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Ultrasonic Stream Depth Sensors

Home Forums Environmental Sensors Ultrasonic Stream Depth Sensors

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    • #1124
      Tom Sayles
      Participant

      I recently ordered a MB7040 I2CXL-MaxSonar-WR sensor [I like the i2c interface and don’t need mm resolution] and @Shicks said “That sensor may not be the best option for you”.

      I wrote up a bit of a concept paper for what I’m hoping to do and posted it at http://toms-wow.blogspot.com/2015/01/open-source-crowd-source-stream-gauge.html

      What are your thoughts and experiences on Ultrasonic Stream Depth Sensors?

    • #1125
      Shannon Hicks
      Keymaster

      Tom, I checked out that new sensor, the I2C interface from Maxbotix is a new feature, it might be handy, but I think the serial output is just as easy to use. My main concern is that the 7040 model is kind of a general purpose rangefinder used for object detection, usually indoors. In the datasheet, it warns that different target sizes will result in different range measurements, even if they are at the same distance. Basically, there is no filtering or target size compensation. The MB7389 model that I use is specifically designed to measure water level, so it has a special filter that returns the largest signal (the water surface), so all other sources of noise and reflections are ignored.

      And most importantly, the MB7389 has internal temperature compensation that is applied at each power-up. Without this, the varying temperature of an outdoor environment will make a non-compensated sensor rather inaccurate. And my recent tests have shown that we need to also use the maxbotix external temperature compensation sensor (only $5) in order to eliminate all of the effects of temperature variations.

      I’ve had many communications with the technicians at Maxbotix in the past year, and they assured me that the MB7389 is the best model for water level measurements with TTL-level serial output, so I would recommend that you try that one.

      The rest of your post on your blog sounds interesting. That’s the kind of content we’d like to have here on this site as well, so you should post it here on a blog post so users here can comment easily on it.

      • #1128
        Tom Sayles
        Participant

        @Shicks, thanks for the heads up on the temperature compensation. I had already been thinking about measuring temperature at the top, bottom and water surface [hopefully using an I2C-IR sensor I’ve been playing with] in the stilling well. From there calculating the thermal gradient and applying a calibration curve shouldn’t be too difficult, just takes time to collect and pre-process the calibration data. In the end it’s just a multi-dimensional look-up table that needs to be applied at the time of the measurement.

        Since test and calibration are among the things I do in my day job for a major electronics manufacturer, calibration was already on my radar. And I have some ideas on how to simplify / automate the collection of the initial calibration data, in situ. With enough data points on a calibration target, I should be able estimate the multi-dimensional response surface and generate the calibration table.

        All of the above assumes that the raw values aren’t good enough for my application. Since I’m looking more for large changes (10s of cm) over relatively short periods of time (15 min to 1 hr), and since my error tolerance between measured elevation and actual elevation is also on the order of 10s of cm, the raw data with the MB7040 might be good enough.

        I’m interested to see some of your test data, especially if you have any error estimates.

    • #1129
      sollins
      Participant

      Steve – I gather this, rather than the blog, is the best place for questions.

      So, any idea when you might have a new design for the ultrasonic level kit ready to post? W. Oregon has wet winters and dry summers so it would help my planning if I knew whether we might get this built and installed this wet season or we should just plan on getting this running for next fall.

      • #1137
        Shannon Hicks
        Keymaster

        I will be assembling a couple of Ultrasonic loggers with a colleague in a few weeks and we will document the process and post it on this site. However, we’ll be using the Seeeduino Stalker v2.3 board, so you’d have to modify the plans if you use a different board, or if you’re lucky you might be able to find a spare v2.3 board somewhere online.

    • #1648
      ElsyKhong
      Participant

      Hi..i am a new user here. As per my knowledge in the datasheet, it warns that different target sizes will result in different range measurements, even if they are at the same distance. Basically, there is no filtering or target size compensation. The MB7389 model that I use is specifically designed to measure water level, so it has a special filter that returns the largest signal (the water surface), so all other sources of noise and reflections are ignored.

      assemble pcb

    • #1496
      Danny Waz
      Participant

      You are not missing something. It would be more accurate to say “ultrasonic stage height sensors”, because depth is merely retrieved, not sensed. This is problematic when one cannot easily survey the sensor as you said, even more problematic for sensing streams with moving beds. Presently, something like a pressure transducer can measure depth in-situ, but non-contact methods almost universally require an a priori stage-depth relationship. In the early 2000s, the USGS (John Costa, Kurt Spicer, et. al.)showed it’s possible to measure depth with ground-penetrating radar, but that’s not exactly economical or practical.

      One of my current projects is tacking exactly that problem. It’s not ready for prime time yet, but if you are working on similar technology and wish to collaborate, feel free to private message me.

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