Topic: WeatherLink Distorting Indoor Temperature?

[pfletch101]

It has been pointed out here.....using the console, the only way to get temps showing x.o degrees is through the ISS, any other temps ( 6372, 6382, 6345 ) show x degrees.

Except (as I keep saying) if you pick up the data on an Envoy8X console. But you would then need to use the WDTU software and its SQL database to access the data - the standard WL DLL is not compatible.

As I keep saying,  the point is to be able to access the data directly from my own application. Running the WDTU software and accessing a database server just to get data from a $100+ sensor that (the data) should (IMHO) be much more easily and directly accessible is not an acceptable option. However, thanks for making it clear that this would be my only option.

[dalecoy]

Point taken.  Davis doesn't fit your needs.  Perhaps you might let them know that.

When you find a solution, please come back and let us know.  If you have to build something, and make it available for sale, it looks like you will have at least one customer (LABob).

[pfletch101]

The solution I ultimately chose (to supplement the Davis package that I am purchasing for the weather side) was this device: http://www.lascarelectronics.com/temperaturedatalogger.php?datalogger=424. It is not perfect, since it is around the same price as the add-on Davis sensor, and does not have a direct access API, but it can be made to do the job.

The specs of this device are comparable to/slightly better than those of the Davis sensor, and there is a (more expensive, of course!) higher spec version, if you think you need it. There is also a slightly cheaper temperature only version. The 'package' is quite a neat one for visible indoor use, and it is easy to set up and configure. It runs (allegedly for months, at low sample rates) on an internal battery which is recharged when necessary by plugging it in to a regular powered USB port. Setup and configuration are straightforward. To use data from it for your own application, you have to leave its software running and read the data file in which it stores the data, but this is a text file in CSV format, and is not locked between writes, so the necessary code is trivial. To monitor multiple locations, just add more sensors (at full price!) - you only need one instance of the software running.

[dalecoy]

Thanks for posting that.

... internal battery which is recharged when necessary by plugging it in to a regular powered USB port.

Please let us know if the temperature measurement is affected, while the internal battery is being recharged (and/or if connected to a USB port).

[pfletch101]

The manufacturers warn that the temperature measurement may be affected when it is charging (though not if it is just plugged in, once fully charged), but my observations suggest that any effect is minimal. The sensor chip itself seems to be very well ventilated - if you breathe in its direction, you see a short but substantial temperature and (especially) humidity spike on its local display.

[pfletch101]

Having got both my Vantage Pro 2 system and my standalone indoor temperature/humidity sensor set up and talking to my monitoring and control software, I thought that it might be interesting to look at the longer term correlation between them, and to relate it to whether the weather station is connected to a powered up computer. The attached files show the results of a 48 hour study.

The .jpg shows the 'experimental setup'. The weather monitor and the TH sensor are both attached to wood blocks on the side of a bookcase in my office. The block on which the weather monitor is mounted is about 1.5" high, so most of its body is in (relatively) free air. The TH sensor is held slightly away from its block by a plastic holder that cradles it, but leaves a reasonable amount of room for airflow round it. The software recorded the reported temperatures every 5 minutes over a 48-hour period during which neither device nor any of the weather monitor's connections were physically touched. The weather monitor contains batteries and is hooked up to its standard power supply, which is powered when the computer attached to it (via a USB Weatherlink) is running. That computer is on and running from the time I get up (between 6:30 and 7:30 am) until I shut it down for the night (between 10:30 and 11:00 pm). The TH Sensor is powered by a rechargeable internal battery and was not physically connected to anything during the time of the test - it 'reports' by means of an intermittent WiFi connection, and simply stores data if the computer it reports to is shut down. My thermostat is set back substantially at night, heat is generated by the computer during the day, and the last few nights have been unseasonably cold, so the recorded (by both devices) nighttime temperature drop is entirely consistent with reality.

The interesting findings in the context of this thread are shown in the two PDFs, which respectively show Excel graphs of the readings of both devices over time and the difference between them (Weather Station minus TH sensor) over time. It will be seen that (compared to the TH Sensor), the Weather Station reads a bit over a degree (F) high when the computer to which it is connected is powered on and a bit under 0.5 degree (F) low when the computer is powered off. The 'stepping ' of the TH sensor's line is because its software stores its readings in Degrees C, to one decimal place of accuracy.

I have not compared the readings of either device to a reference thermometer, so I don't know which is more accurate under standard conditions, but it looks as if the Weather Station's inside temperature reading increases by something in excess of 1.5 degrees F when its attached Weatherlink is connected to a powered USB port, which is really something that should have been predicted and corrected at the design stage, since it must be a function of sensor placement and component heat generation, and it is well outside the claimed error bounds of the device.

[LABob]

What's interesting to me is that the temperature distortion occurs even when the WeatherLink is not actively reading data. You can just plug in a USB cable attached to a 5V power source and that's enough to raise the temperature of the console's sensor. I've tossed around the idea that maybe the USB bus power is feeding a resistor somewhere in the console or WeatherLink that isn't necessary for reading data and have given consideration to disconnecting the power pins to see what happens.

