Strange (good??) phenomenon with my electronic dry cabinet


Andreq

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Jul 12, 2007
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#1
I did a test recently as I reshuffled the things in my electronic dry cabinet. What I discovered is very surprising.

After I turned on the dry cabinet's dehumidifier, the humidity drops to quite low, almost 40%. Instead of adjusting the knob, I decided to turn off the power.

Fro many hours, the reading remained at 40% Does that mean the cabinet is really air-tight?

I did open it to take and keep things. The humidity increased a little, to say 45% or so. And it remained there for a few more hours. And the next day after I came back home, I noticed the reading went back to about 40%!!

I really don't understand. Is there such a thing? I have 2 external hygrometers and 1 in-built hygrometer attached to the dry cabinet. The 2 external ones read about 40% +/- 5% while the dry cabi's one reads 55%. I tend to trust the external ones more.

But in any case, all 3 hygrometers are showing acceptable humidity levels (<60%) even though I have cut off power for 2 days and I did open the cabinet at least twice!

Note the cabinet is not in any air-con room. Just in a typical Singapore home.

Not sure if anyone care to repeat this simple test... I'm still investigating.
 

eleveninth

Senior Member
Jan 17, 2006
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#2
I did a test recently as I reshuffled the things in my electronic dry cabinet. What I discovered is very surprising.

After I turned on the dry cabinet's dehumidifier, the humidity drops to quite low, almost 40%. Instead of adjusting the knob, I decided to turn off the power.

Fro many hours, the reading remained at 40% Does that mean the cabinet is really air-tight?

I did open it to take and keep things. The humidity increased a little, to say 45% or so. And it remained there for a few more hours. And the next day after I came back home, I noticed the reading went back to about 40%!!

I really don't understand. Is there such a thing? I have 2 external hygrometers and 1 in-built hygrometer attached to the dry cabinet. The 2 external ones read about 40% +/- 5% while the dry cabi's one reads 55%. I tend to trust the external ones more.

But in any case, all 3 hygrometers are showing acceptable humidity levels (<60%) even though I have cut off power for 2 days and I did open the cabinet at least twice!

Note the cabinet is not in any air-con room. Just in a typical Singapore home.

Not sure if anyone care to repeat this simple test... I'm still investigating.
And the point is?

save on electricity bill ?
 

Octarine

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Jan 3, 2008
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#3
Check the batteries of the hygrometers, do the salt test for calibration. Get a verified baseline from where you can start investigating.
 

Andreq

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Check the batteries of the hygrometers, do the salt test for calibration. Get a verified baseline from where you can start investigating.
Yeah thanks,will do that. Hope to get to the root of the situation asap.
 

one eye jack

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Jun 11, 2011
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#5
Mystery solved.
Source: http://www.veriteq.com/download/whitepaper/catching-the-drift.pdf

Hysteresis:

Hysteresis is the tendency of measuring devices to not return completely to their original state after a change has been
measured. It&#8217;s also a major source of error.
Unfortunately, despite its ubiquity, too fewdata sheets include hysteresis as a factor intheir accuracy values.Unfortunately, if hysteresis appears at all,it&#8217;s often de-emphasized by being placed far apart from the total accuracy
specification. Hysteresis unmentioned or disconnected textually from an accuracy value could be considered product misrepresentation to a discerning purchaser.

Additional info:
Hygrometer - Wikipedia, the free encyclopedia
 

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bonrya

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Dec 16, 2010
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#6
I have a friend that puts all her gear in a dry cabinet but leaves the power off just as long the meter reads 45% or less. You can keep doing that if you trust your meter I guess. Her gear doesn't have any fungus yet. :bsmilie:
 

Barrios

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#7
Currently, there are 2 common types of dry cabinet in the market; the traditional dessicant-based type and the Peltier-based thermoelectric type. My deduction is that the dessicant in the former will likely to continue absorbing moisture even when power is off. Humidity in the TE type will likely increase quicker when power is off as condensation is formed on the Peltier.
 

one eye jack

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Jun 11, 2011
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#8
Currently, there are 2 common types of dry cabinet in the market; the traditional dessicant-based type and the Peltier-based thermoelectric type. My deduction is that the dessicant in the former will likely to continue absorbing moisture even when power is off. Humidity in the TE type will likely increase quicker when power is off as condensation is formed on the Peltier.
Congratulations,You have the right answer.I forgot about the dessicant in the cab.:) The hysteresis error is still there.
 

