Metrohm NIRS XDS Process Analyzer – MicroBundle - Manual (Page 10)

8 ▪▪▪▪▪▪▪
1.2 Fiber Optic Probe Ends
Interactance Reflectance Probes are used for processes
where the medium is somewhat turbid and will provide a
good reflectance signal back to the instrument. This
includes fermentation products and other materials with
high solids content.
The fiber optic bundle has two channels. One carries the
light to the probe, and the other channel carries the
reflected signal back to the detector for analysis. This
probe requires only one pressure port in a reactor.
The fiber bundle, showing the concentric channels, is
shown at right. This is a “Micro-Bundle” type, which has
40 fibers per set.
Transmission Probes are used for liquids that may be
clear to somewhat turbid. Work may be required to
determine the optimum pathlength, based upon the
sample medium, and the analyte level.
This photo shows threaded transmission probes, which
come with several spacers (2mm shown) which maintain
the probes at a pre-determined distance for consistent
analysis. Use 1” Swagelok® fittings.
Customers may have designed their own interface to the
process, and prefer transmission probes as shown.
These may be placed into the process using 1”
Swagelok® fittings. A method of gapping the ends must
be found, to assure consistent position.
Frequently the process interface is designed so that these
probe “barrels” are left in the process permanently, and
the fiber bundles are slid out for periodic instrument
qualification testing.
Interactance Immersion Probes are suitable for
transmission-style measurements on clear to partly clear
liquids.
In this probe style, the beam is directed through the
sample to a protected mirror, then reflected (back
through the sample again) to the receiving channel. The
advantage is that a transmission measurement is made
with only one probe entrance into a vessel.