Omega Engineering's Transactions in Measurement & Control Vol. 4
Transactions in Measurement & Control, Vol. 4, Flow and Level Measurement is a 113-page, free, downloadable PDF covering the basics of level measurement. Topics include level sensor selection, pressure/density, FG/capacitance and radiation-based instrumentation, and specialty level switches. The direct link is at http://tinyurl.com/42oampo.