HOBO by Onset S-RGD-M002 - Davis (0.2mm) Rain Gauge Smart Sensor

Davis® Rain Gauge Smart Sensors are compatible with all HOBO weather station loggers, HOBOware, and HOBOlink. They offer the same ease-of-use as existing Onset Smart Sensors, providing cost-effective HOBO weather stations for projects on a tight budget. The sensors feature a plug-in modular connector for easy installation, and all configuration parameters are stored in the sensor and automatically communicated to the logger, eliminating the need for programming or extensive setup.

In what environment does this sensor operate?

This sensor operates in an outdoor environment.

What measurements does this sensor support?

The S-RGC-M002 sensor supports the following measurement: Rainfall

Operation

Rain enters the collector cone, passes through a debris-filtering screen, and collects in one chamber of the tipping mechanism. The tipping spoon tips when it has collected an amount of water equal to the increment in which the sensor measures (0.2 mm or 0.01 inch). As the spoon tips, it causes a switch closure and brings the second tipping spoon chamber into position. The rain water drains out through the screened drains in the base of the collector.

Components

The smart sensor includes the components shown on the diagrams on the next page. The smart sensor includes a hardware kit with the items most commonly needed for installation. The items you use from the kit depend on where you install the sensor. You may need to adapt or purchase additional hardware to fit your individual requirements.

Mounting

Mounting Considerations

Use the following guidelines to determine the best location for installing the sensor.

• You must mount the rain gauge smart sensor so that it is level. As built-in bubble level is attached to the base to simplify this process.
• Be sure there is an unobstructed path for water runoff from the drain screens.
• The sensor contains a magnet-operated switch that may not operate correctly if you mount the rain gauge on or near any object that is attracted to a magnet.
• Exposure to winds can reduce the measured rainfall amounts. Mount the sensor where there are no obstructions of rainfall at low angles (such as trees, houses, fences) and as low as possible out of the wind.
• If installing the sensor on a sheet metal roof, insulate the unit by making a platform out of wood. Mount the base of the rain gauge at least 4 cm (1 inch) away from any steel or iron surface and make sure the reed switch is at least 4 cm (1 inch) away from any steel or iron objects (e.g. nails).
• For the most accurate rainfall measurements, it is recommended that you mount the sensor upslope, about 3 meters (10 feet) away from the tripod, on a 1.5 meter high mounting pole (M-MPB). Alternatively, you can mount the sensor on the tripod mast.
• Tall objects can interfere with accurate rain measurements. It is recommended that you place the rain bucket away from the obstruction by a distance greater than three times the height of the obstruction. If that is not possible, raise the rain bucket as high as possible to avoid shedding.
• Avoid splashing and puddles. Be sure the gauge is high enough above any surface that rain will not splash into the top of the collector.
• Vibration can significantly degrade accuracy of the tipping bucket mechanism. In windy locations make sure that the bucket will be vibration-free. Consider using guy wires to secure a pole or tower-mounted bucket.
• To provide long-term protection from moisture entry, the smart sensor adapter must be mounted horizontally and with the cable wires routed with drip loops so that water drains away from the cable entry point as shown in the example below. When mounted properly, the housing is weatherproof (but not waterproof).

Preparing the Sensor

Connecting the Sensor to a Station

To connect the sensor to a station, stop the station from logging and insert the smart sensor’s modular jack into an available smart sensor port on the station. See the station manual for details on operating stations with smart sensors.

Maintenance

For greatest accuracy, you should thoroughly clean the smart sensor at least once or twice a year.

1. Separate the cone from the base.
2. Use a soft damp cloth to clean pollen, dirt, and other debris from the cone, cone screens, and bucket.
3. Use a pipe cleaner to clear the funnel hole in the cone and the drain screens in the base. When all parts are clean, rinse with clear water.
4. Reattach the cone and replace the screen. 

Field Calibration

The sensor is calibrated at the factory so the spoons tip (and record rainfall) for each 0.2 mm or 0.01 inch of rain. To adjust the calibration slightly, use a 5 mm (3/16 inch) wrench to rotate the adjustment screws located underneath the tipping spoons (see diagram in Components). Do not touch the reed switch.

The adjustment guide embossed in the platform shows how far you must rotate both screws in turn to effect a 1% and a 2% change.