Precision of EI-1050 Humidity Sensor | LabJack
 

Precision of EI-1050 Humidity Sensor

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JF
jfcaron's picture
Precision of EI-1050 Humidity Sensor

Hi, we bought a U3 and EI-1034 and EI-1050 sensors to monitor temperature and humidity in our lab environment, and maybe also inside out gas vessels.  I wrote a simple python script that logs the time, internal temperature sensor, and measurements from the two external sensors.  The internal temperature is ~25C, while the two sensors are ~21C and ~20.5C pretty consistently.   I can justify the internal sensor being hotter because it is near the electronics, but the two sensors are just sitting right next to each other.  Could the calibration be off by 0.5C out of the box?

I also tried determining the precision of the humidity sensor, but it seems to have a huge range of possible measurement intervals.  I.e. some values are 0.024% apart, while others are only 1e-5% apart.  Since this is a digital readout, I expected the measurement intervals to be fixed.

Can you comment on the observed results?  Or should I contact Sensirion or Electronics Innovation Corp?

LabJack Support
LabJack Support's picture
The specs for the EI-1034

The specs for the EI-1034 come right from the LM34CAZ datasheet:

https://labjack.com/support/datasheets/accessories/ei-1034

+/- 0.4°F Typical Room Temperature

+/- 1°F Max Room Temperature

So 2 different EI-1034 sensors differing by 0.5degC would be right at the edge of the max accuracy spec.  So within spec, but suspicous and I'd be looking at other sources of error.  First comment ... make sure you are using a low voltage channel (resolution about 600uV or 0.06degF) rather than a high voltage channel (resolution about 5000uV or 0.5degF).

As for the EI-1050, the default resolution for RH is 12-bit so I would expect about 0.024% steps.  I ran a test program here and see steps smaller than that ... noticeably steps of 0.0013 and 0.0006 coming up quite often.  I'll mark this for another opinion here but might need Sensirion to chime in on that.

The accuracy of the EI-1050 (SHT11) is 0.5degC at room temp per specs.

LabJack Support
LabJack Support's picture
The reason for the small

The reason for the small changes in RH is that temperature is part of the RH conversion formula.  So we are seeing a case where the RH binary value has not changed at all but a small change in temperature causes a very small change in the resulting %RH value.