VIII
Appendix 1: Air Temperature and Humidity
General
Normal operation of the unit or system is warranted under the ambient condi-
tions 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*, 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.
* Please Note: The ambient temperature range is restricted to +5...+35 °C, as opposed to the
standard mentioned above.
Under these conditions the unit or system starts and works without any prob-
lem. Beyond these specifications, possible problems are described below.
Ambient Temperature
Units and systems by Studer are generally designed for an ambient tempera-
ture range (i.e. temperature of the incoming air) of +5 °C to +40 °C. When
rack mounting the units, the intended air flow and herewith adequate cooling
must be provided. The following facts must be considered:
• The admissible ambient temperature range for operation of the semicon-
ductor 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 °C to 70 °C.
Frost and Dew
The unsealed system parts (connector areas and semiconductor pins) allow
for a minute formation of ice or frost. However, formation of dew visible to
the naked eye will already lead to malfunctions. In practice, reliable opera-
tion can be expected in a temperature range above –15 °C, if the following
general rule is considered for putting the cold system into operation:
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 between
the air and a cooler surface, together with formation of ice or dew at sensi-
tive areas of the system (contacts, IC pins, etc.). Once internal condensation
occurs, trouble-free operation cannot be guaranteed, independent of tempera-
ture.
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
Appendix
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