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April 17, 2017
about 2 years ago
i’ve done some testing on the rain gauge, and although the spec says it dumps the cups at a rate of 0.011" per click i’ve measured that my rain gauge rate is 0.0123 inches per click.
this may not seem like much, but it’s a 12% error, which over time is fairly significant. if my region gets 38 inches of rain per year, i would be measuring over 42.5 inches.
Here is my method and numbers:
with a small hose i slowly ran water into the gauge via a slow steady trickle and collected the water in a container. i let this run for about an hour while counting the clicks via arduino (the click counting is solid, no misses or bounces). then i stopped the water at a count of 350 clicks, and carefully measured all the water that had accumulated since the start.
i measured the volume of water at 588 mL. this was with a 500 mL measuring cup to make the measurement. it wound up being the full 500 mL plus 3 more ounces, making a total of 588 mL.
I measured the area of the collector at 4.9cm x 11.0cm. Then dividing the volume collected (588 cc) by this area (53.9 sq cm) gives a depth of 10.95 cm, which is 4.31in. at 350 clicks, this is 0.0123 inches per click.
(note: I realize the corners of the collector area are beveled. with a 0.5 cm arc radius the total area is reduced only by 0.2 sq. cm., and did not change the the overall value of inches/click)
can anyone comment on this?
just a note, the datasheet for the WindVane is incorrect in one place. for the direction of 315 degrees (NW), the resistance is 64.9Kohm. this is correct, but the derived value for 5VDC using a 10Kohm divider resistor, the output voltage is 4.33V, not 4.78V.
I’m sure whoever has gotten this far is probably able to figure this out, but if you just plug in the values without testing, you’ll get erroneous readings.
did you get this resolved? i realize this is 8mo old now, but how did you determine the switch is faulty? specifically what resistance value do you read when the vane is pointing NE?
curious, what’d you find out on this?
short answer, yes.
long answer, it depends – the vane is a resistor (or sometimes two) that is switched. the anemometer and rain gauge are just switches. Switches don’t care what voltage is applied, as long as your pullup (or pulldown) resistor limits the current. 1K will be sufficient. But the real question is, what kind of microcontroller are you going to use to count the switches or monitor the Analog voltage input? most hobbyist microcontrollers expect TTL logic levels, either 3.3 or 5V. 12V or 24V would burn out the GPIO controller on those boards
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