EEVblog #603 – Gas Sensor Teardown – Dräger Multiwarn II


What’s inside a Dräger Multiwarn II gas detection warning system used in mining, oil, chemical, and emergency services etc to detect hazardous or explosive atmospheres.
Intrinsic safety design and how both catalytic bead and infrared IR gas detectors work, and pellistors.
And a teardown of a Hydrogen Sulfide (H2S) sensor.

http://www.a11supply.com/images/file/rev1_MultiWarn%20II_En.pdf
http://www.draeger.com/sites/assets/PublishingImages/Products/cin_x-am_5600/US/draeger-sensor-portable-handbook-9046571.pdf
http://www.xinpian.net/MOTOROLA/MC68HC711/MC68HC11E1.pdf
Forum HERE

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    • refreak

      Really interesting teardown, thanks Dave. Looking up PA6 GF25 won’t get you very far on the component. This describes the material of the case. It means Polyamide 6 with 25 wt% glass fiber added.

    • ulix

      No, it isn’t solder!
      It’s called sintered metal, which is used for filters.

    • vimes

      The hydrogen sensor is a H2S hydrogen sulfide sensor.

    • Chris

      That one sensor was a hydrogen sulfide electrochemical sensor. When the gas enters the sensor it undergoes a redox reaction and acts like a small battery producing some current. But you should know these sensors generally contain a strong acid (usually sulfuric acid), so you need to be careful when taking them apart and I shuttered when I saw your fingers touching the electrolyte. You should wear latex gloves when taking those apart. It’s a trap for young players 😀

    • It’s been about 20 years since I designed intrinsically safe equipment but I suspect that the shielding and insulation seen in the teardown would not make this equipment intrinsically safe. The key aspect to intrisic safety is to limit the amout of engery in the hazardous area. It would have been interesting to see more of the battery as I would guess that it would contain current and voltage limiting make it Ex compliant. Further, this equipment looks like it could only be used where the hazard of explosion is relatively low. I suspect that it may not comply with the stringent requirements of some of the groups and classes within the Ex standards.

    • Fred

      I think the chamber uses the Karman-Vortex principle to measure the gas a vortex is established and that is how it measures the gas a few cars mass airflow sensors use the Karman-Vortex principle to measure airflow.
      Just a thought.

    • Jens

      Made in Luebeck, my hometown…

      • Jens

        only 800 meters away from my house 😀

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