which hygrometer to follow


Jan 20, 2005
19
0
1
east of sG
#1
I have a digi dry cabinet and i have put in a few hygrometer.
It about 3 yr old.
I have try change the hygrometer location
and it left in the location for for a few weeks.
The cabinet is nearby a tv but not under sunlight.

So which hygrometer is correct?

 

one eye jack

Senior Member
Jun 11, 2011
822
13
18
#2
The answer:Which hygrometer reading? None. ( I would add the 3 readings and divide by 3 to get the average reading.) but in reality you need to calibrate hygrometer to a reference standard.Below is a DIY method which is accurate.

Measuring instruments are calibrated or set to a reference standard before it is sold but given the mechanical structure
of analogue hygrometer( those that have needle) and digital type.The digital type require you to know which adjustable trimpot (potentiometer or adjustable resistor to adjust).I have copied the summary of this webpage,you can go there to see the pictures and step by step instructions.

Summary of Steps to Calibrate - for Printing

For needle type you can do an accurate calibration but need time and if you have more than one then you need to duplicate the setup and then average the readings and adjust accordingly.8-12 hours to do a calibration.

How to Calibrate a Hygrometer
From Lianne McLeod, DVM, former About.com Guide
.8 of 8Previous NextPrintable Summary of Steps

.To calibrate a hygrometer you will need:
•1/2 cup table salt
•approximately 1/4 cup water
•coffee cup
•hygrometer
•large re-sealable freezer bag
1. Place 1/2 cup of salt in the coffee cup, and add the water. Stir for a bit to totally saturate the salt (the salt won't dissolve, it will be more like really wet sand).

2. Place the salt/water mix in a re-sealable plastic bag, along with the hygrometer, and seal the bag. Note: make sure none of the salt/water mix comes in direct contact with the hygrometer.

3. Let this bag aside at room temperature for 8-12 hours, in a location where the temperature is fairly constant.

4. After 8-12 hours, check the reading of the hygrometer. It is best to read it while still in the bag.

The relative humidity in the sealed bag with the salt/water mix should be 75 percent (mine read about 72 percent).

5. For adjustable hygrometers, adjust to read 75 percent. You will have to do this very quickly, or remember how much you need to adjust the setting (e.g. mine read 72 percent rather than 75 percent, so I would need to adjust the dial up 3 percentage points).

If yours is not adjustable (like mine), simply make a note of how "off" your hygrometer reads. If it reads below 75 percent, you will need to add the difference to your actual readings. If your hygrometer read above 75 percent on the calibration, you will need to subtract the difference from your actual reading.
In my example: after sitting in the bag, my hygrometer read 72 percent, when it should have read 75 percent -- a difference of 3 percent. I now add 3 percent to the readings I take on the hygrometer (e.g. in a tank) to get the actual relative humidity.

Remember: always give a hygrometer about 2 hours to stabilize before taking a reading, as changes in the relative humidity may take a while to register accurately on a hygrometer.

Edit: Additional information:From Wikipedia http://en.wikipedia.org/wiki/Hygrometer

Difficulty of accurate humidity measurementHumidity measurement is among the more difficult problems in basic meteorology. According to the WMO Guide, "The achievable accuracies [for humidity determination] listed in the table refer to good quality instruments that are well operated and maintained. In practice, these are not easy to achieve." Two thermometers can be compared by immersing them both in an insulated vessel of water (or alcohol, for temperatures below the freezing point of water) and stirring vigorously to minimize temperature variations. A high-quality liquid-in-glass thermometer if handled with care should remain stable for some years. Hygrometers must be calibrated in air, which is a much less effective heat transfer medium than is water, and many types are subject to drift[2] so need regular recalibration. A further difficulty is that most hygrometers sense relative humidity rather than the absolute amount of water present, but relative humidity is a function of both temperature and absolute moisture content, so small temperature variations within the air in a test chamber will translate into relative humidity variations.

From: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’s also a major source of error.
Unfortunately, despite its ubiquity, too few
data sheets include hysteresis as a factor in
their accuracy values.

Unfortunately, if hysteresis appears at all,
it’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.

Calibration by saturated salt solution http://www.omega.com/temperature/z/pdf/z103.pdf
 

Last edited:
Jan 20, 2005
19
0
1
east of sG
#3
hi, thanks for the info.
just to add, there are 1 hydrometer which is bought brand new to it...
will try to calibrate the other hydrometer to check the reading.
 

daredevil123

Moderator
Staff member
Oct 25, 2005
21,662
69
48
lil red dot
#4
How to do a salt test... if your meter cannot calibrate, just read the difference from 75% and apply the difference every time you look at your hygrometer.

