Author Topic: Davis Anemometer Knowledge Base  (Read 13745 times)

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Offline wxtech

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Davis Anemometer Knowledge Base
« on: September 07, 2011, 06:47:22 PM »
Make this a forum/community project.  We should compile an anemometer knowledge base of our information and publish a wiki somewhere.   
I have an original VP on my workbench set up to test the Davis anemometer.  I have already tested what happens when the black, red, green & yellow wires in the cable are opened or shorted.
Now I have a Tektronix Type 114 pulse generator feeding pulses into the anemometer cable.  I'm monitoring the waveshape period & symmetry on a digital oscilloscope.
I will test in several frequencies from 0 to 1 KHz.  This will verify the test and results that I did on April 1, 2010 and reported in this forum http://www.wxforum.net/index.php?topic=7546.msg72629.
I will compare waveshapes of low wind speeds and maximum wind speeds using a standard length anemometer cable and an extended anemometer cable.
I have pictues of disassembled sensors, wiring diagrams and a parts list.
This is a call for what tests you suggest that I do over the next few days.  You are invited to contribute your tests or sources of information and help publish the wiki.
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline Jim18655

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Re: Davis Anemometer Knowledge Base
« Reply #1 on: September 07, 2011, 08:21:07 PM »
How about what happens when an extension cable is made reversed? It seems to be a very common problem.

Offline wxtech

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Re: Davis Anemometer Knowledge Base
« Reply #2 on: September 07, 2011, 09:08:18 PM »
How about what happens when an extension cable is made reversed? It seems to be a very common problem.
Excellent idea.  I'll add that to the open/shorted wires troubleshooting section.
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline Jim18655

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Re: Davis Anemometer Knowledge Base
« Reply #3 on: September 07, 2011, 09:15:37 PM »
Quote
I will compare waveshapes of low wind speeds and maximum wind speeds using a standard length anemometer cable and an extended anemometer cable.

How about with the Davis extension cable and maybe an equal length of Cat 5 or 6 cable to see if any difference due to the capacitance of the cable?

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Re: Davis Anemometer Knowledge Base
« Reply #4 on: September 11, 2011, 12:56:26 AM »
An update on the testing:  I did the wiring shorts/opens testing.  Started taking speed waveshapes using a Climatronics wind bird tester.  It has a variable speed motor to drive the anemometer.  The first anemometer that I tested produced two cycles per revolution of the shaft.  I don't know why that happened.  I took down an operating anemometer and now that one is on my bench, see the picture http://www.lexingtonwx.com/assets/images/dscn3065.jpg.  I'm using an R M Young fuselage to hold the Davis anemometer hub while the tester motor turns the shaft.  You can see on the o'scope that the waveshape is non-symmetrical.  This test is producing 17-18 mph on the console.  The test speed ranges are 5-7 mph, 17-18 mph, 32-34mph, 58-60 mph, 95-98 mph.
Someone who knows, please refresh information about the different anemometer cups, cup size dimensions.  I have one where the magnet is vertical, others the magnet is horizontal.
I'm using a Davis original VP and various anemometers.  I will provide clear pictures, waveshapes with measurements, and diagrams soon.
« Last Edit: September 11, 2011, 01:06:06 AM by wxtech »
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline wxtech

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Re: Davis Anemometer Knowledge Base
« Reply #5 on: September 15, 2011, 06:59:21 PM »
I'm working, I'm working.  I have written a 5 page anemometer and vane description with troubleshooting, pictures and a schematic.  I'll have to decide which and how many waveshapes to include.  I have spec sheets on the potentiometer and the reed switch.  I'll include reed switch theory information.
I'll put it up soon for your perusal and editing.
Al
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline Weather Display

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Re: Davis Anemometer Knowledge Base
« Reply #6 on: September 15, 2011, 10:37:18 PM »
you will probably cover it, but if not, maybe info on potential ground short problems and how to deal with a reed switch that has become stuck closed?
Brian
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Offline wxtech

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Re: Davis Anemometer Knowledge Base
« Reply #7 on: September 18, 2011, 05:56:41 PM »
I have about 8 pages written so far.  It will be easier if I make the information in an HTML document because of the pictures and waveshapes.
Attached are the direction waveshapes.
The SIM sends out a direction excitation 8 ms pulse every 2.5 seconds (yellow wire).  It is applied to the top end of the potentiometer.  The pot slider selects a portion of that voltage depending on the angular position of the vane.  The waveshapes show the direction excitation pulse on channel 1.  Channel 2 on each waveshape is the returned direction pulse to the SIM (green wire).
1direction_north_1.jpg = vane pointed north @ 1º, channel 2 pulse is 0 volts
2direction_east.jpg = vane pointed east, channel 2 pulse is .75 volts
3direction_south.jpg = vane pointed south, channel 2 pulse is 1.5 volts
4direction_west.jpg = vane pointed west, channel 2 pulse is 2.25 volts
5direction_north_359.jpg = vane pointed north @ 359º, channel 2 pulse is 3 volts
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

