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Publication No. 980673-055 Rev. A
Airflow
Requirements
EADS North America Test and Services
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
The following is a typical example calculation. Assume that you
have a 1260-22 Module with an Option –01T Installed and that
there are ten paths used on the module and that each path is
conducting 20 Amps each and each are conducting at a 50 %
duty cycle. From the equation above
P
= 8.0 W + (0.8 W x .5) x 10 relays + (20A
TOTAL
10 channels
P
= 52.0 Watts
TOTAL
Note that if the same conditions existed except conducting at a
100% Duty cycle the total power would be 100.5 Watts! After
the
Module
power
requirements must be evaluated.
VXI Modules are specified to require a particular airflow to
maintain a specific temperature rise. The air flow required and
the resultant back pressure (pressure drop across the module)
values determine a specific operating point that is plotted or
compared against a VXI chassis cooling curve. If the operating
point is below the chassis cooling curve, there is a high
probability that the module will remain within its specified
temperature rise. If the operating point lies above the chassis
cooling curve the temperature rise may exceed the specified
value.
The following procedure details how to calculate the cooling
requirements for the 1260-22.
1. Determine the maximum temperature rise allowed across
the module. This is typically 10 °C, but could be higher or
lower depending the chassis ambient temperature, and the
overall reliability requirements of the module.
2. Determine the required airflow to maintain the specified
temperature rise of the module. This is calculated from the
module power (calculated in previous section), the desired
temperature rise, and the specific heat of air. For a given
temperature rise the required air flow is:
Airflow(liters/sec) = 0.83/Temp Rise(°C) x Module
As an example, for a 10 °C rise and a module power of
56.5 Watts:
Airflow(liters/sec) = 0.83/10 °C x 56.5Watts = 4.7
liters/sec
3. Determine the pressure drop across the module when the
1260-22 User Manual
is
calculated
the
required
Power (Watts)
Module Operation 3-13
2
x 0.02Ω x.5) x
airflow
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