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Calibrating Digital Hygrometer by Salt Test Method

A guide to calibrating a digital hygrometer using the salt test method

It’s always a good idea to check the accuracy of your hygrometer. You can use the Salt Test method on both digital and analog hygrometers. Most hygrometers today can either be adjusted or calibrated to an accurate reading. The salt test method won’t fail you, and it’s very easy to do.

MATERIALS NEEDED:

- Small sandwich ziplock baggy
- Bottle cap from 2 liter soda bottle (works best)
- Table salt
- Hygrometer (whichever one you want to test, digital or analog)

Now that you have all of your materials handy, follow these steps and you’ll be on your way to effectively checking the accuracy of your hygrometer.

STEP 1:

Fill bottle cap with standard table salt; fill about 3/4 of the way up.

STEP 2:

Add tap water to the bottle cap to saturate the salt. If you see water floating on top of the salt, you’ve added too much water. Easy fix for this is to grab a paper towel, and soak up all of the excess water. You want more of a slurry consistency of water and salt. Again, if you see water actually floating on top of the salt, soak up the excess with a paper towel.

STEP 3:

Place both hygrometer and bottle cap (with salt/water mixture) inside of a small ziplock baggy, as pictured above. Wait 4 hours and come back for a reading check.

STEP 4:

If your hygrometer is perfectly accurate, it will read 75%. Most hygrometers will be +/- 3 %. If your hygrometer is digital and has a calibration button, follow the directions that it came with to calibrate to 75%. Digital hygrometers have a calibration button you push, while analog hygrometers have a screw which allows you to adjust the needle accordingly.

If your hygrometer is not adjustable, you’ll just have to make a note and remember how far off it is.

That’s all there is to it!

You’ve just calibrated/tested your hygrometer using the famous Salt Test Method.

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notes:

1. source = http://www.cigarpass.com/index.php/salt-test-calibrate-hygrometer.html

2. TO BUY DIGITAL THERMOHYGROMETER- PLS CLICK THIS SITE:

http://soldering102.blogspot.com/search/label/ThermoHygrometer , we have 6 models to choose from


Relative Humidity

Relative humidity is a term used to describe the amount of water vapor that exists in a gaseous mixture of air and water vapor.

The relative humidity  \left(\phi\right) of an air-water mixture is defined as the ratio of the partial pressure of water vapor  \left({e_w}\right) in the mixture to the saturated vapor pressure of water  \left({{e^*}_w}\right) at a prescribed temperature.

Relative humidity is normally expressed as a percentage and is calculated by using the following equation:[1]

 \phi  =  {{e_w} \over {{e^*}_w}} \times 100%


Humans are very sensitive to humidity, as the skin relies on the air to get rid of moisture. The process of sweating is your body's attempt to keep cool and maintain its current temperature. If the air is at 100-percent relative humidity, sweat will not evaporate into the air. As a result, we feel much hotter than the actual temperature when the relative humidity is high. If the relative humidity is low, we can feel much cooler than the actual temperature because our sweat evaporates easily, cooling ­us off. For example, if the air temperature is 75 degrees Fahrenheit (24 degrees Celsius) and the relative humidity is zero percent, the air temperature feels like 69 degrees Fahrenheit (21 C) to our bodies. If the air temperature is 75 degrees Fahrenheit (24 C) and the relative humidity is 100 percent, we feel like it's 80 degrees (27 C) out.

People tend to feel most comfortable at a relative humidity of about 45 percent.Humidifiers and dehumidifiers help to keep indoor humidity at a comfortable level.



Buildings

When controlling the climate in buildings using HVAC systems the key is to control the relative humidity in a comfortable range - low enough to be comfortable but high enough to avoid problems associated with very dry air.

When the temperature is high and the relative humidity is low, evaporation of water is rapid; soil dries, wet clothes hung on a line or rack dry quickly, and perspiration readily evaporates from the skin. Wooden furniture can shrink causing the paint that covers these surfaces to fracture.

When the temperature is high and the relative humidity is high, evaporation of water is slow. When relative humidity approaches 100 percent, condensation can occur on surfaces, leading to problems with mold, corrosion, decay, and other moisture-related deterioration.

Certain production and technical processes and treatments in factories, laboratories, hospitals and other facilities require specific relative humidity levels to be maintained using humidifiers, dehumidifiers and associated control systems.


