The Davis Rain Gauge Heater
A client recently challenged AccuWeather to provide local daily rainfall readings to their publication, challenging the records from the nearby airport. I was more than happy to oblige, and it gave me a chance to install a device coveted by the weather enthusiast community -- the Davis Rain Collector Heater.
As mentioned before on this blog, we have a Davis Vantage Pro 2 Weather Station outside our building, transmitting live weather observations to the Internet from AccuWeather HQ. The rain gauge and temperature sensors are on a tripod in our yard and the anemometer is on the roof.
THE PROBLEM WITH ELECTRONIC RAIN GAUGES:
The problem with this station, and in fact every electronic weather station used by hundreds of thousands of weather observers worldwide, is that they don't measure winter precipitation correctly. What I mean by this is that snow or ice falls in the gauge and freezes up, sending no liquid into the tipping bucket which records rainfall. Sometimes additional rain falls on top of the frozen mess, making not only the original storm inaccurate, but subsequent storms as well. Eventually it melts on a sunny day, sending a stream of water through, which is interpreted as rainfall on a sunny day.
Until recently, the only way around this was to catch snow in a large plastic gauge, then bring it inside for heating via a low evaporation source such as a light bulb or microwave. I've been there, done that, and it can be challenging waiting for the precipitation to melt, especially if you're trying to take a midnight ob before going to bed.
DAVIS' SOLUTION:
In response to this need, Davis created the Rain Collector Heater for their original weather stations in 2001, then set predrilled holes to house the heater in their new line of Vantage Pro stations.
It's actually a simple design but it takes some assembly. The heater itself is actually an element which is heated via a standard AC power plug. An insulation blanket wraps inside the gauge cone and keeps the heat inside the gauge. The heater has a thermostat which keeps the element between 85 and 110 Fahrenheit. The heater can also be turned off via a switch on the power box.
BUT WAIT... HEAT MEANS... HEAT
Before ordering the unit, I got a bad feeling. The rain gauge on the Vantage Pro is right on top of the temperature sensor. Would it affect the readings? I emailed Davis support, and helpful support guy Larry admitted that the heater was not designed for the proximity of the temperature sensor in the VP, and it could affect the readings "by several degrees" depending on how cold it was. Even the fan-aspirated radiation shield for the temperature sensor (which comes on a different version of the VP) would not help.
LARRY'S SOLUTION:
Larry recommended a second gauge, at an additional cost of $75, which I could separate from the main station. Could it be wireless I asked? The answer was "no" because, while you can use the Anemometer transmitter kit for remote windspeed (and we are) you can't have more than one main unit (ISS). I figured I'd locate the new gauge on a nearby tripod and run the data cable from tripod to tripod.
THE HEATER BEFORE CONNECTING WIRES
ASSEMBLY BEGINS:
After receiving the parts, I realized it wasn't going to be a simple installation. Below is a graphic of the parts that came with it:
A simplified version of the steps listed in the manual, which can be found here [PDF], is listed below.
1. Disassemble the gauge
2. Attach and secure the heater assembly to the inside of the rain gauge (may require drilling, screwing)
3. Twist two sets of wires together, attach under screws (like speaker wire worked in the old days)
4. Get power wire into gauge (requires drilling) and secure
5. Wrap insulation blanket around inside of rain gauge cone
6. Run wires into power box, twist and attach like above
7. Reassemble
This was more assembly than I anticipated, especially with all the wire twisting and attaching. It seems like they should have done more with the assembly, but I'm sure that would drive up the cost (which is already $160 for the heater itself).
ISSUES THAT I RAN INTO THAT WEREN'T IN THE MANUAL:
1. One of the #6-32 screws didn't fit in the holes that were predrilled in the new gauge. I'm not sure whether the hole was too little or the screw was too big but it gave me a good bit of consternation.
2. The wires had 7 millimeters of insulation stripped off; the manual recommended 10 mm and I would recommend 12-13 mm. Twisting wires and screwing them down is hard work. The more you have to work with the better. The spaces are also very cramped so welcome to a difficult time in getting the wires screwed down.
3. When drilling the hole for the cable to go up into the rain gauge (why they couldn't have pre-drilled that one too is beyond me), I used the largest drill bit I had and it was a tight fit.
4. They didn't address what to do with the existing data cable. The illustration seems to say that you should attach the heater assembly on top of it, which doesn't sound like a great idea. As you can see in the final photo below, I had it routing around one of the drains in an attempt to keep it away from the heater. After I put it all back together though, there's no telling how close it might be to the assembly now.
STILL A LONG ROAD AHEAD:
And even then, I had two significant challenges ahead of me. For one: I realized after I got the second raingauge that it didn't come with any mounting hardware to put it on a tripod. Randy The Facilities Manager and I came up with a temporary solution, which was to use Randy's Mondo-Size Cable Ties (tm) to tie the new raingauge (with heater inside) on top of the old gauge (which was no longer used). This may end up being our permanent solution, so long as I am satisfied that the temperature readings aren't being affected (hopefully, heat will rise as it tends to do).
The second challenge was the power -- how do you get power to a rain gauge in the middle of the yard without leaving an unsightly extension cord? That one has still not been solved and for now we're running an extension cord to the nearby facilities trailer which has power already.
THE FINAL TEST:
All in all, though, it went pretty smoothly and I was surprised to see it working in the end. By the way, you can check to see if it's working by simply holding your hand over the gauge to feel the heat rising. This can be deceiving however, especially if the thermostat has switched off. I recommend an Infrared thermometer with a "max" setting like the one I reviewed here last month. Waving that baby around in the cone yielded 83 degrees on Saturday when I came back to check on the gauge. Since it was cloudy and 40 outside, that means it's working. So for now, I await some frozen precipitation here in Central PA to give it a good test.
There have been several threads of discussion over on the Davis Vantage Pro Board on the WeatherMatrix Forums, and there is an interesting poll there for any of you who currently run one of these devices.
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