[video=youtube;amSMJ2pUIdE]http://www.youtube.com/watch?v=amSMJ2pUIdE[/video]
 

one eye jack

Senior Member
Jun 11, 2011
822
13
18
#5
hi, thanks for the info.
just to add, there are 1 hydrometer which is bought brand new to it...
will try to calibrate the other hydrometer to check the reading.
In that case,calibrate the new one as the battery is fresher.You can put more than one hygrometer
in the bag/container to save time.Do note that when you see the "Lo Bat" signal on some digital display
it means time to change battery as the reading may be "off" somewhat.That's the reason for calibration. :)
 

Apr 18, 2012
381
1
18
#6
I use cooking salt to test my.
is there appropriate.???
 

Daoyin

Senior Member
Nov 25, 2008
2,808
6
38
West
#8
I have a hydrometer placed on the botton shelf of my dry cabinet. Invariably its readout differs from the one supplied by the dry cabinet supplier. So long as both readings differ by not more than 5%, I wouldn't bother about calibration etc. The main purpose of having two meters is to provide an indicator if and when one of them breaks down.
 

one eye jack

Senior Member
Jun 11, 2011
822
13
18
#9
I have a hydrometer placed on the botton shelf of my dry cabinet. Invariably its readout differs from the one supplied by the dry cabinet supplier. So long as both readings differ by not more than 5%, I wouldn't bother about calibration etc. The main purpose of having two meters is to provide an indicator if and when one of them breaks down.
You are a trusting person or shall we say you believe in technology but don't really know how things really work.
In a modern technological world measurement standards are based on fixed assumed parameters.That is a measurement
is taken at a fixed (ideal) temperature,atmospheric pressure and whatever parameter that is relevant to a particular
measurement quantity.Of course once the measurement is performed outside of the fixed parameters like in real life/world
conditions it becomes a relative measurement.This is where errors occur.

You may not appreciate the importance but I give an example many are familiar with like GPS (global positioning systems).
Originally it was created using satelite technology as a triangulation method employing several satelites to calculate
the position of places or objects on earth for military purposes.As you know the earth itself is rotating on it's axis as well as rotating through space around the sun.Not only that but satelites are rotating or orbiting earth itself.So how to synchronise these variables so that there is a minimum of error? Common to these variables is TIME
as it take time to complete a task or cycle.So the accuracy of time is paramount to the accuracy of GPS system.
So if time is "off" by a fraction of a second the GPS will have an error in terms of distance measured in meters or feet.
Now imagine you are trying to aim a bomb or missile what would the result be? A miss is as good as a mile,money wasted
in terms of cost of munition/weapon and worst of all military advantage lost.

So in a modern technological world the accuracy of time is a valuable asset and in advanced countries like the west they
have instruments that measure or keep time accurate time for scientific purposes.Have you heard of atomic clocks? They use the predictable behaviour of certain elements at atomic level to compare differences in time.Around the world,clocks
are referenced to GMT time ie. the atomic clock at Greenwich,England. I believe Singapore operates an atomic clock also.

Now we come back to the hygrometer,as you said you would not bother if they varied by 5% from each meter but is your hygrometer accurate when compared to the reference (predictable humidity of salt/water)? What if both meters are really off by 10% although they are 5% from each other? so that works out to plus minus 10 - 15% from the reference.Now do you see the picture just like GPS in terms of distance and having fungus in the dry cabinet? :)
 

Last edited:
#10
You are a trusting person or shall we say you believe in technology but don't really know how things really work.
In a modern technological world measurement standards are based on fixed assumed parameters.That is a measurement
is taken at a fixed (ideal) temperature,atmospheric pressure and whatever parameter that is relevant to a particular
measurement quantity.Of course once the measurement is performed outside of the fixed parameters like in real life/world
conditions it becomes a relative measurement.This is where errors occur.

You may not appreciate the importance but I give an example many are familiar with like GPS (global positioning systems).
Originally it was created using satelite technology as a triangulation method employing several satelites to calculate
the position of places or objects on earth for military purposes.As you know the earth itself is rotating on it's axis as well as rotating through space around the sun.Not only that but satelites are rotating or orbiting earth itself.So how to synchronise these variables so that there is a minimum of error? Common to these variables is TIME
as it take time to complete a task or cycle.So the accuracy of time is paramount to the accuracy of GPS system.
So if time is "off" by a fraction of a second the GPS will have an error in terms of distance measured in meters or feet.
Now imagine you are trying to aim a bomb or missile what would the result be? A miss is as good as a mile,money wasted
in terms of cost of munition/weapon and worst of all military advantage lost.

