Power And Module Cooling Considerations; Airflow Requirements - Racal Instruments 1260-82 User Manual

1260-82 User Manual
Power and
Module Cooling
Considerations
Airflow
Requirements
The 1260-82 is a VXI module providing precise switching of
optical channels using defraction limited collimating lenses which
enhance both thermal stability and repeatability. Because of this,
certain precautions should be applied when using the switch
module in a VXI chassis.
VXI Modules are required to specify 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 module 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 1260-82.
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 and 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
For a 10 °C rise and a 1260-82 module power of 12
Airflow(liters/sec) = 0.83/10 °C x 12 Watts = 1.0
3. Determine the pressure drop across the module when the
required airflow ( liters/sec) is forced through the module. This
can be determined by looking at pressure drop vs. airflow plot
for the 1260-82 Module in Figure 3-4. Find the required
airflow and then read the corresponding pressure in mm H
For the case above, with an airflow of 1.0 liters/sec the
pressure drop read from Figure 3-4 is 0.12 mm H
Power (Watts)
Watts:
liters /sec
Module Operation 3-13
O.
2
O.
2