Topic: VP2 FARS airflow

[WxLover16]

It just occured to me, thinking about how the design of the VP2 FARS is, that natural passive airflow can't get to the sensors (due to it being inside of the sensor chamber), except for underneath, which is only for the fan to pull air up to it. Am I correct that natural wind cannot filter through to the sensors (through the sides/shield plates) with it being cutoff due to the chamber? Especially on a day like today where the wind has my console saying (kite flying weather). I'm sure that Davis designed it with this in mind and knew what they were doing. Just curious.

[ValentineWeather]

Yes if the fan is off you will see higher than normal temperatures daytime with the fan aspirated shield unless there's stiff wind.

Now the Dfars shield is the naturally aspirated shield with fan add on so no issue here if fan goes off.

[WxLover16]

Yes if the fan is off you will see higher than normal temperatures daytime with the fan aspirated shield unless there's stiff wind.

Now the Dfars shield is the naturally aspirated shield with fan add on so no issue here if fan goes off.

I'm just referring to the 24hr FARS, totally different design, which is what mine is. My fan never goes off. I know the passive shield/DFARS are designed to let passive air get to the sensors.

[ValentineWeather]

Yes if the fan is off you will see higher than normal temperatures daytime with the fan aspirated shield unless there's stiff wind.

Now the Dfars shield is the naturally aspirated shield with fan add on so no issue here if fan goes off.

I'm just referring to the 24hr FARS, totally different design, which is what mine is. My fan never goes off. I know the passive shield/DFARS are designed to let passive air get to the sensors.

Apparently I don't understand what you are asking.

[WxLover16]

Yes if the fan is off you will see higher than normal temperatures daytime with the fan aspirated shield unless there's stiff wind.

Now the Dfars shield is the naturally aspirated shield with fan add on so no issue here if fan goes off.

I'm just referring to the 24hr FARS, totally different design, which is what mine is. My fan never goes off. I know the passive shield/DFARS are designed to let passive air get to the sensors.

Apparently I don't understand what you are asking.

This is the meat of my post:

"Am I correct that natural wind cannot filter through to the sensors (through the sides/shield plates) with it being cutoff due to the chamber? Especially on a day like today where the wind has my console saying (kite flying weather)."

I'm just wondering if the sensor is able to catch any passive wind and not just aspirated.

[ValentineWeather]

Yes if the fan is off you will see higher than normal temperatures daytime with the fan aspirated shield unless there's stiff wind.

Now the Dfars shield is the naturally aspirated shield with fan add on so no issue here if fan goes off.

I'm just referring to the 24hr FARS, totally different design, which is what mine is. My fan never goes off. I know the passive shield/DFARS are designed to let passive air get to the sensors.

Apparently I don't understand what you are asking.

This is the meat of my post:

"Am I correct that natural wind cannot filter through to the sensors (through the sides/shield plates) with it being cutoff due to the chamber? Especially on a day like today where the wind has my console saying (kite flying weather)."

I'm just wondering if the sensor is able to catch any passive wind and not just aspirated.

Seriously? Maybe take it up with Davis engineers asking what wind speed the fan gets overpowered and becomes passive aspiration.

[WxLover16]

Yes if the fan is off you will see higher than normal temperatures daytime with the fan aspirated shield unless there's stiff wind.

Now the Dfars shield is the naturally aspirated shield with fan add on so no issue here if fan goes off.

I'm just referring to the 24hr FARS, totally different design, which is what mine is. My fan never goes off. I know the passive shield/DFARS are designed to let passive air get to the sensors.

Apparently I don't understand what you are asking.

This is the meat of my post:

"Am I correct that natural wind cannot filter through to the sensors (through the sides/shield plates) with it being cutoff due to the chamber? Especially on a day like today where the wind has my console saying (kite flying weather)."

I'm just wondering if the sensor is able to catch any passive wind and not just aspirated.

Seriously? Maybe take it up with Davis engineers asking what wind speed the fan gets overpowered and becomes passive aspiration.

Yes I'm serious. That's a good idea also but first was just posing the question here because I know there's alot of knowledgeable weather/engineering people on this site and someone is bound to be in the know on this.