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Re: Davis Anemometer Knowledge Base
« Reply #8 on: September 18, 2011, 05:57:46 PM »
2 remaining waveshapes of the 5
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline xykotik

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Re: Davis Anemometer Knowledge Base
« Reply #9 on: September 18, 2011, 06:50:24 PM »
While I don't plan on hacking my Vue hardware anytime soon, I really like these topics.

In my mind's mind, I have designed an anny/vane that I think could work.  All of this two-channel pulse business you are describing makes me think I'm not too far off.

I guess just a high density optical encoder is what I would use for the anny.  Very low friction, no magnets, sealed unit. Just spins and makes pulses.  For the vane, my mind's design uses a two-channel encoder of the same compact and sealed type, both channels have the same frequency, just offset and overlapping.  We use them for speed/direction/acceleration monitoring of robotic arms in medical/OR equipment.  They are about 25mm diameter and about 15mm thick. Four wires. The microscopic laser-cut screen/encoder is inside a sealed unit, directly around the shaft (actually a hole, that you pass (and grub-screw) a shaft through), with very low friction.  To that, just add an adjustable pass-through opto-switch with a flag, so it knows where north is, and how many pulses (and phase/direction) from there to know which way the wind is blowing.  It re-calibrates itself every time it passes that point (provided the flag/sensor hasn't been moved relative to North).


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Offline wxtech

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Re: Davis Anemometer Knowledge Base
« Reply #10 on: September 18, 2011, 07:17:01 PM »
I designed/built my first wx station many years ago, long before my Davis, Lacrosse, 1-wire hardware.  The direction vane used a gray code optical encoded shaft.  That's a direct readout of the 0-360 resolution.  A simpler encoder was 16 points instead of the 360 points.  I couldn't afford to buy an optical shaft encoder, so I built my own.  Shaft encoders are smaller/cheaper now.
Your idea of using two channels would give up/down direction for the degrees pulse counter.
« Last Edit: September 18, 2011, 07:19:46 PM by wxtech »
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline wxtech

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Re: Davis Anemometer Knowledge Base
« Reply #11 on: September 19, 2011, 01:10:16 AM »
I'm posting the wind speed waveshapes for 17 mph, 34 mph, 62 mph, & 95 mph.  For this test, a motor is turning the cups hub, driving the magnet across the reed switch.  I haven't done any analysis of the numbers yet.  The reed switch is normally open and closes when the magnet is near.  The SIM pulls the black wire up to 3 volts.  When the reed switch closes, the black wire is pulled to ground, 0 volts.
The on/off ratio should be the same for all wind speeds.  This is not a calibrated speed test.  This is a test to analyze device operation.
data:
17 mph; 7.353 Hz; 136 ms period; reed switch closed 20 ms
34 mph; 14.88 Hz; 67.2 ms period; reed switch closed 10.4 ms
62 mph; 29.76 Hz; 33.6 ms period; reed switch closed 4.8 ms
95 mph; 52.08 Hz; 19.2 ms period; reed switch closed 2.8 ms
The jitter is worse at 95 mph as seen at the cursor.
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline SLOweather

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Re: Davis Anemometer Knowledge Base
« Reply #12 on: September 19, 2011, 12:34:54 PM »
The direction vane used a gray code optical encoded shaft.  That's a direct readout of the 0-360 resolution.

That'd be 9 level? Did you build it with just the 360 degrees, and leave the other 152 unused? Even at 360, that's pretty fine optics and chopper wheel. I was working on one at about that time that I think was only 3 level (8 bits, 8 compass points).

I built a single hole optical chopper for the anny, too, and used the halves of L'eggs panty hose containers for the cups. It was all out of copper pipe parts.

Never got any electronics made for reading everything, though. Gray code is pretty interesting.

