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Operating Guidelines
The IR-50 Series utilises a thin thermoresistive conducting film
of amorphous (diamond-like) carbon. Infrared radiation is the result of heating
this film by passing an electric current through it.
Either a constant voltage or a constant current power source is
suitable for driving these parts, however it is the temperature of the source
that is important.
The maximum temperature of the film should not exceed 750°C in
continuous operation. A faint red luminescence of the film is observed during
continuous operation at temperatures near 750°C. Short term heating up to
850°C is possible but will reduce the lifetime of the unit.
The specifications shown below assume an infrared source operating
without a radiator and at ambient temperature and pressure. Operation with a
radiator will cause the part to cool and hence the temperature of the part will
drop and the drive voltage will need to be increased to compensate. Operating
in an enclosed space or a high ambient temperature will generally cause the
part to overheat and the drive voltage will need to be reduced to
compensate.
The IR-50 Series is the perfect solution for an application that
requires fast electrical modulation. However, it can also be used in a steady
state (DC) mode. In applications where steady state power is used (or if used
with electrical modulation but with a duty cycle of greater than 50%), it is
recommended that the nominal input power specifications not be exceeded in
order to avoid overheating of the membrane. On the other hand, by reducing the
length of the heating pulse or by increasing the frequency of modulation, the
membrane will not have sufficient time to reach 750°C. In this case, the
pulsed power can be increased to allow 750°C to be maintained. The chart
below shows the factor by which the voltage can be increased as frequency is
increased. This chart assumes a 50% duty cycle. Use this Voltage Ratio to
maintain constant temperature.
Using a 50% duty cycle and the appropriate power factor as
determined above, a 50% modulation depth is achievable at modulation
frequencies of more than 60 hertz. This modulation depth can be achieved at
even higher frequencies (more than 100 hertz) if a 25% duty cycle were used
along with a correspondingly higher power factor (sufficient to maintain the
membrane temperature at 750°C). Please contact us for assistance in
determining the proper power factor for the duty cycle to be used in your
application.
Please note that over driving or contact with the thin film
will cause these devices to fail. |
The IR-50 range of broadband infra red lamps is based
around a very low thermal mass diamond-like carbon thin film element. Due to
the low thermal mass, the infra red lamp can be pulsed at frequencies up to
100Hz with good modulation depth, or contrast between the on and off states. It
is therefore suitable for use with quantum detectors like photoconductive PbS
and PbSe, which otherwise would require a chopper to avoid excess low frequency
"flicker" (1/f) noise.
