______________________________________________________________ Maintenance
VAISALA ______________________________________________________________________ 211
14. Re-install the measurement head cover and lock it carefully.
15. Close the interface unit and mount the upper interface unit cover
after fine alignment and calibration is finalized.
Replacing Measurement CPU/Window
Receiver LTC112
The measurement units of the LT31 transmitter and receiver are equipped
with identical measurement CPUs LTC112. In case of a faulty window
receiver, the measurement CPU has to be replaced as well. The procedure
is identical for the receiver and transmitter measurement unit.
NOTE
To replace the measurement CPU LTC112, the measurement unit has to
be opened. For this reason, it is highly recommended to dismount the
complete measurement unit and carry out the replacement work on a
clean workbench in a dry room.
To remove the complete measurement unit, the AC power has to be
switched off first and then the measurement head cover has to be
removed.
1. Remove the upper interface unit cover and open the interface unit
with the provided key.
NOTE
Switch the AC switch off before you proceed with the next steps. In case
of the optional LTBB111, switch the battery backup switch off as well.
See Figure 40 on page 83.
2. Loosen the three lock screws at each side of the measurement head
cover and carefully remove the cover from the measurement head.
See Figure 95 on page 140.
3. The measurement unit is fixed with two fastening screws. Through
the mast adapter of the support unit, these two hex-socket screws,
size 4, can be reached. See Figure 78 on page 118.
The following steps should be carried out in a closed room
. The
measurement unit cover has to be opened carefully.
1. Loosen the four fastening screws of the cover plate, hex-socket size
5, and remove the cover with air duct. See Figure 72 on page 115.
2. To replace the LTC112, the optics unit has to be removed first.
Two fastening screws (hex-socket size 3) and one fastening bolt
(socket wrench, size 7) have to be loosened. See Figure 121 on