What are possible sources of error in settlement cell readings?
Air bubbles are commonly cited as sources of error, but with proper installation, both factors are easily controlled. By far, the most significant sources of error are barometric pressure (when using a non-vented VW sensor) and temperature variations. Air bubbles: If air bubbles are present in the liquid, they can cause errors, because air is lighter and compresses more easily than liquid. However, the cell leaves the factory pre-filled with de-aired water. Special headers at the reservoir end of the tubing are overfilled, so the liquid is under pressure and remains under pressure until the final step when the tubing is connected to the reservoir. At connection time, the tubing squirts out liquid rather than sucking in air. Thus, air bubbles are not usually a problem. Temperature: Temperature problems can be controlled by minimizing the length of tubing that is affected by the ambient temperature. Also the reservoir should be protected from the direct heat of the sun. Liquid Level Main
