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Subject: Re: Humidity sensor - peculiar behavior
References: <email@example.com> <firstname.lastname@example.org> <email@example.com>
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Date: Sat, 11 Jan 2003 16:38:34 -0500
NNTP-Posting-Date: Sat, 11 Jan 2003 16:38:36 EST
Organization: Bell Sympatico
Yes. I had a Bionaire humidity and temperature sensor that was exposed
to a high percentage of humidity (my breath) and never recovered.
I don't know how accurate they are but the matching between 3 units
was within 2%. . Price was $20.00 US
On Sat, 11 Jan 2003 18:50:34 GMT, Marc_F_Hult
>On Sat, 11 Jan 2003 14:53:40 GMT, Marc_F_Hult
>wrote in message :
>>If the effects you measure ( up to 40% change) are due to temperature
>>in the air caused by heat dissipated by electronics as you postulate, the
>>sensor is badly out of spec. See the last graph on the spec sheet.
>>Note that Honeywell suggests a way to measure air at near 100% relative
>>humidity (which is difficult to do) by locally reducing the RH to about 90%.
>>This involves setting the sensor on top of a 120W resistor. Nuff said.
>>I have a bunch of HIH-3610 including several that have never been out of
>>factory sealed packaging. Send me your snail-mail and I'll loan you a couple
>>to test/examine. I paid about $18 each when they first began shipping from
>>the Mexico factory so these are from early production. Dunno who might be
>>charging the $40 you paid. If you decide that you need to replace yours, you
>>can have one for what I paid.
>>Other technical information of interest including humidity equations,
>>constants, and concepts:
>>Curious that none of the responders mentioned reading the product
>>FWIW, I typically mount the HIH-3610 (and Panasonic PNA4603H for light and
>>thermistor/LM34 for temperature ) on one side of a small pcb and a quad op
>>amp and voltage references/regulators on the other side. This [facilitates]
>>mounting the pcb in a case with the sensors in appropriate position with
>>respect to case openings and would isolate the HIH-3610 from the thermal
>>effects you postulate.
>>I drive a HIH-3610 from a LM4040 voltage ref buffered by one section of a
>>LM324. The three outputs (humidity, light, and temperature) are buffered by
>>the other three LM324 sections. Fancy-antsy op amps aren't needed at room
>>temperature to get adequate 0-5vdc (or 0-10vdc) signals . CAT-5 wire has
>>twisted pairs for the 13.8vdc supply (from a sealed lead battery with a
>>"float" regulator/supply) and the three DC signals. You can gild the lily by
>>regulating the 13.8 vdc at the pcb with a 12vdc Low Drop Out TO-92 package
>>regulator. Sprinkle with capacitors "to taste".
>>HTH ... Marc
>I should add that the HIH-3610 does not take kindly to being subjected to
>100% (condensing)RH. IIRC, Honeywell recommends drying the sensor out for 10
>hours at <10 RH. The sensor may not recover completely, but should recover to
>within 3% or so. If you started your calibration with 100% humidity, this may
>be part or all of your problems.
>HTH ... Marc
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