[jerryg]

Well i am no expert but i am running 4 of the shields co-located for testing purposes. The design of the shield is pretty neat using the 7 outer plates with the holes to shield the inner tubes from direct sun heating. When the plates heat up the holes allow the built up heat to flow upwards like smoke up a chimney. Then there are the outer tube, inner tube which shield the isolation chamber for the sensor. The air between the outer and inner tube is scrubbed by the fan drawing air and pulling any heat out the top. The air is scrubbed by the fan between the inner tube and the isolation chamber. This design was used because of the low air flow of the Davis fan having to run on solar and batteries. The commercial shields don't use the outer plates to shield the tubes and instead use a very high volume air flow. Now i had a fan fail this summer and i notice that the temp was running nearly a degree higher than the other 3 with the fans running. The wind was blowing around 10 to 15 mph. I can not say how the air flow would be inside the shield but there could be some kind of flow through the shield tubes with the top and bottom being open to air flow. So the temp goes up but not overly so. I guess i could unplug one of my test shields and watch it over a few days to see for sure what the temp would show in low wind. It would be interesting to see how it compares to a non fars shield temp increase.

[WxLover16]

Well i am no expert but i am running 4 of the shields co-located for testing purposes. The design of the shield is pretty neat using the 7 outer plates with the holes to shield the inner tubes from direct sun heating. When the plates heat up the holes allow the built up heat to flow upwards like smoke up a chimney. Then there are the outer tube, inner tube which shield the isolation chamber for the sensor. The air between the outer and inner tube is scrubbed by the fan drawing air and pulling any heat out the top. The air is scrubbed by the fan between the inner tube and the isolation chamber. This design was used because of the low air flow of the Davis fan having to run on solar and batteries. The commercial shields don't use the outer plates to shield the tubes and instead use a very high volume air flow. Now i had a fan fail this summer and i notice that the temp was running nearly a degree higher than the other 3 with the fans running. The wind was blowing around 10 to 15 mph. I can not say how the air flow would be inside the shield but there could be some kind of flow through the shield tubes with the top and bottom being open to air flow. So the temp goes up but not overly so. I guess i could unplug one of my test shields and watch it over a few days to see for sure what the temp would show in low wind. It would be interesting to see how it compares to a non fars shield temp increase.

Thanks for your informative reply. You may not be an expert but you summed it up very nicely. Are all 4 of your shields 24 hr FARS? If I had the money I would most certainly buy just an ISS (24hr FARS most likely) to test it. You really should do that experiment. I'm guessing without the fan, the shield would heat more with no fan aspiration and only little passive aspiration.

[jerryg]

Yes they are, i have all of them running on 12 volt power, i don't like the solar/battery set up. You can buy the parts to make your own set up from Scaled Instruments, i believe the cost for the bits and pieces is around 87 dollars without the solar stuff. I like to test various things with the shields. I run one as my primary set up and another as backup the other two i play with. I try different fans and run different levels of voltage to speed up or slow down the fans. I am now trying a 16 inch plate in place of the 7 small Davis plates and so far no difference in performance.  Could save a little money on plates but have to make the big plate fit the shield and paint it, so time or money your choice lol.

[WxLover16]

Yes they are, i have all of them running on 12 volt power, i don't like the solar/battery set up. You can buy the parts to make your own set up from Scaled Instruments, i believe the cost for the bits and pieces is around 87 dollars without the solar stuff. I like to test various things with the shields. I run one as my primary set up and another as backup the other two i play with. I try different fans and run different levels of voltage to speed up or slow down the fans. I am now trying a 16 inch plate in place of the 7 small Davis plates and so far no difference in performance.  Could save a little money on plates but have to make the big plate fit the shield and paint it, so time or money your choice lol.

I just looked and saw your location is in SE texas. Have you had any of your temp sensors fail due to consistently high summertime humidity? I sometimes worry about that here in North GA.

[jerryg]

Yes i have had several failures with long term high humidity. Most of the failures happened after i increased the air flow with 12 volt fans, too much moisture inside the sensor filter. I run my fan at half voltage to cut down on the air flow. Also i am now using the sht31 sensors and they are supposed to be better at handling high humidity for long periods of time. We shall see.