Offline johnd

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Re: Davis Anemometer Knowledge Base
« Reply #13 on: September 19, 2011, 12:53:32 PM »
17 mph; 7.353 Hz; 136 ms period; reed switch closed 20 ms
34 mph; 14.88 Hz; 67.2 ms period; reed switch closed 10.4 ms
62 mph; 29.76 Hz; 33.6 ms period; reed switch closed 4.8 ms
95 mph; 52.08 Hz; 19.2 ms period; reed switch closed 2.8 ms

These data would tie in with the VP stations continuing to use a 2.25 sec gating period to convert revolutions to MPH (exactly as per the old WMII systems). The basic equation is that - at lower wind speeds - 1 cups revolution (ie one switch closure event) in a 2.25sec interval equates to 1MPH. (Which also explains why the VP display cannot display other than integer MPH, though the Vue ISS is obviously somehow cleverer, at least when received by an Envoy8x console.)

But at higher wind speeds (say >50MPH) this relationship starts to degrade - presumably the console is using a LUT to convert Hz to MPH to compensate for the imperfect or non-linear aerodynamics of the cups.
« Last Edit: September 19, 2011, 01:08:06 PM by johnd »
Prodata Weather Systems
Prodata's FAQ/support site for Davis stations
Includes many details on 6313 Weatherlink console.
UK Davis Premier Dealer - All Davis stations, accessories and spares
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Sorry, but I don't usually have time to help with individual issues by email unless you are a Prodata customer. Please post your issue in the relevant forum section here & I will comment there if I have anything useful to add.

Offline wxtech

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Re: Davis Anemometer Knowledge Base
« Reply #14 on: September 22, 2011, 04:42:11 PM »
Well, I'm scared to push the GO button.  But the DRAFT version of my/our Davis Anemometer Knowledge Base is ready for your criticism and suggestions.  Provide your information and add more topics.  I just hope this will be the place to get the information that we know about the wind sensor.
http://www.lexingtonwx.com/anemometer/
We still have to answer how to deal with a reed switch that has become stuck closed?  Also devise suggestions for dealing with a tight shaft and bearings.
After it graduates from the draft form, where should it be parked?
Al
P.S. I will add spec sheets on the pot and reed switch.  I will include information on magnetic reed switches.  If you want more pictures, go to the old failed DIY anemometer project. http://www.lexingtonwx.com/anemometer/diy/
« Last Edit: September 22, 2011, 05:13:56 PM by wxtech »
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline dalecoy

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Re: Davis Anemometer Knowledge Base
« Reply #15 on: September 22, 2011, 06:08:12 PM »
Absolutely great!

Technical error: actually, it's an RJ-14 connector, although the "common" nomenclature is RJ-11.  [The picky difference is that the RJ-11 uses 2 conductors and the RJ-14 uses 4 and the RJ-25 uses 6 conductors]

Two suggestions:

1.  It would be helpful to have instructions and a circuit diagram for how to build a "test switch" like the one Davis sends, to "substitute" for the anemometer and troubleshoot whether a problem is with the anemometer or with the ISS.

2.  Discussion of length of extension cable, including one or two waveforms showing how the waveshape changes (and thus the extension limits the maximum speed).

Added later: I think it's entirely fine to refer to the connector by the common terminology (RJ-11), I just wanted to be picky.
Re: stuck reed switch.  Never had one, but I speculate that it might be possible to unstick one by use (external to the housing) of a very strong neodymium magnet.  
« Last Edit: September 22, 2011, 06:14:39 PM by dalecoy »

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Re: Davis Anemometer Knowledge Base
« Reply #16 on: September 22, 2011, 06:59:41 PM »
I've generally labelled the 4P4C as lives on the end of say the serial data logger as an RJ11 (4 cable) and the RJ12 being either 6P4C (4cable) or 6P6C (six cable)

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Re: Davis Anemometer Knowledge Base
« Reply #17 on: September 22, 2011, 07:09:43 PM »
All good suggestions.  I have a speed test switch,a NE555 speed pulse generator, and a direction tester.  I don't know what Davis sends.
I forgot about the cable length waveshape, that'll be interesting.
I've never seen a stuck switch on an anemometer.  But Weather Display asked for the solution.
I didn't know about the RJ-11/14.
Al Washington, Lexington, Ga.,  NWS Coop station=LXTG1, Fischer Porter, SRG, MMTS. 
CoCoRaHS=GA-OG-1. CWOP=CW2074.  Davis VP2+ WLIP 5.9.2, VP(original) serial, VWS v15.00 p02. ImageSalsa, Win7 & Win8 all-in-one.

Offline dalecoy

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Re: Davis Anemometer Knowledge Base
« Reply #18 on: September 22, 2011, 08:24:16 PM »
All good suggestions.  I have a speed test switch,a NE555 speed pulse generator, and a direction tester.  I don't know what Davis sends.

From another forum:  "The anemometer test cable is a short cable about 1 foot long which simulates a southerly wind direction. A push-button on the end of the test cable can be pushed to simulate wind speeds up to about 15mph."

