Problem:

Runoff from rainfall.

The typical method for measuring rainfall is with a tipping bucket rain gage. The rain gage contains a small “bucket” that tips over and spills out a measured amount of water. With each tip a switch contact is closed thus indicating the prescribed amount of rain fell. All Logic Beach data loggers include a General Purpose Digital Input (GPDI) which can be configured as a counter or an event input. The counter input is ideal for use with tipping bucket rain gages. So, how do you connect a tipping bucket rain gage and how can we utilize the power of HyperWare to provide more rainfall information than just total accumulation?

Solution:

Typical Tipping Bucket Rain Gauge

The tipping bucket rain gage typically contains a normally open magnetic reed switch hich is connected directly to the GPDI. Every tip of the rain gage will increment the counter. Depending upon the program sample rate you may count the tips over a given period of time then calculate and record rainfall within that time period or, as in the example program, time/date stamp every tip and then perform math and summation functions to arrive at total rainfall accumulation, five minute rainfall sums and total tips.

Logic Beach data loggers also provide additional analog inputs which are available to collect wind speed and direction data, insolation data and relative humidity or temperature. Logic Beach data loggers are expandable so it is easy to configure a data logging system specific to your meteorology application.

Solution Details

Hardware:
Since all Logic Beach data loggers are configured with a GPDI input any model is a capable of accepting a rain gage contact closure. It is best to review all required sensors and their output signals to determine the most cost effective data logging solution. If using only a tipping bucket rain gage the ModuLogger MNL-2 data logger may be the best selection. It is a single input GPDI unit, ideal for rain gages. The ModuLogger series offers two models, the ModuLogger MINI which can accommodate the tipping bucket rain gage and 4 other analog (VDC, mADC and Thermocouples) inputs or the standard ModuLogger data logger which can be configured with a combination of analog and digital inputs, up to 44 analog, 44 digital or a mix of both. This should provide plenty of inputs for even the most complex weather station. There is also the HyperLogger series which is a data logging system housed in a water resistant enclosure for outdoor use. Additionally, regulated power supplies are available for sensor excitation and photovoltaic system for remote power.

Software:
The output of the tipping bucket rain gage reed switch connects to the GDPI. The GDPI input is configured as a counter and a sample rate is selected.

In this particular program NET the output of the counter is directed into a Summation Icon for a running total of tips. The counter output is also fed into a Math Icon to convert the tips into an amount which then feeds four new branches of the program. The first branch to examine controls when information is recorded. This is the comparator branch. The Comparator Icon looks at the tip and a constant and recognizes the tip (1) is greater than the constant (0.5) and momentarily enables the memory icons. This allows only rain fall data to be recorded and prevents the recording of 0 rainfall to memory. In other words we are recording only when it is raining.

Another branch uses the Summation Icon for total rainfall accumulation. This is the rainfall per tip Memory Icon labeled Total. This particular application is using a metric tipping bucket rain gage so each tip is 0.2 mm of rain. Another NET branch is a simple math calculate to arrive at mm/Hr, a large number of tips within the sample rate period you will result in a high mm/Hr number indicating intensity. Also indicating intensity is a Delay Icon and a Periodic Output Icon which is programmed to start recording rainfall with the first tip then output the total rainfall within the following five minute period. This is done by programming the delay icon to enable immediately but turn off 5 minutes after disable. The output then enables the POI which cycles the summation icon every five minutes forcing an output to memory. The Green LED is just an ON indication during the five minute “intensity” period.

HyperWare is extremely flexible allowing for more rainfall information to be recorded than what is presented here. Averages, maximums, and minimums, and much more can be programmed into a data logger to collect the information you need.