Disclosed RH generators include a lower component having a first chamber and an upper component including a second chamber, the upper component being coupled to the lower component to couple the first chamber to the second chamber. The first chamber is configured to contain liquid water and generate 100% RH, while the second chamber is configured to contain salt and generate a second RH less than 100% RH. A first membrane is positioned between the first chamber and the second chamber to allow water vapor to pass between the first and second chambers while blocking liquid water, the salt, and other larger molecules. The upper component is couplable to an RH probe with a second membrane separating the second chamber from the RH probe, which allows water vapor to pass between the second chamber and the RH probe to expose the RH probe to the second RH.