Topic: Seperating senors on the VP2

[Mason]

Hey everyone. I'm new to the forum. I really like the site.   My question is can you seperate the rainguage from the temperature shield on a vp2 6153 station?  I'm a coop observer for the nws and I want to compare my mmts temperature senor that the nws supplies me with to the vp2 24 hour fars and i want both senors to be as close as possible to each other which means i need to remove the rainguage. Any suggestions?  I just ordered the station recently and haven't recieved it yet.  I'm not sure if it's possible or if i need to buy a new housing etc.  I'm hoping someone out there has done this and can point me in the right direction.

Mason

[ocala]

Welcome to the forum Mason.
Unless you are doing a roof mount of the sensors most people just put them on a 4X4.
Is there any way the NWS sensor could be mounted on the backside of the post?

[Mason]

the mmts temperature sensor nws installed is installed on a 2" pipe at 5 ft above ground in an open area.  I plan on installing the vp2 in a similar fashion in the same area as the mmts senor.  I just need to detach the rainguage from vp2 senor assembly and have the temperature shield isolated by itself.  I talked to my nws coop manager about my test and he said to make sure there wasn't any other senors (esp. black ) near the vp2 temperature shield to make the mmts temp senor and the vp2 temp sensor as similar as possible.  hope that makes sense.

[tomcj2]

The Rain collector just plugs into the ISS , so there should be no reason that you cannot separate them.  You would probably have to purchase or make  another mounting bracket.  Perhaps you can find what you are looking for in this Davis publication.
http://www.davisnet.com/product_documents/weather/app_notes/apnote_32.pdf

Before you do anything you should phone Davis and run your idea past a Technician.

[Mason]

Thanks for the advice.  I agree with contacting a davis tech and getting their input>

[LFWX]

What advise did you get from Davis?

While looking up part numbers for the various parts of the rain collector (I need the cone to build an analog, 'CoCoRHS' type, collector that I can use to verify my readings) I ran across something that may help. In fact I now plan to seperate my collector also.

You can purchase the base for the VP2 rain collector (without tipping buckets), use it as the mount for your existing radiation shield and ISS, then use your original base (with tipping bucket and cone) to re-locate the rain collector in an ideal location.

The base is part # 07342-074 and sells for $15.00 from Davis.
http://www.davisnet.com/weather/products/weather_product.asp?pnum=07342.074
I would say the price is reasonable considering they want $2.00 for the little debris screen that blows away.

For anyone else wanting a cone to create an anolog collector
The cone is part # 07342-025 and sells for $20.00 from Davis
http://www.davisnet.com/weather/products/weather_product.asp?pnum=07342.025

PS
Just remeber that 1 inch of rain in the Davis collector is 544ml, so for an analog collector you would need a graduated cylinder, and then do some math, or you would need to create your own calibrated measuring tube. I'll post pictures when I get some time to build mine.

[Weather Display]

yes, its no problem to separate the rain gauge from the ISS (by extending the cable)

[wxtech]

Hey everyone. I'm new to the forum. I really like the site.   My question is can you seperate the rainguage from the temperature shield on a vp2 6153 station?  I'm a coop observer for the nws and I want to compare my mmts temperature senor that the nws supplies me with to the vp2 24 hour fars and i want both senors to be as close as possible to each other which means i need to remove the rainguage. Any suggestions?  I just ordered the station recently and haven't recieved it yet.  I'm not sure if it's possible or if i need to buy a new housing etc.  I'm hoping someone out there has done this and can point me in the right direction.

Mason

Welcome to the forum Mason.  I've been a Coop since April 2004, station LXTG1.  I have a cluster of 3 steel posts (chain link poles) mounted about 30 inches apart in a triangle.  See photo below.  I use a WaterLog H-340 rain gauge instead of the Davis rain gauge but I use the Davis VP2 system (ISS/console/etc).  In the photo, the rain gauge black funnel has been removed.
I compare my Davis/VWS to the Numbus MMTS and adjust the temp on the VP2 console.  Since I can't calibrate the MMTS, I have to designate it as the station reference calibrated temperature.  I can calibrate the Davis VP2 in .1º degree offsets.
My MMTS and VP2 temperatures are within 1ºF (usually 0.0ºF to 0.2ºF difference) of each other when the temperature is stable.   In mornings/afternoons when the temperature changes fast, the temperature difference is sometimes greater than 1ºF.  The MMTS responds to temp changes faster than the VP2.
The MMTS and Davis VP2 sensors are at the same height and seperated by 30 inches laterally.
The reason for the difference in temperature is that the Davis sensor is mounted on a solid plate within the shield and has a large thermal mass.  The MMTS sensor is a pencil thin (low thermal mass) and mounted inside an open space with vertical air flow.

P.S.  For non coops information, the MMTS (Maximum Minimum Temperature System) is the property of Uncle Sam.  The Regional Cooperative Program Manager installs it and we just operate it for NWS. 

[Mason]

I want to thank everyone for their input and ideas.  I have a question for WXTech.  What offset do you have on your vp2 to match up with your mmts? thanks in advance.

[wxtech]

I want to thank everyone for their input and ideas.  I have a question for WXTech.  What offset do you have on your vp2 to match up with your mmts? thanks in advance.

-1.5ºF
I'm amazed that it's so much.  The Coop Rep affirmed that the Nimbus is absolutely correct.  I used to verify my temps with a psychrometer (now broken).  I'll order some calibrated glass thermometers and check again. 
Let us all know what difference you have when you get setup.
Do you have NWS rain measuring equipment also?  What types?

[Mason]

my setup has been complete for around one week now. i took and made the rain bucket and mounting bracket on the iss white instead of seperating the senors.  Right now i'm running a -1.1 degree offset on my vp2 to line up with my mmts. i was also surprised with the spread but the coop rep checked the accuracy of the mmts and assured me that it was spot on.  as far as nws rain guages, i have a srg and a fisher porter guage here on site

[Anthony]

I finally had some measureable precip since I installed my stratus 4" manual guage for CoCoRaHS. It measures 0.21" and my OS WMR-968 measured 0.20. So since the OS measures in 0.04 inceaments. That puts the OS prety much spot on.

[Mason]

anthony,

i have a couple different types of tipping buckets plus the stratus gage plus some nws gages.  the tipping style gages do quite well in rainfall rates less than .25" per hour but once the rate increases much above that the spread in readings become more apparent.  my rainwise mkIII rain gage does the best with the vp2 a close second.  wait until you get a t-storm and see if your manual gage lines up with you os gage.

[wxtech]

anthony,

i have a couple different types of tipping buckets plus the stratus gage plus some nws gages.  the tipping style gages do quite well in rainfall rates less than .25" per hour but once the rate increases much above that the spread in readings become more apparent.  my rainwise mkIII rain gage does the best with the vp2 a close second.  wait until you get a t-storm and see if your manual gage lines up with you os gage.

My observations exactly.