What is the ideal humidity for electronics?

The `ideal' humidity would be very low, simply because humidity lends itself to corrosion of the circuit boards and connectors. When humidity reaches a higher level, items such as rusting of any of the steel components, corrosion of the circuit boards and connections tend to deteriorate.

So unless you're in a sealed chamber where humidity can be controlled, you might want to consider things like room dehumidifiers or even central air conditioning in the summer to help control the humidity levels. In the winter months, humidity tens to be less in the colder climates and that's part of the reason that humidifiers are installed on furnace systems among other things. Humidity control is more for `creature comfort' than anything else.

But this leads to another problem, which is static electricity when the humidity is too low.That too, can be bad for circuit boards because a static discharge can reach potentials of several thousand volts.

According to CompTIA A+, a safe humidity is between 50 and 80 percent.


Read more: http://wiki.answers.com/Q/What_is_the_ideal_humidity_for_electronics#ixzz1E0kmT3DA


references:
1. wikipedia
2. http://science.howstuffworks.com/dictionary/meteorological-terms/question651.htm
3. http://wiki.answers.com/Q/What_is_the_ideal_humidity_for_electronics

EMISSIVITY OF COMMON METALS

EMISSIVITY OF COMMON METALS

Note: Because the emissivity of a given material will vary with temperature and surface finish, the value in these tables should be used only as a guide for relative or differential temperature measurements. The exact emissivity of a material should be determined when high accuracy is required.


METALS

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Alloys

20-Ni, 24-CR, 55-FE, Oxidized

392 (200)

.90

20-Ni, 24-CR, 55-FE, Oxidized

932 (500)

.97

60-Ni, 12-CR, 28-FE, Oxidized

518 (270)

.89

60-Ni, 12-CR, 28-FE, Oxidized

1040 (560)

.82

80-Ni, 20-CR, Oxidized

212 (100)

.87

80-Ni, 20-CR, Oxidized

1112 (600)

.87

80-Ni, 20-CR, Oxidized

2372 (1300)

.89

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Aluminium

Unoxidized

77 (25)

.02

Unoxidized

212 (100)

.03

Unoxidized

932 (500)

.06

Oxidized

390 (199)

.11

Oxidized

1110 (599)

.19

Oxidized at 1110¡F (599¡C)

390 (199)

.11

Oxidized at 1110¡F (599¡C)

1110 (599)

.19

Heavily Oxidized

200 (93)

.20

Heavily Oxidized

940 (504)

.31

Highly Polished

212 (100)

.09

Roughly Polished

212 (100)

.18

Commercial Sheet

212 (100)

.09

Highly Polished Plate

440 (227)

.04

Highly Polished Plate

1070 (577)

.06

Bright Rolled Plate

338 (170)

.04

Bright Rolled Plate

932 (500)

.05

Alloy A3003, Oxidized

600 (316)

.40

Alloy A3003, Oxidized

900 (482)

.40

Alloy 1100-0

200-800 (93-427)

.05

Alloy 24ST

75 (24)

.09

Alloy 24ST, Polished

75 (24)

.09

Alloy 75ST

75 (24)

.11

Alloy 75ST, Polished

75 (24)

.08

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Bismuth

Bright

176 (80)

.34

Unoxidized

77 (25)

.05

Unoxidized

212 (100)

.06

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Brass

73% Cu, 27% Zn, Polished

476 (247)

.03

73% Cu, 27% Zn, Polished

674 (357)

.03

62% Cu, 37% Zn, Polished

494 (257)

.03

62% Cu, 37% Zn, Polished

710 (377)

.04

83% Cu, 17% Zn, Polished

530 (277)

.03

Matte

68 (20)

.07

Burnished to Brown Color

68 (20)

.40

Cu-Zn, Brass Oxidized

392 (200)

.61

Cu-Zn, Brass Oxidized

752 (400)

.60

Cu-Zn, Brass Oxidized

1112 (600)

.61

Unoxidized

77 (25)

.04

Unoxidized

212 (100)

.04

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Cadmium

77 (25)

.02

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Carbon

Lampblack

77 (25)

.95

Unoxidized

77 (25)

.81

Unoxidized

212 (100)

.81

Unoxidized

932 (500)

.79

Candle Soot

250 (121)

.95

Filament

500 (260)

.95

Graphitized

212 (100)

