Sensirion Temperature/Humidity Sensor

RancheroMan

Hello all,

I have recently purchased the Sensirion Temp and Humidity Sensor from Parallax for a Weather Station project I am starting.

Does anyone have a recommendation for an appropriate enclosure/radiation shield for this unit?

I'm looking for something I can build myself for $10-$20.

Thanks

RDL2004

Here is a message board where you will find some ideas:

www.weather-watch.com/smf/index.php/board,54.0.html

Check the topics on "radiation shields" and the thread on the home-made weather station that was in Nuts and Volts Magazine.

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- Rick

Franklin

You might also try here kronosrobotics.com/Projects/pagoda.shtml

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- Stephen

Tracy Allen

For the solar radiation shield, the design using the flowerpot saucers looks nice, especially the one that was originally in Spanish. The flowerpot saucers are kind of deep for the purpose of good air flow, and I wonder how effective the fan is in that design. I'd like to see a smoke test. I've seen a similar design using what I think were small pizza plates, which are not quite so deep. I use (and sell) the Davis 7714, which is a similar multi-layer design.

There are a couple of things to keep in mind. One of the most important is to have a double or triple ceiling over the sensor. The purpose of that is to lessen the heat load from the sun above. Also, there is generally a double plate on the bottom to reduce heat load from below, and that is important if the device is to be installed over a hard surface that will get hot, as opposed to a surface like lawn. Ventilation from the sides and a surface coating that reflects well in both the visible and infrared is also important. The plates should not be deep so as to trap the rising hot air, and the hot air has to have an escape path above the level of the sensor itself. In general, larger is better. A location in the shade of a tree or bush or arbor is better than nothing and is often better than a shelter. In testing shelters having identical exposure and placement, the one reading the lowest temperature is considered the best.

Another issue is protection from contamination. That is a consideration in agricultural fields. Sprays like sulfur are deadly for these sensors, and an agricultural fogger is very effective at delivering spray to every nook and cranny. Another difficult situation is near or on the ocean.

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Tracy Allen
www.emesystems.com

RancheroMan

Thanks for the links......gives me a few more ideas.

Do you think it is a wise idea to paint the sensor with a silicon conformal coating to prevent oxidization? Is it too risky as one may get the conformal in the humidity sensor port?

What have others done? Toss it under a radiation shield and call it good?

Thanks

Tracy Allen

Yes, I always coat the sensor connections only with conformal silicone resin. For outdoor deployment, I use the SHT75, which is the one with the long neck. The coating covers the capacitor and the connections and does not come near the sensor flow-thru openings.

The Parallax version is a SHT11 chip mounted on a dip carrier with a pullup resistors for the data line. Be sure you add the suggested pulldown resistor for the clock line and a capacitor across the power close to the chip. You'll probably need a good socket for it. It could probably last a long time without a conformal coating, but if you do apply it, obviously be very careful not to get any of the stuff into the sensor opening.

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Tracy Allen
www.emesystems.com

RancheroMan

Thanks for all the help!

I see a trip to the home improvement store in my near future!

Franklin

Here is another way, the reference to the hardware store reminded me of this one www.mulveyfamily.com/weather/Sensor_Grenade.doc

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- Stephen

steve_b

I didn't click on the all the links provided, but you can build your own "Stevenson Screen"

Somebody said...
http://en.wikipedia.org/wiki/Stevenson_screen

You can take some louvred cupboard panels and put them back to back and build a box. (then just get a top and bottom)

Keep it up off the ground and out of the shade....basically in an area without obstructions for a few meters around it!

I wouldn't put a vent fan in there or anything (not unless you are measuring dry and wet bulb temperatures to determine a calculated Relative humidity)
And in this case there are distinct calculations for a motorized vent and a non-motorized (and also for elevations).

There's been a bit of discussion about the type of material the shield should be made of.
Plastic, engineered wood (that recycled wood/plastic stuff)....types of paints....vinyl/latex...etc...
Anyhow, if you aren't looking for accuracy to a tenth of a degree, don't worry about material (well, metal is an obvious no!)
So long as you are up off the ground and not in the middle of a concrete parking lot, you'll probably be alright!

cheers

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<FONT>Steve



What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
Lee Travino after the second time being hit by lightning!

RancheroMan

I went to Home Depot this weekend and picked up some plastic flower pot plates and some threaded rod to put it all together. The white paint is drying right now, but I'll post some pictures of what I came up with. I'm leaving provisions to add a small fan down the road. I figured I'd test out the non-fan design first and see how it goes.