A saturated salt solution can be used for checking the accuracy of RH probes. The science behind the test is, that a saturated salt solution will establish and keep a constant relative humidity in an enclosed space. Test bottles can be used multiple times if stored properly.
Most commonly used is a sodium chloride (NaCl) solution, which gives a nominal value of about 75%. This value is dependent on the ambient temperature. A chart comes with the test bottle showing, that for a temperature change between 60°F and 95°F, the relative humidity varies between 75.61% and 74.87%. A bottle for testing 33% RH with Magnesium Chloride is also available.
The salt bottles have been adapted to fit Ligomat’s RH BluePeg probes. To accommodate the probes a shortened sleeve from Lignomat is inserted into the top of the bottle, another insert is placed at the bottom to stop the RH probe from dropping too low. The blue caps are used to close the bottle during storage. A cable with sleeve-cover is included with each test bottle.
After the cable is connected to the RH probe and the probe inserted into the bottle, the sleeve-cover is pushed into the lip of the sleeve to prohibit any air exchange and allow the air inside the bottle to reach the nominal RH value. Any of Lignomat’s RH meters can be used to measure the RH probes after acclimation:
If RH BluePeg probes are used for in-situ moisture testing of concrete in compliance with ASTM standard F2170, checking the calibration of the RH BluePeg probes with the 75% salt solution is allowed. Check for a difference of less than +/- 2% between the actually measured and the nominal RH value. For more requirements about RH probe calibration check see ASTM F2170 standard, available from the ASTM web-site.
Lignomat offers to check RH probes three times in-house free of charge during the first year.
For more information please contact Customer Service at 1-800-227-2105.
Lignomat USA Ltd, 14345 NE Morris Ct., Portland OR 97230, USA,
Email: sales@Lignomat.com, www.Lignomat.com