Studer SW V4.0 OnAir 1000 Operating And Service Instructions page 10

Appendix
Appendix 1: Air Temperature and Humidity
General
Ambient Temperature
Frost and Dew
VIII
Normal operation of the unit or system is warranted under the following
ambient conditions defined by EN 60721-3-3, set IE32, value 3K3.
This standard consists of an extensive catalogue of parameters, the most
important of which are: ambient temperature +5...+40 °C, relative humidity
5...85% (i.e., no formation of condensation or ice); absolute humidity
1...25 g/m³; rate of temperature change < 0.5 °C/min. These parameters are
dealt with in the following paragraphs.
Under these conditions the unit or system starts and works without any
problem. Beyond these specifications, possible problems are described in
the following paragraphs.
Units and systems by Studer are generally designed for an ambient tem-
perature range (i.e. temperature of the incoming air) of +5...+40 °C. When
rack mounting the units, the intended air flow and herewith adequate cool-
ing must be provided. The following facts must be considered:
• The admissible ambient temperature range for operation of the semi-
conductor components is 0 °C to +70 °C (commercial temperature range
for operation).
• The air flow through the installation must provide that the outgoing air
is always cooler than 70 °C.
• Average heat increase of the cooling air shall be about 20 K, allowing
for an additional maximum 10 K increase at the hot components.
• In order to dissipate 1 kW with this admissible average heat increase, an
air flow of 2.65 m³/min is required.
Example: A rack dissipating P = 800 W requires an air flow of 0.8 * 2.65 m³/min
which corresponds to 2.12 m³/min.
• If the cooling function of the installation must be monitored (e.g. for fan
failure or illumination with spot lamps), the outgoing air temperature
must be measured directly above the modules at several places within
the rack. The trigger temperature of the sensors should be 65 to 70 °C.
The unsealed system parts (connector areas and semiconductor pins) allow
for a minute formation of ice or frost. However, formation of dew visible
with the naked eye will already lead to malfunctions. In practice, reliable
operation can be expected in a temperature range above –15 °C, if the fol-
lowing general rule is considered for putting the cold system into opera-
tion:
If the air within the system is cooled down, the relative humidity rises. If it
reaches 100%, condensation will arise, usually in the boundary layer be-
tween the air and a cooler surface, together with formation of ice or dew at
sensitive areas of the system (contacts, IC pins, etc.). Once internal con-
densation occurs, trouble-free operation cannot be guaranteed, independent
of temperature.
Before putting into operation, the system must be checked for internal for-
mation of condensation or ice. Only with a minute formation of ice, direct