[neilh20]

Hi @dan-wachusett – I’d be interested to hear how your measurements work out.

This is what I did for acceptance testing (and characterizing) on a number of different types of depth sensors for a 2013 project – https://www.envirodiy.org/measuring-low-water-in-streams-accurately/

The update since then is the hydrologists I work with use the LT-500 for reliability and accuracy, and also been moving over from the Onset U30 to using the Mayfly.

I wonder, has anybody received a specification for the Hydros-21 Gen 2? .

Typically I find that manufactures create internal releases (generation 2?) as an internal cost reduction, with the same specification. Though every manufacturer is unique, so wondering what Metergroup changes might be :)).    Insitu and Keller (and others)  have different lines of depth sensors for different measurement accuracy and methods.  The challenge for any manufacturer is the basic pressure sensor is similar – a pressure dependent resistor – piezo resistor. Temperature dependency of resistors is well studied, but challenging to work with when bumping up against a specific resistor technology’s limits – so different manufactures have different signal processing and manufacturing calibration for better linearity of the pressure sensor.

 

[neilh20]

faaaaantastic  !!!

My data looks good from the May 12.    Thankyou so much to everybody who has pulled that together.

[neilh20]

Hello Anthony, yes thanks for the clarification.

As an engineer, I am often asked is the solution more painful than the problem it is solving!

The problem breakdown, when looking through the eyes of hydrologists  ; a) is the remote sensors working?, b) is the delivered data to the web reliable? either visually or downloaded  c) how to back-up all the costly data collected to a safe repository for a complete history. (TNC sensibly does this for its data collected)

In terms of the current situation with the “corrupted catalog crosswalk”,

when its working (a) it is possible to see that the remote sensor is working, and the date under the sparkline plots appears accurately to represent the latest record deposited.

(b) for me when the data is delivered it is reliable, though could be incomplete. I use the sample_number, and plot it to quickly visualize any data loss.

(c) for the backup it can be obtained through local Mayfly uSD via boot net.  To be able to download a coherent  .csv  is definitely an advantage and is definitely valuable to be able to scrape it through an automated mechanism.   I’ve found the  wofpy interface complicated and has its own problems for the same type of variable.

Appreciate the work that is going on to fix it.

 

[neilh20]

Hi James, as I understand it you are right – its difficult to get an accurate rating curve under such conditions. That is the geology.  That is why there are hydrologists, and it takes having someone with experience to find  if there is a geological place  where a rating curve can be built.    regards

[neilh20]

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

[neilh20]

Hi James, yes there is the challenge.     My take way from the report was that providing its exceeding 1cfs or 0.028m3/sec it can be done fairly accurately with traditionally USGS methods – which sounds like you are well in that range.  For environmentally significant flows in drought California we are often looking at less than 1cfs/0.028m3/sec

The CTD-12 scale is  0 to 10,000mm with 0.5% accuracy across depth range,   with the specification stating “no sharp changes in temperatures”. Resolution is different than accuracy.  Specifically they are saying no temperature compensation.   So the type of raw sensor (typically piezo electric, resistive) and how it responds to temperature change is critical – I’ve put out a lot of data on instruments I’ve used on how the apparent reported water depth changes with temperature. In some cases with lower cost instruments a small temperature change causes the reading to wildly swing across the range. So for the CTD-12 the range is +50mm to -50mm.     So if you can find a measurement situation where which has pretty stable temperature change  in water temperature (ice melt?) and can calibrate your CTD-12 across that temperature change,  its likely to be provide useful readings.  The places that have stable temperature’s are typically in ground water, if pumping they are also likely to have a large range of water movement – ideal perhaps for the CTD-12.  When I checked with the manufactures over a year ago they where thinking about doing temperature compensation, but no statements yet on that.

So then I would think you are looking for the water column depth to vary significantly over the range of your instrument.   Or for locations you have, what is the range of depth change for the flows. Can you place a sensor on the upstream side of the culvert

For environmental flows the hydrologists I’m working find that the Insitu LT500 is their instrument of choice with a 0.1% total accuracy (including temperature compensation) over 0-3m. It is however a top-end instrument when it comes to the sensor, the cable, and the stripped cable to be able to feed it in to a Mayfly modbus.

I’m personally trying to do more calibration an trialing with the Keller Nanolevel which is 0-3m and is a large capacitive based sensor.  However the first Mayfly I deployed with it, got stolen after 9mnths, fortunately the sensor cable pulled away so still have the sensor.  I’m looking to connect it over WiFi, so still working on that.

[neilh20]

I’ve been seeing gaps, lost data in downloaded .csv  ~ hopefully comes back.

Checking this morning there has been no gaps as I can find from the downloaded .csv in my test site since

UTC 2021-05-12 11:45   or PDT    2021-05-12 3:45

 

[neilh20]

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.

[neilh20]

Sometimes there is no easy answers. I recently went to presentation that included this analysis for

https://creeklands.org/wp-content/uploads/2021/02/CLC-Micro-Flows-2020.pdf

So partly what range of flow are you looking for and what accuracy.

 

[neilh20]

Hello James,  yes I have a few hybrids that are working,  that’s the way that they have been working up to now. I would think you’d want to test  your 10 ASAP.   For me the devices that did not work, they just they didn’t work. So for testing its they either work or not.  As an electrical engineer I did do an analysis and laid out what I had done,  but it didn’t really make a difference.

This is a custom build, to a specified qty, which I will place on Tuesday. I had thought of a kick starter framework, but that was going to take more time. There is NO excess to sell on a market later, as that gets so complicated. 

Manufactures want to be paid up front for what they build.

I got all the parts and the PCB yesterday, so building the proto tomorrow to verify the parts. All the details will be available as an open source hardware build, so it can be build later, either yourself or choosing a supplier of your choice. I’m sure they have small manufacturing shops in NZ. Also the hardware can be easily modified if required.

 

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