RainSavor Updates
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Electrical adjustments are being made to reduce noise in the data. More field tests are being conducted in the OSU Solar Array. Mounting designs and the incorporation of the thermistor in the mechanical design are actively being worked on.
The weekend of 1/30/2021 begins the day long tests. Rain is forecasted during this time period. Later in the week multi day tests will start. While these tests are operating any gathered data will be analyzed for performance, verification, and debugging purposes. All documentation, including operations guides, will be made or completed while these tests are in progress.
The siphon design has been adapted to fit the Davis Instruments funnel and the electronics are almost complete. We are preparing to conduct field tests in a couple locations around the Oregon State University campus. During these tests, we will also experiment with mounting systems to determine the most effective method for final deployment.
Final design parameters have been selected and evaluations of expected collection conditions specified. Various siphons have been tested for functionality - all of which seem to be successfully creating siphon events at approximately equal intervals of water collection. The frame that will be used for primary water collection is modelled and siphon designs ready for printing. We are in the process of integrating electrical and mechanical design components and aim to perform field tests in the next couple weeks.
There are a couple options for temperature sensing for a system like this and this can still be updated for future implementations. The main argument lies between using a thermistor or a thermocouple for temperature measurements. This system uses a thermocouple for a couple of reasons. The first is the dimensions of the sensor itself. The thermocouple has a small metal rod at the end of the wire with the tip sensing rather than the whole rod. In comparison the thermistor is a silicon rod that senses with the entire rod. Since the amount of fluid being probed is very small it wouldn’t be feasible to submerge the entire thermistor, the thermocouple makes the physical aspect of sensing much simpler. Each type also has different supporting circuitry. The thermocouple is more complicated with an entire breakout board being connected while the thermistor only requires a resistor in a voltage divider layout. The advantage on size and ease of implementation belongs to the thermistor for the minimal space. Unfortunately, there is an additional downside to the thermistor where the resistor changes value dependent on the temperature as well, which is difficult to fix in software. The thermocouple doesn’t have this challenge as the breakout board handles everything already and uses a cold solder as a temperature control point and varies much less than a thermistor. We decided it was worth the added complexity and space to have the thermocouple and greater temperature accuracy. Below are some temperature tests of the two methods that helped us come to this decision.
This graph shows how the thermistor and thermocouple react to extreme temperature changes and how noisy they can be. Note that the Y axis is different for the two sensors. The thermocouple measurements are in degrees Celsius while the thermistor is a value of voltage read in by the microcontroller ADC. Generally the thermocouple has less noise in the temperature signal and has a faster response to a drastic change in temperature.
To get more information out of the temperature graph comparisons the thermistor y axis was altered to match the scale of the thermocouple graph as a relationship to the input voltage. This allows for a more direct comparison that shows the limits of the thermistor in the upper temperatures and the greater variances across the graph. We aren't expecting rain to be the temperature of boiling water, so this drawback of a thermistor isn't important. Regardless these two graphs helped us to decide that a thermocouple is worth using. The effects of temperature on the resistor in the voltage divider network of the thermistor is slightly seen here, where the thermistor has a bigger or smaller error to the thermocouple at different temperatures.
The only reason temperature is needed is to give us more accurate descriptions of the water EC. The EC is fairly dependent on the temperature of the water and can have a large swing when the temperature is higher or lower than 25 degrees Celsius. Anyone using this system has the option to ignore the temperature sensing component but risks having data that isn’t as accurate.
Electronics prototypes are being built and tested; experimentation with probe functionality in various conditions is also being researched to determine the capabilities of the EC measurement system. Additionally, design drawings and various mechanical prototypes involving different styles of siphoning and EC measurement collecting are being developed.
A mechanical engineer and two electrical engineers have been assigned to develop this device.