Evaporometer
Electrical: Evan Hockert
Mechanical: Dylan Nguyen
Data Processing: Marat Muzaffarov
Past Team Members Gurpreet Singh, Colin Hale-Brown, Emily Pannell
The Evaporometer: a rain gauge that is
- Affordable (<$500 with labor)
- Open-sourced
- Fully automated
- Maintenance free
Rain gauges are centuries old tools, with relatively few changes offered in the past 50 years, despite problems seen in most gauges during period of high rainfall, and high maintenance effort needed to keep them functional. Yet, the data is invaluable to the researchers who study weather patterns and measuring precipitation accurately is an important way:
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To help farmers grow crops and sustain extremer weather events
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To monitor droughts in areas reliant on agriculture
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To prepare for weather-related natural disasters
At the OPEnS lab, we developed a modern low-cost, open-source load cell based rain gauge system called the Evaporometer for collecting rainfall and evaporation data. There are no moving parts and the Evaporometer is designed to operate with minimal maintenance. As a rain gauge, it will collect the water falling on it and record the change in mass of water collected over time. To measure evaporation, it will record water leaving as the change in mass decreases over time until dry in the similar way as Atmometer (E-T Gauge) measures the Evapotranspiration. Atmometer(E-T Gauge)
Photo: Evaporometer installed at Hyslop Farms for field testing
Load Cell: 0-2 Kg ± 0.03% (resolution: 0.001g)
Temperature Sensor: -40°C - 125°C ± 0.2°C (resolution: 0.001°C)
Battery Life: 2 months at 5-minutes intervals (1 year with solar)
Operating Temperature: -0.1°C to 60°C
Allowable Environment Temperature: -40°C to 60°C
The Evaporometer resolves 0.1 mm of rainfall with stores water sufficient to supply 100 mm of evaporation.
Using the siphon, we can measure unlimited depth with less than 5% error measuring rainfall rates to 40 mm/hr.
The Evaporometer's mechanical hardware includes a SLA 3D printed rain collection container, a cut-to-size fiberglass rope "wick" that is housed within the rain collection container, a siphon that is included in the aforementioned container, spacers for mounting, and an electronics box for housing the circuitry components. The top container collects rain water, and the weight of that container is monitored by the load cell, which records the weight data over time. The siphon and wick help maintain the accuracy of the system by preventing overflows and debris collection respectively. The top container is mounted onto the load cell with is itself mounted to the electronics box. The whole system is deployed using a bracket mounting system that connects the electronics box to a 1 1/4" pipe.
Photo: Rain Collector: The siphon draws water from 20 mm above the floor of the container and initiates draining when the free water surface is 30 mm from the top of the container
We are developing a screen around the rain collection bucket to minimize the wind effect on the weight measurment. The windscreen has been designed to allow the siphoning of water from the bucket.
Photo: Windscreen prototype
The Evaporometer circuit consists of a 2 kg load cell, a custom PCB, analog to digital converter - ADS1232, feather MO microcontroller, Hypnos board for logging data to SD and sleep function, solar panel, 5V solar manager, and the battery to power the circuit. The load cell measures the weight of the rain collection container at 5 minute interval to measure rainfall and evaporation, and store the data into SD.
Photo: Schematic of Evaporometer Circuit
Evaporometer has the option to interface with dataloggers using SDI-12.
Software implementation here
Using this feature requires a logic level shifter from 5v (SDI-12) to 3.3v (Feather GPIO). Also, using this feature allows for Evaporometer to be powered via the 12v line from the SDI-12 bus (not shown in image). We used a TRACO TSR1-2450 DC-DC Converter Switching Regulator to drop from 12v to 5v
Photo: SDI-12 Compatable Circuit
Photo: Evaporometer connected to SDI-12 bus from Stevens Water Steelhead Datalogger
The Evaporometer circuit measures the weight increases due to rainfall and weight loss due to evaporation with respect to time as shown in figures below:
Photo: Recorded weight from Novemeber 2023
- Bill of Materials (as of Feb 9 2022)
- Inventory (Work in Progress)
- Power Budget (Work in Progress)
Our current goal is to validate the nosie reducing ability of the windscreen.