Topic: Anemometer flipping to north and back

[johnnice]

I've had my VP2 some 11 years.  The problem has been around for some time but I finally thought I'd deal with it.  The wind here is mostly between SE and SW.  Every couple of minutes the displays, both pc and console, show a due north indication before returning to the correct SE/SW.  I am certain it is not due to wind change.  I replaced the anemometer - and cable:  no change.  I replaced the ISS transmitter:  no difference.  I've updated the console to firmware 3.80 and done a full power-off/battery-out reset.  Still the same.  I thought I would bring wlink op to 6.0.5 but group  policy editor won't let the upgrade run.  All the external connections are good;  I've just run out of ideas.  Any thoughts welcome.

Thanks

John

[miraculon]

I replaced the anemometer - and cable:  no change.  I replaced the ISS transmitter:  no difference.

This is strange, since I would almost bet that it is an intermittent open circuit on the wind direction signal.

When you say that you replaced both the wind set and the ISS transmitter, which one was replaced first? Is the new anemometer directly connected to the ISS with no extension cables?

You might take a look here for a good troubleshooting guide for the Davis wind set.

Note this section:

Wiring errors:
yellow wire open causes a north indication
green wire open causes a north indication
red wire open causes a north indication and prevents wind speed from being indicated (not likely since your speed seems OK)
black wire open prevents wind speed to be indicated
yellow to green shorted causes a north indication
yellow to red shorted causes a north indication
green to red shorted causes a north indication
black to yellow shorted, wind speed zero
black to green shorted, wind speed zero and direction erratic
black to red shorted, wind speed zero, intermittent short causes wind speed error

There is a test circuit that you might build. I don't know if it is possible to borrow the anemometer/vane tester from Davis, since you are in the UK.



Greg H.

[johnnice]

I agree.  The cable routed from the anemometer isn't near any other conductors, either, which makes induction errors unlikely.  Thanks for the circuit - I'm going to build a test box;  putting it on a 30-ft cable means I shal be able to operate it while I'm in front of the console.

Best rgds

John

[johnnice]

Interesting development:  I had a reply from Davis who suspect some sort of grounding problem.  They suggested I power down the console and remove the logger.  I did so and watched the wind direction for 6 minutes.  Just one 360, and as the wind today is light and variable that's to be expected.  I've reported back to Davis and await their response.

ps, I made up a resistor network and substituted that for the anemometer.  No 360 flips.

John

[mjc775]

Interesting development:  I had a reply from Davis who suspect some sort of grounding problem.  They suggested I power down the console and remove the logger...

As you can see by the following graph, this has been happening on my VP2 intermittently as well - for a few years now, more often on low wind days: http://www.findu.com/cgi-bin/wind.cgi?call=n7feq&last=108&xsize=800&ysize=200&tz=420

When you removed the logger to fix the problem - did the logger stay removed, or did you remove it just long enough to unplug it then plug it back in? I'm hoping fixing the issue could be something as simple as the later, and I don't need a new logger.

[johnnice]

Replacing the logger brought the problem straight back.  I suspect Davis is now realizing that the problem is wholly theirs:  without a Davis logger installed, there isn't a problem.  Their silence could be because they're waiting for their attorneys to tell them if there's a class action waiting to happen 

[miraculon]

Replacing the logger brought the problem straight back.  I suspect Davis is now realizing that the problem is wholly theirs:  without a Davis logger installed, there isn't a problem.  Their silence could be because they're waiting for their attorneys to tell them if there's a class action waiting to happen 

That is really strange. What type of logger is it? (WLIP, serial or USB)

The grounding comment from Davis has me wondering if it might be a ground loop between your computer and the logger. (if not WLIP)

Could you try plugging in the logger again, but with no connection to a computer from the logger? (or ethernet if applicable)

Greg H.

[johnnice]

The logger is a USB device, but I don't propose to do any more research:  I have better things to do with my time.  It has cost me quite a lot of money to prove that Davis' constant spouting about how it must be the anemometer or the cable is wrong.  There is a grounding problem of some sort and Davis knows it; otherwise it wouldn't have been able to give me a fix.  It's time Davis came clean with a sensible, usable response to the problem.  That being said, I'm not sure it can be a ground loop.  The ISS and console are both insulated boxes.  The only ground connection is via the logger to the pc.  It's probably more likely to be either a common mode  problem, or a dirty 5V from the pc.

[johnd]

A few comments:

Am I right in thinking this is a cabled VP2? Ground loop effects are pretty much non-existent on wireless VP2 systems AFAIK. It's the connection from the anemometer at some height (and therefore exposed to electrical potential significantly different from ground potential) right through to eg a PC power supply that tends to exacerbate these rare problems with cabled stations. I know  it's not worth spending time over but I wouldn't be surprised if you put your test resistors up at the same height  as the anemometer that you wouldn't see similar issues.

To be fair to Davis, in 99% of cases like this with wind direction issues it IS the anemometer or cable at fault. And some users take a lot of persuading to check the cable thoroughly so I'm not surprised that there was some repeated insistence to check the cable. Unfortunately, it sounds like your case is a rare exception to this.

I have never really understood the instruction to remove the logger from the console as a test for ground loops. (Maybe there is a reason but I've yet to learn what it is.) Simply disconnecting (in this instance) the USB lead should be a sufficient test, preferably while running the console on battery power only (ie AC mains adapter unplugged) just to rule out any possibility of a defective console mains adapter.

