PerkinElmer Lambda 650, Hardware Manual

Page: 52 / 72

52 . Using the Instrument
Instrument Purging (Lambda 850 and 950 only)
WARNING
Always purge the instrument with an inert gas such as Nitrogen. Never
use a flammable gas such as Hydrogen.
Oxygen absorbs radiation in the UV range below 190 nm, while water vapor absorbs
radiation in the NIR range between 1350 nm and 1450 nm, 1850 nm and 1950 nm, and also
between 2520 nm and 3000 nm. Best accuracy for measurements in these spectral regions
can only be obtained when the spectrometer is purged with nitrogen.
The entire optical compartment of the spectrometer is sealed. Radiation from the source
lamps enters the optical compartments through a window. The sample compartment is also
sealed from the optical compartment by windows. Thus the entire optical radiation path from
virtually the source lamp to the detector can be purged largely free of water vapor and
oxygen.
Fittings are provided on the left side of the spectrometer for connection of a supply of
nitrogen, as shown in Figure 16. The inlet nearest the rear of the instrument is for the
sample compartment and the one nearest the front of the instrument is for the main optical
compartment. After purging these compartments the nitrogen escapes to atmosphere.
Figure 16 Connectors for the purge gas supply
You should keep the sample compartment closed during routine operation to prevent the
ingress of water vapor and oxygen. Do not leave the sample compartment cover open for
longer than is necessary to perform operations within the sample compartment. After closing
the sample compartment purge for several minutes before starting the measurement.
When the spectrometer has been standing for some time unpurged, an initial flow of 20
L/min is recommended. After the spectrometer has been thoroughly purged, the flow can be
reduced to between 6 L/min to 7 L/min.
When you have a good deal of work in a spectral region where water vapor or oxygen
absorb the radiation, we recommend that you purge the spectrometer more or less
continuously. This has the advantage that startup times are markedly shorter. This
advantage is somewhat offset by the increased consumption of nitrogen.
Purge inlets