Use of the Triple Point of Water and Melt Point of Gallium Cells as Standards at Sea

Triple point of water and gallium melt cells may prove very useful at sea for the calibrations checks demanded of high accuracy free-fall type CTD platforms being developed for the World Ocean Circulation Experiment program of deep ocean study. In ship\´s motion simulations at ENDECO, Inc., standards mounted on a pendulum platform showed no detectable temperature shifts due to low frequency, large amplitude induced disturbances. During a three hour swing cycle, maximum acceleration was estimated at 340 cm²with no more than 1/4 milli C variation on either cell. A standard platinum resistance thermometer along with an automatic resistance thermometer bridge, were employed for the measurements. The triple point of water ( C) and the melt point of gallium ( C) are ideal for calibrations in the oceanographic temperature range. Convinced such standards will be stable at sea, ENDECO will produce practical standards configurations to accommodate anticipated ENDECO CTD sensor geometrics.