ACR Electronics SmartReader Plus Reference Manual page 86

SmartReader Plus Data Loggers
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13. If the results are satisfactory, save the calibration changes to the logger (remember to set
the RH channel's equation number back to 71).
Saturated Salt Test
Using saturated salt solutions is the most accurate field technique for RH calibration.
To check your humidity data logger with saturated salt solutions, gather the following
equipment and materials:
· Wide mouth canning jars, 1000ml with metal lids
· #9 stoppers (Fisher #14-130N)
· Powder Funnel (Fisher #10-346-5B)
· Long Stem Funnel (Fisher #10-325D)
· Cardboard or wooden box
· Styrofoam chips (or other insulating material)
· Reagent grade salts:
1. LiCl (anhydrous), 75gm (Fisher #L-121)
2. MgCl2 x 6H2O, 150gm (Fisher #M-33)
3. NaCl, 50gm (Fisher #S-271)
· De-ionized or distilled water, 75ml for each solution
Prepare for the saturated salt test by following these steps:
1. Use the powder funnel to carefully place the salt into the center of the jar bottom.
2. Slowly pour the water onto the mound of salt, using the long stem funnel, taking care not
to splash any water or salt onto the inner walls of the jar.
3. Gently swirl the saturated solution. If the salt dissolves entirely, with no crystals remaining
on the bottom, the solution is not saturated and more salt must be added. There must be
crystals remaining on the bottom but they must not be exposed above the water level.
4. Put a nail through the jar lid and bend into a small hook. Tape the head of the nail (or
use rubber cement) to create an airtight seal of the opening. The logger with RH sensor
(or EH-020A) can be inserted into the jar by first hanging it on the nail loop then screwing
on the lid to the jar.
5. The saturated salt solutions should be kept in a well insulated environment to minimize
any temperature changes. The equilibrium RH over saturated salt solutions is only
slightly temperature dependent. However, for close calibration work to 5% RH or better, it
is important to keep the temperature of the salt solution and the air space above it
identical. To ensure this, the temperature of the lab should be constant.
To perform the saturated salt test, follow these steps:
1. Setup your relative humidity logger with a sample rate of 20 seconds and equation 81 on
the RH channel(s). Make sure you have selected Normalized Byte data units.
2. Place the jars into the box with 1 to 2 inches of Styrofoam chips on the bottom, then fill all
remaining air spaces between the jars and the interior spaces of the box with the chips.
3. Cover the box with cardboard in which 6cm (2.5") diameter holes have been cut to allow
access to the tops of the jars for insertion of the logger or RH module.
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