|Sensors for measuring hydrogen.|
Crystec Technology Trading GmbH
Company Controller Oxygen Hydrogen
For the measurement of hydrogen concentration in gases,
the high thermal conductivity of hydrogen can be used. Hydrogen conducts heat much
better than air (factor 7), nitrogen and most other gases. Only Helium has also a
similar high heat conductivity (6 times higher than air).
In the measuring cell a metallic wire is heated by electric current. The surrounding gas cools the wire and after short time a temperature equilibrium is reached. The temperature of the metallic wire determines its resistivity, which is measured by a wheatstone measurement bridge.
The sensor from Stange is such a heat conductivity sensor.
The measurement in complex gas mixtures is possible, if the equipment is designed for comparing measurements.
In the measuring chamber two measuring points are located. These are circumfluented by the test gas, according
to the diffusion principle, and reach a temperature dependent on the heat conductivity of the sample gas. If the
measuring gas contains hydrogen, then the temperature and thus also the DC voltage output (4-20mA)changes on the
For the evaluation of the test signal and the recalculation to a display, showing hydrogen concentration, you can use a Stange controller, maybe your temperature controller which is installed already on your furnace or any other suitable display device.
This sensor is appropriate especially for usage in nitriding furnaces.
Everywhere, where combustible gases are used, it is important to check the production area.
Especially in the ambience of
conveyer furnaces or
industrial furnaces, which are used for
hydrogen anneal it can happen that in case of a failure,
that critical gas concentration is reached in the ambiance. With the ambient air gas sensor such events can
be supervised and monitored effectively.
This sensor works with a catalytic bead in the measurement cell. The heated pellistor causes catalytic oxidation of available flammable gases by air on its surface. In the same manner as within the heat conductivity sensor the resistivity of the heating wire is measured by a wheatstone measurement bridge. However in this case, not the cooling of the wire is determined but the heating of the wire, cause by the chemical reaction of the hydrogen or inflammable gas with air at the surface of the pellistor.
The ambient air sensor reacts to
The sensor is calibrated on 60% of the lower explosion limit of hydrogen. This corresponds to a concentration of 2,5% hydrogen in air. This gas concentration is still harmless, but an indication for threatening danger. Hydrogen is always taken as reference gas, thus safe alarm limits are ensured also for other gases. Up to three sensors are attached to one base station. In the event of failure, a potential-free contact is closed. This signal can be further processed in the controller of the furnace.
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