Back in the days when RS232 loggers were more common the answer to this issue was to fit an opto-isolator in the RS232 lead. This is less easy with USB but I see that cheaper USB isolators are starting to appear on the market. (USB isolators have been around for years but they've typically been more costly professional devices.) I'm talking about something like this:

https://uk.farnell.com/olimex/usb-iso/usb-isolator-1000vdc-for-pc-laptop/dp/1795095

Please note that I'm not recommending you buy this - I've never tried one of these and my electronics knowledge is not good enough to be sure that it fits the bill. But it's an example of the sort of isolator that ought to work.

[johnnice]

I agree it seems odd that removing the logger should fix it, but it does.  I'm not so sure it's a ground loop as my system has only one grounding point:  the pc.  It's most likely to be a common-mode problem, but it's still weird, weird enough apparently for Davis not to want to spend time and resources in fixing it.  Rare it may be, but one other user of this site has it.

I'm interested in the isolator. (I had tried searching for one but all I found were a number of snake oil solutions for hi-fi aficionados.)  Anyway, I think I'll give it a whirl.  If it doesn't work it can go back.  Three cheers for the Distance Selling Regs!

[JRC]

A friend had this exact same problem with his wired Vantage Pro 2 and USB logger. We solved it by fitting a USB Isolator.

[johnnice]

Yesterday I had messages from two Davis support techs.  Tech 1 said "It's a cable fault.  Even if you can't see anything it's a cable fault".  REALLY helpful.  Tech 2 (who had written before) suggested an isolator.  Two correspondents on here also suggested one.  I looked up the one he suggested, a USB-ISO isolator.  The data sheet particularly mentioned common-mode blocking.  As my system has only one ground point  -  the PC's mains plug  -  I had tended to suspect common-mode rather than ground loops.  Anyway, I ordered one.  In the UK it's available from Amazon for £stg 63.  From Farnell it's £stg 32.  Nuff said;  I ordered from Farnell.  Whilst sorting through my IT odds-box for a USB A-B cable I came across an old Belkin 4-port hub.  I can't recall what I bought it for but I seemed to remember it was quite a superior device.  Just for fun I connected the logger cable through it.  Now, the wind at present is light, variable northerly so I can't be sure, but the indication of north now seems about the same as every other indication between 315 and 45 degrees.  I am now whistling for a nice south-westerly blow to confirm things.

[johnnice]

The USB isolator (from Olimex) has done the trick.  Many thanks to the people who suggested trying it.  Not too many thanks to Davis, though, whose constant spouting "It must be the anemometer or cable" cost me quite a lot of money:  changing the anemometer (and cable) then the ISS transmitter board.  Anyway, all's well now.

[92merc]

Just for future reference, is this it?
https://www.mouser.com/ProductDetail/Olimex-Ltd/USB-ISO?qs=hO3QYTFrOd09eOKVRIujMQ%3D%3D&gclid=EAIaIQobChMInvusqbKi4QIVm__jBx1H4glZEAQYBSABEgJmLPD_BwE

[johnnice]

Yes, that's it.  Worked well for me but your mileage may vary 

[mjc775]

While this is good news for those with the USB logger, I am using the WLIP logger and my wind direction woes continue. “Must be the cable”. I just don’t have the time or desire to climb onto the roof of my 2-story house to replace the cable.


Sent from my iPhone using Tapatalk

[johnnice]

You might like to try what Davis advised me to do - which proved it was not an anemo fault:  power down the console AND remove the battery.  Remove the logger and power up again.  I did it, and in six minutes there was no north flip.  That's when I ordered the USB isolator.  Maybe another user here has had problems with the IP logger.  In any event, this was Davis's test to prove the fault off the anemo.  I do know that there were problems with the old RS-232 logger and they were relieved with an RS-232 opto-isolator.  If the WLIP is RS-232 it might be giving the isolator a whirl.

HTH

John

[johnd]

The IP logger is not RS232, it is Ethernet. Two comments both just repeating what I've said previously (on the basis of supporting literally thousands of Davis stations & loggers over many years):

1. The vast majority of incidents of this kind are indeed to do with the anemometer itself or the cable (or cable/socket junction).

2. I've never understood the need to remove the logger from the console when testing for ground loops etc. Simply disconnecting the logger cable should be a sufficient test in most cases, though running the console on battery power alone would be an added check (but not recommended with the IP logger).

[johnnice]

I tried running on the battery:  no difference

I tried dissing the logger but leaving it installed:  no difference

It's certainly a weird problem.  The Davis PSU has no measurable connection with mains earth.  Anyway, I am now free of north flips

[johnd]

I tried running on the battery:  no difference
I tried dissing the logger but leaving it installed:  no difference

That's fine - I wasn't trying to suggest otherwise in your particular instance but merely that in this sort of fault report it is nearly always the anemometer/cable at fault. In the rare cases where there are other causes then interference entering through the console mains adapter can be one of the culprits so it's best to rule this out by running on battery only (where possible).

It's certainly a weird problem.  The Davis PSU has no measurable connection with mains earth.  Anyway, I am now free of north flips

The way I've always understood it is (as mentioned upthread) an anemometer located at some height sees variable air potential relative to ground. This is obviously considerably exaggerated during thunderstorms but AIUI there can be lesser effects at other times too. With wireless systems this isn't an issue because the transmitter is isolated from ground. But with cabled system there is potentially a conducting path right through from the anemometer to the PC and it's the resulting stray voltages that can cause interference-type problems. Whether this formally classifies as a ground loop or something else I don't have enough background to say (except that rightly or wrongly it's often included with ground loop effects), but I guess that electronics engineers are relatively familiar with this sort of issue.