If, after time, your sensor is functioning normally but your data is showing a cyclic effect in the absence of water level changes, you are probably seeing barometric changes. The amount is usually 0.5 to 1.5 feet of water. This can be caused by actual water level changes in the aquifer in response to barometric pressure changes. This effect can occur in tight formations where the sensor will immediately pick up barometric changes but the aquifer will not. If you think you are having this type of problem you will have to record the barometric pressure, as well as the water level pressure and compensate the data.
This can also be caused by a plugged vent tube in the cable. If a desiccant tube is not installed or if the desiccant is fully saturated, water may have condensed in your vent tube causing it to plug. If it appears that the vent tube is plugged, consult your INW/Seametrics service technician.