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Date: | Fri, 8 Mar 2013 14:21:37 -0500 |
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Bob K,
Just caught up on e-mail (well, not completely - who can (even with Dew in an IV?).
Here's a very complete article on humidity measurement
http://archives.sensorsmag.com/articles/0997/humidity/main.shtml
Chilled mirror gygrometers are the most accurate commercial instruments to use
http://www.ge-mcs.com/en/moisture-and-humidity/chilled-mirror-hygrometers/optica-chilled-mirror-hygrometer.html
Controlling RH is very difficult to do. I messed around with the subject many years ago for environmental testing for an Air Force contract.
Bob Landman
H&L Instruments
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Friday, March 08, 2013 1:33 PM
To: [log in to unmask]
Subject: Re: [TN] Humidity Measurements: Relative or Absolute
Bob,
You are correct. I was partially asleep. Where is Dewey when you need him to say that 'everything is relative'?
Going to be pretty tough to measure absolute humidity in a quick and easy manner.
One item I found suggested avoiding the term "absolute humidity".
Steve C
-----Original Message-----
From: Robert Kondner [mailto:[log in to unmask]]
Sent: Friday, March 08, 2013 12:37 PM
To: 'TechNet E-Mail Forum'; 'Steven Creswick'
Subject: RE: [TN] Humidity Measurements: Relative or Absolute
Steve,
Relative Humidity: http://en.wikipedia.org/wiki/Relative_humidity
http://www.youtube.com/watch?v=CL5cgXwKUXc
If the absolute humidity is high (even 30%) but the temperature is also high, I think the humidity indicators will show low humidity exposure.
I think that relative humidity is crucial to component water absorption or drying.
But I wonder if package cracking doing to expansion of gases entrapped in the package material (plastic) is a function of the absolute vapor content in that material.
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Creswick
Sent: Friday, March 08, 2013 11:35 AM
To: [log in to unmask]
Subject: Re: [TN] Humidity Measurements: Relative or Absolute
Bob,
I have always considered them to be absolute. If relative - relative to what?
Do the cardboard indicators provide a temp range for which they are valid?
Steve C
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Friday, March 08, 2013 11:24 AM
To: [log in to unmask]
Subject: [TN] Humidity Measurements: Relative or Absolute
Hi,
As I start looking at humidity measurement devices I started to wonder if IPC humidity numbers are Relative or Absolute? Does anyone know off hand. I need to go buy some specs.
I would have thought Absolute but the cardboard indicators are temperature sensitive as are the desiccant drying systems in dry cabinets.
If the temperature is high, say > 100C then a part will "Bake Out"
regardless of the absolut humidity, is that right?
Bob K.
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