Eventually bought one, two and subsequently four hygrometers for testing and using them on sealed boxes; Cheap items bought from qoo10...
Did some internet searching, first ended on doing 'saturated salt solution' test, which should give 75%RH. Thought it was enough to "calibrate" or note down the deviate values since those cheapo hygrometers doesn't come with adjustment dial...
Reading using Sodium Chloride (table salt) - 80%RH
Completing the salt test, all four hygrometers are placed in the Digi-Cabi for finally confirmation. Waited more than 24hrs (to be sure), but was shocked and puzzled to see significant mismatched readings from all fours (deviation values taken into account)...
Conclusion: Cheapo hygrometer are nonlinear across the range...
Back to internet again, this time finally found the more accurate testing method -> Potassium Carbonate solution. Bought it from ebay and shipped from US...
Same as salt solution, Potassium carbonate is used instead...
Quick recap on science:
Salt --- %RH
SODIUM CHLORIDE (Table salt) --- 75.30%
POTASSIUM CARBONATE --- 43.16%
Using PC is best as it gives the ideal level.
Items that I used:
Distilled water or tap water if don't have
Potassium Carbonate
Cap or container
Ziplock bag
hygrometer
Calibration steps:
Step 1: Mixed with water to create a sludge or muddy solution. Slight heat will be generated with PC reacting with water.
Step 2: Put solution and hygrometer in ziplock bag.
Step 3: Wait for 8-24 hrs for humidity to stabilise and note down the reading from hygrometer.
Below are the readings when tested with PC. As you can see, SC is asking -5 whereas PC is showing +1.
Potassium Carbonate mixture
Reading using Potassium Carbonate - 42%RH
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100% confident to put my meters to good use in my sealed boxes... Up next - Using PC in my sealed boxes instead of common Silica Gel.
I'm still testing on using PC in my sealed container, which holds my C8.
Day 1 - 53%RH
Day 2 - 50%RH
Day 3 - 46%RH
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I still have some amount of PC left, anyone interested to calibrate their hygrometer can pm me to get some. Collection will be at Redhill mrt only...
