Overview and Installation
|
1-1
MODEL 120HD HyDrOGEN ANALyzEr
General Description
Function
The Model 120HD portable hydrogen unit analyzes a gas sample, mea-
sures the hydrogen concentration and then digitally reports the percent
volume of hydrogen in air.
Principle of Operation
The 120HD analyzer functions using the same prin-
ciple as a katharometer. It operates by having two
parallel tubes both of which contain gas and heating
coils. The gases are examined by comparing the rate
of loss of heat from the heating coils into the gas. The
coils are arranged in a bridge circuit so that resistance
changes due to unequal cooling can be measured.
One channel normally holds a reference gas and the
mixture to be tested is passed through the other chan-
nel. The thermal conductivity of a gas is inversely
related to its molecular weight. For example, hydro-
gen has approximately six times the conductivity of
nitrogen.
The known or “standard” gas used with the 120HD is moisture-saturated
air that is contained in the small chambers where the “comparison” coils
are located. The coils are heated by an electric current and remain in bal-
ance as long as they are surrounded by gases of similar conductivity and
are at like temperatures. However, when the test coils are exposed to gases
of different mixtures and different thermal conductance, their tempera-
ture changes and the bridge circuit becomes unbalanced. The result is that
the digital screen readout changes based on the variation in the hydrogen
concentration. In this way, it is possible to determine the percent of hy-
drogen present in the mixture.
