Accuracy SHT11 sensor in high humidity
Shiva
Posts: 5
Hi,
I've connected the SHT-11 sensirion sensor to my Basic 2p40 stamp and ran the demo program·SHT11_Demo.BS2. This program can be found here:
http://www.cotc.edu/rromei/Temp%20Humd%20Kit%20Documentation.pdf
The values of the sensors were ok, I ran the demo program in a room with a humidity of about 40%.
Next I decided to put the sensor in a high humidity terrarium. Now I·get values of about 115%.. That's at least 15% too much!
What could be wrong? I must say, I had·to connect wires of about 2 feet long to the sensor. IMO that's shouldn't matter. There are no shortcuts and·there are no visible droplets on the sensor.
Does this sensor actually work in high humidity chambers? Do I need another formula or what?
Please share your thoughts and idea's!
I've connected the SHT-11 sensirion sensor to my Basic 2p40 stamp and ran the demo program·SHT11_Demo.BS2. This program can be found here:
http://www.cotc.edu/rromei/Temp%20Humd%20Kit%20Documentation.pdf
The values of the sensors were ok, I ran the demo program in a room with a humidity of about 40%.
Next I decided to put the sensor in a high humidity terrarium. Now I·get values of about 115%.. That's at least 15% too much!
What could be wrong? I must say, I had·to connect wires of about 2 feet long to the sensor. IMO that's shouldn't matter. There are no shortcuts and·there are no visible droplets on the sensor.
Does this sensor actually work in high humidity chambers? Do I need another formula or what?
Please share your thoughts and idea's!
Comments
Relative Humidity is not easy to measure !!
A thing that could have happened in your case is that the temperature in your terrarium was higher than the temperature of your sensor. In that situation water can condensate on your sensor. This COULD be an explanation for your 115% reading.
An other simple explanation could be that your sensor is not properly calibrated. In such a case I use a piece of damp cloth which I put over the sensor without really touching it !!. With a little patience I then find the 100% point.
But first I would recommend to experiment a little more with the SHT-11 to get familiar with the readings and the behaviour (time to settle, the effect of temperature and moving air, things like that) .
Regards,
Klaus
soT and soRH, and the final temperature and humidity, TC and rhTrue.
Could you write down a couple of sets of those numbers and let us see them? That would help to decide if there is something amiss in the simplified calculation, as opposed to something wrong with the sensor.
I have used these in situations where the humidity periodically become high, in environmental monitoring with a diurnal cycles.
One situation where they did not work out, though, was in a concrete curing chamber, where water was continuously being sprayed, so it was constantly 100%. The goal was to detect interruptions in the curing procedures for product qualification. The sensors drifted to high readings, over 100%. I am not sure what caused that though. There may have been direct water spray and there may even have been lime residues, which would be really bad. The folks at Sensirion grant that constant exposure to condensing environments will cause the sensor to drift up, and then it takes a thorough drying cycle to recondition it.
I'd like to hear what you find out in the terrarium environment. I'd like to think that it is not so harsh.
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Tracy Allen
www.emesystems.com
I have yet to get the sensiron temp/humid sensor (probalby next week!!)....so I can't say much about the calibration of the sensor.· or how it works.
Anyhow, I work for environment Canada and look after some of their sensors.
The way we check the calibration of our relative humidity measurement is to use a 'sling psychrometer'....or if you don't have one...then 2 separate thermometers.
We use the one thermometer to measure 'dry' temps and we attach a "muslin" sleave to the other one and soak it in water nad let it climatize for 5-10minutes or so.· Depending on the environment (really dry or really) wet, we might leave it less or long to settle.
Since I'm in Canada, and have to check the calibration in the winter, we can't use the muslin sleave.· So we create an ice bulb....can explain this another time.
Anyhow, the muslin sleave is basically a bit of 'cheesecloth-like' material.·
So, with these 2 temp readings (wet & dry), we use a table to determine the relative humidity.· We also need to know the height above sea level too.
There is an equation out there....but why reinvent the wheel eh!!
Anyhow, I'll attach the html page I use when in the field.
Note....this IS canada...and the temps ARE in Celsius!· So get your calculators out if you want Farenheit!
Was curious....how long did your sensor display an RH of over 100%?· We encounter this when moisture gets on our sensor or after we've reinstalled it....takes time to pull back in to the right spot...but initially it is wrong!
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Steve
http://members.rogers.com/steve.brady
http://www.geocities.com/paulsopenstage
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."