A Good Hygrometer (pics)

Nan's Nook : Archives : Grow Chambers & Clean Rooms : Nan's Nook Fruiting Teks Q&A: Humidity: A Good Hygrometer (pics)
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Perlite Lowered My Humidity?  10 02/18 09:32pm Shroomzila

By nuecrew (Nue) on Sunday, November 18, 2001 - 07:58 pm:

Knowing your level of Humidity is important to know at the cusp of pinning/fruiting. Quote described a metal framed hygrometer that could be found at cigar shops. I went to the local cigar shop. Having many to choose from, prices ranged from $4.95 to $115. I found one dial guage for $25 that went immediatly to 100% from my breath and returned within 30 seconds to room level of 60%. It also had a calibration screw. It is the "Polytherm" model. Made in Germany the word polytherm is also the brand name of the filiment that senses the moisture in the air. A man at a sailing supply store that calibrates many different nuatical instruments said he takes a washcloth soaked in hot water, wrung out and wraps this around the hygrometer to achieve 100% humidity and then calibrates the instrument to 100%. As you can see I have spent over $100. The digital defaults to "HI" after 85%Rh, the dual guage $10 cheapo is only accurate between 40-60%Rh. The large one fills the bill but is too big. I think I finally found her in the polytherm. Thanks Quote! Very sensitive and accurate.guagenamegroup

By nuecrew (Nue) on Monday, November 19, 2001 - 12:25 am:

www.mushroommagic.com/guage.htm has a $16 made in Germany guage. www.humidorhabana.com/humidifiers2.htm has the "polytherm" unit in the picture but for $25 more than I paid yesterday. On ebay there is a rotating seller(chevrier instruments) that auction sets of 5 guages similar in size(70mm/2.75in.) and quality of the mushroommagic guage. They also sell sets of 50mm guages that I have doubts about. Past history show winning bids as low as $15(starting bid) and tops of $24. Squoping could be high from Quebec. Hope I helped someone.


Posted by: MTech2 Jun 18 03, 05:52 PM GMT
Just wanted to say Hello!!....as I am new to the Nook. And I have got to tell you this place is great !! I'd say it's in the top five myco sites.
Anyways, I thought you guys....and gals....might be interested in a nice little Hygrometer/Temp unit I found.I bought two of these bad boys and ran ran a calibration (put in sealed bag with a super-saturated salt solution) and both read 75% on the nose. This is exactly what it should be reading...so I know it is accurate.
They have a range from 0-99%, Hi-Lo memory, and an remote sensor so you can have the actual unit outside your chamber.
These units normally sell for $42....they're on sale for $24.....I'm not trying to push this stuff I was just looking a long time for a good (and cheap) hygrometer....and I think I found one!

This meter takes both temp and relative humidity from the remote sensor. I checked the sensors calibration and it was right on. The specs. give the meter a +/- 4% RH at the extreme ends of the scale (0 and 99%). I haven't used it yet in my fruiting chamber but when I do I will let you know the results.

http://www.technika.com/Sper/s800039.htm

Just click on "Order On-Line" and it will show the discounted price.

 

By ion ewe (Ion) on Wednesday, November 21, 2001 - 08:29 pm:

I am surprised nobody has mentioned the use of psychrometers on this board. A psychrometer is a set of two mercury thermometers with the bulbs positioned over a small fan. One of the therms has a cotton wicking pouch tied over it's bulb. You saturate this "wet bulb" with distilled H2O, and switch on the fan. You watch the levels of mercury in the therms rise and fall until they settle for at least five seconds. Record the temps and use an included slide rule or graph to determine relative humidity. It is kind of a pain, but if you're hellbent on perfection, these things are usually accurate to within a half of a percent when used correctly!
On a side note, it's not really that important to know exactly what your humidity is unless you're living in an abnormal atmosphere (extreme elevation above sea level, a desert, below sea level, etc.). Just make sure it's foggy in there.

-ion

By quote: (Quote) on Friday, November 16, 2001 - 01:31 pm:

Hygrometer Calibration

Analog (dial-type) hygrometers are often shipped from the factory out of spec. To calibrate, you need plain table salt, a few drops of water and a see-through Tupperware container with a tightly fitting lid.

Place about 1 teaspoon of salt in a small shallow open container, such as the cap to a jar. Add a few drops of water to the salt. You DO NOT want a solution or to dissolve the salt, only get it damp. Place the container with the salt solution in the Tupperware container. Next, place the hygrometer in the Tupperware container face down. This will allow you to view and check the reading of the hygrometer before you open the container. CAUTION - do not spill any salt or solution on your hygrometer! Place the lid on the Tupperware container making sure it fits tight. Allow to stabilize for at least 6 hours. Without opening the container, check your reading. It should read exactly 75%. If not, note the deviation and or adjust the hygrometer.


