Sensebender Micro
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@tbowmo Good hint. But it is happening to all three sensbeners for at least one month now. (different orders). I now got 4 more so I will test again soon.
Over xmas I tested also with magnesium chloride hexahydrate. magnesium chloride hexahydrate produces exactly 33%rel.
All 3 sensbenders report exactly 39% or 40%. So they are also here 7% off. But almost the same value and very reproducible - so thats great!
@tbowmo I'm now almost sure that my test-setup has no faults very reproducable and read many articles - I plan to verify my findings with someone who has a professional calibrated device.
I saw in a museum nearby that they have professional calibrated devices :-)
So I will test against those :-)
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Have you tried to "bake" your sensebenders, in case they have been exposed to high humidity for a longer time?
They are, as far as I know, produced in a part of China, which are known to have very high humidity. (been traveling there a lot some years ago)
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@nivoc
I can confirm your results: I am running two different sensors in the same room next to each other. The sensebender is always above the dht-22. Right now it is
52% to 47.8% rel. humidity, while the temperature is 17.8 to 17.9 (which is nearly equal). -
But I tested tonight with distilled water - so should be exactly 100%. And again (I didn't know that thats possible) I got 104 and 107% so slightly above (still increasing). Thats great b/c that means all values are about 7-8% too high.
At 33% the reading was about 40%
At 75% the reading was about 83%
At 100% the reading was about 106%So reading minus 8% gives a pretty accurate result. In the next few days i will test 3 more sensbender.
Distilled Water (100% expected):
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Read the spec for the humidity sensor used in the sensebender (Si7021 integrated humidity / temperature sensor.)
Precision Relative Humidity Sensor: ± 3% RH (max), 0–80% RH
To my reading this is actually 6% wrong reading to one of the sides - so when you are measuring yours to be 8% off, is caused that you are using the device outside of humidity range 100% and max is 80%Link to spec:
https://www.silabs.com/Support Documents/TechnicalDocs/Si7021-A20.pdfWhat I want you to know, if your device is reading within 6 % of the value - it's still reading correct. and when you compare ex DHT22 that device also have some reading variation error. Do not expect to get 100% perfect value for 2 devices...
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@bjacobse Yes and no :-)
Yes 100% is outside of the spec.
And no. 33% with Magnesium Chloride Hexahydrate is inside the spec and I get 40% instead of 33-34%.
Max off should be 3% above or? Means 37% - but fair enough. Should be ok for household use.
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@bjacobse Yes and no :-)
Yes 100% is outside of the spec.
And no. 33% with Magnesium Chloride Hexahydrate is inside the spec and I get 40% instead of 33-34%.
Max off should be 3% above or? Means 37% - but fair enough. Should be ok for household use.
@nivoc said:
@bjacobse Yes and no :-)
Yes 100% is outside of the spec.
And no. 33% with Magnesium Chloride Hexahydrate is inside the spec and I get 40% instead of 33-34%.
Max off should be 3% above or? Means 37% - but fair enough. Should be ok for household use.
I hope the Temp measurements are not off by that much.
i don't need .00001 accuracy or anything. but i feel a big difference between 70 and 72 in my house. -
@nivoc said:
@bjacobse Yes and no :-)
Yes 100% is outside of the spec.
And no. 33% with Magnesium Chloride Hexahydrate is inside the spec and I get 40% instead of 33-34%.
Max off should be 3% above or? Means 37% - but fair enough. Should be ok for household use.
I hope the Temp measurements are not off by that much.
i don't need .00001 accuracy or anything. but i feel a big difference between 70 and 72 in my house. -
@bjacobse Yes and no :-)
Yes 100% is outside of the spec.
And no. 33% with Magnesium Chloride Hexahydrate is inside the spec and I get 40% instead of 33-34%.
Max off should be 3% above or? Means 37% - but fair enough. Should be ok for household use.
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@nivoc
Yes you are right, +-3 from your humidity solution on 33%, then the reading could be in the interval 33-3=30% or up to 33+3=36% and should not show 40%did you get same false readings from other sensebender humidity sensors?
@bjacobse Yes I have 3 sensbener running from 2 different orders. All 3 are very near by each other. So at 33% they all read something near to 40%.
I have 4 more sensbenders to build. However I continue to test tonight with a Boveda-Pack that claims to bring the hum in a containter to exactly 69%. I did 4 test's so far and also used different technics. So i get more and more confident.
But the very good thing is - it looks every reproducible. So the value may be off but reproducable accurate off by about 8%. When I completed my test it will be very easy to correct it within the software.
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@nivoc said:
@bjacobse Yes and no :-)
Yes 100% is outside of the spec.
And no. 33% with Magnesium Chloride Hexahydrate is inside the spec and I get 40% instead of 33-34%.
Max off should be 3% above or? Means 37% - but fair enough. Should be ok for household use.
I hope the Temp measurements are not off by that much.
i don't need .00001 accuracy or anything. but i feel a big difference between 70 and 72 in my house. -
there are some measurements in the old design thread here http://forum.mysensors.org/topic/510/minimal-design-thoughts
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Got it from http://cpc.farnell.com/1/1/57932-evatron-pp42m-case-sensor-ivory-71x71x27mm.html.
Not the cheapest, but definitely worth the money as it is very good quality. There are other colours available (white and black) https://www.jprelec.co.uk/store.asp/c=552/Gas-Sensor-Case -
@tbowmo: I have some of these too, it's nice box. i got these from tme. cheaper :)
http://www.tme.eu/fr/details/box-sens-white/boitiers-dappar-dalarme-et-de-capt/supertronic/
