Initial Operation
7
1.3
Measuring Principle
The patented method of the HydroTracer determines the absolute water content. The mass of
the water is measured within the reactor. The percentage of moisture of the sample is
calculated by division with the sample weight.
1 The test material is heated in the
sample tray; water evaporates
2 The hot humid gas ascends
3 The Reagent exchanges water by
hydrogen
4 The sensor measures the
concentration of hydrogen
5 The cooled gas descends and can
absorb water again
The sample is weighed and filled into the sample tray. The sample tray is shifted into the
HydroTracer, being a part of the reactor. A heater warms the sample to a temperature chosen
by the operator. The water within the sample material evaporates. The volatile water rises to
the upper part of the reactor. Two pipes connecting the heated sample tray with the cooled
upper part where the reagent is placed. The reagent tray is a small flat tray filled with
approximately 0.1 g calcium hydride. When the humid air flows over the reagent, gaseous
water reacts with calcium hydride according the following equation:
𝐶𝑎𝐻
2
+ 2 𝐻
2
𝑂 ⟶ 𝐶𝑎(𝑂𝐻)
2
+ 2 𝐻
2
So water vapor is exchanged against hydrogen and calcium hydride converts to calcium
hydroxide (chalk lime).
The cooled, dried gas enters again the lower part of the reactor. The gas circulation is
supported by natural convection, created by a special configuration of the vertical pipes. By
this method even hygroscopic materials are completely dried. The final concentration of
hydrogen in the reactor is proportional to the water content of the sample before the
measurement.
The ambient air also contributes water to the reactor atmosphere. To achieve accurate results
it is necessary to determine the air humidity and the air density. Integrated sensors measure
the humidity of the ambient air, the temperature and the air pressure. With this data the
software determines the water of the air humidity which is deduced off the final result.
The concentration of hydrogen is measured by a sensor detecting the thermal conductivity of
the gas.
