OSRAM POWERTRONIC PT-FIT I ECG for HID lamps, with cable clamp - Manual (Page 20)

THE PRODUCT IN OPERATION
20
2.3.6.4. Practical assessment of the service life and
thermal properties of an ECG
There are two ways of clarifying the life expectancy of an
ECG.
1) Without any temperature measurement
Comparing the t
a
values of the ECG with the t
a
tempera-
ture data shown on its technical datasheet can give an
indication of the ECG life expectancy
2) With temperature measurement in a luminaire
Set an ambient temperature for the luminaire (e.g. + 25 °C)
→ Measure the temperature at the t
c
test point of the ECG
to be compared and conclude the life expectancy of the
ECG using the data sheet applicable to it.
→ If you only compare nominal or catalog values, then the
data on the t
a
temperature should be preferred over
those on t
c
temperature.
→ However, real measurements of the t
c
temperature of
the ECG within a luminaire (not burning independently)
and obtaining the ECG life expectancy via the indica-
tions in its data sheet, is a substantially more meaning-
ful and realistic approach.
→ The contact of the ECG with the luminaire and the
associated improvement in heat dissipation will have
a decisive infl uence on its real life expectancy.
Real life measurement of the t
c
temperature and compa-
rison with the data specifi ed on ECG life expectancy as
a function of t
c
temperature is the only reliable way of
ob taining the life expectancy of an ECG.
CAUTION:
A simple comparison of the absolute nominal values for
the t
c
temperatures of ECGs produced by different manu-
facturers does not have any meaning in relation to their
properties or life expectancy, as the point at which the t
c
measurement is made can be chosen freely by the manu-
facturer.
Illustrative example of such a calculation:
ECG 1:
Nominal values: t
c
= 80 °C, t
a
= +55 °C, 40,000 h service life
at t
c
= 80 °C
→ With an ECG ambient temperature of 55 °C the max. t
c
is reached, and thus a life expectancy of 40,000 h can
be deduced.
ECG 2:
Nominal values: t
c
= 80 °C, t
a
= +55 °C, 40,000 h service life
at t
c
life = 70 °C
→ With an ECG ambient temperature of 55 °C the max. t
c
temperature is reached; however, the t
c
life has been
exceeded by 10 °C, which corresponds to a service life
of approx. 20,000 h.
→ With an ECG ambient temperature of
55 °C - 10 °C = 45 °C a t
c
temperature of
80 °C - 10 °C = 70 °C is obtained (corresponding to t
c
life), leading to a service life of 40,000 h being obtained.
Conclusion:
In spite of having the same nominal and maximum t
c
and t
a
temperatures, ECG 1 reaches a service life of 40,000 h at its
max. permitted ECG ambient temperature t
a
.
In contrast, ECG 2 is only given a service life of half that
duration; 20,000 h. In order to reach the same service life of
40,000 h, ECG 2 must operate at temperature t
c
life = 70 °C.
In this case it should be verifi ed whether the ambient tem-
perature would have to be reduced by 10 °C.