OSRAM POWERTRONIC PT-FIT I ECG for HID lamps, with cable clamp - Manual (Page 24)

THE PRODUCT IN OPERATION
1) Shutdown mechanism – increase in the re-ignition peak
In conventional operation the re-ignition peak is a peak in
the lamp's operating voltage, after current and voltage
pass through zero. With sinusoidal lamp current, the cur-
rent decreases little by little, before reaching zero. As a
result of the continuously decreasing current the lamp
plasma cools down. This reduces further its conductivity
until the supply voltage is no longer capable of re-igniting
the plasma and the lamp fi nally goes out.
One of the main advantages of operation using
POWERTRONIC
® ECGs lies in the reduced occurrence of
re-ignition peaks. Since the zero crossing of the current is
very steep in these devices, the times in which little or no
current fl ows are very short, and the plasma has less
chance of cooling down.
Finally, a high-pressure discharge lamp using an ECG can
be operated for longer. The smaller re-ignition peaks are
to a large extent responsible for the longer service life
through ECG operation as compared to conventional
choke operation.
2) Shutdown mechanism – rectifying effect
Uneven heated electrodes, the malfunction of an electrode
or discharge in the outer bulb are all possible causes of
asymmetric operating mode (rectifying operation) of high-
pressure discharge lamps. The rectifying effect causes a
high DC voltage component. As a result, a conventional
choke will go into saturation, which will drastically reduce
choke impedance. In extreme cases the lamp current will
be restricted only by the ohmic resistance of the choke.
This may result in the choke and ignitor overheating.
With POWERTRONIC ® ECGs, current and voltage are
constantly monitored and adjusted by a microcontroller.
POWERTRONIC
® ECGs shut down before rectifying ef-
fects can lead to damage of the ECG thus allowing them
to offer a clear plus in terms of safety over conventional
control gears.
2.3.12. Noise levels
POWERTRONIC
® ECGs are so quiet in operation that even
in a quiet environment they can hardly be detected.
Their limit is generally < 30 dB(A).
In comparison to this, here are guideline values for
acceptable room noise intensity:
• For an offi ce: 35 dB(A)
• In a shop: 35 dB(A)
Factors that infl uence the noise intensity levels are the noise
emitted by each separate electronic control gear, the
acoustic properties of the luminaires in which they are
fi tted, the way the ECGs are mechanically attached into
the luminaires, the sound absorption properties of the
room, as characterized by volume and reverberation time,
as well as the total number of electronic control gear units.
24
Tip:
In order to develop a luminaire that makes as little noise as
possible, a suffi cient decoupling of the ECG and the lumi-
naire body is essential; i.e. the ECG should not have full
contact with the luminaire chassis, but it should be only
connected at points or mounted using the rubber absor-
bers that are also used for CCGs.
This method of mounting may under some circumstances
lead to thermal problems (the maximum permissible tem-
perature at the t
c
point may be exceeded due to the bad
thermal coupling), as the heat may be best dissipated with
full-surface mounting. Solving this problem with an appro-
priate casing construction and/or method of mounting the
luminaire (with forced ventilation or cooling, or enhanced
convection) has the advantage of reducing the operating
sound and therefore it should be taken into consideration.
Tests have shown that noise levels depend on the operat-
ing temperature of the electronic control gear. This factor
has a particular role if the ECG has been mounted accor-
ding to the above-mentioned recommendations. In extreme
cases it may not be possible to do without an additional
heat sink.
In addition, noise levels rise disproportionately with increa-
sing temperatures in the ECG. For this reason it is recom-
mended to run the ECG at a temperature lower than the
maximum permissible operating temperature. In practice,
this means that the lower the temperature at the t
c
test
point, the lower the noise level. The ideal solution would
be to use the double strategy of mounting the ECG in an
acoustically decoupled manner and running it at a lower
temperature.
2.3.13. Dimming
High-pressure discharge lamp systems based on high-
pressure sodium vapor or metal halide lamps can gene-
rally be operated at reduced power. However, it should
be kept in mind that dimmed operation will bring with it
losses in light quality and effi ciency (lm/W). For this reason
dimming of HID lamps can only be recommended for out-
door lighting applications. Therefore, POWERTRONIC
® PTi
and PT-FIT devices do not provide any dimming function.
In the interests of energy savings and CO
2
reduction, there
is now a demand for dimming capacity of lighting installa-
tions used for outdoor applications. The loss of light quality
can be tolerated late at night, as the number of motorists
reduces rapidly during the course of the night. For this rea-
son, OSRAM has developed the ideal ECG solution with
the PTo family, which has been fi tted out with the 3DIM
feature. 3DIM stands for DALI
® , StepDIM and AstroDIM.