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### Topic: HoneyWell HIH-4000-001 Humidity Sensor Temp compensation (Read 2876 times)previous topic - next topic

#### carpenterbee

##### Sep 13, 2012, 08:01 am
While playing with my new HIH-4000-001 Humidity sensor, I'm trying to make sense of the temperature compensation that comes in the sensor documentation.

It lists;
********************************************************************************************************************
Temperature Compensation        True RH = Sensor RH/(1.0305+0.000044T-0.0000011T²)T in C
(True RH = Sensor RH/(0.9237-0.0041T+0.000040T²) T in C)
**********************************************************************************************************************
There is no equals sign between the words Temperature Compensation and the following two lines.
There is no line between the second two lines so I don't believe division is indicated.  I'm just wondering
what this is.  I'm rather mystified.  I'd post this in the math section but I didn't find one.  LOL Knew I should have paid more attention to math in school.

Is this two different ways to get the value? The sensor is pretty close in comparison to the inside humidity of my Oregon Scientific (OS) weather station whose calibration is also unknown.  LOL  OS reads 40RH and the sensor 4 inches away reads 46RH.

To get the sensor RH I'm reading it with a UNO analog pin, dividing the reading by 1023 and multiplying by 100.
Since the sensor is ratiometric to Vcc from 4 volts to 5.8 volts, I'm assuming this is a valid method with a 10 bit ADC.
My Vcc is exactly 5.002 Vdc. I'm using the default analog reference on the UNO.

I did a search on this forum and found two mentions of the HIH-4000-001 but neither mentioned compensation. Well at least I don't think so.  The second thread was in French and I'm 40 years out of High School French class.  LOL

Thanks;
Walt
Walt
North Carolina

#### Chagrin

#1
##### Sep 13, 2012, 10:11 am
That doesn't make sense at all. Adding to the non-sensicalness, take a look at http://sensing.honeywell.com/index.cfm?ci_id=140301&la_id=1&pr_id=145588 which states that the compensation is "True RH = (Sensor RH)/(1.0546 - 0.00216T), T in oC"

Between -10C and 42C, the first formula varies by .0006, the second by .146, and the other by .11.

I'd suggest contacting Honeywell for an explanation.

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