Humidity accuracy

[Rbuk]

I put four 13 bit tags together in the same room so that I could calibrate them. I used a Flir thermal imaging camera to measure the temperature (22ºC) and calibrated them using the web interface. Now two are showing RH of 64%, one indicates 65% and one 66%. The room is controlled by a Mitsubishi dehumidifier that's indicating 60%.

Is there a way of calibrating the RH measurement?

Thanks

[Zhiheng Cao]

The humidity sensor is rated at +/-1% accuracy without need for calibration. The 64, 65%, 66%  results seem to be consistent with the 1% error rating. The question is what is the error rating of your Mitsubishi dehumidifier?

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[mda]

My 13 bit tag shows 57% humidity when sitting right next to my Nest thermostat which show 42%

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[Zhiheng Cao]

Does Nest's humidity sensor allow you to calibrate it?

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[Rbuk]

Thanks for confirming the spec of the tag but you didn't really answer my question. I have a winter's worth of confidence invested in the Mitsubishi dehumidifier and I know that when it indicates 60% I don't have condensation in my home. I would like to calibrate my tags to indicate humidity relative to the dehumidifier so that I can judge whether I should move the unit to a different room and then monitor the effects of that change.

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[mda]

The nest does not have calibration for humidity (as best I can tell)

[mda]

I brought all 7 of my 13 bit tags together and put them next to my Nest (about 1 foot away).

The tags show humidity of: 57%, 56%, 56%, 58%, 55%, 57%, 58% (all are set to 1 minute auto-update and have updated within the last minute)

For comparison, the Nest shows 50% humidity (has been stable for the last few hours).

[mda]

As another test, I turned on the AC to bring down the humidity, and the Nest now reads 46% humidity. 

My tags (all updated in the last minute) now read: 54%, 54%, 54%, 56%, 53%, 55%, 55%

It would be nice if we could calibrate humidity. Thanks.

[Zhiheng Cao]

Thanks for the suggestions; we will add the humidity calibration in the next 2.1.12 app release. 

The difference between nest and tag humidity reading can be caused by the time constant in responding to humidity change, and the fact that the sensor in tag is enclosed in plastic casing with 16 small holes.  The relative humidity movement should all match up with a constant offset. 

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[mda]

Thanks!

[Zhiheng Cao]

You can calibrate humidity (RH%) using the Web interface now.

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[mda]

Thanks !

[mytaglist.com support]

The digital humidity sensor we use is this one: 

https://www.sparkfun.com/products/12064

See the user comments about its accuracy. The datasheet specifies the humidity error: http://www.meas-spec.com/downloads/HTU21D.pdf

It is manufactured by Humirel (http://www.meas-spec.com/humirel.aspx) in France. Humirel is founded in 1998 just for the purpose of designing humidity and temperature sensing ICs (http://investing.businessweek.com/research/stocks/private/snapshot.asp?privcapId=124857). It is the first company to release digital humidity sensor, their product is so widely used, that other companies sells compatible chips such as Si702x from SiliconLabs (http://www.silabs.com/products/sensors/humidity-sensors/Pages/default.aspx) that follow not only same footprint but also exactly same I2C address and protocol.

On Wednesday, June 11, 2014 9:52:57 PM UTC-7, mda wrote:

Thanks !

[mda]

i am unable to calibrate most of my 13 bit tags. When i set the humidity then click calibrate then click save it shows the correct humidity. Then as soon as i ping the tag it shows the wrong humidity (10-20 % higher than calibration point). I have tried dozens of times. A couple of the tags calibrate fine, then rest behave like this. What can i do to get them calibrated? Thanks.

[mytaglist.com support]

I could not reproduce this. If I calibrate the humidity to some value, it will stay there after "refresh" or "ping". Did you do anything special?

[mda]

Nope, just dragged the slider, clicked Calibrate, clicked Save, then clicked ping. Odd.

[Zhiheng Cao]

This apparently was because you already applied calibration to this tag before. This bug has been fixed and now you can apply calibration as many times as you need. 

On Sun, Jun 22, 2014 at 11:52 AM, mda <michael...@gmail.com> wrote:

Nope, just dragged the slider, clicked Calibrate, clicked Save, then clicked ping. Odd.

[mda]

thanks !

On Sunday, June 22, 2014 10:35:00 PM UTC-7, mytaglist.com support wrote:

This apparently was because you already applied calibration to this tag before. This bug has been fixed and now you can apply calibration as many times as you need. 

On Sun, Jun 22, 2014 at 11:52 AM, mda <michael...@gmail.com> wrote:

Nope, just dragged the slider, clicked Calibrate, clicked Save, then clicked ping. Odd.

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