Relative humidity (RH) is the ratio between the amount of water vapor that is present in the air to the maximum amount of water vapor that can be theoretically present in the air at a specific temperature. Therefore, RH measurements are directly correlated to the temperature of the air at the time that the measurement was conducted by the iButton Hygrochron (the DS1923).
One reason for erroneous RH values is that they might have been measured at different temperatures. Whenever the temperature of the air changes, the saturation vapor density of the air changes as well.
In order for the measured RH values to make sense, they need to be corrected by RH Temperature Compensation. This procedure is covered in page 53 of the DS1923 datasheet:: https://datasheets.maximintegrated.com/en/ds/DS1923.pdf.
Please note that the DS1923's humidity sensor can produce readings that are higher than the actual humidity that it is exposed to. This effect increases when the RH reaches a value of 70% or greater. The procedure for Software Saturation Drift Compensation can be executed to correct for this phenomena. This procedure and an example are available in the DS1923 datasheet at the bottom of page 53.
RH values greater than 100% are not within the safe operating range of the Hygrochron, and may be another reason why negative RH values are logged. Exposing the Hygrochron to unsafe levels of RH may damage the device. A "Safe Operating Range" diagram can be found on page 6 of the DS1923 datasheet, and can serve as a guideline.
The directions to download the Hygrochron Viewer:
The Hygrochron Viewer requires J# Redistributable Package in order to function. Click on the URL below and choose the correct version for your architecture (32-bit or 64-bit). Then, download and install the redistributable.
After this installation is complete install the Hygrochron Viewer.
1) If you haven't already, download and install the 1-Wire Drivers (see link below).
2) Download the 1-Wire SDK for Windows (see link below).
3) Open the 1-Wire SDK's zip file and navigate to here:
4) On your PC make a directory from where you would like to launch HygrochronViewer (for example, call it "HygroView").
5) Copy/Extract the files inside the zip file in Examples/OW.NET/C#/bin to your new directory.
6) Launch HygrochronViewer by double-clicking the executable.