Instrumentation for Measuring Physical Properties of a Lake

Instrumentation has been designed, developed, calibrated, and installed for recording temperature profiles and flow rates at several points in Cayuga Lake in the vicinity of a fossil-fueled power plant. Four buoys and one rigid pole in the lake are used for the instrument installations and are connected to shore via coaxial cable. The temperature and flow rate data are transmitted over the cable by audio tones frequency modulated by the variable being measured. The cable also carries power for the instruments and low frequency command signals for sampling various instruments at the buoys and the pole. Time division multiplex is used for sampling of up to 24 signals from each of the buoys and the pole and to permit transmission of the data via the one coaxial cable. At the shore, the data can be extracted and recorded in digital or analog format. The output of a digital-to-analog converter deflects a paper chart recorder for monitoring purposes. The sampled signals are connected to a Bell Telephone voice quality line to permit remote access to the data, a useful feature for equipment maintenance.