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Andreq

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Hey guys, thanks for more input.

Hysteresis... Interesting that it can be applied to hygrometers as well. I remember this term in my college science. But only as applied to the elasticity of matter.

I'm not sure if it's really due to hysteresis that I'm observing this strange phenomenon. There are 2 reasons:

1. I took different hygrometers which had already acclimatized to the surrounding atmosphere, ie they were already in a steady state. And then I put them into the dry box. I'm not sure if this can minimize hysteresis. Eventually, all of them still recorded low humidity levels.

2. All the hygrometers showed a drop in readings from their previous steady state. I'm not so concerned with the absolute humidity readings now, since every one has a certain amount of errors in them. In other words, the relative readings all agreed with one another within +/-10%.

It's really baffling. After I opened the dry box door, with the electrical power cut off, the humidity could rise from about 40% to 50%. Ok that's expected.

Then after I closed it, the readings slowly dropped back to about 40% and remained there. Note: Like I said above, it doesn't matter what the absolute reading is. The point is, all hygrometers reported a drop in humidity. Which means there's something inside the dry box which is causing the humidity to be reduced. Dessicant is a good possibility as suggested by Barrios. But surely the dry box's dessicant is not that effective? :O At least not for so long. Otherwise, we wouldn't need to use electricity at the same time!

I could open and close the dry box's door a few times in a day. No electricity at all. And the humidity would eventually drop.

I didn't have time to do the salt test yet. But will do so perhaps this weekend. This experience is really an eye opener.
 

Barrios

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#10
The dessicant will continue to absorb moisture in the cabinet until it reaches its max capacity. Thereafter, the heater will kick in to draw out the moisture from the dessicant. The cycle continues. Right now, nobody has a clue as to what type of drying unit your cabinet is employing. The brand itself will tell the type.
 

one eye jack

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Jun 11, 2011
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#11
It's really baffling. After I opened the dry box door, with the electrical power cut off, the humidity could rise from about 40% to 50%. Ok that's expected.

Then after I closed it, the readings slowly dropped back to about 40% and remained there. Note: Like I said above, it doesn't matter what the absolute reading is. The point is, all hygrometers reported a drop in humidity. Which means there's something inside the dry box which is causing the humidity to be reduced. Dessicant is a good possibility as suggested by Barrios. But surely the dry box's dessicant is not that effective? :O At least not for so long. Otherwise, we wouldn't need to use electricity at the same time!

I could open and close the dry box's door a few times in a day. No electricity at all. And the humidity would eventually drop.

I didn't have time to do the salt test yet. But will do so perhaps this weekend. This experience is really an eye opener.
Correct me if I am wrong,as Barrios said there are 2 types of cabs, dessicant and peltier element (heater).The dessicant type is effective that's why it is used,either a substantial amount is required because as basic physics state "matter
cannot be destroyed only changed or transformed".So what will happen to the moisture/water? Either a chemical reaction takes place in the dessicant and gets transformed meaning it has a life span or water is absorbed and will saturate the dessicant until it can no longer absorb water for which a peltier element/heater is used to dry the dessicant or air and can keep the cycle of absorbtion going.
 

Andreq

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I vaguely recall mine's dessicant type. If so, I'm just surprised at how effective it is even without the electricity turned on.

Let me check and keep you guys updated.
 

Barrios

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#13
If few hygrometers are calibrated from one accurate source, you will probably see all those calibrated hygrometers to be showing very close readings, if not identical, from each other. Just to share:

 

Octarine

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#14
If few hygrometers are calibrated from one accurate source, you will probably see all those calibrated hygrometers to be showing very close readings, if not identical, from each other.
Do you mind sharing the source of these hygrometers?
 

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