Leaky Dissolved O2 Sensor?

 After acquiring a few weeks of experience with the new dissolved oxygen sensor on AMOS, I am unfortunately a bit disappointed with its performance. Software-wise and electrically it worked great. They have some nice simple I2C and serial commands for getting data and calibrating, and you can get temperature compensated data at a rate of about 1 Hz. The bad part is that the calibration doesn't seem to hold for more than a few hours. The sensor probe is a galvanic one, in the sense that it uses an anode and cathode surrounded by an electrolyte to produce an electric current (and small voltage) when oxygen molecules cross over the probe's membrane. If I fill the probe with electrolyte (requires ~ 2 ml), calibrate, and then do a test run with AMOS, the results seem generally pretty good. If I go out again even just a few hours later, the results seem a bit lower, and then lower still the next day. Even re-calibrating doesn't really seem to work very well if it has been a long time since the initial filling of electrolyte solution. The membrane on the probe is quite thin, and a bit flimsy (slightly thicker than saran wrap), so I'm wondering if it just doesn't make a very tight seal? The online shop where I bought the sensor sent me an email request to review it, so I gave it a mediocre 3 stars with a description of the issues I was having. They said that they would forward my comments to the manufacturer, so we'll see if I hear back. 

Anyway, here are some pretty good results obtained near downtown Fredericton on Saturday, about an hour after filling with electrolyte and calibrating:

The dissolved O2 readings were all within a narrow band of 9.1 to 9.2 mg/L, which is a normal, expected level for the amount of oxygen dissolved in water. 

Later that afternoon I took AMOS out to Woolastook to collect some more data, but this time the readings started off a bit under 9 mg/L, jumped around a bit, and then seemed to gradually drift lower to under 5 mg/L as AMOS traveled along the 4 km route:

Today I re-visited Woolastook, and performed a re-calibration before leaving, but did not re-fill any of the electrolyte. This time the dissolved O2 started off at around 7 mg/L, and then dropped down to nearly 0 mg/L about halfway through the test: 

Since I saw a number of small fish swimming around, I don't think the level could have possibly been that low! I'll try going back tomorrow, but will top up the electrolyte again to see what difference that makes. The probe manual is vague about how often re-calibration is required, but does say that the electrolyte should last for about 2 years before it is depleted. Perhaps there is an issue with dragging the probe behind AMOS? It is mostly horizontal while AMOS is moving. Or maybe the probe membrane is getting damaged by dragging it through shallow water, grass, etc. close to the shoreline? I'll try not to waste too much more time on this, but these things kind of bother me! 😖

Better Data For 2020

There are at least a couple of ways that AMOS could be updated to provide users with improved water quality data. One would be to add some industrial water quality probes that are capable of collecting calibrated data for a wide variety of parameters. Another would be to improve the data presentation software that is used to represent the data that AMOS collects. Some progress was made on both these fronts this week.

In order to continue updating the map-based data presentation software that AMOS uses, I first needed to get a new Esri ArcGIS license, as the free one I was using had expired. Luckily Esri offers a free account with some limitations for developers, which turned out to be good enough for my purposes. Using some temperature data that AMOS had collected last October, I was able to generate this nice color coded water temperature plot:

I think the color coded points on the data map look better than having blobs of varying sizes on the map. With color coding, you can also imagine a feature where data could be interpolated in the locations between sampling points by taking a weighted average of the surrounding points.

I have also been asking around and getting quotes from 4 of the major water quality probe manufacturers. Basically I would like to have a multi-sonde that comes with probes for temperature, turbidity, pH, dissolved oxygen, and blue-green algae. All of the manufacturers seem to support communications interfaces with 3rd party dataloggers, typically using RS-232 or RS-485. So far I have gotten prices from a couple of the manufacturers, and am waiting for quotes from the other two. The sensors are not cheap, so I want to do my research and make sure that the ones I decide on will be able to provide AMOS with reliable, accurate measurements.

In preparation for an experimental catamaran version of AMOS, I found a hot-wire cutting device on Amazon that looks like it should be suitable for cutting through 2" sheets of pink insulation:

Hopefully it will help me to make more even cuts in the foam with fewer gouges and less time spent sanding.

Starting to Get Real

A few small things happened this week that helped to reinforce my belief that AMOS can be a viable product.

On Friday, some market research reports that I had requested through Venn Innovation and MaRS Knowledge & Insights came in. In total there were 9 different reports mostly dealing with water monitoring technology. I've only read 2 of the reports so far, but it is clear that the World's water supply is increasingly being threatened by pollution, global warming, changes in weather, and other factors, and that there is a growing demand for reliable, effective monitoring technology for making sure that our water is safe. It seems clear to me that automated robotic water sampling will be needed in the future; hopefully AMOS can be part of that.

On the software side of things, with the help of the ArcGIS API, I came up with a pretty simple interface for planning a route for AMOS:

You basically just left-click the waypoints in the sequence that you want AMOS to follow, or right-click on a point to remove it. Then click the 'Save' button to save the route to a text file for upload to AMOS. It sure beats entering GPS coordinates by hand. I've made mistakes that have resulted in some serious head scratching when AMOS started to head off to the latitude and longitude of my typo.

In Nature Robotics now has an official presence on Twitter: @nature_robotics (https://twitter.com/nature_robotics). It was encouraging to see how many people there are on Twitter that are actively engaged in water monitoring and research about water. Many thousands to be sure. In Nature Robotics now follows a little over 200 of them, and will be following more gradually.

Over the course of the last 21 months that I've spent working on AMOS-related things, some spare parts have managed to accumulate around our basement. My part-time employer (Measurand Inc.) is having a Secret Santa gift exchange this year, with the rule being that the gift must be hand-made or less than $15 in price. Since I drew the Occupational Health and Safety Coordinator, I thought I could make some use of a spare humidity sensor and Arduino to help him make sure things aren't too hot, cold, humid, or dry in the workplace: