Sensirion SHT11 temperature calibration

jreeve

Hello All. I'm using the Sensirion SHT11 temp/humidity sensor with a BOE and have a question about the calibration of the temperature. I've noticed that out of the box the sensor gives temperatures about 2 C higher than the temperature from a digital thermometer positioned right next to the sensor. Is it "normal" for the sensor to be this far off?

I've been correcting the readings by applying a little tweak to the supplied code, changing the amount that is subtracted off in the calculation below. The original version subtracts 400, rather than 418 for C or 430 for F. This does work at room temperature, but would it also work across a range of temperatures? Thanks for any help.

By the way, the SHT11 is mounted in a socket on a carrier board about six inches away from the BOE, to avoid the heat from the BOE.

Cheers, John R.

' Note: Conversion factors are multiplied by 10 to return the
' temperature values in tenths of degrees
tC = soT ** $1999 - 418 ' convert to tenths C
tF = soT ** $2E14 - 430 ' convert to tenths F

Franklin

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- Stephen

RDL2004

It could be that your digital thermometer is off. Measuring temperature is tricky, one or two degrees is not much at all. Unless you have a calibrated NIST traceable thermometer, it's hard to know where the error really is.

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- Rick

pwillard

These sensors are supposed to be "hard" calibrated at the factory. I agree that it might be your thermometer is off. I once had to calibrate a themocouple and used a bowl of icewater to determine where "32" should be. Have you done that with your thermometer?

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There's nothing like a new idea and a warm soldering iron.

stephenwagner

What are you using to power the temp sensor???

If you are using a stamp pin, HIGH pin, 1, you will have errors.

The sensor needs a good +5VDC or better.

I had the same issues. Once I powered it with +5VDC, the issues resolved.

The SHT11 is spot on as specified.

SJW

jreeve

Thanks for all the comments. I'm powering the sensor from Vdd on the BOE, so the power supply should be okay. I'll try calibrating it against some low vs. high temperatures. We're getting both on the same day in my neck of the woods. Thanks, John R.

RDL2004

Note that the margin of error of temperature measurement with the Sensirion devices gets pretty large as you move away from "room temperature". Their humidity accuracy is much better.

edit:

http://www.sensirion.com/en/pdf/product_information/Data_Sheet_humidity_sensor_SHT1x_SHT7x_E.pdf

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- Rick

Post Edited (RDL2004) : 9/13/2007 2:39:12 PM GMT

Chris Savage

The Duplicate Post was removed (again).

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Chris Savage
Parallax Tech Support