HEIDENHAIN TNC 370D - Manual (Page 10)

July 02 Mounting and Electrical Installation TNC 370 D 3–7
3.2 Heat Generation and Cooling
Please note that the reliability of electronic equipment is greatly reduced by continuous operation at
high temperatures. Be sure to make the necessary arrangements to keep within the permissible
ambient temperature range.
Permissible ambient temperature in operation: 0 °C to 45 °C (32 to 113 °F)
The following means may be employed to ensure adequate heat removal:
· Provide sufficient space for air circulation.
· Build in a fan to circulate the air inside the control cabinet. The fan must reinforce the natural
convection. It must be mounted so that the warm air is extracted from the logic unit
and no pre-warmed air is blown into the unit. The warmed air should flow over surfaces that
have good thermal conductivity to the external surroundings (for example sheet metal).
· For a closed steel housing without assisted cooling, the figure for heat conduction is 3 Watt/m²
of surface per °C air temperature difference between inside and outside.
· Use of a heat exchanger with separate internal and external circulation.
· Cool by blowing external air through the control cabinet to replace the internal air. In this case
the fan must be mounted so that the warm air is extracted from the control
cabinet and only filtered air can be drawn in. HEIDENHAIN advises against this method of
cooling, since the function and reliability of electronic assemblies are adversely affected by
contaminated air (fine dust, vapors, etc.). Besides these disadvantages, a filter that is not
adequately serviced leads to a loss in cooling efficiency. Regular servicing is therefore vital.
3.3 Humidity
Permissible humidity:
< 75% in continuous operation,
< 95% for not more than 30 days p.a. (randomly distributed).
In tropical areas it is recommended that the TNC not be switched off, so that condensation is
avoided on the circuit boards. The heat generation prevents condensation and has no further
disadvantages.
3.4 Mechanical Vibration
Permissible vibration:
< 0.5 m/s2
3.5 Degree of Protection
Visual display unit when mounted
Protection class IP54
Keyboard unit when mounted Protection class IP54
HR 410 handwheel Protection class IP54
IP54 = Protection against dust and splashwater