On 17 May 2012, at 18:27 , vasile surducan wrote:
AFIK SHT75 does not need any temperature compensation, as long the
self heating and by purpose heating (with internal resistor) is
avoided. But I'm not using the computational algorithm from the
library for RHT display so maybe Eur can answer better to you.
I don't do temperature compensation of the humidity signal. I do
apply a correction -as mentioned in the datasheet- of both the
humidity and the temperature signal. The coefficients of these
corrections are the same for SHT1x and SHT7x.
Sensirion makes just a single humidity sensor. They test these
sensors in an automated setup. They classify the sensors according to
accuracy and repeatability and sell the accurate sensors for a higher
price. The hardware is the same for all models.
Intel does the same for microprocessors. They increase the clockspeed
in an automated test until the processor fails and then sell it for a
"rated" clockspeed that is, say 20% lower.
http://en.wikipedia.org/wiki/Clock_rate
This is common in semiconductor fabrication.
The coefficients *have* changed since 2002. It seems that the old
ones are in the code, but I'm reluctant to apply a quick fix. I will
test with new hardware and put in new coefficients, but that will
take a while. If anybody has new hardware lying around and means to
calibrate, you are welcome to mess with my code. Please comment out
the old calculation lines.
Calibration works well over saturated salt solutions:
http://www.smartec.nl/pdf/apphs1002.pdf
i.e. NaCl, a common household chemical, gives 75.3% RH.
On Thu, May 17, 2012 at 3:02 PM, jfmateos
<[email protected]> wrote:
This library uses the v3 coefficients for temperature compensation on
read relative humidity, but the most recent version of SHT11 is v4 an
requires different coefficients.
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