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Weather Station Hardware => Oregon Scientific Hardware => Topic started by: Tottemannen on December 13, 2010, 07:16:45 AM
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Hi!
The thermo/hygro sensor does not work correctly (weather station wmr100n). When the temperature goes under about minus 12 degree Celsius, the humidity stay constant for example 85%, and will not change until the temperature is warmer than minus 12 degree. Anyone got a clue what the problem is?
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I have the same problem with the same system that I just received for Christmas except mine does it at exactly 10c. I sent emails to OS and they were not much help except to offer an RMA, which I have not done yet.
-BA
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I had almost the same prob.
Both Temp and Hum were fixed. Ended up replacing my THGN801 sensor. Got the new one yesterday and it works fine. It seems that when the sensors die the values reported are fixed at the last value (at least as reported into Weather Display). Values on the OS WMR200 went to '---'.
I've had my system for about 18 months....not very impressed with the reliability of these OS systems.
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Greencat,
Missed this while I was on vacation. Dont do an RMA, while its nice to see they are offering a replacement, they are not very knowledgeable about their own product. Surprise surprise.
OS sensors (wmr968 and compatible) will not report humidity changes once the temp drops below -10C (14F). I have seen this on my thgr968 (stock channel Zero sensor), and 'extra' sensors such as thgr268, the radio shack version of thgr268, and the THGN123N (this is the quote Ultra cold end-quote weather version... #-o ).
I assume this same bug occurs on the 100/200 sensors as well but at about minus 12 degree Celsius
Not sure why they built-in this feature.... but its there.
Andrew
I have the same problem with the same system that I just received for Christmas except mine does it at exactly 10c. I sent emails to OS and they were not much help except to offer an RMA, which I have not done yet.
-BA
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Minglegs,
Different problem, not the same as the -10/-?? humidity bug, you are losing communication with your sensors. WD and VWS will flatline at last reported value if comms are lost, while the console shows --- when this happens.
Andrew
I had almost the same prob.
Both Temp and Hum were fixed. Ended up replacing my THGN801 sensor. Got the new one yesterday and it works fine. It seems that when the sensors die the values reported are fixed at the last value (at least as reported into Weather Display). Values on the OS WMR200 went to '---'.
I've had my system for about 18 months....not very impressed with the reliability of these OS systems.
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mackbig,
You were right. They finally agreed to send me a new THGN801, which I thought was very good customer service. However, it behaves exactly like the original, it does not report humidity changes below -10C. At least I have a spare now.
-BA
Greencat,
Missed this while I was on vacation. Dont do an RMA, while its nice to see they are offering a replacement, they are not very knowledgeable about their own product. Surprise surprise.
OS sensors (wmr968 and compatible) will not report humidity changes once the temp drops below -10C (14F). I have seen this on my thgr968 (stock channel Zero sensor), and 'extra' sensors such as thgr268, the radio shack version of thgr268, and the THGN123N (this is the quote Ultra cold end-quote weather version... #-o ).
I assume this same bug occurs on the 100/200 sensors as well but at about minus 12 degree Celsius
Not sure why they built-in this feature.... but its there.
Andrew
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I have a THGN123N ultra-cold wireless sensor in my freezer, which is around -20C. I use it to monitor the temperature but never paid much attention to the RH. I looked at the RH data just now and it only ever reports 60% or 85% RH and never anything in between. I'd be willing to bet this is a technical limitation of the type of sensor (resistive) that OS uses to measure RH.
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It will report other values, but whatever the value happens to be when it hits -10 is what it will show till it goes back above. Perhaps you have only thawed your thermo twice since putting it in deep freeze.
I looked at my 2010 data, I have 975 reporting intervals below -10. 24 different values between 42 and 79%
I believe the sensor works fine, they just chose not to xmit the numbers after -10 for some reason. You can see this when it comes out of a -10 period. It will be 42% at -9.9 dry air flash freeze or something hit minus 10 or colder overnight... then in the morning it will warm up and be at 71% when it cross back into above -9.9. These values track pretty good to the vp2 and other nearby stations.
That's why I dont understand, it works but they chose to make it not work.
Andrew
I have a THGN123N ultra-cold wireless sensor in my freezer, which is around -20C. I use it to monitor the temperature but never paid much attention to the RH. I looked at the RH data just now and it only ever reports 60% or 85% RH and never anything in between. I'd be willing to bet this is a technical limitation of the type of sensor (resistive) that OS uses to measure RH.
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It would be interesting technically (at least to me) to see if OS uses a similar t/h sensor chip a lot of other manufacturers use, including Davis, to figure out where the -10 cutoff is coming from. These sensor chips are spec'd to -40F/C. http://www.sensirion.com/en/01_humidity_sensors/01_humidity_sensor_sht10.htm
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I'll try moving it into the fridge and watch when the RH starts changing.
Regarding sensors used by OS and Davis:
OS uses a humidity sensor which has several interleaved metallic fingers on a ceramic substrate. They measure the AC resistance between the metal fingers and use a look-up table or some curve fits to convert the resistance reading to humidity. Unfortunately, temperature also has a big effect on the resistance, so they must factor that in too.
The lower the humidity, the higher the resistance. The colder it is at a given humidity level, the higher the resistance. Once the resistance gets too high, an inexpensive unit like OS sells cannot accurately measure resistance any more. The bottom line is that these sensors work great at medium and high humidities but fall apart when it gets really cold and/or really dry.
Perhaps this is why OS chose to stop reading humidity at low temps. For example, I looked on the data sheet for one sensor, the Ghitron HCZ-D5 (just an example, I have no reason to think this is the one OS uses). It does not give data to convert the resistance reading to humidity below a temperature of 5C.
Don't quote me on this, but I believe the Davis units use capacitive humidity sensors, and these have the opposite problem -- they work quite well at low humidity but not as well when the humidity soars.
Seems to me the ideal setup would use two sensors -- a resistive one for high humidity and a capacitive unit for when things get dry and/or cold.
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Davis, LaCrosse, and not sure who else currently use Sensirion Co. type sensors (http://i588.photobucket.com/albums/ss324/DanS_photo_09/DavisTempChip.jpg)
Older systems (and from what you say, OS still uses) use the resistive "finger" type you mention (http://i588.photobucket.com/albums/ss324/DanS_photo_09/humiditysensor-1.jpg) .
My older ws-2310 still uses the resistive type to measure humidity but the coating substance changed properties and became inaccurate. I found that substances that contain Polyethylene glycol (PEG) work great in restoring this.
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My older ws-2310 still uses the resistive type to measure humidity but the coating substance changed properties and became inaccurate. I found that substances that contain Polyethylene glycol (PEG) work great in restoring this.
I was going to mention Dipity Do, but Dan is much better at explaining it. =D>