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Honeywell HIH-5030 Humidity Sensor


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#1 jhenise

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Posted 16 June 2013 - 09:23 AM

Hello All,

I am a scientist by trade (chemist) so I am not a stranger to quantative reasoning, thermodynamics, and physics.

However when it comes to electronics I am a hack! Maybe you can help me understand some things!!

I have hooked up a Honeywell HIH-5030 humidity sensor to my LabJack U6:
http://sensing.honey...ument/1/re_id/0

It is s sensor that takes a DC supply voltage and outputs a voltage linearly with humidity.

I hooked the supply pins to GND and VS, and Vout directly to AIN0.
I am using DAQ Factory to acquire and manage the data.

The equation for converting voltage to relative humidity (RH) is:

((Vout/VS)-0.1515)/0.00636 = (RH )

and with temperature compensation (T = oC):

(((Vout/VS)-0.1515)/0.00636) / (1.0546-0.00216*T) = (RH )

I seem to get good results like this.

However I see diagrams where there resistors and capacitors hooded up with the sensor like this for example:

http://test.tag4m.co...3/hih-50302.jpg

Can someone please explain what the resistors and capacitors are for in the above circuit?

Thanks!!
JEFF

#2 LabJack Support

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Posted 17 June 2013 - 09:28 AM

The cap from VDD to ground is called a de-coupling capacitor. If the chip needs a sudden surge of current, this capacitor can provide it and helps to prevent a quick dip in the supply voltage. Such caps are routinely used with just about any integrated circuit, and it certainly does not hurt, but the VS terminals do have a lot of capacitance in the U6 so you likely do not need this. The 2 resistors on the output appear to be a voltage divider. I'm not sure what 3K3 is? Perhaps it is supposed to be 20k and 33k? If so that would divide the output by about 1.6. You don't need to divide the output for the U6. I see that the output is proportional to Vsupply, so you want to make sure you are using another AIN to measure Vsupply and use that real-time value in your equations, rather than assuming a constant 5.0V.

#3 jhenise

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Posted 19 June 2013 - 10:19 AM

Awesome! thanks for the reply!
This all makes sense now..

Yes I am using and analog input to measure VS, that is what provides the value of VS in the equation above.

I posted a little video about this project:



#4 LabJack Support

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Posted 19 June 2013 - 01:56 PM

Awesome! thanks for the reply!
This all makes sense now..

Yes I am using and analog input to measure VS, that is what provides the value of VS in the equation above.

I posted a little video about this project:


That is a pretty clean setup you have. Most of our prototyping projects end up as a messy collection of wires spread out over a table. The logging from DAQFactory is really nice as well. All the relevant info is right there. It looks like a promising project.


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