[CW2274]

The 24hr FARS design is specifically meant for aspiration, it's not a passive design and it would be a poor performer as such. It would take a pretty good constant breeze to negate the effects of not having a fan. How much breeze, dunno. Don't ever plan on finding out. 

[WxLover16]

Yes i have had several failures with long term high humidity. Most of the failures happened after i increased the air flow with 12 volt fans, too much moisture inside the sensor filter. I run my fan at half voltage to cut down on the air flow. Also i am now using the sht31 sensors and they are supposed to be better at handling high humidity for long periods of time. We shall see.

I've been thinking of taking 1 battery out for slightly higher daytime aspiration but getting close to winter and with increasing winds I'm thinking it would be less of an issue; I might think about it in spring when things heat up again. Thankfully I ordered my station late enough (mid February) to get an AS revision with an SHT31 already in it so I'm glad that supposedly it will work better at higher humidity without crapping out.

[CW2274]

Before I went a/c, I pulled both batteries for max daytime aspiration.

[WxLover16]

Before I went a/c, I pulled both batteries for max daytime aspiration.

I would also do that but I like the thought of having at least SOME form of aspiration at all times, keeps things from going stagnant. I haven't quite pulled the trigger on AC yet but my thinking is I won't need it going into winter. It's something to think about for the spring for sure.

[jerryg]

I agree about the fan that is why i have a backup running all the time so any failure and i can just swap channels on the transmitters and make repairs when i get time. It is nice to know that at least the temps might not go bonkers with a fan failure lol.

[CW2274]

Before I went a/c, I pulled both batteries for max daytime aspiration.

I would also do that but I like the thought of having at least SOME form of aspiration at all times, keeps things from going stagnant

Just ONE reason a/c is sooooo nice to have....

[WheatonRon]

Before I went a/c, I pulled both batteries for max daytime aspiration.

I would also do that but I like the thought of having at least SOME form of aspiration at all times, keeps things from going stagnant

Just ONE reason a/c is sooooo nice to have....

Maybe someday there will be AC power that can be delivered wirelessly to an ISS via bluetooth or the like from a house 50' away rather than digging a trench through the yard upsetting the dogs, spouse, etc., etc.!

[CW2274]

Before I went a/c, I pulled both batteries for max daytime aspiration.

I would also do that but I like the thought of having at least SOME form of aspiration at all times, keeps things from going stagnant

Just ONE reason a/c is sooooo nice to have....

Maybe someday there will be AC power that can be delivered wirelessly to an ISS via bluetooth or the like from a house 50' away rather than digging a trench through the yard upsetting the dogs, spouse, etc., etc.!

Obviously not all can accommodate, but it's well worth the effort if one wants the utmost in a reliable, unquestionably aspirated ISS.

[johnd]

Maybe someday there will be AC power that can be delivered wirelessly to an ISS via bluetooth or the like from a house 50' away rather than digging a trench through the yard upsetting the dogs, spouse, etc., etc.!

It's funny how some device categories just don't seem to capture developer interest, eg there's only one SBC - Raspberry Pi - that's really taken off in terms of worldwide sales. Sure, there are plenty of other SBC's around, but they all seem to be bit players relative to RPi for one reason or another, eg Chinese in origin and, typically, poorly marketed and supported in world markets; so very limited sales and no large ecosystem develops. But the popularity and success of RPi proves that there's a market there.

What I'm thinking of in the context of FARS is a self-contained solar power supply that could reliably deliver eg 3v@100mA to a decent-quality, long-life, high efficiency fan motor. Something like a Davis 6612 unit in fact, but that's arguably a bit too big and certainly too costly. Don't try and build it into the radiation shield - there's really not room for eg a 5W panel and the other bits you need for a FARS PSU that's suitable for use worldwide and not just sunny California.

The BoM for such a unit shouldn't be more than $40-50 (maybe $10 each for case, panel, battery and simple charge regulator) I would have thought, maybe significantly less in large production runs, and so the end-user price ought to be in the $120-150 range. Not cheap, agreed, but affordable for anyone who might be spending $500 or more on a weather station. And it would potentially have many other applications for users wanting a solar PSU delivering eg 5v @ 100mA 24/7/365 for any electronics device that requires outside mounting and independent power.

