3.3
Cooling Considerations
Temperature affects the life and reliability of high power electronic devices. As the
temperature of the device increases, generally reliability and life expectancy
decrease; TWTAs are no exception. Please follow the cooling considerations for
your amplifier to ensure many trouble free years of use.
e2v technologies engineers have many years of experience, working with customers
to integrate equipment successfully and to ensure that long and reliable product lives
are achieved. The information contained within this section has been gained from
both field experience and theoretical cooling system design knowledge. As most
installations differ, the advice given is only general. Any specific aspects of
installation design can be discussed further by contacting, or faxing the Stellar
Product Support Team at e2v technologies.
3.3.1
Some Cooling Facts and Figures
Minimum Air Flow . . . . . . . . . . . . . . .
28 litre/s (60 feet
3
/minute)
Minimum Duct Area . . . . . . . . . . . . . . . . . .
58 cm
2
(9 inch
2
)
Total Maximum Core Duct Length:
corrugated
. . . . . . . . . . . . . . . . . . . . .
0.5 m (1.65 feet)
smooth . . . . . . . . . . . . . . . . . . . . . . . .
1 m (3.3 feet)
Typical internal power dissipation
(no RF drive): . . . . . . . . . . . . . . . . . . . . . . . . .
900 VA
Typical temp.
difference
across device . . . . . . . . . . . . . . . .
40
8
C
Absolute max temp.
difference
across device
. . . . . . . . . . . . .
50
8
C
where temp.
difference
= temp.
out
7
temp.
in
The amplifier utilises an efficient, integral, forced-air cooling system and is equipped
with two thermal sensors to protect it in the event of an over-temperature condition.
When the temperature of either thermal sensor exceeds preset levels, the amplifier is
automatically removed from the XMIT mode and placed into the STBY mode. In the
STBY mode the dissipation within the amplifier is greatly reduced and if the airflow is
normal, the amplifier will rapidly cool. At this stage, the installation cooling system
should be visually inspected for blockages and cleaned as necessary. When normal
airflow is confirmed, the amplifier can be taken back into the XMIT mode.
The amplifier is automatically placed in the OFF mode if the over-temperature
condition exists for more than 4 minutes. The mains supply should be removed and
the amplifier isolated before a full inspection is made of the installation cooling system.
The amplifier should be left for 20 minutes before any attempt is made to re-start.
Following an over-temperature condition, the TWT OVER TEMPERATURE or
BASEPLATE OVER TEMPERATURE fault conditions are set, these can be monitored
via the user interface or accessed through the serial communications port (see
section 5).
When deciding on the location of the amplifier the following points should be
observed:
*
It is important not to obstruct the air inlet or the air exhaust
*
In any system, prevent hot exhaust air from recirculating to the inlet, otherwise
the inlet air temperature will increase, resulting in potential thermal runaway.
This is a prime consideration when designing common ducting systems for
multiple amplifiers.
HBN63xx-1, Issue 8, Page 11
