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HYDROS 21 no longer vented… any idea when this changed?

Home Forums Environmental Sensors HYDROS 21 no longer vented… any idea when this changed?

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    • #15522
      fisherba
      Participant

      We just discovered that our latest HYDROS 21 sensor no longer has a venting tube like it did when it was a CTD-10. We *think* that the transition from Decagon to Meter kept the vent at first, but this came as a surprise.

      I think our current sensors were purchased from Meter in November 2020. When we purchased, we didn’t notice that Meter specifies barometric correction IF (and only if) you have their data logger (btw, read their data logger promo site if you want to learn how to sell stuff… wow).

      For perspective, fondriest.com still claims that the HYDROS 21 has a vent. (Maybe the ones they have in stock are vented?)

      I’m curious if anyone knows when this change happened and if Meter bothered to announce it, or if it was a silent change.

      Also, hopefully this thread will notify others that it’s no longer vented and you will need a BME-280 or a BMP-280 plus a calculated correction in your sketch for future HYDROS 21 water level measurements.

    • #15523
      Shannon Hicks
      Participant

      Are you using a sensor with bare wires at the end, or with the molded stereo plug?  Is it a red cable or a black cable?  We’ve bought hundreds of CTD-10 and now the Hydros 21 sensors (only the name changed when the company changed from Decagon to Meter, and there was no design change).  We bought a bunch earlier this year, and every one we’ve ever used has a small Gore-Tex sleeve about a foot from the end of the cable that provides the vent used for the pressure sensor atmospheric reference.  Even their new Generation 2 Hydros 21 sensor (due to be released soon) that we’ve been testing recently has the vent.  If your sensor doesn’t have a vent somewhere along the cable, then either it’s an error and it’s missing, or you’re using a bare-wire terminated cable and the end of the cable allows the air into the jacket to provide the reference (the newer cables have a dedicated air tube inside the cable whereas the old cables relied on the airspace between the wires).   Either way, I recommend contacting Meter Group tech support, they’ve always provided great customer support for us over the past 7 or 8 years that we’ve been using their sensors.  Did you try putting the sensor in a bucket of water at a constant depth and then logging depth over a few days to see if you see atmospheric pressure affecting the data?

    • #15524
      neilh
      Participant

      Do note that the specifications says accuracy  0.5% of 10,000m or +/-50mm (edit  corrected to 50mm). This  implies that you want to keep it at a constant (20C?) while sitting in the bucket, and even then the apparent water level can wander up  +50mm  or down -50mm and still be within specification.    If the temperature changes then the accuracy specification doesn’t apply.

      https://www.metergroup.com/environment/products/hydros-21-water-level-monitoring/

      Water depth
      Range: 0−10,000 mm
      Resolution: 1 mm
      Accuracy: ±0.5% of full scale at 20 °C

      NOTE: Depth measurement accuracy assumes no abrupt temperature variations.

      For environmentally significant flows (low water depth measurement, with high temperature variation) it has a lot of noise on the signal.

      Great instrument for measuring borehole water pumping ground water that is usually a constant temperature and large variation in depth.

    • #15526
      Matt Barney
      Participant

      @fisherba – Thanks for sharing this! I’ll be very interested to learn what Meter tells you.

      I see what you mean on their product page: “When used with the ZL6 data logger, you won’t require an additional sensor for measuring—and referencing—barometric pressure.”

      However, both the sensor manual and the Integrator Guide in the Downloads section describe the vent for atmospheric correction, as expected — definitely an inconsistency.

      FWIW, my most recent HYDROS 21 purchase was March 18th, and it’s got the vent. The part description on the Meter invoice says “40683-S CTD-10 (HYDROS 21) Sensor, Stereo end, 10 meters”. It’s got the new black cable, but I don’t know whether that indicates it’s a gen 2; the website only appears to mention gen 1. The only other change I can see visually is that the hook on the mesh Kellem cord grip could be more easily removed because it’s held on with a threaded link, rather than being clamped directly to the grip.

      -Matt

      • #15529
        Shannon Hicks
        Participant

        Matt,  they haven’t begun selling the Generation 2 CTD sensor yet, so what you have is a Gen 1 sensor with the new cable on it.  And we always order our sensors without the metal strain relief since we always end up cutting them off anyway, so you can specify that when you place your order.

    • #15531
      neilh
      Participant

      Hi Shannon, do you know if they are using temperature compensation for the sensor on the Generation2. ? thanks

      • #15532
        Shannon Hicks
        Participant

        Yes, the pressure transducer on the Gen 2 sensors seems to be temperature compensated just like it was on the Gen 1 sensor.  They also use the temperature sensor for calculating the specific conductivity readings.  I wasn’t going to mention that I have one since they sent it to me ahead of release for testing so we could make sure our Modular Sensors library was fully compatible with the new generation (it is).  But another user posted a few weeks ago that they received a Gen 2 sensor recently, so I guess it’s not a secret anymore.  I don’t know when they’ll be released and available for purchase, lots of industries are experiencing delays in production and manufacturing right now, including EnviroDIY, so putting delivery dates on anything these days is difficult.

        • #15538
          James_NZ
          Participant

          Just an update here. Katie from METER group thinks the GEN2 will be released within a matter of weeks. She is holding our payment and will send us a shipment of GEN2s when they are available.

          James

    • #15533
      fisherba
      Participant

      The sensors the student ordered have the stereo plug and a red cable.

      @neilh, we have a calculated temperature compensation in Modular Sensors if you ever need it. It’s extremely negligible in groundwater temp ranges.


      @mbarney
      , the Meter discrepancy is a bit annoying. Was your March order a bare wire or stereo plug?

       

    • #15534
      Shannon Hicks
      Participant

      Sounds like a manufacturing error to me.  I’d suggest contacting Meter and tell them about it because I’ve never seen an unvented CTD from them and there’s no conceivable way it would work correctly without one.

    • #15535
      fisherba
      Participant

      @shicks have you read their current product specs? Don’t take my word for it.

      • #15536
        Shannon Hicks
        Participant

        Yes, I’ve read the website, and talked with the Meter Group engineers on many occasions.  I think the wording on the simplified product brochure just isn’t written clearly.  If you read the detailed Integrator’s Guide, you’ll see that it says this:

        Differential pressure measurement referenced to atmospheric pressure so no external pressure sensor is needed

        See attached screenshot.  The Generation 2 integrators guide also has this exact same wording, and the Gen 2 sensor I currently have in my hand right now has the vent.  So I think they simply forgot to install the vent on the sensor you have because there is no design change regarding the requirement of a vent at the logger-end of the cable.  Their website brochure is written in a way to promote the fact that you don’t need a separate barometric pressure logger like you might if you bought a standalone submersible logger that has no atmospheric reference.  Contact Meter Group and send them a photo of your sensor, and then let us know what they say.

         

    • #15541
      Matt Barney
      Participant

      @fisherba My March order has the stereo plug.

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