New web tags <#THWindex> and <#THSWindex>

[gemini06720]

Steve, I have added the new tags to my file.

My console is showing a temperature of 14.3°C, humidity of 86%, winds at 0.0km/h and a TWSW index of 13 - the 'THWindex' tag is showing 14.3 and the 'THSWindex' tag is showing 0.0 - should it not be the reverse?

[steve]

My THSW index also shows zero, but I didn't know whether that was because the temperature here doesn't get high enough. I ran Weatherlink to see what values it came up with, and it gave the same values as Cumulus (including the zero THSW index).

[gemini06720]

Steve, on my console, the temperature is now at 14.4°C, the humidity is now at 85%, winds still at 0.0km/h, the heat index is 14 and the TWSW index has gone up to 14 ... the 'THWindex' tag is now displaying 14.4 and the 'THSWindex' tag is still displaying 0.0

What does you console display show for the THSW? Should the 'THSWindex' tag not display what the console is displaying for the THSW?

According to the Davins Instrument Vantage Pro2 console manual "The THSW Index uses humidity and temperature like for the Head Index, but also includes the heating effects of sunshine and the cooling effects of wind (like wind chill) to calculate an apparent temperature of what it “feels” like out in the sun."

I do not think I will use the new tags until I know more what they are suppose to display...

[steve]

As far as I can tell 'Heat Index' and 'THW Index' are not the same thing. They are separate items in the Davis DLL. Currently, on the console I have

Heat Index = 12
THSW Index = 9
I don't know how to get the console to display THW Index, assuming it's not the same as Heat Index.

In Cumulus I have:

Heat Index (calculated by Cumulus) = 11.6
THW Index (read from the console/DLL) = 7.2
THSW Index (read from the console/DLL) = 0.0

Yes, I would expect Cumulus to give the same value for THSW Index as the console, but as Weatherlink also gives 0.0 then I assume there's a bug in the Davis code somewhere.

[gemini06720]

Yes, I would expect Cumulus to give the same value for THSW Index as the console, but as Weatherlink also gives 0.0 then I assume there's a bug in the Davis code somewhere.

Or maybe, just maybe, there might be a bug/error in the WeatherLink software...

I could not find anything related to THW (those 3 letters and the words the 3 letters stand for) in the Davis Instrument Vantage Pro2 console manual... ...Might those 3 letters only be the 'creation' of the WeatherLink software designers...

[steve]

I could not find anything related to THW (those 3 letters and the words the 3 letters stand for) in the Davis Instrument Vantage Pro2 console manual... ...Might those 3 letters only be the 'creation' of the WeatherLink software designers...

Interestingly, the Davis 'derived variables' document makes no reference to THW Index. It has Heat Index, which just uses Temperature and Humidity, and THSW Index, which uses Temp/Hum/Solar/Wind, but no mention of THW.

Oh well, I've done what I can.

[gburnett]

Hi Steve, thanks so much for your efforts with the Davis THSW tag. My console has a value but the tag contains 0.0. Is this likely to be fixable or should I learn to live without it? Thanks
Gary

PS My weatherlink software does show a value for THSW. ver 5.9.3

[steve]

PS My weatherlink software does show a value for THSW. ver 5.9.3

That's interesting, I'd assumed it was a bug in the firmware as I couldn't get WL to show a value. It could still be a bug in the DLL, or maybe I have just used the wrong value when I call it - I'll check my code.

What firmware version does your VP2 have?

[gburnett]

Hi Steve, thanks for prompt response. Version 1.90

[steve]

I'm reasonably confident that I am making the correct call on the DLL, so I think it must be a bug in the DLL. The DLL must be supposed to calculate the value, as there is no mechanism for getting the value out of the console (it's not in the LOOP data). The only solution would therefore seem to be for Cumulus to calculate it for itself.

[gburnett]

Hi Steve, might this pdf help with the calculation of THSW in cumulus?
http://climetua.fis.ua.pt/legacy/main/c ... ExpVar.pdf

[steve]

I already have that document (it's on the Davis web site) but it doesn't give the formula for THSW. I have another Davis document which is an extended version of that document, which goes into more detail about THSW but still doesn't seem to give a direct formula. Lots of lookup tables are involved (which is the way the console approximates many of its derived variables).

[faa440]

Hi Steve,
I noticed Davis recently came out with a revision (2.6.1, March 29, 2013) to their Serial Communication Reference Manual and in that revision made reference to description corrections to the THSW index in the LOOP 2 format table. I know you had previously tried to pull the THSW index into Cumulus (only works with VP2 and Vantage Vue systems), but the value comes up as "0.0". Is it possible the Davis corrected document below might provide new instructions on how to pull the actual THSW index from the LOOP 2 data stream?
Thanks for looking into this.

Version 2.6.1 Revisions
1. Documented how to configure reception through repeaters.
2. Added Document revision and date to footers on all pages.
3. Corrected the response of the BAR= command from <ACK> to "OK"
4. Fixed offset of Leaf data in HILOW format table.
5. Corrected descriptions of dew point, wind chill, heat index, and THSW index in LOOP 2 format table.

http://www.davisnet.com/support/weather ... s_v261.pdf

[steve]

Cumulus doesn't use the serial protocol, so doesn't have access to the LOOP2 packet (or the LOOP packet, for that matter). The latest version of the DLL does use the LOOP2 packets if available, but the documentation doesn't say whether it uses the THSW index from that rather than calculating it from the LOOP packet data as before. But in any case, I have tried the latest DLL and there are problems with it, so I can't use it anyway.

[Touchtone]

As far as I know Davis does not have a THW Index, only a Heat Index & THSW Index.
According to Davis publication DS6152_62_53_63 (Rev. G. 27 Apr 11) page 7, under Temperature Humidity Sun Wind Index it says Sources & Formulation Used is:
United States National Weather Service (NWS)/NOAA
Steadman (1979) modified by US NWS/NOAA & Davis Instruments to increase range of use & allow for cold weather use.

Variables used:
Instant Outside temperature, Instant Outside Relative Humidity, 10 Minute Average Wind Speed, 10 Minute Average Solar Radiation.

Formulation Description:
Uses Heat Index as Base Temp, affects of wind & solar are either added or subtracted from this base to give an overall effective temperature.

This is applicable to the Vantage Pro2 weather stations.
Hopefully this may help.