Calibration of your Hygrometer (Humidity Gauge) taken from:

http://www.csonka.com/calibration.htm

Analog hygrometers are manufactured with a factory tolerance of +/- 5% points of humidity (and sometimes more) through the normal range of 40-80%. Although humidity gauge is pre-set at the factory, its' calibration may be off within this range for various reasons.

A simple, easy to do at home means of calibrating hygrometers uses standard salt and a sealed container. Table salt, when used properly, will maintain an exact 75% humidity in a perfectly sealed environment. So, to do this, you'll need three items. First, obtain an airtight container such as a see-through tub with a tight fitting snap-on lid (the kind usually found in most kitchens). Alternately, a heavy-duty zip-lock bag will do. Second, you'll need about a teaspoon of salt. Third, any small, shallow open container is needed (to hold the salt in) such as a screw cap from a plastic bottle.

Place the salt in its small container and add a few drops of water to moisten it. Don't dissolve it yet. With just a few drops of water, you'll get what you need, which is damp salt. Next, carefully place the salt in its small container, along with your hygrometer, into the airtight container. Please do not get any moistened salt on the gauge. Also, check to see that the starting point (current reading) is anywhere in the 40% to 80% range.

Seal the container tightly. Note: if you have any doubt as to whether or not it is a perfectly sealed environment, double-it-up by putting it in a second container, or into a second baggie. Do not try to remove the remaining air trapped inside. Now, wait for at least 5 or 6 hours until the environment has stabilized. Do not open the container. Read the gauge's humidity % level. It should be exactly 75%. If it is not, note the deviation as being the amount your hygrometer is out of calibration. If for example, it reads 68%, the gauge is 7% low. If on the other hand it reads 80%, the gauge is 5% high.

Now, remove the gauge from the container and locate a very small jeweller´┐Żs flathead screwdriver. If it fits through the small hole in the center of the rear plate, it should work well. Put it in that hole, and turn it slowly while watching the dial on the front. If your gauge was low by 4%, turn the screwdriver clockwise and make the dial rest 4% points higher than it did previously. Conversely, if your gauge was high by 6%, turn the screwdriver counter-clockwise and make the dial rest 6% points lower than it did previously. That's it. Your gauge is now calibrated and you should feel very comfortable with its accuracy from this point on.

By plinkerdink420 (Plinkerdink420) on Friday, November 16, 2001 - 02:07 pm:

i threw out my analog a few months ago and bought a digital yesterday... only when i got home i realized that it only reads the "outside" temp and "inside" temp and humidity... so the probe will do me no good... my question is this... if i put the unit inside my terr. from time to time to check the humidity will it get screwed up? should i just go buy something else?

By nuecrew (Nue) on Friday, November 16, 2001 - 03:43 pm:

It sounds like you have the same kind I have. I found when the humidity gets over about 85 percent the display defaults to the word "Hi". I do like the remote probe thing.
 


Calibration of your Hygrometer (Humidity Gauge)

Analog hygrometers are manufactured with a factory tolerance of +/- 5% points of humidity (and sometimes more) through the normal range of 40-80%. Although humidity gauge is pre-set at the factory, its' calibration may be off within this range for various reasons.

A simple, easy to do at home means of calibrating hygrometers uses standard salt and a sealed container. Table salt, when used properly, will maintain an exact 75% humidity in a perfectly sealed environment.

So, to do this, you'll need three items. First, obtain an airtight container such as a see-through tub with a tight fitting snap-on lid (the kind usually found in most kitchens). Alternately, a heavy-duty zip-lock bag will do. Second, you'll need about a teaspoon of salt. Third, any small, shallow open container is needed (to hold the salt in) such as a screw cap from a plastic bottle.

Place the salt in its small container and add a few drops of water to moisten it. Don't dissolve it yet. With just a few drops of water, you'll get what you need, which is damp salt. Next, carefully place the salt in its small container, along with your hygrometer, into the airtight container. Please do not get any moistened salt on the gauge. Also, check to see that the starting point (current reading) is anywhere in the 40% to 80% range.

Seal the container tightly. Note: if you have any doubt as to whether or not it is a perfectly sealed environment, double-it-up by putting it in a second container, or into a second baggie. Do not try to remove the remaining air trapped inside. Now, wait for at least 5 or 6 hours until the environment has stabilized.

Do not open the container. Read the gauge's humidity % level. It should be exactly 75%. If it is not, note the deviation as being the amount your hygrometer is out of calibration. If for example, it reads 68%, the gauge is 7% low. If on the other hand it reads 80%, the gauge is 5% high.

