Help with Davis VP2 Sensor Locations

Hardware Weather Station Siting and Setup Tips
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21

Robert,

It sounds like what you are proposing is exactly what I’m planning on doing within the limitations of the VP2 and my house configuration.

Regarding the rain gauge… Davis tech support says that your rain gauge solution won’t work. I.e., with the VP2, you cannot simply disconnect the VP2’s rain gauge from the ISS and move it. Apparently the rain gauge is physically built in to the ISS. (However, the VP1’s rain gauge could be moved.) If you move the rain gauge, you also move the solar panel, solar radiation sensor, and temp/humidity sensor.

So, the only way to “move” the VP2’s rain gauge is to buy another one. Personally, I think is this is a stupid design, but tech support assured me that it’s built that way on purpose.

Regarding the anemometer… You’re right - extending the cable is trivial. What you are suggesting about simply extending the anemometer cable was my first idea. However, that’s the easy part…

The hard part is running the cable. My house has 36" eves all the way around the house, most of which are between 15 and 25 feet off the ground. It also has a cedar shake roof, which is slipperier than wet cat ca-ca when it rains (which is a lot in Seattle). The combo of these make it VERY difficult to run wires. So a wireless anemometer makes the install MUCH easier and safer.

Below is a drawing to show what I’m dealing with. The drawing is NOT to scale with the front of the house being much higher off the ground. Also, I didn’t draw the front entrance deck just to the right of the MBR Deck (where the ISS would be mounted). There’s a big notch in the entrance deck from which grows an 18 foot bush. The only way to get to the corner where run the anemometer cable would be to put an 18 foot ladder right on top of the plant.

Note that the two anemometer masts are just design ideas to figure out which is the best choice. The one attached to the back side of the vent box is better and easier to install AFTER climbing up the slippery shake roof. The other is much more difficult to install and requires a 12 foot mast, but is much safer to install.

The second drawing is the same model from the back side. It doesn’t look far from the edge of the roof to the top until you step on the shakes. And watch your foot slide.

One of the reasons that I draw models is to parse through complex issues. Most problems look easy when you start. Some have easy fixes if you find the right solution. The ISS location is one of those. Some, like the anemometer, get much more complex when you work through the detailed design steps of actually implementing the solution.

Regards,

Dan.

22
Regarding the rain gauge... Davis tech support says that your rain gauge solution won't work. I.e., with the VP2, you cannot simply disconnect the VP2's rain gauge from the ISS and move it. Apparently the rain gauge is physically built in to the ISS. (However, the VP1's rain gauge could be moved.) If you move the rain gauge, you also move the solar panel, solar radiation sensor, and temp/humidity sensor.

with the Davis VP1
the davis VP rain gauge can be separated from the ISS, and then just lengthen the wire…thats what I did
but with the VP2, which I do not have, I still think there must be a way to separate them all out ?

23

Brian,

I’d love to agree with you. It doesn’t make any sense to me either. However, Davis tech support insists that the rain gauge can’t be separated from the ISS.

One of the reasons I posted this was to get feedback from other VP2 owners. So, is tech support right? Wrong? Inquiring minds want to know!

Regards,

Dan.

24

:bs: Sure you can separate them, but it’s probably reasonable that Davis doesn’t want to get too involved in it. The simplest way is to buy the rain gauge base from Davis, and use it to mount the ISS and transmitter box separately, see this thread with a lot of discussion on this issue, the part number, and a picture of the actual part I got from Davis.

25

There’s no major mechanical difference between VP1 and VP2 except that the SIM board is associated with radiation shield on the VP1 but with the rain gauge on VP2. The key difference in practice is that you would need to extend the temp/hum sensor cable if separating rain gauge and shield on the VP2, which isn’t required on the VP1 design. Davis are insistent that the temp/hum sensor is designed to work with the expectation that this sensor cable will be short. I know that some folk do extend this cable with apparently acceptable (though probably unverified) results but it is very much stepping outside the Davis recommendations, which are based on the electrical specifications for the input from the humidity sensor AFAIK.

So yes you can achieve mechanical separation of the two parts on the VP2 without too much trouble (though you need to work out exactly how the shield is to be mounted post-separation because the standard fixing point is no longer available, since the whole ISS is fixed via the rain gauge base) but don’t be too surprised if the humidity readings go outside specification, unless you do as Niko suggests and source a second rain gauge base so that you can keep the SIM board and shield in close proximity. My view is that the simplest and least hassle (though obviously not the cheapest) way of approaching this problem is just to buy a separate 7852 rain gauge and leave the ISS intact. But unless you can mount the rain gauge close to ground level in an open space then your rainfall readings are likely to be significant under-estimates (by eg 10-20%) of the true rainfall, so you might decide not to worry too much about rainfall acuracy and leave the ISS in one piece anyway.

