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jesawyers
01-21-2006, 04:44 AM
Hello All,

I'm working with a SHT11 Sensor Module and a BS2P40 on the P40 Demo Board.· I'm reading a temperature from the SHT11, but it has an offset (high) of about 8-9 degF from the acutal room temperature.· I'm using my wife's digital meat thermometer·http://forums.parallax.com/images/smilies/shocked.gif to verify the actual temperature along with one of those digital clocks that show indoor temperature and they both agree that the SHT11 is high by 8-9 degF.

So my first guess was that the internal heater for the SHT11 is on, so I loaded the advanced SHT11 demo software·and executed the·Heater_Off subroutine in the "Initialize" section.··· This made no difference.

So does anybody have any ideas or seen this before?

John

Jon Williams
01-21-2006, 05:01 AM
Getting from raw counts to temperature is a bit tricky with the SHT11, but in my experiments I only ever saw it off by a couple degrees.· Dr. Tracy Allen has done a lot of work with this sensor, you might have a look at his page.

http://www.emesystems.com/OL2sht1x.htm

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Jon Williams
Applications Engineer, Parallax

musk
01-21-2006, 10:53 PM
Just a note that the Sensirion data sheet reflects temp accuracy of +/- 0.4 deg C at 25deg C for this device.




"Single chip sensor module, fully calibrated with digital 2-wire output. 0-100%, -40 to 120°C, fully immersible, accuracy +/- 3%RH, +/- 0.4°C @ 25°C, response time humidity sensor 4s"


http://www.sensirion.com/en/02_sensors/00_products.htm?cat=3&category=humidity%20sensors

steve_b
01-22-2006, 12:21 AM
that's its accuracy at that temp....I've seen some sensors with a HUGE curve on them....not linear at all!
Check the data sheets and see if they have a temp calibration curve chart....

Even those old mercury thermometers (and alcohol ones) have curves to them.

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·

Steve

"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."

musk
01-22-2006, 01:19 AM
Not to belabor the point but, the datasheet reflects· "~" ·+/-1 degC accuracy for the range 0 to 40 deg C (32 to 104 deg F) for this device.