[WheatonRon]

Maybe someday there will be AC power that can be delivered wirelessly to an ISS via bluetooth or the like from a house 50' away rather than digging a trench through the yard upsetting the dogs, spouse, etc., etc.!

It's funny how some device categories just don't seem to capture developer interest, eg there's only one SBC - Raspberry Pi - that's really taken off in terms of worldwide sales. Sure, there are plenty of other SBC's around, but they all seem to be bit players relative to RPi for one reason or another, eg Chinese in origin and, typically, poorly marketed and supported in world markets; so very limited sales and no large ecosystem develops. But the popularity and success of RPi proves that there's a market there.

What I'm thinking of in the context of FARS is a self-contained solar power supply that could reliably deliver eg 3v@100mA to a decent-quality, long-life, high efficiency fan motor. Something like a Davis 6612 unit in fact, but that's arguably a bit too big and certainly too costly. Don't try and build it into the radiation shield - there's really not room for eg a 5W panel and the other bits you need for a FARS PSU that's suitable for use worldwide and not just sunny California.

The BoM for such a unit shouldn't be more than $40-50 (maybe $10 each for case, panel, battery and simple charge regulator) I would have thought, maybe significantly less in large production runs, and so the end-user price ought to be in the $120-150 range. Not cheap, agreed, but affordable for anyone who might be spending $500 or more on a weather station. And it would potentially have many other applications for users wanting a solar PSU delivering eg 5v @ 100mA 24/7/365 for any electronics device that requires outside mounting and independent power.

Maybe this is being built into the VP3 which is why it has taken so long for that product to be developed! Seriously, a great idea, and you are right--if properly developed and marketed, it would have application well beyond the PWS market!

[SLOweather]

Maybe someday there will be AC power that can be delivered wirelessly to an ISS via bluetooth or the like from a house 50' away rather than digging a trench through the yard upsetting the dogs, spouse, etc., etc.!

There already is. Point a spotlight at the solar panel.

[WheatonRon]

Maybe someday there will be AC power that can be delivered wirelessly to an ISS via bluetooth or the like from a house 50' away rather than digging a trench through the yard upsetting the dogs, spouse, etc., etc.!

There already is. Point a spotlight at the solar panel.

Since my solar panel must face south and my house is to the east, a great idea! I will contact my neighbor and see if he wants to do that for me using his AC power! Thanks for the suggestion!

[alexstaar]

Sorry for reviving an old tread... Thought this may help answer the original question. My original 24-hour FARS batteries appear to have finally kicked out on me. They are one month from being 2 years old, on the original fan as well. I went out the other day shortly after sunset to check that the fan was still running... silence. Did the plastic wrap test... no suction. I did the same thing just a few weeks ago around 5am, just before sunrise, and the fan was still running. The fan still runs during the day with solar radiation, so I know it's not the fan. I tried charging them for a few hours with a battery charger with no avail. So I've ordered 4 of the the OEM batteries (should arrive tomorrow). I will say I'm surprised how long they lasted and how long the fan has lasted! 

I did not notice a temperature anomaly (warmer) at night when the fan was not running. We have 4 Vaisala temp sensors (non-aspirated) on campus about 1 mile from my house. My VP2 (with SHT-31) has always lined up very well with temperatures on the sensors on campus, especially at night. After noticing my fan was not working at night, I've kept a close eye on them to compare with my VP2 24-hour FARS with no fan running at night. I have not noticed an major differences between them. They are still on the order of +/- 0.5ºF or so. As of this writing, the Vaisalas indicate 41.2ºF and my VP2 says 40.8ºF. I also have my old SHT-11 mounted in a temp/hum station at 18 feet above the ground (ISS is at 6 feet above the ground). The two sensors are still showing their expected differences in temps being at different levels (usually only ~1ºF) and humidities right on par. The SHT-31 even hit 98% the other night with no aspiration after a heaving rain (tornado outbreak near Huntsville, AL  ).

So to answer the question (based on my observations the last few days), I do not believe no fan running at night has a significant impact to the temperature/humidity sensor readings. I'm sure this is NOT the case during the day, however, when the sun is heating up the radiation shield with no aspiration. Hope this helps!