26

I thought the latest RH sensor is digital, so it’s surprising the cable length would be that critical.

27

OK gents, just to make sure that I have this right and that we are on the same page…

  1. In addition to a VP2 Wireless, I buy a Davis rain collector base: Part Number 07342.074 (http://www.davisnet.com/weather/products/weather_product.asp?pnum=07342.074)

  2. Disconnect the rain collector on the ISS and attach it to the extra Davis rain collector base (“07342.074”).

  3. Mount the stand-alone rain collector with base “07342.074” about 2 feet up my temp/humidicty pole.

  4. Mount the SIM module, solar panel, solar radiation sensor, and temp/humidity sensor about 8’ up the temp/humidity pole.

  5. Run a connection cable (which I’ll also have to buy) from the stand-alone rain collector up the pole about 6’ and plug it into the SIM.

Is this correct?

Thanks and regards,

Dan.

28

Prodata,

I don’t understand this. Is the temp/hum sensor part of the rain gauge? When you mount the rain gauge in a separate rain gauge base, why would you want to (or have to) move any other component there?

Regards,

Dan.

29

NO, if you buy a 2nd complete rain gauge (about $80 IIRC) it is built on its own base. You only need to buy the bare base (about $25 IIRC) if you are going to disassemble the rain gauge/ISS assembly. In that case you leave the rain gauge parts on the original base, remove the temp enclosure and transmitter enclosure from the original assembly and remount them on the 2nd base. For the extra $50 you get a solution that’s a direct plug in without extending any cables.

(Also answers your question to prodata.)

30

Here is a manual on how it comes apart.
http://www.davisnet.com/product_documents/weather/manuals/VP2_Fan_Aspirated_ISS_Rev_C.pdf

31

Niko,

The bare base is $15. $10 for the cable. The full collector is $75.00. Why would I want to spend an extra $50 if it wasn’t necessary?

Regards,

Dan.

32

Only if you didn’t feel confident disassembling your $600 weather station, not everyone is handy with a screwdriver :wink:

33

Niko,

I guess I’m missing something I thought it was merely a matter of transferring the rain gauge from one mounting plate to the other and plug in the cable. What am I missing?

Thanks,

Dan.

34

The base is an integral part of the rain gauge, so (assuming a non-FARS ISS) what you would do is:

Put the console in setup mode
Open the transmitter box
Unplug the rain gauge cable from the board and feed it back out of the box.
Unplug the temp.hum sensor cable from the board and feed it back out of the box
Separate the transmitter unit from the whole assembly (it clips on)
Remove the rain gauge cone
Undo the three screws holding the temp/hum shelter to the rain gauge base and separate that unit from the base (being careful not to mess up the rain gauge tipper assembly which is fragile and stays on that original base)
Replace the rain gauge cone
Reinstall the temp/hum and transmitter units to the new base
Reconnect the temp/hum to the transmitter with the existing cable
Extend the cable from the rain gauge to the new base and connect to the transmitter
Put the console back in regular mode

No big deal for me, maybe not for you either, but I wouldn’t want to assume that’s true for everyone reading this and have them break an expensive piece of equipment.

35

Niko,

Why do I want to move the temp/humidity and transmitter to the new base? All I want to do is move the rain gauge. It seems like it would be a lot simpler just to move the rain gauge and add a longer cable.

Regards,

Dan.

36

The base cannot be separated from the rain gauge, as I wrote it is an integral part of the gauge. The gauge components are assembled on the base.

37

Niko,

Ok. I understand that. But it seems like it would be a simple matter to move the rain gauge components to the new rain gauge base. Then plug in the cable.

Are the rain gauge components somehow assoicated with the other components? Temp/Humidity? Solar Panel?

Regards,

Dan.

38

That should have read, “Then plug in the cable from the new base to the old base.”

Regards,

Dan.

39

OK, since you insist I’ll refine my statement. It would be certainly possible to remove the rain gauge components from the old base and re-install them on a new base. However, in my humble opinion there is an excellent chance of breaking a part, and a very excellent chance of upsetting the calibration.

40

Niko,

OK! That makes sense.

In all this discussion no one has mentioned this breakage/calibration issue before. Or I didn’t notice it). All of the rest of the issues, including complexity, didn’t make sense. This alone is a very good reason to buy a new rain gauge.

Thanks and regards,

Dan.

p.s., in the last 61 years of my life, I’ve had a lot of people throw a lot of strongly stated information about the “right” way to do things. In most cases, they didn’t understand the problem, were just giving their uneducated opinion, or assumed that I wouldn’t understand the reasons behind something. Through hard experience, I’ve learned to keep pushing 'til things made sense. It tends to reduce my screw-ups. 8)

p.p.s. I worked on automatic flight control systems in the Air Force. Complex doesn’t bother me. Calibration does.