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Temperature data spikes revisited

Discussion specific to Fine Offset and similar rebadged weather stations
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Gina
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Temperature data spikes revisited

Post by Gina » Fri 24 Sep 2010 8:54 pm

I now have two parallel systems from console onwards with common transmitter and outdoor sensors. So both consoles are receiving the same data packets from the transmitter. Both systems are using G-Weather running under Linux Mint 9. These upload their data to parallel web sites on my server. Here are the temperature plots for today - note the difference in the spikes!
24hrs-Temperature-a.png
24hrs-Temperature-b.png
This would tend to show that the problem is not entirely at the transmitter end though a couple of spikes are common. This looks like the start of a whole new investigation.

The intention of this setup was to let me develop G-Weather without interrupting the main weather site. This difference was quite a surprise!
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geoffw
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Re: Temperature data spikes revisited

Post by geoffw » Fri 24 Sep 2010 9:27 pm

Looks like you're going to have to investigate influences on the receiver/console! Is anyone else using two receivers from one station who can compare results?
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daj
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Re: Temperature data spikes revisited

Post by daj » Fri 24 Sep 2010 9:38 pm

I have two receivers for mine. I use one for live and the other to feed Cumulus 2 occasionally.

I've never compared the two consoles /data closely. Maybe I should if that would help
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Super-T
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Re: Temperature data spikes revisited

Post by Super-T » Fri 24 Sep 2010 11:18 pm

If it's so easy to add another transmitter then do your neighbours have a similar transmitter Gina?

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Ned
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Re: Temperature data spikes revisited

Post by Ned » Fri 24 Sep 2010 11:42 pm

I had problems with temp spikes under windy conditions after resiting the wind sensor away from the transmitter, needing a 15m extension cable. They have been tamed using EWTempdiff (set to 0.5) in cumulus.ini. which ignores any spike greater than 0.5°C. It works great, but in particular circumstances (spike exactly equals EWTempdiff during a temp trend in the opposite direction to the spike) the graph can get stuck on a flat line until the temp gets within range again. It's only happened twice so far, and I fixed it by restarting Cumulus.
I've got a CAT5 cable ready to be installed, which I hope will reduce spikes at source.
Gina, are your spikes occuring with shielded or unshielded cables?

Gina
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Re: Temperature data spikes revisited

Post by Gina » Sat 25 Sep 2010 8:15 am

daj wrote:I have two receivers for mine. I use one for live and the other to feed Cumulus 2 occasionally.

I've never compared the two consoles /data closely. Maybe I should if that would help
It would certainly be interesting, thank you :) Maybe turn off the Cumulus spike removal if it's on.
Super-T wrote:If it's so easy to add another transmitter then do your neighbours have a similar transmitter Gina?
No, I'm pretty sure of that.
Ned wrote:Gina, are your spikes occuring with shielded or unshielded cables?
I have a shielded cable from the wind sensors though the shield is not connected to the tx unit ATM (using the new unit, unmodified). Some spikes appear to be coming from the transmitter but not all of them.
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goldrush
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Re: Temperature data spikes revisited

Post by goldrush » Sat 25 Sep 2010 8:28 am

I had a similar problem initially using extension cable to wind sensors.
You should use Cat 5 Twisted pair shielded cable and earth the shield, the special "grounding wire" and unused pairs at one end the transmitter end only, ensuring a good direct "earth" connection.
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Gina
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Re: Temperature data spikes revisited

Post by Gina » Sat 25 Sep 2010 11:04 am

Not cat5 but I am using twisted pair screened cable - 2 pair rather than 4 pair - and I had the screen connected to the negative battery terminal of the transmitter unit. That seemed to pretty much cure the spikes at the time. When I swapped the old tx unit for the new, I didn't want to open it up in case there was a fault and I wanted to return it. Now everything seems fine with it I may solder a wire onto the power supply negative, as before. I'm also going to connect it to an earth spike near the Stevenson screen box.

Two hours later... I have now connected the cable screen to an earth spike - a piece of copper water pipe (cleaned off) hammered a foot or so into the ground (the thickness of the topsoil).
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Gina
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Re: Temperature data spikes revisited

Post by Gina » Sat 25 Sep 2010 1:51 pm

I have now moved the no.2 console and hung it on the wall that's nearest the transmitter. It's away from computers there and nearer the transmitter. That was about 14:30, for reference. Now to wait and see...
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Gina
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Re: Temperature data spikes revisited

Post by Gina » Sun 26 Sep 2010 1:10 pm

Seems the spikes have gone :) Two measures for the transmitter and one for the receiver (one console). viz. Mast "grounded" by a wire from the jubilee clip that fastens it to the fence post to an earth spike nearby and the cable screen (from wind sensors) similarly earthed. Then the new console that seemed to be getting extra spikes was moved away from interference generating computers and nearer the transmitter.
24hrs-Temperature-a0.png
This second plot comes from the console I moved. I may try moving it back later and see if it picks up interference.
24hrs-Temperature-a1.png
I had noticed that the data spikes I was getting got smaller after we had a lot of rain so I checked the mast earth and found the earth wire had become disconnected. So I reconnected it. The mast is all metal - being galvanised iron at the bottom and copper at the top - and I think the wet grass and ground around the base may have been conducting static electricity away.

It seems that earthing the screen of the wind sensor cable was enough and it's not necessary to earth the tx battery negative or connect it to the screen.
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Gina
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Re: Temperature data spikes revisited

Post by Gina » Wed 29 Sep 2010 3:53 pm

AAAARRRRGGGGHHH!!!

First console with old Athlon XP laptop
24hrs-Temperatureb0.png
New console on AMD 64X2 desktop
24hrs-Temperatureb1.png
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Re: Temperature data spikes revisited

Post by nking » Wed 29 Sep 2010 5:59 pm

Hi Gina, Have you changed the transmitter for the new one?

Gina
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Re: Temperature data spikes revisited

Post by Gina » Wed 29 Sep 2010 9:26 pm

nking wrote:Hi Gina, Have you changed the transmitter for the new one?
Yes.
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Re: Temperature data spikes revisited

Post by nking » Wed 29 Sep 2010 9:59 pm

An obvious question/answer :roll:

Gina
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Re: Temperature data spikes revisited

Post by Gina » Thu 30 Sep 2010 5:45 pm

Now you see them... now you don't :roll:
24hrs-Temperaturec0.png
24hrs-Temperaturec1.png
This is a 48 hour temperature plot - an odd spike, then a burst of them, then none...
48hrs-Temperature.png
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