Sensors for measuring hydrogen.
Crystec

Crystec Technology Trading GmbH
Semiconductor Equipment

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Hydrogen Measurement

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.

Wheatstone 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 measuring section.
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.


Wasserstoffsensor Technical Data:
  • Measuring gas temperature: 500..600°C (retort temperature)
  • Measuring gas pressure: overpressure min. 5mbar
  • Measurement range, components
  • Hydrogen: 10..60, 0..75, 0..100 Vol% and ppm-range
  • Ammonia: 10..90 Vol%
  • Carbon-containing gases: 0..10 Vol%
  • Output: 4-20 mA
  • Time performance: output delay 6..20s
  • Warm up period: Nitriding temperature, dependent on the furnace


Ambient Air Gas Sensor using a Catalytic Bead

Everywhere, where combustible gases are used, it is important to check the production area. Especially in the ambience of vertical furnaces, horizontal furnaces, 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.

Raumluftsensor Technical Data:
  • Dimensions: Diameter 60mm Length 110mm
  • Mounting: installation on top-hat rail (EN 50022)
  • Electrical connection to sensor base unit:
  • Power supply: 8.....15V DC
  • Current consumption: approx. 200mA
  • Operational status indicator: integrated LED
  • Switching output relay with change-over contact
Crystec Technology Trading GmbH will be pleased to further discuss details with you.
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