[dalecoy]

Quite interesting.  And I certainly encourage you to provide this data to Davis. 

I do have one question (a description I'm not sure I understood):

.....The weather monitor contains batteries and is hooked up to its standard power supply, which is powered when the computer attached to it (via a USB Weatherlink) is running. That computer is on and running from the time I get up (between 6:30 and 7:30 am) until I shut it down for the night (between 10:30 and 11:00 pm).

I presume this is about the console, and the AC supply for the console ("its standard power supply"). 

Are you indeed saying that the external power supply for the console is not "powered up" when the computer is off? 

[pfletch101]

Quite interesting. And I certainly encourage you to provide this data to Davis.

What is the most effective way of doing this?

I do have one question (a description I'm not sure I understood):

.....The weather monitor contains batteries and is hooked up to its standard power supply, which is powered when the computer attached to it (via a USB Weatherlink) is running. That computer is on and running from the time I get up (between 6:30 and 7:30 am) until I shut it down for the night (between 10:30 and 11:00 pm).

I presume this is about the console, and the AC supply for the console ("its standard power supply"). 

Are you indeed saying that the external power supply for the console is not "powered up" when the computer is off?

Yes. and yes. The console's power supply is plugged in to the UPS which protects and powers the computer and is powered down when the computer is turned off for the night. The console is then supported by the internal batteries.

[pfletch101]

What's interesting to me is that the temperature distortion occurs even when the WeatherLink is not actively reading data. You can just plug in a USB cable attached to a 5V power source and that's enough to raise the temperature of the console's sensor. I've tossed around the idea that maybe the USB bus power is feeding a resistor somewhere in the console or WeatherLink that isn't necessary for reading data and have given consideration to disconnecting the power pins to see what happens.

I think that it is likely that the Weatherlink is drawing its power from the USB port, so, even if you are right about the heating coming from unnecessary power usage, it would not work if the USB port were unpowered.

[dalecoy]

Quite interesting. And I certainly encourage you to provide this data to Davis.

What is the most effective way of doing this?

I would call Davis tech support, and ask them where you should send this research.

Yes. and yes. The console's power supply is plugged in to the UPS which protects and powers the computer and is powered down when the computer is turned off for the night. The console is then supported by the internal batteries.

...Although I agree with your supposition that it's the USB connection (power to the logger) that is causing the temperature shift, you actually have two connections that are "powered off".  Perhaps for thoroughness you might repeat the test with the console AC power maintained during the night.

[pfletch101]

...Although I agree with your supposition that it's the USB connection (power to the logger) that is causing the temperature shift, you actually have two connections that are "powered off".  Perhaps for thoroughness you might repeat the test with the console AC power maintained during the night.

Your wish is my command!

As we both (I think) assumed, the console power being connected or not does not appear to make any difference to the findings. The attached pdfs show graphs of indicated temperature for the two devices and of the difference between their readings against time over a 24-hour period in which they were untouched and the console was left powered (the console power supply plugged directly into the utility mains rather than into the computer's UPS).

[dalecoy]

Yes, but "experimental verification" beats "assumed" by quite a margin.

[pfletch101]

Yes, but "experimental verification" beats "assumed" by quite a margin.

Agreed! 

[pfletch101]

I have had an email 'conversation' with a tech support person at Davis about this, and got essentially the same response as LaBob: initial concern (plus the statement that they had never encountered this issue before!), followed by denial of the possibility that this was anything but (conceivably) a defect in my specific hardware. Since I don't believe that, and do have a solution which allows me to measure indoor temperature where I want to measure it and monitor it remotely independently of where my console is (or what it says the indoor temperatue is), I am not keen to carry on banging my head against this particular brick wall, but I am very disappointed in Davis.

[pfletch101]

Please let us know if the temperature measurement is affected, while the internal battery is being recharged (and/or if connected to a USB port).

I have now had an opportunity to look into this question a little more carefully (since the TH device's battery life is at least as good as the manufacturer claims, it doesn't need charging very often!). It appears, at an ambient temperature of 24 degrees C, that the temperature measured and reported by the device increases by 0.3 degrees C when its battery is down to approximately 30% of full charge and it is plugged in to a USB charger port to recharge. The differential then drops as the device charges (presumably as the charging current drops off), so that when it attains full charge (after 36-48 hours) and stops charging there is no perceptible drop in measured/indicated temperature. Without a collocated and at least equally accurate independent temperature recording device, which I haven't got, it is not possible to determine the exact time course of the temperature differential while it is charging.

The bottom line, however, is that any measurement error caused by resistive heating from charging current is well within this device's overall accuracy specifications. Would that Davis could (truthfully!) claim something similar about their consoles and errors cause by backlights and WeatherLink units.!