In other words, three resistors and a pushbutton.

Offline dalecoy

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Re: Davis Anemometer Knowledge Base
« Reply #19 on: September 22, 2011, 08:47:30 PM »
I've generally labelled the 4P4C as lives on the end of say the serial data logger as an RJ11 (4 cable) and the RJ12 being either 6P4C (4cable) or 6P6C (six cable)

Technically, the RJ12 connector is the same as an RJ25, except made for solid wire rather than stranded.  In other words, technically it should have six wires. 

Also, as Flag correctly typed it, there is technically no dash in the registration number.  It's RJ11, RJ12, RJ14, RJ25, etc.

Those are really picky points, and of course we are free to call them whatever we wish, so when the article says "4 conductor RJ-11 male plug", I don't think anyone will misunderstand.

Offline C5250

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Re: Davis Anemometer Knowledge Base
« Reply #20 on: September 22, 2011, 11:20:38 PM »
But at higher wind speeds (say >50MPH) this relationship starts to degrade - presumably the console is using a LUT to convert Hz to MPH to compensate for the imperfect or non-linear aerodynamics of the cups.

It does, there are two different lookup tables, one for small cups, and another for large cups. The tables return whole integers, so that is probably the main reason the display is only whole integers (for mph anyhow), as no interpolation is done.

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Offline johnd

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Re: Davis Anemometer Knowledge Base
« Reply #21 on: September 23, 2011, 03:07:48 AM »
It does, there are two different lookup tables, one for small cups, and another for large cups. The tables return whole integers, so that is probably the main reason the display is only whole integers (for mph anyhow), as no interpolation is done.

Yes, but what was in my mind, was that there might also be a LUT in the SIM board firmware, which I can't rule out, although I agree that it's unlikely - Occam's razor would suggest little point in having more than one LUT. The console LUTs are indeed in the firmware and have been updated in the past year or two - another good reason for having up-to-date firmware (though IIRC I had a suspicion that the wind-tunnel based corrections were calculated with a 7911 anemometer rather than 6410 and so might not have been totally accurate with S winds.)

In terms of why integers, I think you start from the point that at low speeds, eg up to 40-50mph where no significant correction is being made, the mph figures are actually being measured as integers (ie with a single magnet on the cups you can't have more than one switch closure per revolution of the cups, ie in the 2.25 secs period which equates to 1mph). Then when you do start to make corrections (ie >50mph), the accuracy of the speed value is not going to better than +/-1mph at best and so there's no point in reporting other than integer values, which also has the happy consequence of conserving space in the firmware if only integers are used as return values and presumably also fits in with the original firmware architecture.
Prodata Weather Systems
Prodata's FAQ/support site for Davis stations
Includes many details on 6313 Weatherlink console.
UK Davis Premier Dealer - All Davis stations, accessories and spares
Cambridge UK

Sorry, but I don't usually have time to help with individual issues by email unless you are a Prodata customer. Please post your issue in the relevant forum section here & I will comment there if I have anything useful to add.

Offline dalecoy

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Re: Davis Anemometer Knowledge Base
« Reply #22 on: September 23, 2011, 10:32:49 AM »
I've generally labelled the 4P4C as lives on the end of say the serial data logger as an RJ11 (4 cable)...

Just to complete the picky technical stuff:  that 4P4C is absolutely not an RJ11.  And it has no official "RJ" (i.e., registered) designation.

Offline johnd

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Re: Davis Anemometer Knowledge Base
« Reply #23 on: September 23, 2011, 10:42:47 AM »
Just to complete the picky technical stuff...

Well, yes, this is quite a picky and mildly technical thread. But sometimes people ask quite simple questions that actually only have a technical answer. If you (someone, I mean, not you personally) want to understand the details of the answer then you have to appreciate the technicalities. So when someone asks 'why won't the VP2 console display decimal MPH values?' there is a good valid answer - it's not that Davis are being bloody-minded or cheapskates (well, not only that  :grin:).
Prodata Weather Systems
Prodata's FAQ/support site for Davis stations
Includes many details on 6313 Weatherlink console.
UK Davis Premier Dealer - All Davis stations, accessories and spares
Cambridge UK

Sorry, but I don't usually have time to help with individual issues by email unless you are a Prodata customer. Please post your issue in the relevant forum section here & I will comment there if I have anything useful to add.

Offline dalecoy

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Re: Davis Anemometer Knowledge Base
« Reply #24 on: September 23, 2011, 03:05:00 PM »
And the community should assist wxtech in making it as technically accurate as practical.