.76

Graphitized

572 (300)

.75

Graphitized

932 (500)

.71

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Chromium

100 (38)

.08

Chromium

1000 (538)

.26

Chromium, Polished

302 (150)

.06

Cobalt, Unoxidized

932 (500)

.13

Cobalt, Unoxidized

1832 (1000)

.23

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Columbium

Unoxidized

1500 (816)

.19

Unoxidized

2000 (1093)

.24

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Copper

Cuprous Oxide

100 (38)

.87

Cuprous Oxide

500 (260)

.83

Cuprous Oxide

1000 (538)

.77

Black, Oxidized

100 (38)

.78

Etched

100 (38)

.09

Matte

100 (38)

.22

Roughly Polished

100 (38)

.07

Polished

100 (38)

.03

Highly Polished

100 (38)

.02

Rolled

100 (38)

.64

Rough

100 (38)

.74

Molten

1000 (538)

.15

Molten

1970 (1077)

.16

Molten

2230 (1221)

.13

Nickel Plated

100-500 (38-260)

.37

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Dow Metal

0.4-600 (-18-316)

.15

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Gold

Enamel

212 (100)

.37

Plate(.0001)

Plate on .0005 Silver

200-750 (93-399)

.11-.14

Plate on .0005 Nickel

200-750 (93-399)

.07-.09

Polished

100-500 (38-260)

.02

Polished

1000-2000 (538-1093)

.03

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Haynes Alloy C

Oxidized

600 2000 (316-1093)

.90-.96

Haynes Alloy 25

Oxidized

600-2000 (316-1093)

.86-.89

Haynes Alloy X

Oxidized

600-2000 (316-1093)

.85-.88

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Inconel

Sheet

1000 (538)

.28

Sheet

1200 (649)

.42

Sheet

1400 (760)

.58

X, Polished

75 (24)

.19

B, Polished

75 (24)

.21

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Iron

Oxidized

212 (100)

.74

Oxidized

930 (499)

.84

Oxidized

2190 (1199)

.89

Unoxidized

212 (100)

.05

Red Rust

77 (25)

.70

Rusted

77 (25)

.65

Liquid

2700-3220 (1516-1771)

.42-.45

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Iron, Cast

Oxidized

390 (199)

.64

Oxidized

1110 (599)

.78

Unoxidized

212 (100)

.21

Strong Oxidation

40 (104)

.95

Strong Oxidation

482 (250)

.95

Liquid

2795 (1535)

.29

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Iron, Wrought

Dull

77 (25)

.94

Dull

660 (349)

.94

Smooth

100 (38)

.35

Polished

100 (38)

.28

Lead

Polished

100-500 (38-260)

.06-.08

Rough

100 (38)

.43

Oxidized

100 (38)

.43

Oxidized at 1100¡F

100 (38)

.63

Gray Oxidized

100 (38)

.28

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Magnesium

100-500 (38-260)

.07-.13

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Magnesium Oxide

1880-3140 (1027-1727)

.16-.20

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Mercury

32 (0)

.09

Mercury

77 (25)

.10

Mercury

100 (38)

.10

Mercury

212 (100)

.12

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Molybdenum

100 (38)

.06

Molybdenum

500 (260)

.08

Molybdenum

1000 (538)

.11

Molybdenum

2000 (1093

.18

Oxidized at 1000¡F

600 (316)

.80

Oxidized at 1000¡F

700 (371)

.84

Oxidized at 1000¡F

800 (427)

.84

Oxidized at 1000¡F

900 (482)

.83

Oxidized at 1000¡F

1000 (538)

.82

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Monel

Monel, Ni-Cu

392 (200

.41

Monel, Ni-Cu

752 (400)

.44

Monel, Ni-Cu

1112 (600)

.46

Oxidized

68 (20)

.43

Oxidized at 1110¡F

1110 (599)

.46

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Nickel

Polished

100 (38)

.05

Oxidized

100-500 (38-260)

.31-.46

Unoxidized

77 (25)

.05

Unoxidized

212 (100)

.06

Unoxidized

932 (500)

.12

Unoxidized

1832 (1000)

.19

Electrolytic

100 (38)

.04

Electrolytic

500 (260)

.06

Electrolytic

1000 (538)

.10

Electrolytic

2000 (1093)

.16

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Nickel Oxide

1000-2000 (538-1093)

