RH data is overflowing and rolling over. What can be done to fix this?
In cases of severe contamination such as the presence of conductive dust or liquid, readings can become significantly higher and will wrap around. To protect against this, it is recommended to use the factory-installed ePTFE cover. Generally, after contamination a bake and hydrate process will recover accuracy however in severe contamination cases, accuracy may be irrecoverable.
The cover is designed to be compatible with normal convection reflow soldering. The cover is not designed to be replaced. We have seen some customers that use excess heat in soldering and the cover shrinks to the point that it is no longer effective. Some customers have had issues with some conformal coating material drying between the cover and the protective tape used while conformal coating is applied. This results in the protective cover peeling off with the tape when the tape is removed after the conformal coating dries. Both of these issues should be avoided. While the cover can be replaced with care to avoid sensor surface contamination, the recommended rework procedure for a device where the cover has been damaged or has peeled off is to replace the device.
Sensor's RH readings at high humidity drift over time. After exposure once the humid environment drops to a lower RH, there is a shift in the sensor's accuracy.
Prolonged exposure to high humidity will cause gradual drift of the humidity sensor. All Si70xx sensors have on-chip heaters that can be used to counter local high humidity, help prevent condensation, and reduce the drift. Please refer to AN607, pg.28, for a more detailed explanation on how to estimate RH with heating. For example, turning on the heater with control setting 0x3 heats the sensor about 5C (depending upon system design) which results in approximately 23% drop in the local RH reading.