HEIDENHAIN TNC 335 Technical Manual - Manual (Page 38)

3-8
TNC 360 2 Assembly Hints 8/95
2 Assembly Hints
2.1 Electrical noise immunity
Please note that the vulnerability of electronic equipment to noise increases with faster signal
processing and higher sensitivity. Please protect your equipment by observing the following rules
and recommendations.
Noise voltages are mainly produced and transmitted by capacitive and inductive coupling. Electrical
noise can be picked up by the inputs and outputs to the equipment, and the cabling.
Likely sources of interference are:
–
Strong magnetic fields from transformers and electric motors,
– Relays, contactors and solenoid valves,
– High-frequency equipment, pulse equipment and stray magnetic fields from switch-mode
power supplies,
– Mains leads and leads to the above equipment.
Electrical interference can be avoided by:
–
A minimum distance between the logic unit (and its leads) and interfering equipment > 20 cm.
– A minimum distance between the logic unit (and its leads) and cables carrying interference
signals > 10 cm.
(Where signal cables and cables which carry interference signals are laid together in metallic
ducting, adequate decoupling can be achieved by using a grounded separation screen)
– Screening according to DIN VDE 0160.
– Potential compensating lines
∅ ≥
6 mm² (see Grounding diagram).
– Use of original HEIDENHAIN cables, connectors and couplings.
2.2 Heat generation and cooling
Please note that the reliability of electronic equipment is greatly reduced by continuous operation at
elevated temperatures. Please take the necessary measures to keep the unit within the permissible
ambient temperature range.
Permissible ambient temperature in operation: 0° C to 45° C (BF 110: 0° C to 40° C)
The following means may be employed to ensure adequate heat removal:
–
Provide sufficient space for air circulation.
– Build in a ventilator 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-up air should flow over surfaces
which have good thermal conductivity to the external surroundings (e.g. 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.
– Cooling by blowing external air through the control cabinet to replace the internal air. In this
case the ventilator 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.). In addition to these disadvantages, a filter which is
not adequately serviced leads to a loss in cooling efficiency. Regular servicing is therefore
absolutely vital.