.59-.86

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Palladium Plate

Nickel (.00005 on .0005 silver)

200-750 (93-399)

.16-.17

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Platinum

Platinum

500 (260)

.05

Platinum

1000 (538)

.10

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Platinum, Black

100 (38)

.93

Platinum, Black

500 (260)

.96

Platinum, Black

2000 (1093)

.97

Oxidized at 1100¡F (593¡C)

500 (260)

.07

Oxidized at 1100¡F (593¡C)

1000 (538)

.11

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Rhodium Flash (0.0002 on

0.0005Ni)

200-700 (93-371)

.10-.18

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Silver

Plate (0.0005 on Ni)

200-700 (93-371)

.06-.07

Polished

100 (38)

.01

Polished

500 (260)

.02

Polished

1000 (538)

.03

Polished

2000 (1093)

.03

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Steel

Cold Rolled

200 (93)

.75-.85

Ground Sheet

1720-2010 (938-1099)

.55-.61

Polished Sheet

100 (38)

.07

Polished Sheet

500 (260)

.10

Polished Sheet

1000 (538)

.14

Mild Steel, Polished

75 (24)

.10

Mild Steel, Smooth

75 (24)

.12

Mild Steel, Liquid

2910-3270 (1599-1793)

.28

Steel, Unoxidized

212 (100)

.08

Steel Oxidized

77 (25)

.80

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Steel Alloys

Type 301, Polished

75 (24)

.27

Type 301, Polished

450 (232)

.57

Type 301, Polished

1740 (949)

.55

Type 303, Oxidized

600-2000 (316-1093)

.74-.87

Type 310, Rolled

1500-2100 ((816-1149)

.56-.81

Type 316, Polished

75 (24)

.28

Type 316, Polished

450 (232)

.57

Type 316, Polished

1740 (949)

.66

Type 321

200-800 (93-427)

.27-.32

Type 321, Polished

300-1500 (149-815)

.18-.49

Type 321 w/BK Oxide

200-800 (93-427)

.66-.76

Type 347, Oxidized

600-2000 (316-1093)

.87-.91

Type 350

200-800 (93-427)

.18-.27

Type 350 Polished

300-1800 (149-982)

.11-.35

Type 446, Polished

300-1500 (149-815)

.15-.37

Type 17-7 PH

200-600 (93-316)

.44-.51

Type 17-7 PH Polished

300-1500 (149-815)

.09-.16

Type C1020, Oxidized

600-2000 (316-1093)

.87-.91

Type PH-15-7 MO

300-1200 (149-649)

.07-.19

Stellite, Polished

68 (20)

.18

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Tantalum

Unoxidized

1340 (727)

.14

Unoxidized

2000 (1093)

.19

Unoxidized

3600 (1982)

.26

Unoxidized

5306 (2930)

.30

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Tin

Unoxidized

77 (25)

.04

Unoxidized

212 (100)

.05

Tinned Iron, Bright

76 (24)

.05

Tinned Iron, Bright

212 (100)

.08

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Titanium

Alloy C110M, Polished

300-1200 (149-649)

.08-.19

Alloy C110M, Oxidized at 1000¡F (538¡C)

200-800 (93-427)

.51-.61

Alloy Ti-95A, Oxidized at 1000¡F (538¡C)

200-800 (93-427)

.35-.48

Anodized onto SS

200-600 (93-316)

.96-.82

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Monel

Unoxidized

77 (25)

.02

Unoxidized

212 (100)

.03

Unoxidized

932 (500)

.07

Unoxidized

1832 (1000)

.15

Unoxidized

2732 (1500)

.23

Unoxidized

3632 (2000)

.28

Filament (Aged)

100 (38)

.03

Filament (Aged)

1000 (538)

.11

Filament (Aged)

5000 (2760)

.35

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Uranium Oxide

1880 (1027)

.79

MATERIAL

TEMP °F (°C)

e-EMISSIVITY

Zinc

Bright, Galvanized

100 (38)

.23

Commercial 99.1%

500 (260)

.05

Galvanized

100 (38)

.28

Oxidized

500-1000 (260-538)

.11

Polished

100 (38)

.02

Polished

500 (260)

.03

Polished

1000 (538)

.04

Polished

2000 (1093)

.06

Source: http://www.omega.com/literature/transactions/volume1/emissivitya.html

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