Now, remove the gauge from the container and find a very small flathead screwdriver. If it fits through the small hole in the center of the rear plate, it should work well. Put it in that hole, and turn it slowly while watching the dial on the front. If your gauge was low by 4%, turn the screwdriver clockwise and make the dial rest 4% points higher than it did previously.

Conversely, if your gauge was high by 6%, turn the screwdriver counter-clockwise and make the dial rest 6% points lower than it did previously.

That's it. Your gauge is now calibrated and you should feel very comfortable with its accuracy from this point on.

Mycota


Posted by: reshroomED Feb 17 03, 01:21 PM GMT
Wrote this due to reading the humidity cal procedure in the archives



OK we all know that you don't have to be super-accurate with your growth parameters to be a successful shroom-grower. Shit, I've had very few contams (compared to what I read of) with only steam-sterilisation, poor temp control, and hand-misting.
But some people like to create the perfect grow environment. If you're interested enough to try this you'll be (more than likely) using domestic instrumentation to fulfill your measurement needs. Now don't get me wrong, but most of this stuff is crap. Not all but 99%. Temperature measurement is about the only readily available field in which you can feel comfortable with a domestic meter.
As a general note: When buying instumentation, go for old analogue gear. Everyone likes a digital display reading to several decimal places. Mostly you'll find that these displays offer more mis-information than not.


Humidity Measurement

General Measurement
Most forms of measurement are inferential (ie they rely upon the often indirect relationship between two physical conditions), and relative humidity falls into this category. The nature of such measurement is inherrantly non-linear and innaccurate, due to this. A simple thermometer relies upon the fact that liquids will expand/contract at a certain rate per increase/decrease of temperature. If the internal bore of the thermometer is perfectly true the liquid in the bulb will be driven up the bore (seemingly) at an even rate and, if a scale is marked on it, will be proportional to temperature change. But as the liquid level in the bulb decreases so does the head pressure upon it, causing increasing errors as the temperature increases. The error here is negligable but it's a very simple example of error in inferential measurement.

Relative Humidity(RH)
RH measurement also suffers from poor response-time and hence makes short -term fluctuations difficult to detect.
Most old analogue hygrometers measured the expansion/contraction of a peice of horse-hair and related this to relative humidity. Modern digital meters will measure the capacitance or resistance of a specific semiconductor and relate this to relative humidity. Either way, you're still stuck with the problem of inaccuracies due to inferential measurement.
The most accurate and cheap way to do this is buy, or even build, a psychrometer and associated psychrometric tables.
If you've got a hygrometer already and want some degree of accuracy (don't even think decimal places) here's as good a calibration procedure as the average person can perform at home:

Basic Adjustments
There are two basic adjustments to be made for a simple calibration: zero and span (or range). The zero adjustment acts as if moving the scale linearly up or down (ie a meter with a zero adjustment of +5% would read 5% at true zero and 105% at true 100%). The span adjustment acts as if to elasticize the scale (ie a 5% span increase could cause the meter to indicate a negative value at true 0% and one well in excess of 100% when at true 100%). In an analogue meter the zero adjust will be a screw driving a small gear that is part of the needle, or the needle must be physically removed from it's shaft and repositioned accordingly. To acheive this use two small flat-blade screwdrivers to gently lever off the pointer The span adjust will be a telescopic or extending linkage of some sort in the 'works' of the gauge , possibly only accessible by removing glass, pointer, and face-plate. In a digital meter there should be at least two potentiometers (hopefully labelled) that will look like little plastic boxes with screws in the top or end (if no labelling on board, contact manufacturer's service dept). These adjustments are interactive and so the cal procedure must be repeated several times.

Procedure
1. Place in buffer #1and allow to stabilize.
2. Note reading and adjust zero to suit.
3. Place in buffer #2 and allow to stabilise.
4. Note reading and adjust span to suit.
5. Repeat until desired accuracy obtained.

Buffer solutions
Mineral salts, when in a saturated solution in a contained environment, will maintain a constant humidity dependent on temperature. So the idea is to add salt to distilled water in a small tupperware-type container until no more will dissolve (whilst stirring) and then add a little more . You should be seeing undissolved salt crystals on the bottom of the container.
Place this in a larger container with an air-tight lid and allow to stabilize for a few hours. (All standards are based on 25C so doing this in your grow-chamber should meet temp requirements.)
Place meter in large container and seal, taking care not to contaminate meter by direct contact with solution, and allow to stabilize.In the case of analogue gauges, calibrate in the position that the instrument will live in, ie if it will be vertical calibrate it in this position.
Take note of reading and adjust accordingly


Buffer #1
POTASSIUM CHLORIDE 84.34%RH @ 25C

Buffer #2
POTASSIUM SULFATE 97.30%RH @ 25C


This procedure is very basic and little accuracy will be acheived, but at the very least it will give you an idea as to the accuracy of your hygrometer.


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