So in a modern technological world the accuracy of time is a valuable asset and in advanced countries like the west they
have instruments that measure or keep time accurate time for scientific purposes.Have you heard of atomic clocks? They use the predictable behaviour of certain elements at atomic level to compare differences in time.Around the world,clocks
are referenced to GMT time ie. the atomic clock at Greenwich,England. I believe Singapore operates an atomic clock also.

Now we come back to the hygrometer,as you said you would not bother if they varied by 5% from each meter but is your hygrometer accurate when compared to the reference (predictable humidity of salt/water)? What if both meters are really off by 10% although they are 5% from each other? so that works out to plus minus 10 - 15% from the reference.Now do you see the picture just like GPS in terms of distance and having fungus in the dry cabinet? :)
Jeeze, I'm a certified licensed aircraft maintenance engineer with several type ratings currently employed with a Fortune 500 aerospace and defence contractor involved in systems engineering development and design integration and none of us here sound as obsessed with you over the accuracy of a consumer hygrometer in a consumer dry cabinet despite dealing with arithmetic precision down to 10 decimal places or even more from a day to day basis.

I'm not going to jump in shock just because the relative humidity differs sightly or even more than expected. Your equipment is not made of tofu neither does fungus sprout overnight in fact storing your equipment under controlled environmental conditions is hardly necessary if you use them frequently and often enough. We have multi-million dollar electro-optics left on the shelf in an open air environment for weeks on end.
 

Last edited:
Oct 1, 2011
1,799
0
0
Planet Earth
#11
9V-Orion Images said:
Jeeze, I'm a certified licensed aircraft maintenance engineer with several type ratings currently employed with a Fortune 500 aerospace and defence contractor involved in systems engineering development and design integration and none of us here sound as obsessed with you over the accuracy of a consumer hygrometer in a consumer dry cabinet despite dealing with arithmetic precision down to 10 decimal places or even more from a day to day basis......
In short, Kia Su.
 

Octarine

Moderator
Staff member
Jan 3, 2008
12,544
33
48
Pasir Ris
#12
I'm not going to jump in shock just because the relative humidity differs sightly or even more than expected. Your equipment is not made of tofu neither does fungus sprout overnight in fact storing your equipment under controlled environmental conditions is hardly necessary if you use them frequently and often enough.
The magic term is: "sufficient accuracy".
 

#13
From what I have read in the engineering / technical reviews and white papers from NASA with regards to the optimal operating parameters for the ISS Environmental Control and Life Support System (ECLSS), evaluations from their chief microbiologist actually recommends a critical Relative Humidity (RH) of not more than 65% - 70% necessary to impede the growth of microorganisms which will otherwise result in potential biodegradation of materials on-board (the Mir Space Station was heavily infested throughout with exotic moulds and mutated fungus (that have their distinct aroma or stench) till astronauts and cosmonauts were unable to see through some of the portholes clearly).

In actuality, Relative Humidity (RH) on-board the USD$150 billion laboratory / observatory often ranges between 30% and 70% and I don't see them going anal over such large fluctuations in their modules filled with ultra-sensitive scientific experiments and photography equipments but each to his own I guess.
 

Last edited:
May 8, 2012
158
0
16
Singapore
#14
In actuality, Relative Humidity (RH) on-board the USD$150 billion laboratory / observatory often ranges between 30% and 70% and I don't see them going anal over such large fluctuations in their modules filled with ultra-sensitive scientific experiments and photography equipments but each to his own I guess.
I believe they are not Singaporeans right? Cause Singaporeans (including me) more kiasu one leh. :p

Or perhaps it's because they are not handling stuff they bought with their hard-earned money. lol.
 

oldie

New Member
Nov 17, 2005
16
0
0
#15
From my own usage and observation there are not many good dry cabinets in our local market. Most of them today are Taiwanese/China third party branded to local market. These are normally the Peltier semiconductor type which are very easy/cheap to implement. It is also very difficult to buy the dessicant/heater type today. I think only the Japanese Tolihan brand has both types and is rather expensive but very well made. I have been using a Tolihan dessicant cabinet since the early nineties which is still in excellent condition and the electricity consumption is very,very low and quality is excellent even though the hygrometer is analog. However, 2 of my Taiwanese branded Peltier types lasts only for a few years and the rubber seals were not very good. Just my 2 cents....
 

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