Re: Measuring humidity

[Sandy King <sanking@clemson.edu>]

Title: Re: Measuring humidity

Same here. We use air conditioning or heating all year and actually never open the windows except to clean them. This is done with a system called a heat pump. The temperature is held at about 72º F constantly, but RH inside varies from the low 30s in winter to the high 60s in summer.

Right now it is 71ºF and 64% inside, and 63ºF and 72% RH outside. RH trends more or less with outside RH. But, heating in the winter removes a lot of moisture from the air. Obviously, cold air can hold more moisture than hot air. In the summer a typical reading at 8 am would be 70ºF and 90% humidity, but by 1pm the reading would be 90ºF and 50% RH.

Temperature and humidity are major issues for carbon printing. Sensitivity is much higher at 85ºF and 90% RH than at 70ºF and 35% RH. This absolutely has to be factored in when printing.

Sandy

At 11:41 PM -0400 9/28/06, Ender100@aol.com wrote:

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> charset=UTF-8
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> Katherine,
>
> Temperature certainly is a variable, but my home is 70 degrees year
> round and it's the humidity that can vary a lot.  Humidity has a
> LOT of influence-at least with PT/PD.  But then, as you say, I
> am holding my temperature constant-and wearing the same lucky
> undershorts.
>
> Best Wishes,
> Mark Nelson
>
> Precision Digital Negatives -
> The System
> PDNPrint Forum at Yahoo
> Groups
> www.MarkINelsonPhoto.com
>
>
> In a message dated 9/28/06 7:58:11 PM, kthayer@pacifier.com
> writes:
> > But apparently I'm not the only one making this
> > mistake, because 
> > we've all been using RH as if it were a meaningful variable,
> > and 
> > obviously it's not, unless, as you say, temperature is held 
> > constant.  The graphs in the literature showing the
> > relationship 
> > between humidity and dark reaction, and humidity and
> > sensitivity, 
> > were no doubt constructed holding temperature
> > constant.  
> > Unfortunately they don't say that, or specify the
> > temperature, 
> > although I suppose we could assume 25C, isn't that the usual
> > standard 
> > temperature?