Temperature data spikes revisited

[Gina]

wind(or a small breeze) can build up static on an antenna,dependent on atmosferic conditions,like humidity,static charge of the air,nearby elements(trees,poles) so wether the spikes ar build ups or discharges,i don't know.

That possibility was mentioned some time ago and I provided the metal mast with a sound earth in the form of a wire from the mast to a ground spike nearby. This did seem to reduce the spikes on the data plot. The clue was that things were much better in wet weather - when wet grass and ground earthed the mast bottom.

a piece of tin between the tempsensor and the cable connector and soldered to the neg battery lead could work in that case

Yes. it could be that pulses cross over from the connector to the thermistor wires and screening might stop it. But why would extending the wind sensor cable make it worse?

[hans]

low humidity cold air blowing over a cable builds the static charge when the discharge is lower than the build up.
more surface(eg,longer cable) gives a more rapid build up.
the only way for the cable to discharge is through the air(normally),
but that is then the very reason it can't,for it is to dry ,so less conducting.
when the static charge is high enough it will jump over to a low potential at the shortes distance,possibly the tempsensor,so you could have a small sparkplug effect there.
so the cables themselves would need to be grounded(like coax,which unfortunatly is single core).
shielded networkcable(expensive) could do,if the shielding is grounded
easier is to run the wire through a metal pipe,instead of around or along side it,
for static builds up on the surface,not inside a "body"(faraday)

[Gina]

what if it is the base unit all that time,sometimes it't right in front of you and you don't see it........

If you mean the console, I have two and ran a test to check they were both receiving exactly the same data - they were/are.

As far as the cable is concerned, this has a screen which is earthed. In fact it has foil screening around each twisted pair and an overall braided screen.

As for the number of spikes, I'm running the test at 48sec sampling rather than the usual 5mins. Thus I would expect to see 6x the spikes on average.

[Gina]

Seems quite good so far, a spike around 10:30 and several very small ones. I'll be running the 48sec testing for a while yet (in parallel with the standard setup on another PC). Here's the last 12 hours of testing...

12hrs-Temp-only2.png

[Charlie]

Hi again Gina,

I've been poking through the pictures of the transmitter insides (my unit is out of reach right now) but I can't tell if the traces from the anemometer leads go directly to the IC, or if there are external components, or if one side is tied to a rail. If one side is tied to a rail, that would explain why a cap on it makes no difference. If there is an external component, it might be possible to adjust the value to compensate for the cable length.

Also, someone asked if anyone besides Gina sees this issue. My unit has spikes of a degree or two (before the decoupling caps) and I can make them higher with more cable, so I conclude the unit itself is the source of the issue (Not ESD, RFI, or moon phases), and directly related to the anemometer cable length. I have also noticed they are worse when humitity is very high.

[Gina]

Thanks for your post Charlie It got me thinking and I've spent an hour or so carefully studying the photo and the unit itself (the "spare" - the first one I bought) and tracing the circuit. I have made a very interesting discovery. The thermistor (that measures temperature) is actually connected to the wind vane circuit! (as well as connecting to the chip).

The wind vane has a resistor across it (I'll need the microscope to read the value) and the anemometer has a capacitor across it. One side of the anemometer goes to battery negative as was thought likely. I've "unwrapped" the layout diagram and drawn up a conventional circuit diagram :-

AWS_Wind_Sensor_Cct.png

It occurs to me that the temperature may be measured by the same method as the wind vane resistance using a timing circuit. That would explain why I saw two pulses on one of the vane connections and one on the other. To be sure I'll have to get my scope out again and put batteries in the old tx unit. I would need to connect a suitable resistor to represent the wind vane.

[hans]

the condensator is 22uF polarised.(wh1080,no windvane
on mine(wh1081,with vane) it's smd(yellow) some have a regular bigger bleu one
both have the same pcb as outdoor unit,only the vane less has a few components missing
wether the chip is the same? probably

maybe you should replace the condensator,wouldn't be the first one to be a bad one from the start or deteriorated quickly

[Gina]

Sorry to correct you Hans but it's the DCF radio clock ferrite aerial and chip that's the difference between the two models. My units have the blue thermistors and no clock receiver.

[Gina]

The spikes are back!! So is the wind. In fact the wind got up a few hours before the spikes appeared. Maybe there's a correlation, or maybe not. Anyway, I'm learning a lot more about how it works and may eventually come up with the definitive answer - I've not entirely given up even if I have put the tx/thermo/humidity unit back outdoors.

6hrs-Temp-only-g.png

[hans]

mine both have the dcf clock function,the cheaper one has no usb and winddirection,maybe i have my type numbers mixed up,sorry.

maybe the condensator is there to compensate for the spikes(bouncing of the reed contacts)
might be worth to try to replace it

[Gina]

mine both have the dcf clock function,the cheaper one has no usb and winddirection,maybe i have my type numbers mixed up,sorry.

Ah yes, I see. The one without USB is a different model.

maybe the condensator is there to compensate for the spikes(bouncing of the reed contacts) might be worth to try to replace it

Yes, I did try a capacitor across the reed contacts - didn't make any difference.

[Gina]

To see wind speed and temperature I've added a 12 hour wind speed plot.

12hrs-Temp-only.png

12hrs-Wind.png

Can't say I see much correlation. I think the wind vane resistance may be a better candidate. I'll see if I can produce a plot of resistance rather than direction.

[hans]

i meant the capasitor on the pcb,th yellow smd part (4,7 uF,couldn't read it on mine)

and you're right,my old one is also known as wh1070
outdoor pcb is identical as the wh1080 one

[Gina]

Yes, the 4.7uF is the timing capacitor for both the wind direction and the temperature as far as I can tell. It seems to be working perfectly well. The capacitor across the anemometer is the smaller yellow one and I can't see any marking on it.

The marking on the resistor across the vane connection looks like 105 ie. 1 megohm. I presume this is to provide a resistance when the vane is unplugged.

[hans]

could be,
as far as i know a reed needs some sort of buffering to counteract the contactbouncing.
it seems to me that the trace where the capacitor,resitor,vane and thermistor are joint is the common "feed" from the chip,then via the sensor back to the chip.
btw ,also found this,he works with unix and the wh1080,
maybe interresting for you
http://www.lemis.com/grog/programs/WH1080.php