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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 +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.
Undertheseconditionstheunitorsystemstartsandworkswithoutanyprob-
lem.Beyondthesespecifications,possibleproblemsaredescribedbelow.
Ambient Temperature
UnitsandsystemsbyStuderaregenerallydesignedforanambienttempera-
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:
• Theadmissibleambienttemperaturerangeforoperationofthesemicon-
ductor components is 0 °C to +70 °C (commercial temperature range for
operation).
• Theairflowthroughtheinstallationmustprovidethattheoutgoingairis
always cooler than 70 °C.
• Averageheatincreaseofthecoolingairshallbeabout20K,allowingfor
anadditionalmaximum10Kincreaseatthehotcomponents.
• Inordertodissipate1kWwiththisadmissibleaverageheatincrease,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.
• Ifthecoolingfunctionoftheinstallationmustbemonitored(e.g.forfan
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.
Beforeputtingintooperation,thesystemmustbecheckedforinternalfor-
mation of condensation or ice. Only with a minute formation of ice, direct
Appendix
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