Lamp Lifetime And Detector Noise; Controlling The Amount Of Light That Reaches The Diode Array - Thermo Scientific Accela PDA Hardware Manual

Lamp Lifetime and Detector Noise

Controlling the Amount of Light that Reaches the Diode Array

Thermo Scientific
The Accela PDA Detector has two lamps. The tungsten-halogen lamp emits light in the
visible region, and the deuterium lamp emits light in the ultraviolet region. With use, the
deuterium lamp emits less and less light before it fails to ignite (see
light output from the tungsten-halogen lamp remains relatively constant until the lamp fails.
Figure 6. Deuterium lamp intensity versus lamp usage hours
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Detector noise is inversely proportional to the amount of light that reaches the diode array
and the sampling time for the photodiodes of the diode array. Decreasing the amount of light
that reaches the diode array and decreasing the sampling time both increase the detector noise
level.
These topics provide guidance on minimizing detector noise and maximizing the useful lamp
lifetime:
• Controlling the Amount of Light that Reaches the Diode Array
• Selecting an Appropriate Diode Array Scan Rate
During a fixed sampling period, the amount of light reaching the diode array is proportional
to the light output from the lamp and the aperture of the manual attenuators (partially open
to completely open).
To compensate for the decreased light output caused by lamp aging, increase the aperture of
the PDA detector's attenuators (see
page 25).
Note At the 20 Hz diode array scan rate, you can compensate for the decreased light
output from the deuterium lamp by increasing the attenuator aperture throughout the
lamp's lifetime of approximately 2000 hours.
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Life (Hours)
"Completing the Installation and Verifying Operation"
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Lamp Lifetime and Detector Noise
Figure 6). In contrast, the
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Accela PDA Detector Hardware Manual
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