HALO Users Manual
Revision G
48
Hydrogen (H
2
)
Hydrogen is a homo-nuclear diatomic molecule that has no measurable absorption in the NIR.
The water absorption peaks are slightly narrowed in Hydrogen. This provides increased
sensitivity of H
2
O measurements (vs. N
2
), but with a slightly reduced upper limit reading.
Hydrogen Chloride (HCl)
Hydrogen Chloride has no measurable absorption in the NIR where we measure moisture. The
water absorption peaks are significantly widened in HCl. This reduces the sensitivity of H
2
O
measurements (vs. N
2
), but provides an increased upper limit reading. HCl is highly hygroscopic.
As HCl propagates through a flow system, it absorbs any water in the flow system it comes in
contact with. This effect causes significant settling times when making measurements in HCl.
When switching between an inert gas and HCl, provide ample time for the flow system to reach
equilibrium before taking measurements. Also, since HCl is highly corrosive, keep the system as
dry as possible to prevent corrosion of the gas handling components.
Hydrogen Bromide (HBr)
Hydrogen Bromide has significant absorption in the NIR near where we measure moisture. This
requires measurement in HBr to be done at a different wavelength. The water absorption peaks
are significantly widened in HBr. This reduces the sensitivity of H
2
O measurements (vs. N
2
).
HBr is extremely hygroscopic. As HBr propagates through a flow system, it absorbs any water in
the flow system it comes in contact with. This effect causes significant settling times when
making measurements in HBr. When switching between an inert gas and HBr, provide ample
time for the flow system to reach equilibrium before taking measurements. Also, since HBr is
highly corrosive, keep the system as dry as possible to prevent corrosion of the gas handling
components. Hastelloy components should be used with HBr.
Chlorine (Cl
2
)
Chlorine has no measurable absorption in the NIR where we measure moisture. The water
absorption peaks are significantly widened in Cl
2
. This reduces the sensitivity of H
2
O
measurements (vs. N2), but provides an increased upper limit reading. Cl
2
is somewhat
hygroscopic. As Cl
2
propagates through a flow system, it absorbs any water in the flow system it
comes in contact with. This effect causes significant settling times when making measurements
in Cl
2
. When switching between an inert gas and Cl
2
, provide ample time for the flow system to
reach equilibrium before taking measurements. Also, since Cl
2
is corrosive, keep the system as
dry as possible to prevent corrosion of the gas handling components.
